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Metformin: Drug information

Metformin: Drug information
(For additional information see "Metformin: Patient drug information" and see "Metformin: Pediatric drug information")

For abbreviations, symbols, and age group definitions used in Lexicomp (show table)
ALERT: US Boxed Warning
Lactic acidosis

Postmarketing cases of metformin-associated lactic acidosis have resulted in death, hypothermia, hypotension, and resistant bradyarrhythmias. The onset of metformin-associated lactic acidosis is often subtle, accompanied only by nonspecific symptoms such as malaise, myalgias, respiratory distress, somnolence, and abdominal pain. Metformin-associated lactic acidosis was characterized by elevated blood lactate levels (>5 mmol/L), anion gap acidosis (without evidence of ketonuria or ketonemia), and increased lactate/pyruvate ratio; and metformin plasma levels generally >5 mcg/mL.

Risk factors for metformin-associated lactic acidosis include renal impairment, concomitant use of certain drugs (eg, carbonic anhydrase inhibitors such as topiramate), ≥65 years, having a radiological study with contrast, surgery and other procedures, hypoxic states (eg, acute congestive heart failure), excessive alcohol intake, and hepatic impairment.

Steps to reduce the risk of and manage metformin-associated lactic acidosis in these high-risk groups are provided in the full prescribing information.

If metformin-associated lactic acidosis is suspected, immediately discontinue metformin and institute general supportive measures in a hospital setting. Prompt hemodialysis is recommended.

Brand Names: US
  • Fortamet [DSC];
  • Glucophage XR [DSC];
  • Glucophage [DSC];
  • Glumetza;
  • Riomet;
  • Riomet ER [DSC]
Brand Names: Canada
  • ACT MetFORMIN;
  • APO-MetFORMIN;
  • APO-MetFORMIN ER;
  • Auro-Metformin;
  • DOM-MetFORMIN;
  • Glucophage;
  • Glumetza;
  • Glycon;
  • JAMP-MetFORMIN;
  • JAMP-MetFORMIN Blackberry [DSC];
  • MetFORMIN FC;
  • MINT-MetFORMIN [DSC];
  • PMS-MetFORMIN;
  • PMSC-Metformin;
  • PRO-MetFORMIN;
  • RAN-MetFORMIN;
  • RATIO-MetFORMIN [DSC];
  • RIVA-MetFORMIN;
  • SANDOZ MetFORMIN FC;
  • Septa-MetFORMIN
Pharmacologic Category
  • Antidiabetic Agent, Biguanide
Dosing: Adult

Note: Riomet ER suspension has been discontinued in the United States for >1 year.

Antipsychotic-induced weight gain, treatment

Antipsychotic-induced weight gain, treatment (off-label use):

Immediate release: Oral: Dosage range studied in trials: 750 mg to 2 g daily in 2 to 3 divided doses. Doses up to 2.55 g/day have also been used. To minimize GI adverse effects, most trials initiated therapy with 250 mg or 500 mg twice daily or 850 mg once daily, and increased the dose gradually based on tolerability (Ref).

Extended release: Oral: Maintenance dosage range in trials: 1 to 2 g once daily. To minimize GI adverse effects, trials initiated therapy with 500 mg once daily and titrated dosage upwards in 500 mg increments every 2 to 6 weeks based on tolerability (Ref).

Diabetes mellitus, type 2, prevention

Diabetes mellitus, type 2, prevention (off-label use):

Note: For select patients with prediabetes, particularly for those with BMI ≥35 kg/m2, age <60 years, and patients with prior gestational diabetes mellitus, in whom lifestyle interventions fail to improve glycemic indices (Ref).

Immediate release: Oral: Initial: 850 mg once daily for 1 month, then increase to 850 mg twice daily; unless GI adverse effects warrant a longer titration period (Ref).

Diabetes mellitus, type 2, treatment

Diabetes mellitus, type 2, treatment:

Note: In patients in whom glycemic targets are not met despite diet, exercise, and metformin, combination therapy is necessary to achieve optimal results (Ref).

Immediate release:

Initial: Oral: 500 mg once or twice daily or 850 mg once daily (Ref).

Dosage adjustments: Oral: The dose should be increased gradually to minimize GI adverse effects. Titration strategies vary widely, but usually done in 500 mg or 850 mg increments every 7 days (range: 5 days to 1 month).

Usual maintenance dosage: Oral: 1 g twice daily or 850 mg twice daily (Ref).

Maximum: Oral: 2.55 g/day. Modest additional benefit has been observed with doses up to ~2.5 g/day; however, GI adverse effects may limit use (Ref). If doses >2 g/day are needed, consider administering in 3 divided doses to minimize GI adverse effects.

Extended release:

Initial: Oral: 500 mg to 1 g once daily

Dosage adjustments: Oral: The dose should be increased gradually to minimize GI adverse effects. Titration strategies vary widely, but usually done in 500 mg increments every 7 days (range: 7 days to 6 weeks).

Maximum: Oral: 2 g/day. If glycemic control is not achieved at maximum dose given once daily, may divide maximum dose and administer twice daily.

Gestational diabetes mellitus, treatment

Gestational diabetes mellitus, treatment (alternative agent) (off-label use): Immediate release: Oral: Initial: 500 mg once or twice daily; increase dosage to meet glycemic targets, typically over 1 to 2 weeks, up to a maximum of 2 to 2.5 g daily in 2 to 3 divided doses. If targets not achieved with metformin alone, insulin may be added (Ref). Note: Insulin is the preferred medication for gestational diabetes as it does not cross the placenta to a measurable extent; all oral agents lack long-term safety data (Ref).

Ovarian hyperstimulation syndrome prevention in patients with polycystic ovary syndrome undergoing in vitro fertilization/intracytoplasmic sperm injection

Ovarian hyperstimulation syndrome prevention in patients with polycystic ovary syndrome undergoing in vitro fertilization/intracytoplasmic sperm injection (alternative agent) (off-label use ):

Note: For use prior to and/or during ovarian stimulation in patients undergoing a gonadotropin-releasing hormone agonist protocol (Ref).

Immediate release: Oral: Initial: 500 mg once daily; increase dose gradually as tolerated up to 2 g/day in divided doses (Ref). Dosage range studied in trials: 1 to 2.55 g/day in 2 or 3 divided doses; use of ER products may reduce GI adverse effects (Ref). Discontinue metformin with a positive pregnancy test (Ref).

Metformin conversion recommendations:

Conversion from IR to ER dosage forms: Patients receiving metformin immediate-release may be switched to metformin extended-release once daily at the same total daily dose, up to 2 g once daily. However, in patients who are doing well with immediate-release metformin, some experts recommend they continue using it, as there is little additional benefit documented with ER tablets (Ref).

Dosage adjustment for concomitant therapy: Significant drug interactions exist, requiring dose/frequency adjustment or avoidance. Consult drug interactions database for more information.

Dosing: Kidney Impairment: Adult

The renal dosing recommendations are based upon the best available evidence and clinical expertise. Senior Editorial Team: Bruce Mueller, PharmD, FCCP, FASN, FNKF; Jason Roberts, PhD, BPharm (Hons), B App Sc, FSHP, FISAC; Michael Heung, MD, MS.

Altered kidney function:

eGFR ≥60 mL/minute/1.73 m2: No dosage adjustment necessary. Monitor renal function at least annually.

eGFR >45 to <60 mL/minute/1.73 m2: No dosage adjustment necessary. Metformin plasma concentrations may be higher compared to patients with an eGFR ≥60 mL/minute/1.73 m2; increase monitoring of renal function (eg, every 3 to 6 months) (Ref).

eGFR 30 to 45 mL/minute/1.73 m2:

Initiation of therapy: Use generally not recommended (Ref); however, initial therapy with 500 mg once daily with the evening meal titrated to 500 mg twice daily, if tolerated, with close monitoring of kidney function has been recommended by some experts (Ref).

Continuation of existing therapy: May continue at a reduced dose up to a maximum of 500 mg twice daily with close monitoring of kidney function (Ref).

eGFR <30 mL/minute/1.73 m2: Use is contraindicated.

Acute kidney injury during therapy: If acute kidney injury occurs or if risk factors are present (eg, severe vomiting or diarrhea), instruct patient to temporarily hold metformin (Ref).

