(met FOR min)
- Metformin HCl
- Metformin Hydrochloride
Excipient information presented when available (limited, particularly for generics); consult specific product labeling.
D-Care DM2: Extended release tablet, as hydrochloride: 500 mg
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]
Tablet, Oral, as hydrochloride:
Glucophage: 500 mg, 850 mg
Glucophage: 1000 mg [scored]
Generic: 500 mg, 850 mg, 1000 mg
Tablet Extended Release 24 Hour, Oral, as hydrochloride:
Fortamet: 500 mg, 1000 mg
Glucophage XR: 500 mg, 750 mg
Glumetza: 500 mg, 1000 mg
Generic: 500 mg, 750 mg, 1000 mg
Brand Names: U.S.
- D-Care DM2
- Glucophage XR
- Antidiabetic Agent, Biguanide
Decreases hepatic glucose production, decreasing intestinal absorption of glucose and improves insulin sensitivity (increases peripheral glucose uptake and utilization)
Vd: 654 ± 358 L; partitions into erythrocytes; concentrates in liver, kidney, and GI tract
Not metabolized by the liver
Urine (90% as unchanged drug; active secretion)
Onset of Action
Within days; maximum effects up to 2 weeks
Time to Peak
Immediate release: 2 to 3 hours; Extended release: 7 hours (range: 4 to 8 hours)
Plasma: 4 to 9 hours; Blood ~17.6 hours
Special Populations: Renal Function Impairment
Peak and systemic exposure is increased and oral and renal Cl is decreased.
Special Populations: Elderly
Total plasma Cl is decreased, half-life is prolonged, and Cmax is increased.
Use: Labeled Indications
Diabetes mellitus, type 2: Management of type 2 diabetes mellitus (noninsulin dependent, NIDDM) when hyperglycemia cannot be managed with diet and exercise alone.
Note: If not contraindicated and if tolerated, metformin is the preferred initial pharmacologic agent for type 2 diabetes management (ADA 2018a).
Off Label Uses
Antipsychotic-induced weight gain
Data from multiple meta-analyses with varying degrees of heterogeneity (primarily in patients with schizophrenia and schizoaffective disorder) support the use of metformin in promoting modest weight loss and preventing weight gain associated with second-generation antipsychotics in adult patients [de Silva 2016], [Mizuno 2014], [Zheng 2015]. Additional data are necessary to further define the role of metformin in this condition.
Based on British Association for Psychopharmacology guidelines on the management of weight gain, metabolic disturbances and cardiovascular risk associated with psychosis and antipsychotic drug treatment, metformin should be considered to attenuate or reduce weight gain caused by antipsychotics after behavioral interventions have failed [Cooper 2016]. Based on the Canadian Network for Mood and Anxiety Treatments (CANMAT) recommendations for the management of patients with mood disorders and comorbid metabolic disorders, metformin is recommended as a second-line option after nonpharmacologic strategies for managing weight gain in patients with bipolar and major depressive disorders and is recognized as often being used as a secondary prevention strategy for antipsychotic-related weight gain [CANMAT [McIntyre 2012]].
Diabetes mellitus, type 2 (prevention)
Data from a multicenter, placebo-controlled clinical trial involving 3,234 nondiabetic patients at high risk for developing diabetes showed that metformin treatment reduced the incidence of diabetes compared to the placebo group [Knowler 2002].
Based on the American Diabetic Association (ADA) guidelines for the Standards of Medical Care in Diabetes, metformin is effective and may be considered for the prevention of type 2 diabetes in patients with prediabetes (ie, impaired glucose tolerance (IGT), impaired fasting glucose (IFG), or an HbA1c 5.7% to 6.4%), especially for those with BMI >35 kg/m2, <60 years, and women with prior history of gestational diabetes.
Based on the Endocrine Society Guidelines for the Diagnosis and Treatment of Polycystic Ovary Syndrome (PCOS), metformin is recommended for prevention of type 2 diabetes in women with PCOS and IGT when lifestyle modification has not been successful [Legro 2013].
Gestational diabetes mellitus (GDM)
Based on the American Diabetic Association (ADA) guidelines for the Standards of Medical Care in Diabetes, metformin may be considered an option in the treatment of gestational diabetes mellitus based on short-term safety and efficacy studies. However, because long-term safety data is not available, insulin is the preferred treatment when pharmacologic therapy is needed.
