RIOMET (metformin hydrochloride oral solution) is an oral anti hyperglycemic drug 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 anti hyperglycemic agents. The structural formula is as shown:

Metformin hydrochloride is a white to off-white crystalline compound with a molecular formula of C₄H₁₁N₅•HCl and a molecular weight of 165.63. Metformin hydrochloride is freely soluble in water and is practically insoluble in acetone, ether, and chloroform. The pKa of metformin is 12.4. The pH of a 1% aqueous solution of metformin hydrochloride is 6.68.

RIOMET contains 500 mg of metformin hydrochloride per 5 mL and the following inactive ingredients: Saccharin Calcium, Potassium Bicarbonate, Xylitol, Hydrochloric Acid, Purified Water and Cherry Flavor.

Last updated on RxList: 1/5/2009

Riomet is indicated as an adjunct to diet and exercise to improve glycemic control in adults with type 2 diabetes mellitus.

There is no fixed dosage regimen for the management of hyperglycemia in patients with type 2 diabetes with RIOMET or any other pharmacologic agent. Dosage of RIOMET must be individualized on the basis of both effectiveness and tolerance, while not exceeding the maximum recommended daily dose. The maximum recommended daily dose of RIOMET is 2550 mg (25.5 mL) in adults and 2000 mg (20 mL) in pediatric patients (10-16 years of age).

RIOMET should be given in divided doses with meals. RIOMET should be started at a low dose, with gradual dose escalation, both 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 RIOMET and identify the minimum effective dose for the patient. Thereafter, glycosylated hemoglobin should be measured at intervals of approximately three 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 RIOMET, 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 RIOMET may be sufficient during periods of transient loss of control in patients usually well-controlled on diet alone.

Recommended Dosing Schedule

Adults — In general, clinically significant responses are not seen at doses below 1500 mg (15 mL) per day. However, a lower recommended starting dose and gradually increased dosage is advised to minimize gastrointestinal symptoms.

The usual starting dose of RIOMET (metformin hydrochloride oral solution) is 500 mg (5 mL) twice a day or 850 mg (8.5 mL) once a day, given with meals. Dosage increases should be made in increments of 500 mg (5 mL) weekly or 850 mg (8.5 mL) every 2 weeks, up to a total of 2000 mg (20 mL) per day, given in divided doses. Patients can also be titrated from 500 mg (5 mL) twice a day to 850 mg (8.5 mL) twice a day after 2 weeks. For those patients requiring additional glycemic control, RIOMET may be given to a maximum daily dose of 2550 mg (25.5 mL) per day. Doses above 2000 mg (20 mL) may be better tolerated given three times a day with meals.

Pediatrics — The usual starting dose of RIOMET is 500 mg (5 mL) twice a day, given with meals. Dosage increases should be made in increments of 500 mg (5 mL) weekly up to a maximum of 2000 mg (20 mL) per day, given in divided doses.

Transfer From Other Anti diabetic Therapy

When transferring patients from standard oral hypoglycemic agents other than chlorpropamide to RIOMET, no transition period generally is necessary. When transferring patients from chlorpropamide, care should be exercised during the first two weeks because of the prolonged retention of chlorpropamide in the body, leading to overlapping drug effects and possible hypoglycemia.

Concomitant Metformin and Oral Sulfonylurea Therapy in Adult Patients

If patients have not responded to four weeks of the maximum dose of RIOMET monotherapy, consideration should be given to gradual addition of an oral sulfonylurea while continuing RIOMET 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 500 mg and glyburide 20 mg were titrated to 1000 mg/20 mg, 1500 mg/20 mg, 2000 mg/20 mg or 2500 mg/20 mg of metformin 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 RIOMET 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 one to three months of concomitant therapy with the maximum dose of RIOMET and the maximum dose of an oral sulfonylurea, consider therapeutic alternatives including switching to insulin with or without RIOMET.

Concomitant Metformin and Insulin Therapy in Adult Patients

The current Insulin dose should be continued upon initiation of RIOMET therapy. RIOMET therapy should be initiated at 500 mg (5 mL) once daily in patients on insulin therapy. For patients not responding adequately, the dose of RIOMET should be increased by 500 mg (5 mL) after approximately 1 week and by 500 mg (5 mL) every week thereafter until adequate glycemic control is achieved. The maximum recommended daily dose for RIOMET is 2500 mg (25 mL). 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 RIOMET. Further adjustment should be individualized based on glucose-lowering response.

Specific Patient Populations

RIOMET is not recommended for use in pregnancy. RIOMET is not recommended in patients below the age of 10 years.

The initial and maintenance dosing of RIOMET 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. Generally, elderly, debilitated, and malnourished patients should not be titrated to the maximum dose of RIOMET.

Monitoring of renal function is necessary to aid in prevention of lactic acidosis, particularly in the elderly. (See WARNINGS.)

RIOMET is available in one strength: 500 mg/5 mL

NDC 10631-206-01 Bottles of 4 fl. oz. (118 mL)

NDC 10631-206-02 Bottles of 16 fl. oz. (473 mL)

Storage

Store at controlled room temperature 15° - 30°C (59° - 86°F) [See USP].

Manufactured for: Ranbaxy Laboratories Inc., Jacksonville, FL 32257, USA by: Ohm Laboratories Inc. Gloversville, NY 12078 USA. April 2008. FDA revision date: 10/20/2008

Last updated on RxList: 1/5/2009

In a U.S. double-blind clinical study of metformin in patients with type 2 diabetes, a total of 141 patients received metformin therapy (up to 2550 mg per day) and 145 patients received placebo. Adverse reactions reported in greater than 5% of the metformin patients, and that were more common in metformin- than placebo-treated patients, are listed in Table 9.

