METFORMIN HYDROCHLORIDE

Metformin hydrochloride tablets, USP are oral antihyperglycemic drugs used in the management of type 2 diabetes. Metformin hydrochloride ( N,N- dimethylimidodicarbonimidic diamide hydrochloride) is not chemically or pharmacologically related to any other classes of oral antihyperglycemic agents. The structural formula is as shown: Metformin hydrochloride, USP is a white to off-white crystalline compound with a molecular formula of C 4 H 11 N 5 • HCl and a molecular weight of 165.63. Metformin hydrochloride, USP is freely soluble in water and is practically insoluble in acetone, ether, and chloroform. The pK a of metformin is 12.4. The pH of a 1% aqueous solution of metformin hydrochloride is 6.68. Metformin hydrochloride tablets, USP for oral administration, contains 500 mg, 850 mg, or 1000 mg of metformin hydrochloride, USP. Each tablet contains the inactive ingredients povidone and magnesium stearate. In addition, the coating for the 500 mg, 850 mg, and 1000 mg contains hypromellose and polyethylene glycol. Chemical Structure

Metformin hydrochloride tablets are indicated as an adjunct to diet and exercise to improve glycemic control in adults and children with type 2 diabetes mellitus.

There is no fixed dosage regimen for the management of hyperglycemia in patients with type 2 diabetes with metformin or any other pharmacologic agent. Dosage of metformin must be individualized on the basis of both effectiveness and tolerance, while not exceeding the maximum recommended daily doses. The maximum recommended daily dose of metformin hydrochloride tablets is 2550 mg in adults and 2000 mg in pediatric patients (10 to 16 years of age). Metformin hydrochloride tablets should be given in divided doses with meals and should be started at a low dose, with gradual dose escalation, to reduce gastrointestinal side effects and to permit identification of the minimum dose required for adequate glycemic control of the patient. During treatment initiation and dose titration (see Recommended Dosing Schedule ), fasting plasma glucose should be used to determine the therapeutic response to metformin and identify the minimum effective dose for the patient. Thereafter, glycosylated hemoglobin should be measured at intervals of approximately 3 months. The therapeutic goal should be to decrease both fasting plasma glucose and glycosylated hemoglobin levels to normal or near normal by using the lowest effective dose of metformin, either when used as monotherapy or in combination with sulfonylurea or insulin. Monitoring of blood glucose and glycosylated hemoglobin will also permit detection of primary failure, i.e., inadequate lowering of blood glucose at the maximum recommended dose of medication, and secondary failure, i.e., loss of an adequate blood glucose lowering response after an initial period of effectiveness. Short-term administration of metformin may be sufficient during periods of transient loss of control in patients usually well-controlled on diet alone. Recommended Dosing Schedule Adults The usual starting dose of metformin hydrochloride tablets is 500 mg twice a day or 850 mg once a day, given with meals. In general, clinically significant responses are not seen at doses below 1500 mg per day. Dosage increases should be made in increments of 500 mg weekly or 850 mg every 2 weeks, up to a total of 2000 mg per day, given in divided doses. The dosage of metformin hydrochloride tablets must be individualized on the basis of both effectiveness and tolerability. Patients can also be titrated from 500 mg twice a day to 850 mg twice a day after 2 weeks. For those patients requiring additional glycemic control, metformin hydrochloride tablets may be given to a maximum daily dose of 2550 mg per day. Doses above 2000 mg may be better tolerated given 3 times a day with meals. Pediatrics The usual starting dose of metformin hydrochloride tablets is 500 mg twice a day, given with meals. Dosage increases should be made in increments of 500 mg weekly up to a maximum of 2000 mg per day, given in divided doses. The dosage of metformin hydrochloride tablets must be individualized on the basis of both effectiveness and tolerability. Recommendations for Use in Renal Impairment Assess renal function prior to initiation of metformin hydrochloride tablets and periodically thereafter. Metformin hydrochloride tablet is contraindicated in patients with an estimated glomerular filtration rate (eGFR) below 30 mL/minute/1.73 m 2 . Initiation of metformin hydrochloride tablets in patients with an eGFR between 30 to 45 mL/minute/1.73 m 2 is not recommended. In patients taking metformin hydrochloride tablets whose eGFR later falls below 45 mL/min/1.73 m 2 , assess the benefit risk of continuing therapy. Discontinue metformin hydrochloride tablets if the patient's eGFR later falls below 30 mL/minute/1.73 m 2 (See WARNINGS and PRECAUTIONS ). Discontinuation for Iodinated Contrast Imaging Procedures Discontinue metformin hydrochloride tablets at the time of, or prior to, an iodinated contrast imaging procedure in patients with an eGFR between 30 and 60 mL/min/1.73 m 2 ; in patients with a history of liver disease, alcoholism or heart failure; or in patients who will be administered intra-arterial iodinated contrast. Re-evaluate eGFR 48 hours after the imaging procedure; restart metformin hydrochloride tablets if renal function is stable. Concomitant Metformin and Oral Sulfonylurea Therapy in Adult Patients If patients have not responded to 4 weeks of the maximum dose of metformin monotherapy, consideration should be given to gradual addition of an oral sulfonylurea while continuing metformin at the maximum dose, even if prior primary or secondary failure to a sulfonylurea has occurred. Clinical and pharmacokinetic drug-drug interaction data are currently available only for metformin plus glyburide (glibenclamide). With concomitant metformin and sulfonylurea therapy, the desired control of blood glucose may be obtained by adjusting the dose of each drug. In a clinical trial of patients with type 2 diabetes and prior failure on glyburide, patients started on metformin hydrochloride tablets 500 mg and glyburide 20 mg were titrated to 1000/20 mg, 1500/20 mg, 2000/20 mg, or 2500/20 mg of metformin hydrochloride tablets and glyburide, respectively, to reach the goal of glycemic control as measured by FPG, HbA 1c , and plasma glucose response (see CLINICAL PHARMACOLOGY: Clinical Studies ). However, attempts should be made to identify the minimum effective dose of each drug to achieve this goal. With concomitant metformin and sulfonylurea therapy, the risk of hypoglycemia associated with sulfonylurea therapy continues and may be increased. Appropriate precautions should be taken. (See Package Insert of the respective sulfonylurea.) If patients have not satisfactorily responded to 1 to 3 months of concomitant therapy with the maximum dose of metformin and the maximum dose of an oral sulfonylurea, consider therapeutic alternatives including switching to insulin with or without metformin. Concomitant Metformin and Insulin Therapy in Adult Patients The current insulin dose should be continued upon initiation of metformin therapy. Metformin therapy should be initiated at 500 mg once daily in patients on insulin therapy. For patients not responding adequately, the dose of metformin should be increased by 500 mg after approximately 1 week and by 500 mg every week thereafter until adequate glycemic control is achieved. The maximum recommended daily dose is 2500 mg for metformin hydrochloride tablets. It is recommended that the insulin dose be decreased by 10% to 25% when fasting plasma glucose concentrations decrease to less than 120 mg/dL in patients receiving concomitant insulin and metformin. Further adjustment should be individualized based on glucose-lowering response. Specific Patient Populations Metformin is not recommended for use in pregnancy. Metformin hydrochloride tablets are not recommended in patients below the age of 10 years. The initial and maintenance dosing of metformin should be conservative in patients with advanced age, due to the potential for decreased renal function in this population. Any dosage adjustment should be based on a careful assessment of renal function. Recommendations for Use in Renal Impairment Assess renal function prior to initiation of metformin hydrochloride tablets and periodically thereafter. Metformin hydrochloride tablet is contraindicated in patients with an estimated glomerular filtration rate (eGFR) below 30 mL/minute/1.73 m 2 . Initiation of metformin hydrochloride tablets in patients with an eGFR between 30 to 45 mL/minute/1.73 m 2 is not recommended. In patients taking metformin hydrochloride tablets whose eGFR later falls below 45 mL/min/1.73 m 2 , assess the benefit risk of continuing therapy. Discontinue metformin hydrochloride tablets if the patient's eGFR later falls below 30 mL/minute/1.73 m 2 (See WARNINGS and PRECAUTIONS ).