Dosing: Hepatic Impairment: Adult

The hepatic dosing recommendations are based up on the best available evidence and clinical expertise. Senior Editorial Team: Matt Harris, PharmD, MHS, BCPS, FAST, Jeong Park, PharmD, MS, BCPS, FCCP, FAST, Arun Jesudian, MD, Sasan Sakiani, MD.

Note: Key pharmacokinetic changes in hepatic insufficiency: Metformin is not metabolized by the liver and is primarily eliminated unchanged by the kidney. The liver is the primary site of lactic acid metabolism and lactic acid–producing events, such as active alcohol consumption, dehydration, hypotension, sepsis, reduced cardiac function, or reduced kidney function, may enhance accumulation of lactic acid. Metformin increases lactic acid production in a dose-dependent manner and may result in overt lactic acidosis when coupled with liver dysfunction (Ref).

Hepatic impairment prior to treatment initiation:

Initial or dose titration in patients with preexisting liver cirrhosis:

Note: In patients with concurrent kidney impairment, eGFR ≤45 mL/minute/1.73 m2 and Child-Turcotte-Pugh A or B, defer to dosing in altered kidney function in adults (Ref). Monitor kidney function frequently (eg, every 1 to 3 months) (expert opinion) during continuation of therapy (Ref).

Child-Turcotte-Pugh class A : No dosage adjustment necessary (Ref).

Child-Turcotte-Pugh class B : 500 mg once daily; may increase by ≤500 mg/day increments every 30 days based on tolerability and response (expert opinion); consider slower titration (eg, every 60 days) in patients on concurrent agents that cause diarrhea (eg, lactulose) or fluid loss (eg, diuretics) (expert opinion); maximum dose: 1.5 g/day (Ref). Note: Do not initiate in patients at risk for lactic acid–producing events (eg, active alcohol consumption, dehydration, hypotension, sepsis, reduced cardiac function, reduced kidney function) (Ref).

Child-Turcotte-Pugh class C: Avoid use (Ref).

Dosage adjustment in patients with chronic, worsening hepatic function during treatment (eg, progression from Child-Turcotte-Pugh class A to B):

Note: In patients with concurrent kidney impairment, eGFR ≤45 mL/minute/1.73 m2 and Child-Turcotte-Pugh A or B, defer to dosing in altered kidney function in adults (Ref). Monitor kidney function frequently (eg, every 1 to 3 months) (expert opinion) during continuation of therapy (Ref).

Progression from baseline to Child-Turcotte-Pugh class A: No dosage adjustment necessary (Ref).

Progression from Child-Turcotte-Pugh class A to B: No dosage adjustment necessary; however, a dose reduction may be required in patients at risk for lactic acid–producing events (eg, active alcohol consumption, dehydration, hypotension, sepsis, reduced cardiac function, reduced kidney function) (Ref).

Progression from Child-Turcotte-Pugh class B to C: If tolerating with appropriate clinical endpoints, use with caution; discontinue metformin therapy in patients at risk for or who experienced a lactic acid–producing event (eg, active alcohol consumption, dehydration, hypotension, sepsis, reduced cardiac function, reduced kidney function) (Ref).

Acute hepatotoxicity during treatment:

Acute worsening of hepatic function (eg, requiring hospitalization): Discontinue metformin during the acute event (expert opinion). Once the acute event has resolved, may resume metformin at pre-event doses (expert opinion). Permanent discontinuation should be considered for patients who recently experienced lactic acidosis, are at high risk of recurrent decompensation, or at risk of lactic acid–producing events (Ref).

Metformin-induced hepatotoxicity: Permanently discontinue metformin therapy. Although metformin is not metabolized by the liver, rare cases of metformin-induced hepatotoxicity have been reported within weeks of initiation, but concurrent use of other hepatotoxic medications is common. Most patients present with jaundice, fatigue, and elevated AST/ALT. Upon discontinuation of metformin, LFTs normalize over days to weeks and reoccurs upon rechallenge (Ref).

Dosing: Pediatric

(For additional information see "Metformin: Pediatric drug information")

Note: Riomet ER suspension has been discontinued in the United States for >1 year.

Diabetes mellitus, type 2; treatment

Diabetes mellitus, type 2; treatment: Note: Allow 1 to 2 weeks between dose titrations. Generally, clinically significant responses are not seen at doses less than 1,500 to 2,000 mg/day (Ref); however, a lower recommended starting dose with a gradual increase in dosage is recommended to minimize gastrointestinal symptoms.

Immediate-release tablet or solution: Children ≥10 years and Adolescents: Oral: Initial: 500 to 1,000 mg once daily or 500 mg twice daily; increase dose every 1 to 2 weeks as tolerated in 500 to 1,000 mg increments; maximum dose: 1,000 mg twice daily or 850 mg 3 times daily (Ref).

Extended-release: Note: Fewer gastrointestinal effects may be seen with extended-release products; however, no pediatric studies have compared extended-release products to standard metformin (Ref).

Children ≥10 years and Adolescents:

Oral suspension: Oral: 500 mg once daily in the evening; titrate dose in 500 mg increments at weekly intervals as tolerated; maximum daily dose: 2,000 mg/day once daily with evening meal.

Tablets: Limited data available: Oral: Initial: 500 to 1,000 mg once daily for 7 to 14 days; may increase dose in 500 to 1,000 mg increments every 1 to 2 weeks as tolerated; maximum daily dose: 2,000 mg/day (Ref). Note: If glycemic control is not achieved at maximum dose, may divide dose and administer twice daily.

Surgical patients (Ref):

Minor surgeries: Discontinue metformin the day of surgery; monitor glucose closely; rapid-acting SUBQ insulin may be required. Continue to withhold metformin for 48 hours following surgery and until normal renal function has been confirmed.

Major surgeries (eg, lasting >2 hours): Discontinue metformin 24 hours prior to surgery; monitor glucose closely; IV insulin infusion may be needed for hyperglycemia during surgery. Continue to withhold metformin for 48 hours following surgery and until normal renal function has been confirmed.

Obesity; severe, adjunct therapy with lifestyle interventions

Obesity; severe, adjunct therapy with lifestyle interventions: Limited data available; data has shown modest efficacy; reported mean BMI reduction −0.86 to −1.16 kg/m2, although reported efficacy endpoints/outcomes in trials are variable (Ref). Overall, due to limited efficacy, some experts do not consider metformin a weight loss treatment option for pediatric obesity (Ref). Optimal treatment duration not established; duration in trials varied from 3 to 12 months. Daily multivitamin supplement may be considered with therapy (Ref).

Immediate release: Dosing regimens variable: Children ≥6 years and Adolescents: Oral: Initial: 500 mg once or twice daily, may titrate upward at weekly intervals by 500 mg/day increments; reported final doses: 1,000 to 2,000 mg/day in 2 divided doses; a meta-analysis showed that metformin 2,000 mg/day intervention was most identified as most effective relative to lower doses or lifestyle modifications in adolescents without diabetes (Ref). Age-dependent efficacy findings are conflicting; some data suggests that metformin may have greater efficacy in prepubertal children and others have shown a greater effect in pubertal subjects (11 to 17 years) (Ref). A low dose (850 mg/day) over a prolonged period (24 months) showed positive effects on body composition (weight and BMI standard deviation scores) and other metabolic and inflammatory markers (eg, fat mass, liver fat, leptin, highly sensitive C-reactive protein) in a small, placebo-controlled trial of 22 subjects (metformin=13; age range: 6 to 13 years) (Ref).

Extended release: Metformin XR: Adolescents: Oral: Initial: 500 mg once daily with dinner for 2 weeks; increase to 1,000 mg once daily for 2 weeks, and then 2,000 mg once daily; may slow titration if adverse gastrointestinal effects (Ref).

Weight gain, atypical antipsychotic-induced; treatment

Weight gain, atypical antipsychotic-induced; treatment: Limited data available:

Immediate release: Note: In trials, all patients were diagnosed with autism spectrum disorder; trials used metformin oral solution (Riomet) and slowly titrated the dose to minimize GI effects and maximize tolerability. After 16 weeks of therapy, patients receiving metformin had a statistically significant decrease in BMI z-scores (primary efficacy outcome) as well as other secondary outcomes (eg, raw weight, BMI) compared to placebo. A 16-week, open-label extension study showed results achieved in the treatment group were maintained without further decreases (Ref).