Table 9. Most Common Adverse Reactions ( > 5.0%) in a Placebo­Controlled Clinical Study of Metformin Monotherapy*

Diarrhea led to discontinuation of study medication in 6% of patients treated with metformin. Additionally, the following adverse reactions were reported in ≥ 1.0 - ≤ 5.0% of metformin patients and were more commonly reported with metformin than placebo: abnormal stools, hypoglycemia, myalgia, lightheaded, dyspnea, nail disorder, rash, sweating increased, taste disorder, chest discomfort, chills, flu syndrome, flushing, palpitation.

Pediatric Patients

In clinical trials with metformin in pediatric patients with type 2 diabetes, the profile of adverse reactions was similar to that observed in adults.

(clinical evaluation of drug interactions done with metformin)

Glyburide — In a single-dose interaction study in type 2 diabetes patients, co-administration of metformin and glyburide did not result in any changes in either metformin pharmacokinetics or pharmacodynamics. Decreases in glyburide AUC and Cmax 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).

Furosemide — A single-dose, metformin-furosemide drug interaction study in healthy subjects demonstrated that pharmacokinetic parameters of both compounds were affected by co-administration. Furosemide increased the metformin plasma and blood Cmax by 22% and blood AUC by 15%, without any significant change in metformin renal clearance. When administered with metformin, the Cmax 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 co-administration of nifedipine increased plasma metformin Cmax and AUC by 20% and 9%, respectively, and increased the amount excreted in the urine. Tmax and half-life were unaffected. Nifedipine appears to enhance the absorption of metformin. Metformin had minimal effects on nifedipine.

Cationic drugs — Cationic drugs (e.g., amiloride, digoxin, morphine, procainamide, quinidine, quinine, ranitidine, triamterene, trimethoprim, or vancomycin) that are eliminated by renal tubular secretion theoretically have the potential for interaction with metformin by competing for common renal tubular transport systems. 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. Although such interactions remain theoretical (except for cimetidine), careful patient monitoring and dose adjustment of RIOMET and/or the interfering drug is recommended in patients who are taking cationic medications that are excreted via the proximal renal tubular secretory system.

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 RIOMET, the patient should be closely observed for loss of blood glucose control. When such drugs are withdrawn from a patient receiving RIOMET, the patient should be observed closely for hypoglycemia.

In healthy volunteers, the pharmacokinetics of metformin and propranolol, and metformin and ibuprofen were not affected when co-administered 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.

Last updated on RxList: 1/5/2009

General

There have been no clinical studies establishing conclusive evidence of macrovascular risk reduction with Riomet or any other oral anti-diabetic drug.

Monitoring of renal function — Metformin is known to be substantially excreted by the kidney, and the risk of metformin accumulation and lactic acidosis increases with the degree of impairment of renal function. Thus, patients with serum creatinine levels above the upper limit of normal for their age should not receive RIOMET. In patients with advanced age, RIOMET should be carefully titrated to establish the minimum dose for adequate glycemic effect, because aging is associated with reduced renal function. In elderly patients, particularly those ≥ 80 years of age, renal function should be monitored regularly and, generally, RIOMET should not be titrated to the maximum dose (see WARNINGS and DOSAGE AND ADMINISTRATION).

Before initiation of RIOMET therapy and at least annually thereafter, renal function should be assessed and verified as normal. In patients in whom development of renal dysfunction is anticipated, renal function should be assessed more frequently and RIOMET discontinued if evidence of renal impairment is present.

Use of concomitant medications that may affect renal function or metformin disposition — Concomitant medication(s) that may affect renal function or result in significant hemodynamic change or may interfere with the dis­position of metformin, such as cationic drugs that are eliminated by renal tubular secretion (see PRECAUTIONS: DRUG INTERACTIONS), should be used with caution.

Radiologic studies involving the use of intravascular iodinated contrast materials (for example, intravenous uro­gram, intravenous cholangiography, angiography, and computed tomography (CT) scans with intravascular contrast materials) — Intravascular contrast studies with iodinated materials can lead to acute alteration of renal function and have been associated with lactic acidosis in patients receiving metformin (see CONTRAINDICATIONS).

Therefore, in patients in whom any such study is planned, RIOMET should be temporarily discontinued at the time of or prior to the procedure, and withheld for 48 hours subsequent to the procedure and reinstituted only after renal function has been re-evaluated and found to be normal.

Hypoxic states — Cardiovascular collapse (shock) from whatever cause, acute congestive heart failure, acute myocardial infarction and other conditions characterized by hypoxemia have been associated with lactic acidosis and may also cause pre renal azotemia. When such events occur in patients on RIOMET therapy, the drug should be promptly discontinued.

Surgical procedures— RIOMET therapy should be temporarily suspended for any surgical procedure (except minor procedures not associated with restricted intake of food and fluids) and should not be restarted until the patient's oral intake has resumed and renal function has been evaluated as normal.

Alcohol intake — Alcohol is known to potentiate the effect of metformin on lactate metabolism. Patients, therefore, should be warned against excessive alcohol intake, acute or chronic, while receiving RIOMET.

Impaired hepatic function— Since impaired hepatic function has been associated with some cases of lactic acidosis, RIOMET should generally be avoided in patients with clinical or laboratory evidence of hepatic disease.