Polycystic ovary syndrome in women with anovulatory infertility
Controlled trials and meta-analyses indicate that pregnancy and live birth rates in obese women with polycystic ovary syndrome (PCOS) and anovulatory infertility are higher with clomiphene than metformin. The addition of metformin to clomiphene may increase ovulation and pregnancy rates but does not increase live birth rates compared with clomiphene alone. Metformin use is associated with a lower risk of multiple pregnancy compared with clomiphene. The relative efficacy of metformin and clomiphene in nonobese women is unclear due to limited data. Guidelines from the Endocrine Society and the Society of Obstetricians and Gynaecologists of Canada (SOGC) recommend clomiphene as the first-line drug for ovulation induction in women with PCOS and anovulatory infertility. Letrozole is also recommended as a first-line choice. For women with clomiphene resistance, the addition of metformin to clomiphene is recommended by the Endocrine Society and National Institute for Health and Clinical Excellence (NICE). The SOGC recommends clomiphene plus metformin specifically for women with clomiphene resistance who are older than 28 years with visceral obesity.
Polycystic ovary syndrome in women with menstrual irregularities
Data from controlled trials and meta-analyses indicate that metformin may improve menstrual patterns in some women with polycystic ovary syndrome (PCOS), but metformin is less effective than combination oral contraceptives. It is unknown whether the improvement in ovulation rate from metformin is associated with a risk reduction for endometrial carcinoma. Endocrine Society clinical guidelines on PCOS consider metformin a second-line therapy for menstrual irregularities in women who cannot take or tolerate hormonal contraception.
Prevention of ovarian hyperstimulation syndrome in women with polycystic ovary syndrome
Controlled trials and meta-analyses indicate that metformin significantly reduces the risk of ovarian hyperstimulation syndrome (OHSS) in women with polycystic ovary syndrome (PCOS) receiving a gonadotropin during in vitro fertilization (IVF). The number needed to treat for metformin to prevent one case of OHSS is 5. Endocrine Society guidelines for management of PCOS suggest using metformin as adjuvant therapy to prevent OHSS in women with PCOS undergoing IVF.
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 I) 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; breast-feeding
Diabetes mellitus, type 2: Oral: Note: Clinically significant responses may not be seen at doses <1,500 mg/day; however, a lower recommended starting dose and gradual increased dosage is recommended to minimize GI symptoms. If HbA1c is ≥9% at initiation of therapy consider dual therapy (metformin + a second antihyperglycemic agent) (ADA 2018a).
Immediate-release tablet or solution: Adults ≥17 years:
Initial: Manufacturer labeling: 500 mg twice daily or 850 mg once daily; alternatively, an initial dose of 500 mg once daily has been recommended (Nathan 2009)
Titrate in increments of 500 mg weekly or 850 mg every other week; may also titrate from 500 mg twice a day to 850 mg twice a day after 2 weeks; usual effective dose is 850 to 1,000 mg twice daily; modest additional benefit may be observed with doses up to ~2,500 mg/day but their use may be limited by adverse GI effects (Nathan 2009). If a dose >2,000 mg/day is considered, it may be better tolerated in 3 divided doses; maximum recommended dose: 2,550 mg/day.
Initial: 500 to 1,000 mg once daily; dosage may be increased by 500 mg weekly up to a maximum of 2,000 mg/day (Glucophage XR, Glumetza) or 2,500 mg/day (Fortamet). If glycemic control is not achieved at maximum dose, may divide dose and administer twice daily.
Conversion from immediate-release to extended-release tablets: Patients receiving metformin immediate release may be switched to metformin ER once daily at the same total daily dose, up to 2,000 mg once daily (2,500 mg for Fortamet)
Transfer from other antidiabetic agents: No transition period is generally necessary except when transferring from chlorpropamide. When transferring from chlorpropamide, care should be exercised during the first 2 weeks because of the prolonged retention of chlorpropamide in the body, leading to overlapping drug effects and possible hypoglycemia.
Concomitant use with insulin or insulin secretagogues: Reduced dose of insulin or insulin secretagogues (eg, sulfonylureas) may be needed.
