Distribution studies with FORTAMET® have not been conducted. However, the apparent volume of distribution (V/F) of metformin following single oral doses of immediate-release metformin 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 immediate-release metformin, steady state plasma concentrations of metformin are reached within 24-48 hours and are generally less than 1 μg/mL. During controlled clinical trials of immediate-release metformin, maximum metformin plasma levels did not exceed 5 μg/mL, even at maximum doses.
Metabolism studies with FORTAMET® have not been conducted. 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.
In healthy nondiabetic adults (N=18) receiving 2500 mg q.d. FORTAMET® , the percent of the metformin dose excreted in urine over 24 hours was 40.9% and the renal clearance was 542 ± 310 mL/min. After repeated administration of FORTAMET® , there is little or no accumulation of metformin in plasma, with most of the drug being eliminated via renal excretion over a 24-hour dosing interval. The t1/2 was 5.4 hours for FORTAMET®.
Renal clearance of metformin (Table 2) 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.
Limited data from controlled pharmacokinetic studies of immediate-release 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 (Table 2). FORTAMET® 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, PRECAUTIONS and DOSAGE AND ADMINISTRATION).
No pharmacokinetic data from studies of pediatric patients are currently available (see PRECAUTIONS).
Five studies indicated that with FORTAMET® treatment, the pharmacokinetic results for males and females were comparable.
|Subject Groups: Immediate-Release Metformin dose a (number of subjects)||C max b ( μg/mL)||T max 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)|
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
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 (Table 2; also see WARNINGS).
No pharmacokinetic studies of metformin have been conducted in patients with hepatic insufficiency.
No studies of metformin pharmacokinetic parameters according to race have been performed. In controlled clinical studies of immediate-release metformin in patients with type 2 diabetes, the antihyperglycemic effect was comparable in whites (n=249), blacks (n=51), and Hispanics (n=24).
In a double-blind, randomized, active-controlled, multicenter U.S. clinical study, which compared FORTAMET® q.d. to immediate-release metformin b.i.d., 680 patients with type 2 diabetes who had been taking metformin-containing medication at study entry were randomly assigned in equal numbers to double-blind treatment with either FORTAMET® or immediate-release metformin. Doses were adjusted during the first six weeks of treatment with study medication based on patients’ FPG levels and were then held constant over a period of 20 weeks. The primary efficacy endpoint was the change in HbA1c from baseline to endpoint. The primary objective was to demonstrate the clinical non-inferiority of FORTAMET® compared to immediate-release metformin on the primary endpoint.
FORTAMET® and metformin patients had mean HbA1c changes from baseline to endpoint equal to +0.40 and +0.14, respectively (Table 3). The least-square (LS) mean treatment difference was 0.25 (95% CI = 0.14, 0.37) demonstrating that FORTAMET® was clinically similar to metformin according to the pre-defined criterion to establish efficacy.
|FORTAMET ®||Immediate-Release Metformin||Treatment difference for change from baseline (FORTAMET ® minus Immediate-Release Metformin) LS mean (2 sided 95% CI a )|
|HbA 1c (%)|
|Baseline (mean ± SD)||7.04 ± 0.88||7.07 ± 0.76||(0.14,0.37)b|
|Change from baseline (mean ± SD)||0.40 ± 0.75||0.14 ± 0.75|
|Fasting Plasma Glucose (mg/dL)|
|Baseline (mean ± SD)||146.8 ± 32.1||145.6 ± 29.5||(0.57, 12.29)|
|Change from baseline (mean ± SD)||10.0 ± 40.8||4.2 ± 35.9|
|Plasma Insulin (μu/mL)|
|Baseline (mean ± SD)||17.9 ± 15.1||17.3 ± 10.5||(-1.47, 1.50)|
|Change from baseline (mean ± SD)||-3.6 ± 13.8||-3.2 ± 8.6|
|Body Weight (kg)|
|Baseline (mean ± SD)||94.1 ± 17.8||93.3 ± 17.4||(-0.22, 0.81)|
|Change from baseline(mean ± SD)||0.3 ± 2.9||0.0 ± 3.7|
|Body Mass Index (kg/m 2 )|
|Baseline (mean ± SD)||31.1 ±4.7||31.4 ± 4.5||(-0.11, 0.26)|
|Change from baseline(mean ± SD)||0.1 ± 1.1||0.0 ± 1.3|
a CI=Confidence Interval
b FORTAMET® was clinically similar to immediate-release metformin based on the pre-defined criterion to establish efficacy. While demonstrating clinical similarity, the response to FORTAMET® compared to immediate-release metformin was also shown to be statistically smaller as seen by the 95% CI for the treatment difference which did not include zero.
Footnote: Patients were taking metformin-containing medications at baseline that were prescribed by their personal physicians.
The mean changes for FPG (Table 3) and plasma insulin (Table 3) were small for both FORTAMET® and immediate-release metformin, and were not clinically meaningful. Seventy-six (22%) and 49 (14%) of the FORTAMET® and immediate-release patients, respectively, discontinued prematurely from the trial. Eighteen (5%) patients on FORTAMET® withdrew because of a stated lack of efficacy, as compared with 8 patients (2%) on immediate-release metformin (p=0.047).
Results from this study also indicated that neither FORTAMET® nor immediate-release metformin were associated with weight gain or increases in body mass index.
A 24-week, double blind, placebo-controlled study of immediate-release 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 (Table 4). Patients randomized to receive immediate-release metformin 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 versus 110.6 U/day, immediate-release metformin plus insulin versus insulin plus placebo, respectively, p=0.04.
|Immediate-Release Metformin /Insulin (n = 26)||Placebo/Insulin(n = 28)||Treatment difference Mean ± SE|
|HbA 1c (%)|
|Change at FINAL VISIT||-2.10||-1.56||-0.54 ± 0.43a|
|Insulin Dose (U/day)|
|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 immediate-release metformin maintained similar glycemic control (HbA1c 7.15 ± 0.61 versus 6.97 ± 0.62 for immediate-release 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 immediate-release metformin plus insulin and placebo plus insulin, p less than 0.01). In addition, this study demonstrated that the combination of immediate-release 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.
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