6 to 9 years: Oral: Initial: 250 mg with evening meal for 1 week, then 250 mg twice daily for 1 week, then 500 mg twice daily.

10 to 17 years: Oral: Initial: 250 mg with evening meal for 1 week, then 250 mg twice daily for 1 week, then 500 mg twice daily for 1 week, then 850 mg twice daily.

Dosage adjustment for concomitant therapy: Significant drug interactions exist, requiring dose/frequency adjustment or avoidance. Consult drug interactions database for more information.

Dosing: Kidney Impairment: Pediatric

Children ≥10 years and Adolescents: Oral: Immediate release, extended release:

eGFR >45 mL/minute/1.73 m2: No dosage adjustment necessary.

eGFR 30 to 45 mL/minute/1.73 m2:

Preexisting impairment: Initiation of therapy is not recommended.

During therapy:

If eGFR falls between 30 and <45 mL/minute/1.73 m2: Consider risk/benefit ratio for continuing therapy.

If eGFR falls to <30 mL/minute/1.73 m2:Discontinue therapy.

eGFR <30 mL/minute/1.73 m2: Use is contraindicated.

Dosing: Hepatic Impairment: Pediatric

Children ≥10 years and Adolescents: Avoid metformin; liver disease is a risk factor for the development of lactic acidosis during metformin therapy.

Dosing: Older Adult

Refer to adult dosing. The initial and maintenance dosing should be conservative, due to the potential for decreased renal function (monitor).

Dosage Forms: US

Excipient information presented when available (limited, particularly for generics); consult specific product labeling. [DSC] = Discontinued product

Solution, Oral, as hydrochloride:

Riomet: 500 mg/5 mL (118 mL, 473 mL) [contains propylene glycol; strawberry flavor]

Riomet: 500 mg/5 mL (118 mL, 473 mL) [contains saccharin calcium; cherry flavor]

Generic: 500 mg/5 mL (5 mL, 8.5 mL, 118 mL, 473 mL)

Suspension Reconstituted ER, Oral, as hydrochloride:

Riomet ER: 500 mg/5 mL (480 mL [DSC]) [contains methylparaben, propylene glycol, propylparaben]

Tablet, Oral, as hydrochloride:

Glucophage: 500 mg [DSC], 850 mg [DSC], 1000 mg [DSC]

Generic: 500 mg, 625 mg, 850 mg, 1000 mg

Tablet Extended Release 24 Hour, Oral, as hydrochloride:

Fortamet: 500 mg [DSC], 1000 mg [DSC]

Glucophage XR: 500 mg [DSC], 750 mg [DSC]

Glumetza: 500 mg, 1000 mg

Generic: 500 mg, 750 mg, 1000 mg

Generic Equivalent Available: US

May be product dependent

Dosage Forms Considerations

Extended release tablets utilize differing release mechanisms: Glucophage XR uses dual hydrophilic polymer matrix systems, Fortamet uses single-composition osmotic technology, and Glumetza uses gastric retention technology.

Dosage Forms: Canada

Excipient information presented when available (limited, particularly for generics); consult specific product labeling.

Tablet, Oral, as hydrochloride:

Glucophage: 500 mg, 850 mg

Glycon: 500 mg, 850 mg

Generic: 500 mg, 850 mg

Tablet Extended Release 24 Hour, Oral, as hydrochloride:

Glumetza: 500 mg

Glumetza: 1000 mg [contains fd&c blue #2 (indigotine), fd&c red #40 (allura red ac dye), fd&c yellow #6 (sunset yellow)]

Generic: 500 mg, 1000 mg

Product Availability

Riomet ER suspension has been discontinued in the United States for >1 year.

Administration: Adult

Oral: Administer with a meal (to decrease GI upset). Administer solution and suspension with supplied dosing cup.

ER tablets: Swallow whole; do not crush, cut, or chew. Administer once-daily doses with the evening meal.

Bariatric surgery: Some institutions may have specific protocols that conflict with these recommendations; refer to institutional protocols as appropriate. IR tablets and oral solution formulations are available.

Fortamet: If safety and efficacy can be effectively monitored, no change in formulation or administration is required after bariatric surgery.

Glucophage XR: If safety and efficacy can be effectively monitored, no change in formulation or administration is required after bariatric surgery; however, close clinical monitoring is advised given that Glucophage XR is designed to release at a constant rate and peaks approximately 6 hours after administration.

Glumetza: Gastric bypass and sleeve gastrectomy expedite transit of food and water through the remaining stomach. Glumetza is designed to be retained in the stomach and is therefore not advised after gastric bypass or sleeve gastrectomy.

Administration: Pediatric

Oral: Administer with a meal (to decrease GI upset).

Immediate release: Glucophage, Riomet: Administer in divided doses with meals. Administer oral solution (eg, Riomet) with supplied dosing cup.

Extended release:

Oral suspension (eg, Riomet ER): Administer with evening meal. Shake well at least 10 seconds before use; use supplied dosing cup to measure dose. Rinse dosing cup with water only after each use to clean.

Tablet (eg, Fortamet, Glucophage XR, Glumetza): Administer once-daily doses with the evening meal; swallow whole; do not cut, crush, or chew; Fortamet should also be administered with a full glass of water.

Use: Labeled Indications

Diabetes mellitus, type 2, treatment: Management of type 2 diabetes mellitus when hyperglycemia cannot be managed with diet and exercise alone.

Use: Off-Label: Adult

Antipsychotic-induced weight gain; Diabetes mellitus, type 2 (prevention); Gestational diabetes mellitus (treatment); Ovarian hyperstimulation syndrome prevention in patients with polycystic ovary syndrome undergoing in vitro fertilization/intracytoplasmic sperm injection

Medication Safety Issues
Sound-alike/look-alike issues:

MetFORMIN may be confused with metroNIDAZOLE

Glucophage may be confused with Glucotrol, Glutofac

High alert medication:

This medication is in a class the Institute for Safe Medication Practices (ISMP) includes among its list of drug classes that have a heightened risk of causing significant patient harm when used in error.

International issues:

Dianben [Spain] may be confused with Diovan brand name for valsartan [US, Canada, and multiple international markets].

Glucon brand name for metformin [Malaysia, Singapore] is also the brand name for glucosamine [Singapore]

Adverse Reactions (Significant): Considerations
Gastrointestinal effects

Transient and/or reversible gastrointestinal adverse reactions, including diarrhea, nausea, flatulence, dyspepsia, vomiting, and abdominal pain, among others, are the most commonly reported adverse reactions to metformin use; intolerance to these reactions is often a reason for discontinuation of therapy (Ref).

Mechanism: Dose-related; mechanism not fully understood. Multiple mechanisms have been proposed that may contribute, including alterations in transporters (eg, organic cation transporter 1 [OCT1]), direct serotoninergic-like effects, increased gut motility, direct or indirect increases in glucagon-like peptide 1 (GLP-1), and disruptions in bile (Ref).

Onset: Varied; typically occurs at initiation of therapy; however, late onset of diarrhea has been reported (Ref). Gastrointestinal adverse reactions generally subside after several weeks of therapy; however, some patients require discontinuation.

Risk factors:

• Rapid dose escalation

• Use of IR formulations (Ref)

• Chronic asymptomatic gastritis (Ref)

• Helicobacter pylori infection (Ref)

Concomitant use of OCT1-inhibiting agents (eg, verapamil, proton pump inhibitors) may be a potential risk factor (Ref)

Lactic acidosis

Postmarketing cases of metformin-associated lactic acidosis (MALA) have resulted in death, hypothermia, hypotension, and resistant bradyarrhythmias. The onset is often subtle, accompanied by nonspecific symptoms (eg, malaise, myalgia, respiratory distress, somnolence, abdominal pain); elevated blood lactate levels (>5 mmol/L); anion gap acidosis (without evidence of ketonuria or ketonemia); and/or increased lactate:pyruvate ratio. Lactic acidosis should be suspected in any patient with diabetes receiving metformin with evidence of acidosis but without evidence of ketoacidosis. Safety data for use in advanced heart failure (stage D) is lacking (Ref).