Vitamin B₁₂ levels — In controlled clinical trials of metformin of 29 weeks duration, a decrease to subnormal levels of previously normal serum Vitamin B₁₂ levels, without clinical manifestations, was observed in approximately 7% of patients. Such decrease, possibly due to interference with B₁₂absorption from the B₁₂-intrinsic factor complex, is, however, very rarely associated with anemia and appears to be rapidly reversible with discontinuation of metformin or Vitamin B₁₂ supplementation. Measurement of hematologic parameters on an annual basis is advised in patients on RIOMET and any apparent abnormalities should be appropriately investigated and managed (see PRECAUTIONS: Laboratory Tests).

Certain individuals (those with inadequate Vitamin B₁₂ or calcium intake or absorption) appear to be predisposed to developing subnormal Vitamin B₁₂ levels. In these patients, routine serum Vitamin B₁₂ measurements at two- to three-year intervals may be useful.

Change in clinical status of patients with previously controlled type 2 diabetes — A patient with type 2 diabetes previously well controlled on RIOMET who develops laboratory abnormalities or clinical illness (especially vague and poorly defined illness) should be evaluated promptly for evidence of ketoacidosis or lactic acidosis. Evaluation should include serum electrolytes and ketones, blood glucose and, if indicated, blood pH, lactate, pyruvate, and metformin levels. If acidosis of either form occurs, RIOMET must be stopped immediately and other appropriate corrective measures initiated (see also WARNINGS).

Hypoglycemia — Hypoglycemia does not occur in patients receiving metformin alone under usual circumstances of use, but could occur when caloric intake is deficient, when strenuous exercise is not compensated by caloric supplementation, or during concomitant use with other glucose-lowering agents (such as sulfonylureas and insulin) or ethanol. Elderly, debilitated, or malnourished patients, and those with adrenal or pituitary insufficiency or alcohol intoxication are particularly susceptible to hypoglycemic effects. Hypoglycemia may be difficult to recognize in the elderly, and in people who are taking beta-adrenergic blocking drugs.

Loss of control of blood glucose — When a patient stabilized on any diabetic regimen is exposed to stress such as fever, trauma, infection, or surgery, a temporary loss of glycemic control may occur. At such times, it may be necessary to withhold RIOMET and temporarily administer insulin. RIOMET may be reinstituted after the acute episode is resolved.

The effectiveness of oral anti diabetic drugs in lowering blood glucose to a targeted level decreases in many patients over a period of time. This phenomenon, which may be due to progression of the underlying disease or to diminished responsiveness to the drug, is known as secondary failure, to distinguish it from primary failure in which the drug is ineffective during initial therapy. Should secondary failure occur with either RIOMET or sulfonylurea monotherapy, combined therapy with RIOMET and sulfonylurea may result in a response. Should secondary failure occur with combined RIOMET /sulfonylurea therapy, it may be necessary to consider therapeutic alternatives including initiation of insulin therapy.

Laboratory Tests

Response to all diabetic therapies should be monitored by periodic measurements of fasting blood glucose and glycosylated hemoglobin levels, with a goal of decreasing these levels toward the normal range. During initial dose titration, fasting glucose can be used to determine the therapeutic response. Thereafter, both glucose and glycosylated hemoglobin should be monitored. Measurements of glycosylated hemoglobin may be especially useful for evaluating long-term control (see also DOSAGE AND ADMINISTRATION).

Initial and periodic monitoring of hematologic parameters (e.g., hemoglobin/hematocrit and red blood cell indices) and renal function (serum creatinine) should be performed, at least on an annual basis. While megaloblastic anemia has rarely been seen with metformin therapy, if this is suspected, Vitamin B₁₂ deficiency should be excluded.

Carcinogenesis, Mutagenesis, Impairment of Fertility

Long-term carcinogenicity studies have been performed in rats (dosing duration of 104 weeks) and mice (dosing duration of 91 weeks), at doses up to and including 900 mg/kg/day and 1500 mg/kg/day, respectively. These doses are both approximately 4X the maximum recommended human daily dose of 2000 mg based on body surface area comparisons. No evidence of carcinogenicity with metformin was found in either male or female mice. However, there was an increased incidence of benign stromal uterine polyps in female rats treated with 900 mg/kg/day. Results in Ames test, gene mutation test (mouse lymphoma cells), chromosomal aberrations test (human lymphocytes), and in vivo mouse micronucleus tests were negative. Fertility of male and female rats was not affected by metformin when administered at doses of 600 mg/kg/day, which is approximately 3X the maximum recommended human daily dose based on body surface area comparisons.

Pregnancy

Teratogenic Effects: Pregnancy Category B

Recent information strongly suggests that abnormal blood glucose levels during pregnancy are associated with a higher incidence of congenital abnormalities. Most experts recommend that insulin be used during pregnancy to maintain blood glucose levels as close to normal as possible. Because animal reproduction studies are not always predictive of human response, RIOMET should not be used during pregnancy unless clearly needed.

There are no adequate and well-controlled studies in pregnant women with metformin. Metformin was not teratogenic in rats and rabbits at doses up to 600 mg/kg/day, which is 2X and 6X the maximum recommended human daily dose of 2000 mg based on body surface area comparison for rats and rabbits, respectively. However, because animal reproduction studies are not always predictive of human response, RIOMET should not be used during pregnancy unless clearly needed. Determination of fetal concentrations demonstrated a partial placental barrier to metformin.

Nursing Mothers

Studies in lactating rats show that metformin is excreted into milk and reaches levels comparable to those in plasma. It is not known whether this drug is excreted in human milk. Because of the potential for serious adverse reactions in nursing infants from metformin, a decision should be made whether to discontinue nursing or to discontinue the drug, taking into account the importance of the drug to the mother. If RIOMET is discontinued, and if diet alone is inadequate for controlling blood glucose, insulin therapy should be considered.