Antipsychotic-induced weight gain (off-label use):
Immediate-release: Oral: Initial: 250 to 500 mg twice daily; may increase after 3 to 7 days to 500 mg two or three times daily based on tolerability. Doses as high as 2,550 mg/day have been studied (Chen 2013, de Silva 2016, Wang 2012).
Extended-release: Oral: Initial: 500 mg once daily for 2 to 6 weeks, then increase to 1,000 mg once daily; may continue dosage increases in 500 mg increments every 6 weeks based on tolerability up to 2,000 mg/day (Carrizo 2009, Rado 2016).
Diabetes mellitus, type 2, prevention (off-label use): Immediate-release tablet or solution: Oral: Initial: 850 mg once daily; Target: 850 mg twice daily (Knowler 2002)
Polycystic ovary syndrome with anovulatory infertility (off-label use): Females: Oral:
Immediate release: 1,500 to 2,000 mg/day in 2 or 3 divided doses (Johnson 2010; Moll 2006; Morin-Papunen 2012)
Extended release: 1,000 mg twice daily (Legro 2007)
Note: Metformin should be initiated at lower doses (500 mg daily) and increased gradually over 1 to 2 weeks to the target dose to minimize adverse effects (eg, GI intolerance) (Johnson 2010; Legro 2007; Moll 2006; Morin-Papunen 2012)
Polycystic ovary syndrome with menstrual irregularities (off-label use): Females: Oral: Immediate release: 500 mg 2 or 3 times daily, up to 1,000 mg twice daily (Costello 2007; Morin-Papunen 2003; Meyer 2007; Moghetti 2000). The dose of metformin should be increased gradually to minimize GI adverse effects (Meyer 2007)
Note: When metformin is used, cyclic progestin therapy may be added for the first 6 months of metformin treatment, until regular cycles are established.
Prevention of ovarian hyperstimulation syndrome with polycystic ovary syndrome (off-label use): Females: Oral: Immediate release: 1,000 mg to 2,550 mg per day as 500 mg 2 or 3 times per day or 850 mg 2 or 3 times per day (Palomba 2013; Palomba 2011; Tang 2006; Tso 2014). The dose of metformin should be increased gradually to minimize GI adverse effects.
Note: Pretreatment with metformin may be started as early as 16 weeks prior (but typically 4 to 5 weeks prior) to as late as the first day of gonadotropin-releasing hormone (GnRH) agonist administration; some studies continued metformin therapy during gonadotropin ovarian stimulation (Tso 2014).
Refer to adult dosing. The initial and maintenance dosing should be conservative, due to the potential for decreased renal function (monitor).
Diabetes mellitus, type 2: Oral: Note: Clinically significant responses may not be seen at doses <1,500 mg daily; however, a lower recommended starting dose and gradual increased dosage is recommended to minimize gastrointestinal symptoms.
Immediate-release tablet or solution:
Children ≥10 years and Adolescents ≤16 years: Initial: 500 mg twice daily; increases in daily dosage should be made in increments of 500 mg at weekly intervals, given in divided doses, up to a maximum of 2,000 mg/day
Adolescents ≥17 years: Refer to adult dosing.
Off-label dosing: Children ≥10 years and Adolescents <18 years: Initial: 500 mg once daily for 7 days, then increase in 500 mg increments at 1- to 2-week intervals to a target dose of 1,000 mg twice daily; maximum: 2,000 mg/day (AAP [Copeland 2013]; ISPAD [Zeitzler 2014])
Children ≥10 years and Adolescents ≤16 years (off-label): Limited data available: Initial: 500 mg once daily; dosage may be increased by 500 mg at 1- to 2-week intervals; maximum dose: 2,000 mg/day (AAP [Copeland 2013]; ISPAD [Zeitzler 2014])
Adolescents ≥17 years: Fortamet, Glucophage XR: Refer to adult dosing.