Mechanism: Dose-related; inhibition of mitochondrial electron transport, an effect that favors anaerobic metabolism and the accumulation of lactate (Ref), resulting in lactic acidosis without evidence of tissue hypoxia (type B lactic acidosis). In addition, if accumulation occurs (eg, in patients with renal impairment) or if high doses are administered (eg, in overdose), glucose utilization decreases and hepatic production of lactate increases (Ref).

Onset: Varied; may occur at any time during treatment.

Risk factors: In general, risk is increased with increased metformin concentration, decreased lactate clearance, and/or increased lactate production.

• Kidney impairment; risk increases with the severity of kidney impairment

• Hepatic impairment

• Reduced tissue perfusion such as in unstable heart failure (Ref)

• Concomitant use of certain drugs that impair kidney function, cause significant hemodynamic changes, interfere with acid-base balance, or increase metformin accumulation

• Patients ≥65 years of age

• Radiologic study with contrast

• Surgery and other procedures due to potential for volume depletion, hypotension, and renal impairment

• Hypoxic states (eg, acute heart failure, acute myocardial infarction, sepsis, shock)

• Excessive alcohol intake

Vitamin B12 deficiency

Long-term use of metformin has been associated with reversible vitamin B12 deficiency and subsequent anemia and neuropathy (Ref).

Mechanism: Time-related; long-term use metformin interferes with the absorption of vitamin B12 (Ref); potential mechanism includes interference of vitamin B12-intrinsic factor absorption in the terminal ileum (Ref).

Onset: Delayed; occurs with chronic use of metformin

Risk factors:

Duration of therapy

Inadequate B12 stores, poor underlying nutrition, and inadequate calcium intake or absorption (Ref).

Adverse Reactions

The following adverse drug reactions and incidences are derived from product labeling unless otherwise specified.

>10%: Gastrointestinal: Diarrhea (IR tablet: 53%; ER tablet: 10%) (table 1), flatulence (12%) (table 2), nausea and vomiting (IR tablet: 26%; ER tablet: 7%) (table 3)

Metformin: Adverse Reaction: Diarrhea

Drug (Metformin)

Placebo

Dose

Dosage Form

Number of Patients (Metformin)

Number of Patients (Placebo)

53%

12%

Up to 2,550 mg/day

IR tablet

141

145

10%

3%

N/A

ER tablet

781

195

Metformin: Adverse Reaction: Flatulence

Drug (Metformin)

Placebo

Dose

Dosage Form

Number of Patients (Metformin)

Number of Patients (Placebo)

12%

6%

Up to 2,550 mg/day

IR tablet

141

145

Metformin: Adverse Reaction: Nausea and vomiting

Drug (Metformin)

Placebo

Dose

Dosage Form

Number of Patients (Metformin)

Number of Patients (Placebo)

26%

8%

Up to 2,550 mg/day

IR tablet

141

145

7%

2%

N/A

ER tablet

781

195

1% to 10%:

Cardiovascular: Chest discomfort, flushing, palpitations

Dermatologic: Diaphoresis, nail disease (Lu 2013)

Endocrine & metabolic: Hypoglycemia, vitamin B12 deficiency (7%)

Gastrointestinal: Abdominal distention, abdominal distress (6%), abdominal pain, abnormal stools, dyspepsia (7%) (table 4), heartburn

Metformin: Adverse Reaction: Dyspepsia

Drug (Metformin)

Placebo

Dose

Dosage Form

Number of Patients (Metformin)

Number of Patients (Placebo)

7%

4%

Up to 2,550 mg/day

IR tablet

141

145

Nervous system: Chills, dizziness, headache (6%)

Neuromuscular & skeletal: Asthenia (9%), myalgia

Respiratory: Dyspnea, flu-like symptoms, upper respiratory tract infection

Postmarketing:

Dermatologic: Lichen planus (Azzam 1997)

Endocrine & metabolic: Lactic acidosis (rare: <1%) (DeFronzo 2016; Eppenga 2014; Salpeter 2010)

Hematologic & oncologic: Hemolytic anemia (Packer 2008)

Hepatic: Hepatic injury (cholestatic, hepatocellular, and mixed) (Babich 1998; Nammour 2003)

Hypersensitivity: Fixed drug eruption (Ramírez-Bellver 2017; Steber 2016)

Nervous system: Encephalopathy (Béjot 2015; Jung 2009; Kang 2013)

Contraindications

US labeling: Hypersensitivity to metformin or any component of the formulation; severe renal dysfunction (eGFR <30 mL/minute/1.73 m2); acute or chronic metabolic acidosis with or without coma (including diabetic ketoacidosis)

Canadian labeling: Hypersensitivity to metformin or any component of the formulation; renal function unknown, renal impairment, and serum creatinine levels above the upper limit of normal range; renal disease or renal dysfunction (serum creatinine ≥136 micromol/L in males or ≥124 micromol/L in females or abnormal creatinine clearance <60 mL/minute) which may result from conditions such as cardiovascular collapse (shock), acute myocardial infarction, and septicemia; unstable and/or insulin-dependent (type 1) diabetes mellitus; acute or chronic metabolic acidosis, including diabetic ketoacidosis, with or without coma, history of ketoacidosis with or without coma; history of lactic acidosis (regardless of precipitating factors); excessive alcohol intake (acute or chronic); severe hepatic dysfunction or clinical or laboratory evidence of hepatic disease; cardiovascular collapse and disease states associated with hypoxemia including cardiorespiratory insufficiency, which are often associated with hyperlactacidemia; stress conditions (eg, severe infection, trauma, surgery and postoperative recovery phase); severe dehydration; pregnancy; breastfeeding

Warnings/Precautions

Disease-related concerns:

• Bariatric surgery: Altered absorption: Use IR tablets or solution after surgery. ER tablets (Glucophage XR [hydrophilic polymer matrix], Fortamet [osmotic technology], Glumetza [gastric-retentive technology]) may have a reduced effect after gastric bypass or sleeve gastrectomy due to the direct bypass of the stomach and proximal small bowel with gastric bypass or a more rapid gastric emptying and proximal small bowel transit with sleeve gastrectomy (Mechanick 2013; Melissas 2013). After gastric bypass (Roux-en-Y gastric bypass [RYGB]), administration of IR tablets led to increased absorption (AUC0- increased by 21%) and bioavailability (increased by 50%) (Padwal 2011). Lactate levels decrease after gastric bypass (RYGB)-induced weight loss irrespective of the use of metformin. Routinely lowering metformin dose after gastric bypass is not necessary as long as normal renal function is preserved (Deden 2018).

• Heart failure: Metformin may be used in patients with stable heart failure (ADA 2022). Use cautiously or avoid in hypoperfusion.

• Hepatic impairment: Use cautiously in patients at risk for lactic acidosis (Brackett 2010; Crowley 2017; Zhang 2014). An increased risk of mortality has been observed with higher metformin doses (eg, >1 g) and more severe liver dysfunction (eg, Child-Turcotte-Pugh C>B>>>A) (Yen 2022). Cases of metformin-induced hepatotoxicity have also been reported (LiverTox 2020; Zheng 2016).

• Renal impairment: Metformin is substantially excreted by the kidney; dosing adjustments may be required.

• Stress-related states: It may be necessary to discontinue metformin and administer insulin if the patient is exposed to stress (fever, trauma, infection, surgery).

Dosage form specific issues:

• ER tablet: Insoluble tablet shell (Glumetza 1,000 mg tablet) may remain intact and be visible in the stool. Other ER tablets (Fortamet, Glucophage XR, Glumetza 500 mg) may appear in the stool as a soft mass resembling the tablet.

• Propylene glycol: Some dosage forms may contain propylene glycol; large amounts are potentially toxic and have been associated with hyperosmolality, lactic acidosis, seizures, and respiratory depression; use caution (AAP 1997; Zar 2007). See manufacturer's labeling.

Other warnings/precautions:

Appropriate use: Not indicated for use in patients with type 1 diabetes mellitus or with diabetic ketoacidosis.

