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 3 times the maximum recommended human daily dose of 2550 mg based on body surface area comparisons. No evidence of carcinogenicity with metformin was found in either male or female mice. Similarly, there was no tumorigenic potential observed with metformin in male rats. There was, however, an increased incidence of benign stromal uterine polyps in female rats treated with 900 mg/kg/day.
There was no evidence of a mutagenic potential of metformin in the following in vitro tests: Ames test ( S. typhimurium), gene mutation test (mouse lymphoma cells), or chromosomal aberrations test (human lymphocytes). Results in the in vivo mouse micronucleus test were also negative.
Fertility of male or female rats was unaffected by metformin when administered at doses as high as 600 mg/kg/day, which is approximately 2 times the maximum recommended human daily dose of 2550 mg based on body surface area comparisons.
14.2 Metformin Hydrochloride Extended-Release Tablets
A 24-week, double-blind, placebo-controlled study of metformin hydrochloride extended-release tablets, taken once daily with the evening meal, was conducted in patients with type 2 diabetes mellitus who had failed to achieve glycemic control with diet and exercise. Patients entering the study had a mean baseline HbA1c of 8.0% and a mean baseline FPG of 176 mg/dL. The treatment dose was increased to 1500 mg once daily if at Week 12 HbA1c was ≥7.0% but <8.0% (patients with HbA1c ≥8.0% were discontinued from the study). At the final visit (24-week), mean HbA1c had increased 0.2% from baseline in placebo patients and decreased 0.6% with metformin hydrochloride extended-release tablets.
A 16-week, double-blind, placebo-controlled, dose-response study of metformin hydrochloride extended-release tablets, taken once daily with the evening meal or twice daily with meals, was conducted in patients with type 2 diabetes mellitus who had failed to achieve glycemic control with diet and exercise. The results are shown in Table 10.
Table 10: Mean Changes from Baseline* in HbA1c and Fasting Plasma Glucose at Week 16 Comparing Metformin Extended-Release Tablets vs Placebo in Patients with Type 2 Diabetes Mellitus
|a All comparisons versus Placebo|
|Metformin Hydrochloride Extended-Release Tablets||Placebo|
|500 mg Once Daily||1000 mg Once Daily||1500 mg Once Daily||2000 mg Once Daily||1000 mg Twice Daily|
|Hemoglobin A 1c (%)||(n=115)||(n=115)||(n=111)||(n=125)||(n=112)||(n=111)|
|Change at FINAL VISIT||–0.4||–0.6||–0.9||–0.8||–1.1||0.1|
|Change at FINAL VISIT||–15.2||–19.3||–28.5||–29.9||–33.6||7.6|
Mean baseline body weight was 193 lbs, 192 lbs, 188 lbs, 196 lbs, 193 lbs and 194 lbs in the metformin hydrochloride extended-release tablets 500 mg , 1000 mg, 1500 mg, and 2000 mg once daily, 1000 mg twice daily and placebo arms, respectively. Mean change in body weight from baseline to week 16 was -1.3 lbs, 1.3 lbs, -0.7 lbs, -1.5 lbs, -2.2 lbs and -1.8 lbs, respectively.
A 24-week, double-blind, randomized study of metformin hydrochloride extended-release tablets, taken once daily with the evening meal, and metformin hydrochloride tablets, taken twice daily (with breakfast and evening meal), was conducted in patients with type 2 diabetes mellitus who had been treated with metformin hydrochloride tablets 500 mg twice daily for at least 8 weeks prior to study entry. The results are shown in Table 11.
Table 11: Mean Changes from Baseline* in HbA1c and Fasting Plasma Glucose at Week 24 Comparing Metformin Hydrochloride Extended-Release Tablets vs Metformin Hydrochloride Tablets in Patients with Type 2 Diabetes Mellitus
|Metformin Hydrochloride Tablets 500 mg Twice Daily||Metformin Hydrochloride Extended – Release tablets|
|1000 mg Once Daily||1500 mg Once Daily|
|Hemoglobin A 1c (%) Baseline Change at FINAL VISIT (95% CI)||(n=67)||(n=72)||(n=66)|
|0.14a (–0.04, 0.31)||0.27 (0.11, 0.43)||0.13 (–0.02, 0.28)|
|FPG (mg/dL) Baseline Change at FINAL VISIT (95% CI)||(n=69)||(n=72)||(n=70)|
|14.0 (7.0, 21.0)||11.5 (4.4, 18.6)||7.6 (1.0, 14.2)|
Mean baseline body weight was 210lbs, 203 lbs and 193 lbs in the metformin hydrochloride tablets 500 mg twice daily, and metformin hydrochloride extended-release tablets 1000 mg and 1500 mg once daily arms, respectively. Mean change in body weight from baseline to week 24 was 0.9 lbs, 1.1 lbs and 0.9 lbs, respectively.
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