Dosing: Renal Impairment
eGFR >45 mL/minute/1.73 m2: No dosage adjustment necessary; monitor renal function at least annually. More frequent monitoring (every 3 to 6 months) and a maximum dose of 2,000 mg/day has been recommended for patients with eGFR >45 to <60 mL/minute/1.73 m2 (ADA [Lipska 2011]; Inzucchi 2014).
eGFR 30 to 45 mL/minute/1.73 m2:
Preexisting impairment: Use is not recommended for initiation of therapy by some experts (AACE [Garber 2017]; ADA [Lipska 2011]; Inzucchi 2014); however, others recommend that in the absence of active kidney disease and/or conditions that predispose to hypoperfusion and hypoxemia (eg, acute heart failure, dehydration) therapy may be initiated at half the usual initial dose (eg, 250 mg/day) with close monitoring and titration (maximum: 1,000 mg/day) (McCulloch 2017).
If eGFR falls between 30 to <45 mL/minute/1.73 m2 during therapy: Consider benefits/risks of continuing therapy. If continuing therapy, a dosage reduction of 50% (maximum: 1,000 mg/day) and monitoring of renal function every 3 months is recommended (ADA [Lipska 2011]; Inzucchi 2014).
eGFR <30 mL/minute/1.73 m2: Use is contraindicated.
Dosing: Hepatic Impairment
The manufacturer recommends avoiding metformin since liver disease is considered a risk factor for the development of lactic acidosis during metformin therapy. However, continued use of metformin in diabetics with liver dysfunction, including cirrhosis, has been used successfully and may be associated with a survival benefit in carefully selected patients; use cautiously in patients at risk for lactic acidosis (eg, renal impairment, alcohol use) (Brackett 2010; Zhang 2014).
Oral: Administer with a meal (to decrease GI upset).
Extended release: Swallow whole; do not crush, break, or chew. Administer once daily doses with the evening meal. Fortamet should also be administered with a full glass of water.
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. Monitor for signs and symptoms of vitamin B12 and/or folic acid deficiency; supplementation may be required.
Oral solution: Store at 15°C to 30°C (59°F to 86°F).
Tablets: Store at 20°C to 25°C (68°F to 77°F); excursion permitted to 15°C to 30°C (59°F to 86°F). Protect from light and moisture.
Abemaciclib: May increase the serum concentration of MetFORMIN. Monitor therapy
Alcohol (Ethyl): May enhance the adverse/toxic effect of MetFORMIN. Specifically, alcohol may potentiate the risk of lactic acidosis Avoid combination
Alpha-Lipoic Acid: May enhance the hypoglycemic effect of Antidiabetic Agents. Monitor therapy
Androgens: May enhance the hypoglycemic effect of Blood Glucose Lowering Agents. Exceptions: Danazol. Monitor therapy
BuPROPion: May increase the serum concentration of OCT2 Substrates. Monitor therapy
Carbonic Anhydrase Inhibitors: May enhance the adverse/toxic effect of MetFORMIN. Specifically, the risk of developing lactic acidosis may be increased. Exceptions: Brinzolamide; Dorzolamide. Monitor therapy
Cephalexin: May increase the serum concentration of MetFORMIN. 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). Consider therapy modification
Dalfampridine: MetFORMIN may increase the serum concentration of Dalfampridine. Dalfampridine may increase the serum concentration of MetFORMIN. Monitor therapy
Dofetilide: MetFORMIN may increase the serum concentration of Dofetilide. Monitor therapy
Dolutegravir: May increase the serum concentration of MetFORMIN. Management: Limit the daily metformin dose to 1,000 mg when used together with dolutegravir. Metformin dose adjustments may also be needed upon discontinuation of dolutegravir. Monitor patient response to metformin closely. Consider therapy modification
Glycopyrrolate (Systemic): May increase the serum concentration of MetFORMIN. Monitor therapy
Guanethidine: May enhance the hypoglycemic effect of Antidiabetic Agents. Monitor therapy
Hyperglycemia-Associated Agents: May diminish the therapeutic effect of Antidiabetic Agents. Monitor therapy
Hypoglycemia-Associated Agents: Antidiabetic Agents may enhance the hypoglycemic effect of Hypoglycemia-Associated Agents. 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. Exceptions: Diatrizoate Meglumine; Diatrizoate Sodium; Ethiodized Oil. Consider therapy modification
Isavuconazonium Sulfate: May increase the serum concentration of MetFORMIN. Monitor therapy
LamoTRIgine: May increase the serum concentration of MetFORMIN. Management: The lamotrigine Canadian product monograph states that coadministration of these drugs is not recommended. Monitor therapy