Pediatric Use

The safety and effectiveness of metformin for the treatment of type 2 diabetes have been established in pediatric patients ages 10 to 16 years (studies have not been conducted in pediatric patients below the age of 10 years). Use of metformin in this age group is supported by evidence from adequate and well-controlled studies of metformin in adults with additional data from a controlled clinical study in pediatric patients ages 10-16 years with type 2 diabetes, which demonstrated a similar response in glycemic control to that seen in adults. (See CLINICAL PHARMACOLOGY: Pediatric Clinical Studies.) In this study, adverse effects were similar to those described in adults. (See ADVERSE REACTIONS: Pediatric Patients.) A maximum daily dose of 2000 mg is recommended. (See DOSAGE AND ADMINISTRATION: Recommended Dosing Schedule: Pediatrics.)

Geriatric Use

Controlled clinical studies of metformin did not include sufficient numbers of elderly patients to determine whether they respond differently from younger patients, although other reported clinical experience has not identified differences in responses between the elderly and younger patients. Metformin is known to be substantially excreted by the kidney and because the risk of serious adverse reactions to the drug is greater in patients with impaired renal function, RIOMET should only be used in patients with normal renal function (see CONTRAINDICATIONS, WARNINGS, and CLINICAL PHARMACOLOGY: Pharmacokinetics). Because aging is associated with reduced renal function, RIOMET should be used with caution as age increases. Care should be taken in dose selection and should be based on careful and regular monitoring of renal function. Generally, elderly patients should not be titrated to the maximum dose of RIOMET (see also WARNINGS and DOSAGE AND ADMINISTRATION).

Last updated on RxList: 1/5/2009

Overdose of metformin hydrochloride has occurred, including ingestion of amounts greater than 50 grams. Hypoglycemia was reported in approximately 10% of cases, but no casual association with metformin hydrochloride has been established. Lactic acidosis has been reported in approximately 32% of metformin overdose cases (see WARNINGS). Metformin is dialyzable with a clearance of up to 170 mL/min under good hemodynamic conditions. Therefore, hemodialysis may be useful for removal of accumulated drug from patients in whom metformin overdosage is suspected.

RIOMET is contraindicated in patients with:

1. Renal disease or renal dysfunction (e.g., as suggested by serum creatinine levels ≥ 1.5 mg/dL [males], ≥ 1.4 mg/dL [females] or abnormal creatinine clearance) which may also result from conditions such as cardiovascular collapse (shock), acute myocardial infarction, and septicemia(see WARNINGS and PRECAUTIONS).
2. Known hypersensitivity to metformin hydrochloride.
3. Acute or chronic metabolic acidosis, including diabetic ketoacidosis, with or without coma. Diabetic ketoacidosis should be treated with insulin.

RIOMET should be temporarily discontinued in patients undergoing radiologic studies involving intravascular administration of iodinated contrast materials, because use of such products may result in acute alteration of renal function. (See also PRECAUTIONS.)

Last updated on RxList: 1/5/2009

Mechanism of Action

Metformin is an antihyperglycemic agent which improves glucose tolerance in patients with type 2 diabetes, lowering both basal and post prandial plasma glucose. Its pharmacologic mechanisms of action are different from other classes of oral antihyperglycemic agents. Metformin decreases hepatic glucose production, decreases intestinal absorption of glucose, and improves insulin sensitivity by increasing peripheral glucose uptake and utilization. Unlike sulfonylureas, metformin does not produce hypoglycemia in either patients with type 2 diabetes or normal subjects (except in special circumstances, see PRECAUTIONS) and does not cause hyperinsulinemia. With metformin therapy, insulin secretion remains unchanged while fasting insulin levels and day-long plasma insulin response may actually decrease.

Pharmacokinetics

Absorption and Bioavailability

Two pharmacokinetic studies have been performed in healthy volunteers to evaluate the bioavailability of RIOMET in comparison with the commercially available metformin tablets under fasting and fed conditions (study 1 and study 2). A third pharmacokinetic study (study 3) assessed effects of food on absorption of RIOMET.

The rate and extent of absorption of RIOMET was found to be comparable to that of Metformin tablets under fasting or fed conditions (see Table 1).

Table 1. Select Mean (± S.D.) Pharmacokinetic Parameters Following Single Oral Doses of 1000 mg RIOMET and Metformin tablets in healthy, nondiabetic adults (n= 36) under fed and fasting conditions

The food-effect study (study 3) assessed the effects of a high fat/high calorie meal and a low fat/low calorie meal on the bioavailability of RIOMET in comparison with administration in the fasted state, in healthy volunteers. The extent of absorption was increased by 21% and 17% with the low fat/low calorie meal and the high fat/high calorie meal, respectively, compared with the administration in the fasted state. The rate and extent of absorption with high fat/high calorie and low fat/ low calorie meal were similar. The mean tmax was 2.5 hours under fasting conditions as compared to 3.9 hours with both low fat/ low calorie meal and high fat/high calorie meals (see Table 2).

Table 2. Select Mean (± S.D.) Metformin Pharmacokinetic Parameters Following Single Oral Doses of 1000 mg RIOMET in healthy, nondiabetic adults (n= 33) under fed (high fat/high calorie meal and low fat/low calorie meal) and fasting conditions (study 3)

Studies using single oral doses of metformin tablet formulations 500 mg to 1500 mg, and 850 mg to 2550 mg, indicate that there is a lack of dose proportionality with increasing doses, which is due to decreased absorption rather than an alteration in elimination.