• Iodinated contrast: Administration of iodinated contrast agents has been associated with postcontrast acute kidney injury (AKI); acute decreases in renal function have been associated with an increased risk of lactic acidosis due to reduced metformin excretion (ACR 2021; manufacturer’s labeling). Current guidelines recommend temporarily withholding metformin prior to or at the time of iodinated contrast administration in patients with known AKI or severe chronic kidney disease (eGFR <30 mL/minute/1.73 m2), or who are undergoing arterial catheter studies (ACR 2021). Some experts also temporarily withhold metformin in patients with an eGFR <45 mL/minute/1.73 m2 or risk factors for lactic acidosis (eg, hypotension, vascular instability, potential hypoperfusion) (Rudnick 2021; Wexler 2021b). If metformin is withheld, reassess kidney function ≥48 hours after contrast administration and resume therapy if kidney function is acceptable (ACR 2021).

• Surgical procedures: Metformin-containing products should be withheld the day of surgery; restart after renal function is stable (ADA 2022).

Metabolism/Transport Effects

Substrate of OCT1, OCT2

Drug Interactions

Note: Interacting drugs may not be individually listed below if they are part of a group interaction (eg, individual drugs within “CYP3A4 Inducers [Strong]” are NOT listed). For a complete list of drug interactions by individual drug name and detailed management recommendations, use the Lexicomp drug interactions program by clicking on the “Launch drug interactions program” link above.

Abemaciclib: May increase the serum concentration of MetFORMIN. Risk C: Monitor therapy

Alcohol (Ethyl): May enhance the adverse/toxic effect of MetFORMIN. Specifically, alcohol may potentiate the risk of lactic acidosis Risk X: Avoid combination

Alpha-Lipoic Acid: May enhance the hypoglycemic effect of Antidiabetic Agents. Risk C: Monitor therapy

Androgens: May enhance the hypoglycemic effect of Agents with Blood Glucose Lowering Effects. Risk C: Monitor therapy

Beta-Blockers (Beta1 Selective): May enhance the hypoglycemic effect of Antidiabetic Agents. Risk C: Monitor therapy

Beta-Blockers (Nonselective): May enhance the hypoglycemic effect of Antidiabetic Agents. Beta-Blockers (Nonselective) may diminish the therapeutic effect of Antidiabetic Agents. Risk C: Monitor therapy

Bortezomib: May enhance the therapeutic effect of Antidiabetic Agents. Bortezomib may diminish the therapeutic effect of Antidiabetic Agents. Risk C: Monitor therapy

Carbonic Anhydrase Inhibitors: May enhance the adverse/toxic effect of MetFORMIN. Specifically, the risk of developing lactic acidosis may be increased. Risk C: Monitor therapy

Cephalexin: May increase the serum concentration of MetFORMIN. Risk C: Monitor therapy

Cimetidine: May increase the serum concentration of MetFORMIN. Management: Consider alternatives to cimetidine in patients receiving metformin due to a potential for increased metformin concentrations and toxicity (including lactic acidosis). Risk D: Consider therapy modification

Dalfampridine: MetFORMIN may increase the serum concentration of Dalfampridine. Dalfampridine may increase the serum concentration of MetFORMIN. Risk C: Monitor therapy

Direct Acting Antiviral Agents (HCV): May enhance the hypoglycemic effect of Antidiabetic Agents. Risk C: Monitor therapy

Dofetilide: MetFORMIN may increase the serum concentration of Dofetilide. Risk C: Monitor therapy

Dolutegravir: May increase the serum concentration of MetFORMIN. Management: Consider alternatives to this combination or use of lower metformin doses. Carefully weigh the risk of metformin toxicities (including lactic acidosis) against the benefit of combining dolutegravir with metformin. Risk D: Consider therapy modification

Erdafitinib: May increase the serum concentration of OCT2 Substrates (Clinically Relevant with Inhibitors). Management: Consider alternatives to this combination when possible. If combined, monitor for increased effects/toxicities of OCT2 substrates and consider OCT2 substrate dose reductions when appropriate. Risk D: Consider therapy modification

Etilefrine: May diminish the therapeutic effect of Antidiabetic Agents. Risk C: Monitor therapy

Fexinidazole: May increase the serum concentration of MATE1/2-K Substrates (Clinically Relevant with Inhibitors). Management: Avoid use of fexinidazole with MATE1/2-K substrates when possible. If combined, monitor for increased MATE1/2-K substrate toxicities. Risk D: Consider therapy modification

Fexinidazole: May increase the serum concentration of OCT2 Substrates (Clinically Relevant with Inhibitors). Management: Avoid use of fexinidazole with OCT2 substrates when possible. If combined, monitor for increased OCT2 substrate toxicities. Risk D: Consider therapy modification

Fludeoxyglucose F 18: MetFORMIN may diminish the diagnostic effect of Fludeoxyglucose F 18. Management: Consider holding metformin for 48 hours or longer prior to PET scans using fludeoxyglucose F18 (FDG-F18) when imaging of the colon or intestine is required. Consider increased monitoring of blood glucose when metformin is held. Risk D: Consider therapy modification

Gilteritinib: May increase the serum concentration of OCT1 Substrates (Clinically Relevant with Inhibitors). Risk C: Monitor therapy

Glycopyrrolate (Systemic): May increase the serum concentration of MetFORMIN. Risk C: Monitor therapy

Guanethidine: May enhance the hypoglycemic effect of Antidiabetic Agents. Risk C: Monitor therapy

Guar Gum (Partially Hydrolyzed): May decrease the serum concentration of MetFORMIN. Risk C: Monitor therapy

Hyperglycemia-Associated Agents: May diminish the therapeutic effect of Antidiabetic Agents. Risk C: Monitor therapy

Hypoglycemia-Associated Agents: Antidiabetic Agents may enhance the hypoglycemic effect of Hypoglycemia-Associated Agents. Risk C: Monitor therapy

Iodinated Contrast Agents: May enhance the adverse/toxic effect of MetFORMIN. Renal dysfunction that may be caused by iodinated contrast agents may lead to metformin-associated lactic acidosis. Management: Management advice varies. Refer to the full drug interaction monograph content for details. Risk D: Consider therapy modification

LamoTRIgine: May increase the serum concentration of MetFORMIN. Management: The lamotrigine Canadian product monograph states that coadministration of these drugs is not recommended. Risk C: Monitor therapy

Maitake: May enhance the hypoglycemic effect of Agents with Blood Glucose Lowering Effects. Risk C: Monitor therapy

MATE1/2-K Inhibitors: May increase the serum concentration of MetFORMIN. Risk C: Monitor therapy

Monoamine Oxidase Inhibitors: May enhance the hypoglycemic effect of Agents with Blood Glucose Lowering Effects. Risk C: Monitor therapy

Nonsteroidal Anti-Inflammatory Agents: May enhance the adverse/toxic effect of MetFORMIN. Risk C: Monitor therapy

Ombitasvir, Paritaprevir, and Ritonavir: May enhance the adverse/toxic effect of MetFORMIN. Specifically, the risk for lactic acidosis may be increased. Risk C: Monitor therapy

Ombitasvir, Paritaprevir, Ritonavir, and Dasabuvir: May enhance the adverse/toxic effect of MetFORMIN. Specifically, the risk for lactic acidosis may be increased. Risk C: Monitor therapy

Ondansetron: May increase the serum concentration of MetFORMIN. Risk C: Monitor therapy

Pacritinib: May increase the serum concentration of OCT1 Substrates (Clinically Relevant with Inhibitors). Risk X: Avoid combination

Patiromer: May decrease the serum concentration of MetFORMIN. Management: Administer metformin at least 3 hours before or 3 hours after patiromer. Risk D: Consider therapy modification

Pegvisomant: May enhance the hypoglycemic effect of Agents with Blood Glucose Lowering Effects. Risk C: Monitor therapy

Prothionamide: May enhance the hypoglycemic effect of Agents with Blood Glucose Lowering Effects. Risk C: Monitor therapy

Quinolones: May enhance the hypoglycemic effect of Agents with Blood Glucose Lowering Effects. Quinolones may diminish the therapeutic effect of Agents with Blood Glucose Lowering Effects. Specifically, if an agent is being used to treat diabetes, loss of blood sugar control may occur with quinolone use. Risk C: Monitor therapy

