Metformin Hydrochloride

METFORMIN HYDROCHLORIDE- metformin hydrochloride tablet, film coated
Liberty Pharmaceuticals, Inc.


Lactic Acidosis:

Lactic acidosis is a rare, but serious, metabolic complication that can occur due to metformin accumulation during treatment with metformin; when it occurs, it is fatal in approximately 50% of cases. Lactic acidosis may also occur in association with a number of pathophysiologic conditions, including diabetes mellitus, and whenever there is significant tissue hypoperfusion and hypoxemia. Lactic acidosis is characterized by elevated blood lactate levels (>5 mmol/ L), decreased blood pH, electrolyte disturbances with an increased anion gap, and an increased lactate/pyruvate ratio. When metformin is implicated as the cause of lactic acidosis, metformin plasma levels >5 µg/mL are generally found.

The reported incidence of lactic acidosis in patients receiving metformin hydrochloride is very low (approximately 0.03 cases/1000 patient-years, with approximately 0.015 fatal cases/1000 patient-years). In more than 20,000 patient-years exposure to metformin in clinical trials, there were no reports of lactic acidosis. Reported cases have occurred primarily in diabetic patients with significant renal insufficiency, including both intrinsic renal disease and renal hypoperfusion, often in the setting of multiple concomitant medical/surgical problems and multiple concomitant medications. Patients with congestive heart failure requiring pharmacologic management, in particular those with unstable or acute congestive heart failure who are at risk of hypoperfusion and hypoxemia, are at increased risk of lactic acidosis. The risk of lactic acidosis increases with the degree of renal dysfunction and the patient’s age. The risk of lactic acidosis may, therefore, be significantly decreased by regular monitoring of renal function in patients taking metformin and by use of the minimum effective dose of metformin. In particular, treatment of the elderly should be accompanied by careful monitoring of renal function. Metformin treatment should not be initiated in patients ≥80 years of age unless measurement of creatinine clearance demonstrates that renal function is not reduced, as these patients are more susceptible to developing lactic acidosis. In addition, metformin should be promptly withheld in the presence of any condition associated with hypoxemia, dehydration, or sepsis. Because impaired hepatic function may significantly limit the ability to clear lactate, metformin should generally be avoided in patients with clinical or laboratory evidence of hepatic disease. Patients should be cautioned against excessive alcohol intake, either acute or chronic, when taking metformin hydrochloride tablets, since alcohol potentiates the effects of metformin hydrochloride on lactate metabolism. In addition, metformin hydrochloride tablets should be temporarily discontinued prior to any intravascular radiocontrast study and for any surgical procedure (see also PRECAUTIONS).

The onset of lactic acidosis often is subtle, and accompanied only by nonspecific symptoms such as malaise, myalgias, respiratory distress, increasing somnolence, and nonspecific abdominal distress. There may be associated hypothermia, hypotension, and resistant bradyarrhythmias with more marked acidosis. The patient and the patient’s physician must be aware of the possible importance of such symptoms and the patient should be instructed to notify the physician immediately if they occur (see also PRECAUTIONS). Metformin hydrochloride tablets should be withdrawn until the situation is clarified. Serum electrolytes, ketones, blood glucose, and if indicated, blood pH, lactate levels, and even blood metformin levels may be useful. Once a patient is stabilized on any dose level of metformin hydrochloride tablets, gastrointestinal symptoms, which are common during initiation of therapy, are unlikely to be drug related. Later occurrence of gastrointestinal symptoms could be due to lactic acidosis or other serious disease.

Levels of fasting venous plasma lactate above the upper limit of normal but less than 5 mmol/L in patients taking metformin hydrochloride tablets do not necessarily indicate impending lactic acidosis and may be explainable by other mechanisms, such as poorly controlled diabetes or obesity, vigorous physical activity, or technical problems in sample handling. (See also PRECAUTIONS.)

Lactic acidosis should be suspected in any diabetic patient with metabolic acidosis lacking evidence of ketoacidosis (ketonuria and ketonemia).

Lactic acidosis is a medical emergency that must be treated in a hospital setting. In a patient with lactic acidosis who is taking metformin, the drug should be discontinued immediately and general supportive measures promptly instituted. Because metformin hydrochloride is dialyzable (with a clearance of up to 170 mL/min under good hemodynamic conditions), prompt hemodialysis is recommended to correct the acidosis and remove the accumulated metformin. Such management often results in prompt reversal of symptoms and recovery. (See also CONTRAINDICATIONSand PRECAUTIONS.)


Metformin hydrochloride tablets USP are oral antihyperglycemic 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 antihyperglycemic agents. The structural formula is as shown:

metformin structure

Metformin hydrochloride USP is a white to off-white crystalline compound with a molecular formula of C4 H11 N5 • 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.

Metformin hydrochloride tablets USP contain 500 mg, 850 mg, or 1000 mg of metformin hydrochloride USP. Each tablet contains the inactive ingredients corn starch, povidone and magnesium stearate. In addition, the coating for each tablet contains hypromellose, talc, titanium dioxide, polyethylene glycol, and propylene glycol.