Metformin hydrochloride tablets are contraindicated in patients with: Severe renal impairment (eGFR below 30 mL/min/1.73 m 2 ) (see WARNINGS and PRECAUTIONS ). Known hypersensitivity to metformin hydrochloride. Acute or chronic metabolic acidosis, including diabetic ketoacidosis, with or without coma. Diabetic ketoacidosis should be treated with insulin.

In a U.S. double-blind clinical study of metformin hydrochloride tablets in patients with type 2 diabetes, a total of 141 patients received metformin hydrochloride tablets therapy (up to 2550 mg per day) and 145 patients received placebo. Adverse reactions reported in greater than 5% of the metformin hydrochloride tablets patients, and that were more common in metformin hydrochloride tablets- than placebo-treated patients, are listed in Table 11 . Table 11: Most Common Adverse Reactions (>5 Percent) in a Placebo-Controlled Clinical Study of Metformin Hydrochloride Tablets Monotherapy* Adverse Reaction Metformin Hydrochloride Tablets Monotherapy (n = 141) Placebo (n = 145) % of Patients * Reactions that were more common in metformin hydrochloride tablets- than placebo-treated patients. Diarrhea 53.2 11.7 Nausea/Vomiting 25.5 8.3 Flatulence 12.1 5.5 Asthenia 9.2 5.5 Indigestion 7.1 4.1 Abdominal Discomfort 6.4 4.8 Headache 5.7 4.8 Diarrhea led to discontinuation of study medication in 6% of patients treated with metformin hydrochloride tablets. Additionally, the following adverse reactions were reported in ≥ 1% to ≤ 5% of metformin hydrochloride tablets patients and were more commonly reported with metformin hydrochloride tablets than placebo: abnormal stools, hypoglycemia, myalgia, lightheaded, dyspnea, nail disorder, rash, sweating increased, taste disorder, chest discomfort, chills, flu syndrome, flushing, palpitation. Cholestatic, hepatocellular, and mixed hepatocellular liver injury have been reported with postmarketing use of metformin. Pediatric Patients In clinical trials with metformin hydrochloride tablets in pediatric patients with type 2 diabetes, the profile of adverse reactions was similar to that observed in adults.