Ranolazine: May increase the serum concentration of MetFORMIN. Management: Limit the metformin dose to a maximum of 1,700 mg per day when used together with ranolazine 1,000 mg twice daily. Monitor patients for metformin toxicities, including lactic acidosis and carefully weigh the risks and benefits of this combination. Risk D: Consider therapy modification

Risdiplam: May increase the serum concentration of MATE1/2-K Substrates (Clinically Relevant with Inhibitors). Management: Avoid use of risdiplam with MATE substrates if possible. If the combination cannot be avoided, monitor closely for adverse effects. Consider a reduced dose of the MATE substrate according to that substrate's labeling if appropriate. Risk D: Consider therapy modification

Ritodrine: May diminish the therapeutic effect of Antidiabetic Agents. Risk C: Monitor therapy

Salicylates: May enhance the hypoglycemic effect of Agents with Blood Glucose Lowering Effects. Risk C: Monitor therapy

Selective Serotonin Reuptake Inhibitors: May enhance the hypoglycemic effect of Agents with Blood Glucose Lowering Effects. Risk C: Monitor therapy

Tafenoquine: May increase the serum concentration of MATE1/2-K Substrates (Clinically Relevant with Inhibitors). Management: Avoid use of MATE substrates with tafenoquine, and if the combination cannot be avoided, monitor closely for evidence of toxicity of the MATE substrate and consider a reduced dose of the MATE substrate according to that substrate's labeling. Risk D: Consider therapy modification

Tafenoquine: May increase the serum concentration of OCT2 Substrates (Clinically Relevant with Inhibitors). Management: Avoid use of OCT2 substrates with tafenoquine, and if the combination cannot be avoided, monitor closely for evidence of toxicity of the OCT2 substrate and consider a reduced dose of the OCT2 substrate according to that substrate's labeling. Risk D: Consider therapy modification

Thiazide and Thiazide-Like Diuretics: May diminish the therapeutic effect of Antidiabetic Agents. Risk C: Monitor therapy

Topiramate: May enhance the adverse/toxic effect of MetFORMIN. Specifically, the risk for lactic acidosis may be increased. MetFORMIN may increase the serum concentration of Topiramate. Topiramate may increase the serum concentration of MetFORMIN. Risk C: Monitor therapy

Verapamil: May diminish the therapeutic effect of MetFORMIN. Risk C: Monitor therapy

Vitamin K Antagonists (eg, warfarin): MetFORMIN may diminish the anticoagulant effect of Vitamin K Antagonists. Vitamin K Antagonists may enhance the hypoglycemic effect of MetFORMIN. Risk C: Monitor therapy

Food Interactions

Food decreases the extent and slightly delays the absorption. Management: Administer with a meal.

Reproductive Considerations

Metformin is approved for the treatment of type 2 diabetes mellitus; however, it is not preferred for use if pregnancy should occur. Regardless of treatment, patients with diabetes who could become pregnant should use effective contraception and those planning to become pregnant should continue contraception until glycemic control is achieved. When diet and exercise alone are not enough for the treatment of type 2 diabetes mellitus, metformin may be continued in select patients who are well controlled prior to pregnancy, such as those who are unwilling or unable to use insulin (ACOG 2018; ADA 2022).

Metformin has been studied in patients with polycystic ovarian syndrome (PCOS) who have reproductive symptoms such as irregular menstrual cycles and infertility.

• Adjunctive use of metformin may improve metabolic features of PCOS in patients when combination oral contraceptives and lifestyle modifications are not effective. Metformin may be most effective for patients with diabetes risk factors, impaired glucose tolerance, or a BMI ≥25 kg/m2 (Teede 2018).

• Metformin (in combination with clomiphene) may be considered for ovulation induction in patients diagnosed with PCOS and anovulatory infertility (and no other infertility factors), who have a BMI ≥30 kg/m2, and who wish to conceive. Pregnancy should be excluded prior to treatment (Teede 2018). Metformin monotherapy is no longer recommended for routine use for ovulation induction in patients with PCOS and anovulatory infertility but may be considered in patients who are unable or unwilling to take more effective agents (ASRM 2017; Teede 2018).

• Adjunctive use of metformin may reduce the risk of ovarian hyperstimulation syndrome (OHSS) and improve pregnancy rate in patients with PCOS and anovulatory infertility who are undergoing in vitro fertilization (IVF) or intracytoplasmic sperm injection (ICSI). Metformin should be discontinued once there is a positive pregnancy test unless it is needed for another indication (Teede 2018).

Pregnancy Considerations

Metformin crosses the placenta; concentrations may be comparable to or higher than those found in the maternal plasma (ADA 2022; Charles 2006; de Oliveira Baraldi 2011; Eyal 2010; Vanky 2005).

Outcome data following first trimester exposure from paternal (Wensink 2022) and maternal (Cao 2021; Cassina 2014; Gilbert 2006; Panchaud 2018; Scherneck 2018; Zeng 2016) use of metformin are available. Maternal and fetal/neonatal outcomes are influenced by underlying maternal disease (eg, gestational diabetes mellitus [GDM] or polycystic ovary syndrome [PCOS]) (Cao 2021; Panchaud 2018; Zeng 2016). An increased risk of birth defects or adverse fetal/neonatal outcomes has not been observed following maternal use of metformin for gestational diabetes mellitus or type 2 diabetes mellitus when glycemic control is maintained (Balani 2009; Coetzee 1984; Ekpebegh 2007; Niromanesh 2012; Rowan 2008; Rowan 2010; Tertti 2008). Studies which evaluated children up to 12 years of age with previous in utero exposure to metformin have shown conflicting outcomes related to BMI and other growth parameters; however, results may be confounded by underlying maternal disease (eg, GDM, PCOS) and concomitant therapy (eg, insulin) (ADA 2022; Brand 2022; Paavilainen 2022; Skibinska 2021). Additional long-term data are needed (ADA 2022).

Due to pregnancy-induced physiologic changes, some pharmacokinetic properties of metformin may be altered. Changes in renal blood flow alter renal clearance; in one study this significantly decreased plasma concentrations of metformin for pregnant patients taking a dose of 1 g/day but not doses of 2 g/day. Changes in renal clearance correlated with changes in creatinine clearance (Eyal 2010; Liao 2020).

Poorly controlled diabetes during pregnancy is associated with an increased risk of adverse maternal and fetal outcomes, including diabetic ketoacidosis, preeclampsia, spontaneous abortion, preterm delivery, delivery complications, major malformations, stillbirth, and macrosomia (ACOG 2018). To prevent adverse outcomes, prior to conception and throughout pregnancy, maternal blood glucose and HbA1c should be kept as close to target goals as possible but without causing significant hypoglycemia (ADA 2022).

Agents other than metformin are currently recommended to treat diabetes mellitus in during pregnancy (ADA 2022). Metformin may be considered for the treatment of GDM in patients who cannot safely or effectively use insulin (eg, due to cost, language barriers, comprehension, cultural issues). However, metformin monotherapy fails to provide adequate glycemic control in all patients. Metformin should not be used in patients with hypertension, preeclampsia, or those at risk for intrauterine growth restriction due to risk of fetal growth restriction or acidosis in the setting of placental restriction. Metformin is not the preferred treatment of type 2 diabetes mellitus during pregnancy (ADA 2022). Metformin, in addition to insulin, may be considered for some pregnant patients with type 2 diabetes mellitus due to potential maternal and neonatal benefits (eg, reduced insulin requirements, less maternal weight gain, fewer caesarean births, reduced incidence of macrosomia), although additional long-term data are needed (Benham 2021; Feig 2020).

PCOS is also associated with adverse pregnancy outcomes, including an increased risk of GDM, miscarriage, pregnancy-induced hypertension, preeclampsia, and preterm delivery. When used in the management of PCOS, metformin may reduce the risk of preterm delivery; however, the incidence of GDM, miscarriage, or preeclampsia are not affected (Cao 2021). Metformin monotherapy has not been found to improve the live birth rate in patients with PCOS when used for ovulation induction or in vitro fertilization (IVF) or intracytoplasmic sperm injection (ICSI) (Magzoub 2022; Tso 2020; Wu 2020). If metformin is used for ovulation induction in patients with PCOS, treatment should be discontinued by the end of the first trimester (ADA 2022). In patients undergoing IVF/ICSI, metformin should be discontinued once there is a positive pregnancy test unless it is needed for another indication (Teede 2018).