Distribution

The apparent volume of distribution (V/F) of metformin following single oral doses of a 850 mg tablet averaged 654±358 L. Metformin is negligibly bound to plasma proteins, in contrast to sulfonylureas, which are more than 90% protein bound. Metformin partitions into erythrocytes, most likely as a function of time. At usual clinical doses and dosing schedules of metformin, steady state plasma concentrations are reached within 24-48 hours and are generally < 1 μg/mL. During controlled clinical trials of metformin, maximum metformin plasma levels did not exceed 5 μg/mL, even at maximum doses.

Metabolism and Elimination

Intravenous single-dose studies in normal subjects demonstrate that metformin is excreted unchanged in the urine and does not undergo hepatic metabolism (no metabolites have been identified in humans) nor biliary excretion. Renal clearance (see Table 3) is approximately 3.5 times greater than creatinine clearance, which indicates that tubular secretion is the major route of metformin elimination. Following oral administration, approximately 90% of the absorbed drug is eliminated via the renal route within the first 24 hours, with a plasma elimination half-life of approximately 6.2 hours. In blood, the elimination half-life is approximately 17.6 hours, suggesting that the erythrocyte mass may be a compartment of distribution.

Special Populations

Patients with Type 2 Diabetes

In the presence of normal renal function, there are no differences between single- or multiple-dose pharmacokinetics of metformin between patients with type 2 diabetes and normal subjects (see Table 3), nor is there any accumulation of metformin in either group at usual clinical doses.

Renal Insufficiency

In patients with decreased renal function (based on measured creatinine clearance), the plasma and blood half-life of metformin is prolonged and the renal clearance is decreased in proportion to the decrease in creatinine clearance (see Table 3; also see WARNINGS).

Hepatic Insufficiency

No pharmacokinetic studies of metformin have been conducted in patients with hepatic insufficiency.

Geriatrics

Limited data from controlled pharmacokinetic studies of metformin in healthy elderly subjects suggest that total plasma clearance of metformin is decreased, the half-life is prolonged, and Cmax is increased, compared to healthy young subjects. From these data, it appears that the change in metformin pharmacokinetics with aging is primarily accounted for by a change in renal function (see Table 3). RIOMET (metformin hydrochloride oral solution) treatment should not be initiated in patients ≥ 80 years of age unless measurement of creatinine clearance demonstrates that renal function is not reduced. (See WARNINGS and DOSAGE AND ADMINISTRATION.)

Table 3. Select Mean (± S.D.) Metformin Pharmacokinetic Parameters Following Single or Multiple Oral Doses   of Metformin

Pediatrics

After administration of a single oral metformin 500 mg dose with food, geometric mean metformin Cmax and AUC differed less than 5% between pediatric type 2 diabetic patients (12 to 16 years of age) and gender- and weight-matched healthy adults (20 to 45 years of age), all with normal renal function.

Gender

Metformin pharmacokinetic parameters did not differ significantly between normal subjects and patients with type 2 diabetes when analyzed according to gender (males = 19, females = 16). Similarly, in controlled clinical studies in patients with type 2 diabetes, the antihyperglycemic effect of metformin was comparable in males and females.

Race

No studies of metformin pharmacokinetic parameters according to race have been performed. In controlled clinical studies of metformin in patients with type 2 diabetes, the antihyperglycemic effect was comparable in whites (n=249), blacks (n=51), and Hispanics (n=24).

Clinical Studies

In a double-blind, placebo-controlled, multicenter U.S. clinical trial involving obese patients with type 2 diabetes whose hyperglycemia was not adequately controlled with dietary management alone (baseline fasting plasma glucose [FPG] of approximately 240 mg/dL), treatment with metformin (up to 2550 mg/day) for 29 weeks resulted in significant mean net reductions in fasting and post prandial plasma glucose (PPG) and hemoglobin A_1c (HbA_1c) of 59 mg/dL, 83 mg/dL, and 1.8%, respectively, compared to the placebo group (see Table 4).

Table 4. Metformin vs Placebo Summary of Mean Changes from Baseline* in Fasting Plasma Glucose, HbA_1c and Body Weight, at Final Visit (29-week study)

A 29-week, double-blind, placebo-controlled study of metformin and glyburide, alone and in combination, was conducted in obese patients with type 2 diabetes who had failed to achieve adequate glycemic control while on maximum doses of glyburide (baseline FPG of approximately 250 mg/dL) (see Table 5). Patients randomized to the combination arm started therapy with metformin 500 mg and glyburide 20 mg. At the end of each week of the first four weeks of the trial, these patients had their dosages of metformin increased by 500 mg if they had failed to reach target fasting plasma glucose. After week four, such dosage adjustments were made monthly, although no patient was allowed to exceed metformin 2500 mg. Patients in the metformin only arm (metformin plus placebo) followed the same titration schedule. At the end of the trial, approximately 70% of the patients in the combination group were taking metformin 2000 mg/glyburide 20 mg or metformin 2500 mg/glyburide 20 mg. Patients randomized to continue on glyburide experienced worsening of glycemic control, with mean increases in FPG, PPG, and HbA_1c of 14 mg/dL, 3 mg/dL and 0.2%, respectively. In contrast, those randomized to metformin (up to 2500 mg/day) experienced a slight improvement, with mean reductions in FPG, PPG, and HbA_1c of 1 mg/dL, 6 mg/dL and 0.4%, respectively. The combination of metformin and glyburide was effective in reducing FPG, PPG, and HbA_1c levels by 63 mg/dL, 65 mg/dL, and 1.7%, respectively. Compared to results of glyburide treatment alone, the net differences with combination treatment were -77 mg/dL, -68 mg/dL and -1.9%, respectively (see Table 5).