Mechanism of Action
Metformin is an antihyperglycemic agent which improves glucose tolerance in patients with type 2 diabetes, lowering both basal and postprandial 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.


Absorption and Bioavailability

The absolute bioavailability of a metformin hydrochloride 500 mg tablet given under fasting conditions is approximately 50% to 60%. Studies using single oral doses of metformin hydrochloride 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. Food decreases the extent of and slightly delays the absorption of metformin, as shown by approximately a 40% lower mean peak plasma concentration (Cmax ), a 25% lower area under the plasma concentration versus time curve (AUC), and a 35-minute prolongation of time to peak plasma concentration (Tmax ) following administration of a single 850 mg tablet of metformin with food, compared to the same tablet strength administered fasting. The clinical relevance of these decreases is unknown.


The apparent volume of distribution (V/F) of metformin following single oral doses of metformin hydrochloride 850 mg 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 hydrochloride tablets, steady state plasma concentrations of metformin are reached within 24 to 48 hours and are generally <1 µg/mL. During controlled clinical trials of metformin hydrochloride tablets, 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 1) 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 1), 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 1 ; 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 hydrochloride tablets 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 1). Metformin hydrochloride tablets 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 1: Select Mean (±S.D.) Metformin Pharmacokinetic Parameters Following Single or Multiple Oral Doses of Metformin Hydrochloride Tablets
Subject Groups: Metformin Hydrochloride Tablets dosea(number of subjects) Cmax b (µg/mL) Tmax c (hrs) Renal Clearance(mL/min)
Healthy, nondiabetic adults:
500 mg single dose (24) 1.03 (±0.33) 2.75 (±0.81) 600 (±132)
850 mg single dose (74)d 1.60 (±0.38) 2.64 (±0.82) 552 (±139)
850 mg three times daily for 19 dosese (9) 2.01 (±0.42) 1.79 (±0.94) 642 (±173)
Adults with type 2 diabetes:
850 mg single dose (23) 1.48 (±0.5) 3.32 (±1.08) 491 (±138)
850 mg three times daily for 19 dosese (9) 1.90 (±0.62) 2.01 (±1.22) 550 (±160)
Elderly f , healthy nondiabetic adults:
850 mg single dose (12) 2.45 (±0.70) 2.71 (±1.05) 412 (±98)
Renal-impaired adults:
850 mg single dose
Mild (CLcr g 61-90 mL/min) (5) 1.86 (±0.52) 3.20 (±0.45) 384 (±122)
Moderate (CLcr 31-60 mL/ min) (4) 4.12 (±1.83) 3.75 (±0.50) 108 (±57)
Severe (CLcr 10-30 mL/min) (6) 3.93 (±0.92) 4.01 (±1.10) 130 (±90)
a All doses given fasting except the first 18 doses of the multiple dose studies b Peak plasma concentration c Time to peak plasma concentration d Combined results (average means) of five studies: mean age 32 years (range 23-59 years) e Kinetic study done following dose 19, given fasting f Elderly subjects, mean age 71 years (range 65-81 years) g CLcr = creatinine clearance normalized to body surface area of 1.73 m2

After administration of a single oral metformin hydrochloride 500 mg tablet 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.

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 hydrochloride tablets was comparable in males and females.

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

Clinical Studies

Metformin hydrochloride tablets

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 hydrochloride tablets (up to 2550 mg/day) for 29 weeks resulted in significant mean net reductions in fasting and postprandial plasma glucose (PPG) and hemoglobin A1c (HbA1c ) of 59 mg/dL, 83 mg/dL, and 1.8%, respectively, compared to the placebo group (see Table 2).

Table 2: Metformin Hydrochloride Tablets vs Placebo Summary of Mean Changes from Baseline* in Fasting Plasma Glucose, HbA1c , and Body Weight, at Final Visit (29-week study)
Metformin hydrochloride tablets Placebo p–Value
(n=141) (n=145)
FPG (mg/dL)
Baseline 241.5 237.7 NS**
Change at FINAL VISIT -53.0 6.3 0.001
Hemoglobin A1c (%)
Baseline 8.4 8.2 NS**
Change at FINAL VISIT -1.4 0.4 0.001
Body Weight (lbs)
Baseline 201.0 206.0 NS**
Change at FINAL VISIT -1.4 -2.4 NS**
* All patients on diet therapy at Baseline ** Not statistically significant

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 3). Patients randomized to the combination arm started therapy with metformin hydrochloride tablets 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 hydrochloride tablets 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 hydrochloride tablets 2500 mg. Patients in the metformin hydrochloride tablets 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 hydrochloride tablets 2000 mg/glyburide 20 mg or metformin hydrochloride tablets 2500 mg/ glyburide 20 mg. Patients randomized to continue on glyburide experienced worsening of glycemic control, with mean increases in FPG, PPG, and HbA1 c of 14 mg/dL, 3 mg/dL, and 0.2%, respectively. In contrast, those randomized to metformin hydrochloride tablets (up to 2500 mg/day) experienced a slight improvement, with mean reductions in FPG, PPG, and HbA1c of 1 mg/dL, 6 mg/dL, and 0.4%, respectively. The combination of metformin hydrochloride tablets and glyburide was effective in reducing FPG, PPG, and HbA1c 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 3).