Breastfeeding Considerations

Metformin is present in breast milk.

Data related to the presence of metformin in breast milk are available from multiple studies (Briggs 2005; Eyal 2010; Gardiner 2003; Hale 2002).

• One study included 5 women who initiated metformin 500 mg twice daily immediately postpartum. Maternal plasma and breast milk were sampled prior to and ~2 hours after the morning dose, 4 to 17 days after delivery. Average concentrations of metformin in breast milk were <0.09 to 0.47 mcg/mL. Using the actual maternal weight from the patient with the highest average breast milk concentration (0.47 mcg/mL), authors of the study calculated the relative infant dose (RID) of metformin to be 1.08%, compared to a weight-adjusted maternal dose of 6.55 mg/kg/day providing an estimated daily infant dose via breast milk of 0.07 mg/kg/day. Adverse events were not observed in the breastfed infants (Briggs 2005).

• Breast milk was sampled in a subset of postpartum women taking metformin 1,500 mg/day (n = 1) or 2,000 mg/day (n = 3) who were part of a larger pharmacokinetic study. Using breast milk collected over one dosing interval, the RID of metformin ranged from 0.14% to 0.43% of the weight-adjusted maternal dose (Eyal 2010).

• According to the manufacturer, the decision to breastfeed during therapy should consider the risk of infant exposure, the benefits of breastfeeding to the infant, and the benefits of treatment to the mother. Using the limited data reported in the literature, the RID of metformin is ~0.11% to 1% of the maternal weight-adjusted dose.

• In general, breastfeeding is considered acceptable when the RID is <10% (Anderson 2016; Ito 2000).

Metformin has been detected in the serum of some breastfeeding infants. Because breast milk concentrations of metformin stay relatively constant, avoiding breastfeeding around peak plasma concentrations in the mother would not be helpful in reducing metformin exposure to the infant (Briggs 2005; Eyal 2010; Gardiner 2003; Hale 2002).

Appropriate glycemic control is required for the establishment of lactation in patients with diabetes mellitus (Anderson 2018). Breastfeeding provides metabolic benefits to mothers with diabetes mellitus as well as their infants; therefore, breastfeeding is encouraged (ACOG 201 2018; ADA 2022). According to the manufacturer, the decision to breastfeed during therapy should consider the risk of infant exposure, the benefits of breastfeeding to the infant, and the benefits of treatment to the mother.

Dietary Considerations

Drug may cause GI upset; take with food (to decrease GI upset). Take at the same time(s) each day. Dietary modification based on ADA recommendations is a part of therapy.

Monitoring Parameters

Urine for glucose and ketones, plasma glucose (individualize frequency based on treatment regimen, hypoglycemia risk, and other patient-specific factors; some patients may be candidates for continuous glucose monitoring) (ADA 2022). Monitor renal function (eGFR) prior to therapy initiation and at least annually or at least every 3 to 6 months if eGFR is <60 mL/minute/1.73 m2 (KDIGO 2020) or at least every 1 to 3 months in patients with hepatic impairment (expert opinion). Initial and annual monitoring of hematologic parameters (eg, hemoglobin/hematocrit and red blood cell indices); monitor folate if megaloblastic anemia is suspected. Monitor vitamin B12 serum concentrations every 1 to 2 years, particularly in patients who have been treated with metformin for ≥4 years, or in patients with peripheral neuropathy, anemia, or risk factors for vitamin B12 deficiency (eg, malabsorption syndromes, reduced dietary intake) (ADA 2022; KDIGO 2020; manufacturer’s labeling).

HbA1c: Monitor at least twice yearly in patients who have stable glycemic control and are meeting treatment goals; monitor quarterly in patients in whom treatment goals have not been met, or with therapy change. Note: In patients prone to glycemic variability (eg, patients with insulin deficiency), or in patients whose HbA1c is discordant with serum glucose levels or symptoms, consider evaluating HbA1c in combination with blood glucose levels and/or a glucose management indicator (ADA 2022; KDIGO 2020).

Reference Range

Recommendations for glycemic control in patients with diabetes:

Nonpregnant adults with diabetes (ADA 2022):

HbA1c: <7% (a more aggressive [<6.5%] or less aggressive [<8%] HbA1c goal may be targeted based on patient-specific characteristics). Note: In patients using a continuous glucose monitoring system, a goal of time in range >70% with time below range <4% is recommended and is similar to a goal HbA1c <7%.

Preprandial capillary blood glucose: 80 to 130 mg/dL (more or less stringent goals may be appropriate based on patient-specific characteristics).

Peak postprandial capillary blood glucose (~1 to 2 hours after a meal): <180 mg/dL (more or less stringent goals may be appropriate based on patient-specific characteristics).

Older adults (≥65 years of age) (ADA 2022):

Note: Consider less strict targets in patients who are using insulin and/or insulin secretagogues (sulfonylureas, meglitinides) (ES [LeRoith 2019]).

HbA1c: <7% to 7.5% (healthy); <8% to 8.5% (complex/intermediate health). Note: Individualization may be appropriate based on patient and caregiver preferences and/or presence of cognitive impairment. In patients with very complex or poor health (ie, limited remaining life expectancy), consider making therapy decisions based on avoidance of hypoglycemia and symptomatic hyperglycemia rather than HbA1c level.

Preprandial capillary blood glucose: 80 to 130 mg/dL (healthy); 90 to 150 mg/dL (complex/intermediate health); 100 to 180 mg/dL (very complex/poor health).

Bedtime capillary blood glucose: 80 to 180 mg/dL (healthy); 100 to 180 mg/dL (complex/intermediate health); 110 to 200 mg/dL (very complex/poor health).

Pregnant patients:

HbA1c: Pregestational diabetes (type 1 or type 2) (ADA 2022):

Preconception (patients planning for pregnancy): <6.5%.

During pregnancy: <6% (if can be achieved without significant hypoglycemia) or <7% (if needed to prevent hypoglycemia).

Capillary blood glucose: Note: Less stringent targets may be appropriate if goals cannot be achieved without causing significant hypoglycemia (ADA 2022).

Gestational diabetes mellitus (ADA 2022):

Fasting: <95 mg/dL.

Postprandial: <140 mg/dL (at 1 hour) or <120 mg/dL (at 2 hours).

Pregestational diabetes mellitus (type 1 or type 2) (ADA 2022):

Fasting: 70 to 95 mg/dL.

Postprandial: 110 to 140 mg/dL (at 1 hour) or 100 to 120 mg/dL (at 2 hours).

Children and adolescents:

Preprandial glucose: 70 to 130 mg/dL (ISPAD [Dimeglio 2018]).

Postprandial glucose: 90 to 180 mg/dL (ISPAD [Dimeglio 2018]).

Bedtime/overnight glucose: 80 to 140 mg/dL (ISPAD [Dimeglio 2018]).

HbA1c: <7%; target should be individualized; a more stringent goal (<6.5%) may be reasonable if it can be achieved without significant hypoglycemia; less aggressive goals (<7.5% or <8%) may be appropriate in patients who cannot articulate symptoms of hypoglycemia, cannot check glucose frequently, have a history of severe hypoglycemia, or have extensive comorbid conditions (ADA 2022; ISPAD [Dimeglio 2018]).

Surgical patients (ISPAD [Jefferies 2018]):

Intraoperative: 90 to 180 mg/dL.

ICU, postsurgery: 140 to 180 mg/dL.

Classification of hypoglycemia (ADA 2022):

Level 1: 54 to 70 mg/dL; hypoglycemia alert value; initiate fast-acting carbohydrate (eg, glucose) treatment.

Level 2: <54 mg/dL; threshold for neuroglycopenic symptoms; requires immediate action.

Level 3: Hypoglycemia associated with a severe event characterized by altered mental and/or physical status requiring assistance.

Mechanism of Action

Decreases hepatic glucose production, decreases intestinal absorption of glucose and improves insulin sensitivity (increases peripheral glucose uptake and utilization)

Pharmacokinetics

Onset of action: Within days; maximum effects up to 2 weeks.

Distribution: Vd: 654 ± 358 L; partitions into erythrocytes; concentrates in liver, kidney, and GI tract.