Table 5. Combined Metformin/ Glyburide (Comb) vs Glyburide (Glyb) or Metformin (Met) Monotherapy: Summary of Mean Changes from Baseline* in Fasting Plasma Glucose, HbA_1c and Body Weight, at Final Visit (29­week study)

The magnitude of the decline in fasting blood glucose concentration following the institution of metformin therapy was proportional to the level of fasting hyperglycemia. Patients with type 2 diabetes with higher fasting glucose concentrations experienced greater declines in plasma glucose and glycosylated hemoglobin.

In clinical studies, metformin, alone or in combination with a sulfonylurea, lowered mean fasting serum triglycerides, total cholesterol, and LDL cholesterol levels and had no adverse effects on other lipid levels (see Table 6).

Table 6. Summary of Mean Percent Change from Baseline of Major Serum Lipid Variables at Final Visit (29-week studies)

In contrast to sulfonylureas, body weight of individuals on metformin tended to remain stable or even decrease somewhat (see Tables 4 and 5).

A 24-week, double-blind, placebo-controlled study of metformin plus insulin versus insulin plus placebo was conducted in patients with type 2 diabetes who failed to achieve adequate glycemic control on insulin alone (see Table 7). Patients randomized to receive metformin plus insulin achieved a reduction in HbA_1c of 2.10%, compared to a 1.56% reduction in HbA_1c achieved by insulin plus placebo. The improvement in glycemic control was achieved at the final study visit with 16% less insulin, 93.0 U/day vs. 110.6 U/day, metformin plus insulin versus insulin plus placebo, respectively, p=0.04.

Table 7. Combined Metformin/ Insulin vs Placebo/ Insulin Summary of Mean Changes from Baseline in HbA_1c and Daily Insulin Dose

A second double-blind, placebo-controlled study (n=51), with 16 weeks of randomized treatment, demonstrated that in patients with type 2 diabetes controlled on insulin for 8 weeks with an average HbA_1c of 7.46 ± 0.97%, the addition of metformin maintained similar glycemic control (HbA_1c 7.15 ± 0.61 versus 6.97 ± 0.62 for metformin plus insulin and placebo plus insulin, respectively) with 19% less insulin versus baseline (reduction of 23.68 ± 30.22 versus an increase of 0.43 ± 25.20 units for metformin plus insulin and placebo plus insulin, p < 0.01). In addition, this study demonstrated that the combination of metformin plus insulin resulted in reduction in body weight of 3.11 ± 4.30 lbs, compared to an increase of 1.30 ± 6.08 lbs for placebo plus insulin, p=0.01.

Pediatric Clinical Studies

In a double-blind, placebo-controlled study in pediatric patients aged 10 to 16 years with type 2 diabetes (mean FPG 182.2 mg/dL), treatment with metformin (up to 2000 mg/day) for up to 16 weeks (mean duration of treatment 11 weeks) resulted in a significant mean net reduction in FPG of 64.3 mg/dL, compared with placebo (see Table 8).

Table 8. Metformin vs Placebo (Pediatrics^a) Summary of Mean Changes from Baseline* in Plasma Glucose and Body Weight at Final Visit

Last updated on RxList: 1/5/2009

Patients should be informed of the potential risks and benefits of RIOMET and of alternative modes of therapy. They should also be informed about the importance of adherence to dietary instructions, of a regular exercise program, and of regular testing of blood glucose, glycosylated hemoglobin, renal function, and hematologic parameters.

The risks of lactic acidosis, its symptoms, and conditions that predispose to its development, as noted in the WARNINGS and PRECAUTIONS sections, should be explained to patients. Patients should be advised to discontinue RIOMET immediately and to promptly notify their health practitioner if unexplained hyperventilation, myalgia, malaise, unusual somnolence, or other nonspecific symptoms occur. Once a patient is stabilized on any dose level of RIOMET, gastrointestinal symptoms, which are common during initiation of metformin therapy, are unlikely to be drug related. Later occurrence of gastrointestinal symptoms could be due to lactic acidosis or other serious disease.

Patients should be counselled against excessive alcohol intake, either acute or chronic, while receiving RIOMET.

Metformin alone does not usually cause hypoglycemia, although it may occur when metformin is used in conjunction with oral sulfonylureas and insulin. When initiating combination therapy, the risks of hypoglycemia, its symptoms and treatment, and conditions that predispose to its development should be explained to patients and responsible family members.

Laboratory Tests

Response to all diabetic therapies should be monitored by periodic measurements of fasting blood glucose and glycosy-lated hemoglobin levels, with a goal of decreasing these levels toward the normal range. During initial dose titration, fasting glucose can be used to determine the therapeutic response. Thereafter, both glucose and glycosylated hemoglobin should be monitored. Measurements of glycosylated hemoglobin may be especially useful for evaluating long-term control (see also DOSAGE AND ADMINISTRATION).

Initial and periodic monitoring of hematologic parameters (e.g., hemoglobin/hematocrit and red blood cell indices) and renal function (serum creatinine) should be performed, at least on an annual basis. While megaloblastic anemia has rarely been seen with metformin therapy, if this is suspected, Vitamin B₁₂ deficiency should be excluded.