Table 3: Combined Metformin Hydrochloride Tablets /Glyburide (Comb) vs Glyburide (Glyb) or Metformin Hydrochloride Tablets (MET) Monotherapy: Summary of Mean Changes from Baseline* in Fasting Plasma Glucose, HbA1c , and Body Weight, at Final Visit (29-week study)
Comb (n=213) Glyb (n=209) MET (n=210) p-values
Glyb vs Comb MET vs Comb MET vs Glyb
Fasting Plasma Glucose (mg/dL)
Baseline 250.5 247.5 253.9 NS** NS** NS**
Change at FINAL VISIT -63.5 13.7 -0.9 0.001 0.001 0.025
Hemoglobin A1c (%)
Baseline 8.8 8.5 8.9 NS** NS** 0.007
Change at FINAL VISIT -1.7 0.2 -0.4 0.001 0.001 0.001
Body Weight (lbs)
Baseline 202.2 203.0 204.0 NS** NS** NS**
Change at FINAL VISIT 0.9 -0.7 -8.4 0.011 0.001 0.001
* All patients on glyburide, 20 mg/day, at Baseline ** Not statistically significant

The magnitude of the decline in fasting blood glucose concentration following the institution of metformin hydrochloride tablets 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 hydrochloride tablets, 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 4).

Table 4: Summary of Mean Percent Change From Baseline of Major Serum Lipid Variables at Final Visit (29-week studies)
Metformin hydrochloride tablets vs Placebo Combined Metformin hydrochloride Tablets /Glyburide vs Monotherapy
Metformin hydrochloride tablets (n=141) Placebo (n=145) Metformin hydrochloride tablets (n=210) Metformin hydrochloride tablets/ Glyburide (n=213) Glyburide (n=209)
Total Cholesterol (mg/dL)
Baseline 211.0 212.3 213.1 215.6 219.6
Mean % Change at
FINAL VISIT -5% 1% -2% -4% 1%
Total Triglycerides (mg/dL)
Baseline 236.1 203.5 242.5 215.0 266.1
Mean % Change at
FINAL VISIT -16% 1% -3% -8% 4%
LDL-Cholesterol (mg/dL)
Baseline 135.4 138.5 134.3 136.0 137.5
Mean % Change at
FINAL VISIT -8% 1% -4% -6% 3%
HDL-Cholesterol (mg/dL)
Baseline 39.0 40.5 37.2 39.0 37.0
Mean % Change at
FINAL VISIT 2% -1% 5% 3% 1%

In contrast to sulfonylureas, body weight of individuals on metformin hydrochloride tablets tended to remain stable or even decrease somewhat (see Tables 2 and 3).A 24-week, double-blind, placebo-controlled study of metformin hydrochloride tablets 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 5). Patients randomized to receive metformin hydrochloride tablets plus insulin achieved a reduction in HbA1c of 2.10%, compared to a 1.56% reduction in HbA1c 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 hydrochloride tablets plus insulin versus insulin plus placebo, respectively, p=0.04.

Table 5: Combined Metformin Hydrochloride Tablets /Insulin vs Placebo/Insulin Summary of Mean Changes from Baseline in HbA1c and Daily Insulin Dose
Metformin Hydrochloride Tablets/ Insulin (n=26) Placebo/ Insulin (n=28) Treatment Difference Mean ± SE
Hemoglobin A1c (%)
Baseline 8.95 9.32
Change at FINAL VISIT -2.10 -1.56 -0.54 ± 0.43a
Insulin Dose (U/day)
Baseline 93.12 94.64
Change at FINAL VISIT -0.15 15.93 -16.08 ± 7.77b
a Statistically significant using analysis of covariance with baseline as covariate (p=0.04)Not significant using analysis of variance (values shown in table) b Statistically significant for insulin (p=0.04)

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 HbA1c of 7.46 ± 0.97%, the addition of metformin hydrochloride tablets maintained similar glycemic control (HbA1c 7.15 ± 0.61 versus 6.97 ± 0.62 for metformin hydrochloride tablets 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 hydrochloride tablets plus insulin and placebo plus insulin, p<0.01). In addition, this study demonstrated that the combination of metformin hydrochloride tablets 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 hydrochloride tablets (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 6).

Table 6: Metformin Hydrochloride Tablets vs Placebo (Pediatricsa) Summary of Mean Changes from Baseline* in Plasma Glucose and Body Weight at Final Visit
Metformin Hydrochloride Tablets Placebo p-Value
FPG (mg/dL) (n=37) (n=36)
Baseline 162.4 192.3
Change at FINAL VISIT -42.9 21.4 <0.001
Body Weight (lbs) (n=39) (n=38)
Baseline 205.3 189.0
Change at FINAL VISIT -3.3 -2.0 NS**
a Pediatric patients mean age 13.8 years (range 10 to 16 years) * All patients on diet therapy at Baseline ** Not statistically significant

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