Monoamine Oxidase Inhibitors: May enhance the hypoglycemic effect of Blood Glucose Lowering Agents. Monitor therapy
Ombitasvir, Paritaprevir, and Ritonavir: May enhance the adverse/toxic effect of MetFORMIN. Specifically, the risk for lactic acidosis may be increased. Monitor therapy
Ombitasvir, Paritaprevir, Ritonavir, and Dasabuvir: May enhance the adverse/toxic effect of MetFORMIN. Specifically, the risk for lactic acidosis may be increased. Monitor therapy
Ondansetron: May increase the serum concentration of MetFORMIN. Monitor therapy
Patiromer: May decrease the serum concentration of MetFORMIN. Management: Administer metformin at least 3 hours before or 3 hours after patiromer. Consider therapy modification
Pegvisomant: May enhance the hypoglycemic effect of Blood Glucose Lowering Agents. Monitor therapy
Prothionamide: May enhance the hypoglycemic effect of Blood Glucose Lowering Agents. Monitor therapy
Quinolones: May enhance the hypoglycemic effect of Blood Glucose Lowering Agents. Quinolones may diminish the therapeutic effect of Blood Glucose Lowering Agents. Specifically, if an agent is being used to treat diabetes, loss of blood sugar control may occur with quinolone use. Monitor therapy
Ranolazine: May increase the serum concentration of MetFORMIN. Management: Limit the metformin dose to a maximum of 1700 mg/day when used together with ranolazine 1000 mg twice daily. Consider therapy modification
Salicylates: May enhance the hypoglycemic effect of Blood Glucose Lowering Agents. Monitor therapy
Selective Serotonin Reuptake Inhibitors: May enhance the hypoglycemic effect of Blood Glucose Lowering Agents. Monitor therapy
Thiazide and Thiazide-Like Diuretics: May diminish the therapeutic effect of Antidiabetic Agents. Monitor therapy
Topiramate: May enhance the adverse/toxic effect of MetFORMIN. Monitor therapy
Trimethoprim: May increase the serum concentration of MetFORMIN. Monitor therapy
Trospium: MetFORMIN may decrease the serum concentration of Trospium. Monitor therapy
Vandetanib: May increase the serum concentration of MetFORMIN. Monitor therapy
Verapamil: May diminish the therapeutic effect of MetFORMIN. Monitor therapy
Gastrointestinal: Diarrhea (IR tablet: 12% to 53%; ER tablet: 10% to 17%), nausea and vomiting (IR tablet: 26%; ER tablet: 7%), flatulence (4% to 12%)
Infection: Infection (21%)
1% to 10%:
Cardiovascular: Chest discomfort, flushing, palpitations
Central nervous system: Headache (5% to 6%), chills, dizziness, taste disorder
Dermatologic: Diaphoresis, nail disease, skin rash
Endocrine & metabolic: Decreased vitamin B12 serum concentrate (7%), hypoglycemia
Gastrointestinal: Nausea (7% to 9%), dyspepsia (≤7%), abdominal distress (6%), abdominal pain (3% to 4%), abdominal distention, abnormal stools, constipation, heartburn
Neuromuscular & skeletal: Weakness (9%), myalgia
Respiratory: Rhinitis (4% to 6%), dyspnea, flu-like symptoms, upper respiratory tract infection
Miscellaneous: Accidental injury (6% to 7%)
<1%, postmarketing and/or case reports: Hepatic injury (cholestatic, hepatocellular, and mixed), lactic acidosis
Concerns related to adverse effects:
• Lactic acidosis: [US Boxed Warning]: Postmarketing cases of metformin-associated lactic acidosis have resulted in death, hypothermia, hypotension, and resistant bradyarrhythmias. The onset is often subtle, accompanied by nonspecific symptoms (eg, malaise, myalgias, respiratory distress, somnolence, abdominal pain); elevated blood lactate levels (>5 mmol/L); anion gap acidosis (without evidence of ketonuria or ketonemia); increased lactate:pyruvate ratio; metformin plasma levels generally >5 mcg/mL. Risk factors for lactic acidosis include patients with renal impairment, concomitant use of certain drugs (eg, carbonic anhydrase inhibitors such as topiramate), ≥65 years, having a radiologic study with contrast, surgery and other procedures, hypoxic states (eg, acute heart failure), excessive alcohol intake, and hepatic impairment. Discontinue immediately if lactic acidosis is suspected; prompt hemodialysis is recommended. Lactic acidosis should be suspected in any patient with diabetes receiving metformin with evidence of acidosis but without evidence of ketoacidosis. Discontinue use in patients with conditions associated with dehydration, hypoperfusion, sepsis, or hypoxemia. Temporarily discontinue therapy in patients with restricted food and fluid intake. The risk of accumulation and lactic acidosis increases with the degree of impairment of renal function.