Last updated on RxList: 1/5/2009

IMPORTANT NOTE: This is a summary and does not contain all possible information about this product. For complete information about this product or your specific health needs, ask your health care professional. Always seek the advice of your health care professional if you have any questions about this product or your medical condition. This information is not intended as individual medical advice and does not substitute for the knowledge and judgment of your health care professional. This information does not contain any assurances that this product is safe, effective, or appropriate for you.

METFORMIN SOLUTION - ORAL

(met-FOR-min)

COMMON BRAND NAME(S): Riomet

WARNING: Metformin can rarely cause a serious (sometimes fatal) condition called lactic acidosis. Stop taking metformin and seek immediate medical attention if you develop any of the following symptoms of lactic acidosis: unusual tiredness, severe drowsiness, chills, blue/cold skin, muscle pain, fast/difficult breathing, unusually slow/irregular heartbeat.

Lactic acidosis is more likely to occur in patients who have certain medical conditions, including kidney or liver disease, conditions that may cause a low oxygen blood level or poor circulation (e.g., severe congestive heart failure, recent heart attack, recent stroke), heavy alcohol use, a severe loss of body fluids (dehydration), X-ray or scanning procedures that require an injectable iodinated contrast drug, recent surgery, or a serious infection. Tell your doctor immediately if any of these conditions occur or if you notice a big change in your overall health. You may need to stop taking metformin temporarily. The elderly are also at higher risk, especially those older than 80 years who have not had kidney tests. (See also Side Effects and Precautions sections.)

USES: Metformin is used with a proper diet and exercise program to control high blood sugar in people with type 2 diabetes (non-insulin-dependent diabetes). Controlling high blood sugar helps prevent heart disease, strokes, kidney disease, blindness, circulation problems, and decreased sexual ability. Metformin belongs to the class of drugs known as biguanides. It works by helping to restore your body's proper response to the insulin you naturally produce, and by decreasing the amount of sugar that your liver makes and that your stomach/intestines absorb.

OTHER USES: This section contains uses of this drug that are not listed in the approved professional labeling for the drug but that may be prescribed by your health care professional. Use this drug for a condition that is listed in this section only if it has been so prescribed by your health care professional.

Metformin may be used with lifestyle changes such as diet and exercise to prevent diabetes in people who are at high risk for becoming diabetic. By helping your body to respond better to insulin, metformin may decrease the risk of diabetes.

HOW TO USE: Read the Patient Information Leaflet if available from your pharmacist before you start using metformin and each time you get a refill. If you have any questions, consult your doctor or pharmacist.

Take this medication by mouth, usually twice a day with meals or as directed by your doctor. Drink plenty of fluids while taking this medication unless otherwise directed by your doctor.

Carefully measure your dose with a special measuring device/spoon. Do not use a household spoon because you may not get the correct dose.

The dosage is based on your medical condition and response to therapy. Your doctor may direct you to take a low dose at first, gradually increasing the dose to lower the chance of side effects such as upset stomach. Your doctor will adjust your dose based on your blood sugar levels to find the best dose for you. Follow your doctor's directions carefully. The usual maximum dose for an adult is 2550 milligrams each day.

If you are already taking another anti-diabetic drug (e.g., chlorpropamide), follow your doctor's directions carefully for stopping/continuing the old drug and starting metformin.

Use this medication regularly in order to get the most benefit from it. Remember to use it at the same times each day.

Inform your doctor if your condition persists or worsens (e.g., blood sugar levels are high). It may take up to 2 weeks before the full benefit of this drug takes effect.

SIDE EFFECTS: See also Warning section.

Nausea, stomach upset, diarrhea, or a metallic taste in the mouth may occur at first as your body adjusts to the medication. If any of these effects persist or worsen, tell your doctor or pharmacist promptly. If stomach symptoms return later (after you are on the same dose for several days or weeks), tell your doctor immediately. Stomach symptoms that occur after the first days of your treatment may be a sign of lactic acidosis.

Remember that your doctor has prescribed this medication because he or she has judged that the benefit to you is greater than the risk of side effects. Many people using this medication do not have serious side effects.

This medication does not usually cause low blood sugar (hypoglycemia). However, low blood sugar may occur, especially if you take other medications for diabetes, drink large amounts of alcohol, do unusually heavy exercise, or do not consume enough calories from food. Symptoms include cold sweat, blurred vision, dizziness, drowsiness, shaking, fast heartbeat, headache, fainting, tingling of the hands/feet, and hunger. It is a good habit to carry glucose tablets or gel to treat low blood sugar. If you don't have these reliable forms of glucose, rapidly raise your blood sugar by eating a quick source of sugar such as table sugar, honey, or candy, or drink fruit juice or non-diet soda. Tell your doctor about the reaction immediately. To help prevent low blood sugar, eat meals on a regular schedule, and do not skip meals. Check with your doctor or pharmacist to find out what you should do if you miss a meal.

Symptoms of high blood sugar (hyperglycemia) include thirst, increased urination, confusion, drowsiness, flushing, rapid breathing, and fruity breath odor. If these symptoms occur, tell your doctor immediately. Your dosage may need to be increased.

A very serious allergic reaction to this drug is rare. However, seek immediate medical attention if you notice any symptoms of a serious allergic reaction, including: rash, itching, swelling, severe dizziness, trouble breathing.

This is not a complete list of possible side effects. If you notice other effects not listed above, contact your doctor or pharmacist.

Contact your doctor for medical advice about side effects. The following numbers do not provide medical advice, but in the US you may report side effects to the Food and Drug Administration (FDA) at 1-800-FDA-1088. In Canada, you may call Health Canada at 1-866-234-2345.