(Clinical Evaluation of Drug Interactions Conducted with Metformin Hydrochloride Tablets) Glyburide— In a single-dose interaction study in type 2 diabetes patients, coadministration of metformin and glyburide did not result in any changes in either metformin pharmacokinetics or pharmacodynamics. Decreases in glyburide AUC and C max were observed, but were highly variable. The single-dose nature of this study and the lack of correlation between glyburide blood levels and pharmacodynamic effects, makes the clinical significance of this interaction uncertain (see DOSAGE AND ADMINISTRATION: Concomitant Metformin and Oral Sulfonylurea Therapy in Adult Patients ). Furosemide— A single-dose, metformin-furosemide drug interaction study in healthy subjects demonstrated that pharmacokinetic parameters of both compounds were affected by coadministration. Furosemide increased the metformin plasma and blood C max by 22% and blood AUC by 15%, without any significant change in metformin renal clearance. When administered with metformin, the C max and AUC of furosemide were 31% and 12% smaller, respectively, than when administered alone, and the terminal half-life was decreased by 32%, without any significant change in furosemide renal clearance. No information is available about the interaction of metformin and furosemide when coadministered chronically. Nifedipine— A single-dose, metformin-nifedipine drug interaction study in normal healthy volunteers demonstrated that coadministration of nifedipine increased plasma metformin C max and AUC by 20% and 9%, respectively, and increased the amount excreted in the urine. T max and half-life were unaffected. Nifedipine appears to enhance the absorption of metformin. Metformin had minimal effects on nifedipine. Drugs that reduce metformin clearance— Concomitant use of drugs that interfere with common renal tubular transport systems involved in the renal elimination of metformin (e.g., organic cationic transporter-2 [OCT2] / multidrug and toxin extrusion [MATE] inhibitors such as ranolazine, vandetanib, dolutegravir, and cimetidine) could increase systemic exposure to metformin and may increase the risk for lactic acidosis. Consider the benefits and risks of concomitant use. Such interaction between metformin and oral cimetidine has been observed in normal healthy volunteers in both single- and multiple-dose, metformin-cimetidine drug interaction studies, with a 60% increase in peak metformin plasma and whole blood concentrations and a 40% increase in plasma and whole blood metformin AUC. There was no change in elimination half-life in the single-dose study. Metformin had no effect on cimetidine pharmacokinetics. In healthy volunteers, the pharmacokinetics of metformin and propranolol, and metformin and ibuprofen were not affected when coadministered in single-dose interaction studies. Metformin is negligibly bound to plasma proteins and is, therefore, less likely to interact with highly protein-bound drugs such as salicylates, sulfonamides, chloramphenicol, and probenecid, as compared to the sulfonylureas, which are extensively bound to serum proteins. Other— Certain drugs tend to produce hyperglycemia and may lead to loss of glycemic control. These drugs include the thiazides and other diuretics, corticosteroids, phenothiazines, thyroid products, estrogens, oral contraceptives, phenytoin, nicotinic acid, sympathomimetics, calcium channel blocking drugs, and isoniazid. When such drugs are administered to a patient receiving metformin hydrochloride tablets, the patient should be closely observed for loss of blood glucose control. When such drugs are withdrawn from a patient receiving metformin hydrochloride tablets, the patient should be observed closely for hypoglycemia. Carbonic anhydrase inhibitors — Topiramate or other carbonic anhydrase inhibitors (e.g., zonisamide, acetazolamide or dichlorphenamide) frequently cause a decrease in serum bicarbonate and induce non-anion gap, hyperchloremic metabolic acidosis. Concomitant use of these drugs with metformin hydrochloride tablets may increase the risk for lactic acidosis. Consider more frequent monitoring of these patients. Alcohol — Alcohol is known to potentiate the effect of metformin on lactate metabolism. Warn patients against excessive alcohol intake while receiving metformin hydrochloride tablets.