Protein binding: Negligible.

Metabolism: Not metabolized by the liver.

Bioavailability: Absolute: Fasting: 50% to 60%.

Half-life elimination: Plasma: 4 to 9 hours; Blood ~17.6 hours.

Time to peak, serum: Immediate release: 2 to 3 hours; ER tablet: 7 hours (range: 4 to 8 hours); ER suspension: 4.5 hours (range: 3.5 to 6.5 hours).

Excretion: Urine (90% as unchanged drug; active secretion).

Pharmacokinetics: Additional Considerations

Altered kidney function: Peak and systemic exposure is increased, and oral and renal clearance is decreased.

Pediatric: Obesity: In 22 pediatric patients who were obese (mean age: 14.5 ± 1.8 years; range: 11.1 to 17.5 years), pharmacokinetic analysis showed that clearance significantly increases and AUC decreases with increasing total body weight (van Rongen 2018).

Older adult: Total plasma clearance is decreased, half-life is prolonged, and Cmax is increased.

Pricing: US

Solution (metFORMIN HCl Oral)

500 mg/5 mL (per mL): $2.46

Solution (Riomet Oral)

500 mg/5 mL (per mL): $1.69

Tablet, 24-hour (Glumetza Oral)

500 mg (per each): $61.78

1000 mg (per each): $133.60

Tablet, 24-hour (metFORMIN HCl ER (MOD) Oral)

500 mg (per each): $8.40 - $55.99

1000 mg (per each): $16.67 - $120.24

Tablet, 24-hour (metFORMIN HCl ER (OSM) Oral)

500 mg (per each): $4.52 - $17.24

1000 mg (per each): $6.38 - $31.40

Tablet, 24-hour (metFORMIN HCl ER Oral)

500 mg (per each): $0.75 - $1.08

750 mg (per each): $1.20 - $1.61

Tablets (metFORMIN HCl Oral)

500 mg (per each): $0.04 - $1.80

625 mg (per each): $37.06

850 mg (per each): $0.06 - $1.20

1000 mg (per each): $0.07 - $2.40

Disclaimer: A representative AWP (Average Wholesale Price) price or price range is provided as reference price only. A range is provided when more than one manufacturer's AWP price is available and uses the low and high price reported by the manufacturers to determine the range. The pricing data should be used for benchmarking purposes only, and as such should not be used alone to set or adjudicate any prices for reimbursement or purchasing functions or considered to be an exact price for a single product and/or manufacturer. Medi-Span expressly disclaims all warranties of any kind or nature, whether express or implied, and assumes no liability with respect to accuracy of price or price range data published in its solutions. In no event shall Medi-Span be liable for special, indirect, incidental, or consequential damages arising from use of price or price range data. Pricing data is updated monthly.

Brand Names: International
  • Adecco (ID);
  • Aglurab (HR);
  • Alexodiab (EG);
  • Amophage (EG);
  • Andibet (CL);
  • Ansures (MY, PH);
  • Bentic (PY);
  • Biguax (CO);
  • Brot (HK);
  • Dabex (MX);
  • Dainipron (HK);
  • Deson (TH);
  • DH-Metglu 850 (VN);
  • DH-Metglu XR 1000 (VN);
  • Diabemet (MY);
  • Diabetmin (HK, MY, SG);
  • Diabetmin Retard (HK);
  • Diabetmin XR (SG);
  • Diabetol (PY);
  • Diabex (AU, KR);
  • Diabex XR (AU);
  • Diafat (PH);
  • Diaformin (BR, HK, UA);
  • Diaformin XR (AU, ID);
  • Diaformina (UY);
  • Diaformina LP (UY);
  • Dialon (AE, BH, KW, LB, QA, SA);
  • Diamet (JO);
  • Dianben (ES);
  • Diaphage (EG, LB);
  • Diaslim (TH);
  • Diformin (FI);
  • Diformin Retard (FI);
  • Dimefor (CO, MX, PE);
  • Dimet (ET);
  • Efomet XR (ID);
  • Euform Retard (PH);
  • Forbetes XR (ID);
  • Fordia MR (VN);
  • Fordica 500 XR (ID);
  • Formet (AU, JO, MY);
  • Formin (BD, IN);
  • Formit (AE, KW, QA, SA);
  • Fornidd (PH);
  • Glafornil (CL);
  • Glibudon (TW);
  • Glicenex (EC);
  • Glicophage (RO);
  • Glifage (BR);
  • Gliformin (CO, PH);
  • Glikos (ID);
  • Glisulin XR (CR, DO, GT, HN, NI, PA, SV);
  • Glucient (NL);
  • Gluciophage XR (VN);
  • Gluco (TH);
  • Glucodown (KR);
  • Glucofage (EC, VE);
  • Glucofor (ID);
  • Glucoform (PH);
  • Glucogen (KR);
  • Glucoles (TH);
  • Glucomet (ET, SG);
  • Glucomin (IL);
  • Glucomine (TW);
  • Glucon (MY);
  • Glucophage (AE, AR, AT, AU, BB, BE, BF, BH, BJ, BM, BS, BZ, CH, CI, CY, CZ, EE, EG, ET, FI, FR, GB, GH, GM, GN, GR, GY, HK, HR, ID, IE, IN, IQ, IR, IS, IT, JM, JO, KE, KW, LB, LR, LU, LV, LY, MA, ML, MR, MT, MU, MW, MX, MY, NE, NG, NO, OM, PE, PH, PK, PT, QA, RU, SA, SC, SD, SE, SI, SK, SL, SN, SR, SY, TN, TR, TT, TW, TZ, UA, UG, VN, YE, ZA, ZM, ZW);
  • Glucophage Forte (CZ, PH);
  • Glucophage Retard (EG, IL, QA);
  • Glucophage SR (GB, IE);
  • Glucophage XR (AE, BB, HK, KW, LB, MY);
  • Glucotin (PH);
  • Gludepatic (ID);
  • Glufor (ID);
  • Glumet (MY, PH, VE);
  • Glumet DC (MY);
  • Glumet Forte (HK);
  • Glumet XR (PH);
  • Glumin (ID);
  • Glumin XR (ID);
  • Glupa (KR);
  • Glustress (TH);
  • Glutamet (ET);
  • Glutomin (EG);
  • Glyciphage (IN);
  • Glycomet (SG, UA);
  • Glycomin (KR);
  • Glymet (AE, BH, CY, ET, IQ, IR, JO, KW, LY, OM, QA, SA, SY, YE);
  • Guamet (HK);
  • Humamet (PH);
  • Humamet XR (PH);
  • I-Max (PH);
  • Ifor (MX);
  • Indform (VN);
  • Insufor (UA);
  • Insumed (PH);
  • Islotin (AR);
  • Lucomet (IE);
  • Maformin (TH);
  • Mefarmil (UA);
  • Meglucon (VN);
  • Melbin (HK, JP);
  • Merckformin (HU);
  • Metaphage (BH);
  • Metchek (NZ);
  • Metdia (VN);
  • Metex XR (AU);
  • Metfar (BD);
  • Metfin (CH, ZW);
  • Metfocell (NL);
  • Metfogamma (DE, LV);
  • Metfor (AE, QA);
  • Metfor XR (PH);
  • Metforal (CR, DO, EC, GT, HN, IT, LT, LV, NI, PA, SG, SV);
  • Metform (BD);
  • Metformax (BE, LU);
  • Metgluco (JP);
  • Metgreen-SR (KR);
  • Metnova (NL);
  • Metophage (IE);
  • Metta SR (ZW);
  • Miformin (TH);
  • Mitforgen (DK, SE);
  • Neoform (PH);
  • Normax (PH);
  • Omformin (BH);
  • Orabet (AT, IE);
  • Panfor SR (PH);
  • Predial (CR, DO, GT, HN, NI, PA, SV);
  • Quexel (CR, DO, EC, GT, HN, NI, PA, SV);
  • Risidon (HK, PT);
  • Siamformet (TH);
  • Siofor (BG, PL, SI, SK);
  • Stagid (PT);
  • Sucranorm (PH);
  • Sukkarto SR (GB);
  • Thiabet (DE);
  • Walaphage (IN);
  • Xmet (ET);
  • Yaltormin (IE)


For country code abbreviations (show table)
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