PRECAUTIONS: Before taking metformin, tell your doctor or pharmacist if you are allergic to it; or if you have any other allergies.

This medication should not be used if you have certain medical conditions. Before using this medicine, consult your doctor or pharmacist if you have: kidney disease, liver disease, conditions that may cause a low level of oxygen in the blood or poor circulation (e.g., severe congestive heart failure, recent heart attack, recent stroke), metabolic acidosis (e.g., diabetic ketoacidosis), serious infection, severe loss of body fluids (dehydration).

Before using this medication, tell your doctor or pharmacist your medical history, especially of: adrenal/pituitary gland problems, severe breathing problems (e.g., obstructive lung disease, severe asthma), blood problems (e.g., anemia, vitamin B12 deficiency), fertility problems (e.g., ovulation problems), alcohol use.

Before having surgery or any X-ray/scanning procedure using injectable iodinated contrast material, tell your doctor that you are taking this medication. You will need to temporarily stop this medication before the time of your surgery/procedure. Consult your doctor for further instructions.

You may experience blurred vision, dizziness, or drowsiness due to extremely low or high blood sugar levels. Use caution while driving, using machinery, or taking part in any other activity that requires clear vision and alertness.

Limit alcohol while using this medication to lower your risk of lactic acidosis.

It may be harder to control your blood sugar when your body is stressed (e.g., due to fever, infection, injury, or surgery). Consult your doctor because this may require a change in your treatment plan, medications, or blood sugar testing.

Kidney function declines as you grow older. This medication is removed by the kidneys. Therefore, elderly people may be at greater risk for side effects such as lactic acidosis or low blood sugar while using this drug.

During pregnancy, this medication should be used only when clearly needed. Discuss the risks and benefits with your doctor. Your doctor may substitute insulin for this drug during your pregnancy. Follow your doctor's instructions carefully.

This medication can cause changes in the menstrual cycle (promote ovulation) and increase the risk of becoming pregnant. Consult your doctor or pharmacist about the use of reliable birth control while using this medication.

It is not known whether this drug passes into breast milk. This drug could have undesirable effects on a nursing infant. Therefore, breast-feeding is not recommended while using this drug. Consult your doctor before breast-feeding.

DRUG INTERACTIONS: Your doctor or pharmacist may already be aware of any possible drug interactions and may be monitoring you for them. Do not start, stop, or change the dosage of any medicine before checking with them first.

Before using this medication, tell your doctor or pharmacist of all prescription and nonprescription/herbal products you may use, especially of: drugs that may affect the kidneys' ability to remove metformin from the body (e.g., cimetidine, cephalexin), "water pills"/diuretics (e.g., furosemide, thiazide diuretics such as hydrochlorothiazide).

Many drugs can affect your blood sugar levels, making it more difficult to control your blood sugar. Before you start, stop, or change any medication, talk with your doctor or pharmacist about how the medication may affect your blood sugar. Check your blood sugar levels regularly as directed by your doctor. Tell your doctor about the results and of any symptoms of high or low blood sugar. (See also Side Effects section.) Your doctor may need to adjust your anti-diabetic medication, exercise program, or diet.

Some medications (e.g., beta blockers such as propranolol) may mask the fast/pounding heartbeat you would usually feel when your blood sugar level falls too low (hypoglycemia). Other symptoms of low blood sugar such as dizziness, hunger, or sweating are unaffected by these drugs.

Check the labels on nonprescription/herbal products carefully. Some products may contain sugar/alcohol and may affect blood sugars. Ask your doctor or pharmacist about using these products safely.

Cimetidine is a nonprescription drug that is commonly used to treat extra stomach acid. Because it may interact with metformin, ask your pharmacist about other products to treat stomach acid.

This document does not contain all possible interactions. Therefore, before using this product, tell your doctor or pharmacist of all the products you use. Keep a list of all your medications with you, and share the list with your doctor and pharmacist.

OVERDOSE: If overdose is suspected, contact your local poison control center or emergency room immediately. US residents can call the US National Poison Hotline at 1-800-222-1222. Canada residents can call a provincial poison control center. Overdose can cause lactic acidosis and low blood sugar. Symptoms of overdose may include: rapid breathing, severe drowsiness, slow/irregular heartbeat.

NOTES: Do not share this medication with others.

You should attend a diabetes education program to learn more about diabetes and all the important aspects of its treatment, including meals/diet, exercise, personal hygiene, medications, and getting regular eye/foot/medical exams.

Keep all medical appointments. Laboratory and/or medical tests (e.g., liver and kidney function tests, fasting blood glucose, hemoglobin A1c, complete blood counts) should be performed periodically to check for side effects and monitor your response to therapy. Check your blood sugar levels regularly as directed.

MISSED DOSE: If you miss a dose, take it as soon as you remember. If it is near the time of the next dose, skip the missed dose and resume your usual dosing schedule. Do not double the dose to catch up.

STORAGE: Store at room temperature between 59-86 degrees F (15-30 degrees C) away from light and moisture. Do not store in the bathroom. Keep all medicines away from children and pets.

Do not flush medications down the toilet or pour them into a drain unless instructed to do so. Properly discard this product when it is expired or no longer needed. Consult your pharmacist or local waste disposal company for more details about how to safely discard your product.

MEDICAL ALERT: Your condition can cause complications in a medical emergency. For information about enrolling in MedicAlert, call 1-800-854-1166 (USA) or 1-800-668-1507 (Canada).

Information last revised July 2008 Copyright(c) 2008 First DataBank, Inc.