• Vitamin B12 concentrations: Long-term metformin use is associated with vitamin B12 deficiency; monitor vitamin B12 serum concentrations periodically with long-term therapy. Monitoring of B12 serum concentrations should be considered in all patients receiving metformin and in particular those with peripheral neuropathy or anemia (ADA 2018d).
• Heart failure: Metformin may be used in patients with stable heart failure (HF); avoid use in unstable or hospitalized patients with heart failure (ADA 2018h). Risk of lactic acidosis may be increased secondary to hypoperfusion. In a scientific statement from the American Heart Association, metformin has been determined to be an agent that may exacerbate underlying myocardial dysfunction (magnitude: major) (AHA [Page 2016]). Use of metformin in patients with HF may be associated with reduced mortality and reduction in hospital readmission for HF (Crowley 2017; Eurich 2013).
• Hepatic impairment: The manufacturer recommends to generally avoid use in patients with hepatic impairment due to potential for lactic acidosis. However, continued use of metformin in patients with diabetes with liver dysfunction, including cirrhosis, may be associated with a survival benefit in carefully selected patients (Brackett 2010; Crowley 2017; Zhang 2014).
• Renal impairment: Metformin is substantially excreted by the kidney; assess renal function prior to initiation of therapy and periodically thereafter using estimated glomerular filtration rate (eGFR); the risk of metformin accumulation and lactic acidosis increases with degree of renal impairment. Use is contraindicated in patients with eGFR <30 mL/minute/1.73 m2. Assess benefits/risks of metformin use in patients with eGFR 30 to 45 mL/minute/1.73 m2; if used, dosage reduction is recommended (ADA [Lipska 2011]; Inzucchi 2014; McCulloch 2017). Some experts recommend avoiding initiation of metformin in these patients (AACE [Garber 2017]; ADA [Lipska 2011]; Inzucchi 2014), while others suggest initiation may be reasonable in the absence of active kidney disease and/or conditions that predispose to hypoperfusion and hypoxemia (McCulloch 2017). Use of concomitant medications that may affect renal function (ie, affect tubular secretion) may also affect metformin disposition. Metformin should be withheld in patients with dehydration and/or prerenal azotemia.
• Stress-related states: It may be necessary to discontinue metformin and administer insulin if the patient is exposed to stress (fever, trauma, infection, surgery).
Concurrent drug therapy issues:
• Drug-drug interactions: Potentially significant interactions may exist, requiring dose or frequency adjustment, additional monitoring, and/or selection of alternative therapy. Consult drug interactions database for more detailed information.
• Elderly: Use with caution; risk of metformin associated lactic acidosis increases with age.
Dosage form specific issues:
• Extended-release tablet: Insoluble tablet shell (Glumetza 1,000 mg tablet) may remain intact and be visible in the stool. Other extended-released tablets (Fortamet, Glucophage XR, Glumetza 500 mg) may appear in the stool as a soft mass resembling the tablet.
• Appropriate use: Not indicated for use in patients with type 1 diabetes mellitus or with diabetic ketoacidosis (DKA).
• Ethanol use: Instruct patients to avoid excessive acute or chronic ethanol use; ethanol may potentiate metformin's effect on lactate metabolism.
• Iodinated contrast: Temporarily discontinue metformin at the time of or before iodinated contrast imaging procedures in patients with an eGFR 30 to 60 mL/minute/1.73 m2; or with a history of hepatic disease, alcoholism, or heart failure; or in patients who will receive intra-arterial iodinated contrast. Reevaluate eGFR 48 hours after imaging procedure; restart if renal function is stable. Alternatively, the American College of Radiology (ACR) guidelines recommend that metformin may be used prior to or following administration of iodinated contrast media in patients with no evidence of acute kidney injury (AKI) and with an eGFR ≥30 mL/minute/1.73 m2; ACR guidelines recommend temporary discontinuation of metformin in patients with known AKI or severe chronic kidney disease ([stage IV or V [ie, eGFR <30 mL/minute/1.73 m2]) or who are undergoing arterial catheter studies (ACR 2017).
• Patient education: Diabetes self-management education (DSME) is essential to maximize the effectiveness of therapy.
• Surgical procedures: Metformin should be withheld the day of surgery (all other oral hypoglycemic agents should be withheld the morning of surgery or procedure) (ADA 2018e). Restart only after normal oral intake resumed and normal renal function is verified.
Urine for glucose and ketones, fasting blood glucose, hemoglobin A1c (at least twice yearly in patients who have stable glycemic control and are meeting treatment goals; quarterly in patients not meeting treatment goals or with therapy change [ADA 2018g]). Initial and periodic monitoring of hematologic parameters (eg, hemoglobin/hematocrit and red blood cell indices); renal function (eGFR) prior to therapy initiation and at least annually (more often in patients at risk of developing renal impairment; every 3 to 6 months if eGFR 45 to <60 mL/minute/1.73 m2; every 3 months if eGFR 30 to <45 mL/minute/1.73 m2 [Lipska 2011]). Monitor vitamin B12 serum concentrations periodically with long-term therapy; folate (if megaloblastic anemia is suspected).
Pregnancy Risk Factor
Adverse events have not been observed in animal reproduction studies. Metformin has been found to cross the placenta in concentrations which may be comparable to those found in the maternal plasma. Pharmacokinetic studies suggest that clearance of metformin may increase during pregnancy and dosing may need adjusted in some women when used during the third trimester (Charles 2006; de Oliveira Baraldi 2011; Eyal 2010; Gardiner 2003; Hughes 2006; Vanky 2005).
An increased risk of birth defects or adverse fetal/neonatal outcomes has not been observed following maternal use of metformin for GDM or type 2 diabetes when glycemic control is maintained (Balani 2009; Coetzee 1979; Coetzee 1984; Ekpebegh 2007; Niromanesh 2012; Rowan 2008; Rowan 2010; Tertti 2008).
In women with diabetes, maternal hyperglycemia can be associated with congenital malformations as well as adverse effects in the fetus, neonate, and the mother (ACOG 2005; ADA 2018c; Kitzmiller 2008; Metzger 2007). 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 (ACOG 2013; ADA 2018c; Blumer 2013; Kitzmiller 2008). Agents other than metformin are currently recommended to treat diabetes in pregnant women (ADA 2018c).
• Discuss specific use of drug and side effects with patient as it relates to treatment. (HCAHPS: During this hospital stay, were you given any medicine that you had not taken before? Before giving you any new medicine, how often did hospital staff tell you what the medicine was for? How often did hospital staff describe possible side effects in a way you could understand?)
• Patient may experience diarrhea, flatulence, nausea, vomiting, or loss of strength and energy. Have patient report immediately to prescriber signs of lactic acidosis (fast breathing, tachycardia, abnormal heartbeat, vomiting, fatigue, shortness of breath, severe loss of strength and energy, severe dizziness, feeling cold, or muscle pain or cramps), signs of low blood sugar (dizziness, headache, fatigue, feeling weak, shaking, tachycardia, confusion, increased hunger, or sweating), pharyngitis, chills, or severe abdominal pain (HCAHPS).
• Educate patient about signs of a significant reaction (eg, wheezing; chest tightness; fever; itching; bad cough; blue skin color; seizures; or swelling of face, lips, tongue, or throat). Note: This is not a comprehensive list of all side effects. Patient should consult prescriber for additional questions.
Intended Use and Disclaimer:Should not be printed and given to patients. This information is intended to serve as a concise initial reference for health care professionals to use when discussing medications with a patient. You must ultimately rely on your own discretion, experience, and judgment in diagnosing, treating, and advising patients.
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