Mechanism of Action
Glimepiride primarily lowers blood glucose by stimulating the release of insulin from pancreatic beta cells. Sulfonylureas bind to the sulfonylurea receptor in the pancreatic beta-cell plasma membrane, leading to closure of the ATP-sensitive potassium channel, thereby stimulating the release of insulin.
In healthy subjects, the time to reach maximal effect (minimum blood glucose concentrations) was approximately 2–3 hours after single oral doses of AMARYL. The effects of AMARYL on HbA1c, fasting plasma glucose, and post-prandial glucose have been assessed in clinical trials [see Clinical Studies].
Absorption: Studies with single oral doses of glimepiride in healthy subjects and with multiple oral doses in patients with type 2 diabetes showed peak drug concentrations (Cmax) 2 to 3 hours post-dose. When glimepiride was given with meals, the mean Cmax and AUC (area under the curve) were decreased by 8% and 9%, respectively.
Glimepiride does not accumulate in serum following multiple dosing. The pharmacokinetics of glimepiride does not differ between healthy subjects and patients with type 2 diabetes. Clearance of glimepiride after oral administration does not change over the 1 mg to 8 mg dose range, indicating linear pharmacokinetics.
In healthy subjects, the intra- and inter-individual variabilities of glimepiride pharmacokinetic parameters were 15–23% and 24–29%, respectively.
Distribution: After intravenous dosing in healthy subjects, the volume of distribution (Vd) was 8.8 L (113 mL/kg), and the total body clearance (CL) was 47.8 mL/min. Protein binding was greater than 99.5%.
Metabolism: Glimepiride is completely metabolized by oxidative biotransformation after either an intravenous or oral dose. The major metabolites are the cyclohexyl hydroxy methyl derivative (M1) and the carboxyl derivative (M2). Cytochrome P450 2C9 is involved in the biotransformation of glimepiride to M1. M1 is further metabolized to M2 by one or several cytosolic enzymes. M2 is inactive. In animals, M1 possesses about one-third of the pharmacological activity of glimepiride, but it is unclear whether M1 results in clinically meaningful effects on blood glucose in humans.
Excretion: When 14C-glimepiride was given orally to 3 healthy male subjects, approximately 60% of the total radioactivity was recovered in the urine in 7 days. M1 and M2 accounted for 80–90% of the radioactivity recovered in the urine. The ratio of M1 to M2 in the urine was approximately 3:2 in two subjects and 4:1 in one subject. Approximately 40% of the total radioactivity was recovered in feces. M1 and M2 accounted for about 70% (ratio of M1 to M2 was 1:3) of the radioactivity recovered in feces. No parent drug was recovered from urine or feces. After intravenous dosing in patients, no significant biliary excretion of glimepiride or its M1 metabolite was observed.
Geriatric Patients: A comparison of glimepiride pharmacokinetics in patients with type 2 diabetes ≤65 years and those >65 years was evaluated in a multiple-dose study using AMARYL 6 mg daily. There were no significant differences in glimepiride pharmacokinetics between the two age groups. The mean AUC at steady state for the older patients was approximately 13% lower than that for the younger patients; the mean weight-adjusted clearance for the older patients was approximately 11% higher than that for the younger patients.
Gender: There were no differences between males and females in the pharmacokinetics of glimepiride when adjustment was made for differences in body weight.
Race: No studies have been conducted to assess the effects of race on glimepiride pharmacokinetics but in placebo-controlled trials of AMARYL in patients with type 2 diabetes, the reduction in HbA1C was comparable in Caucasians (n = 536), blacks (n = 63), and Hispanics (n = 63).
Renal Impairment: A single-dose, open-label study AMARYL 3 mg was administered to patients with mild, moderate and severe renal impairment as estimated by creatinine clearance (CLcr): Group I consisted of 5 patients with mild renal impairment (CLcr > 50 mL/min), Group II consisted of 3 patients with moderate renal impairment (CLcr = 20–50 mL/min) and Group III consisted of 7 patients with severe renal impairment (CLcr < 20 mL/min). Although, glimepiride serum concentrations decreased with decreasing renal function, Group III had a 2.3-fold higher mean AUC for M1 and an 8.6-fold higher mean AUC for M2 compared to corresponding mean AUCs in Group I. The apparent terminal half-life (T1/2) for glimepiride did not change, while the half-lives for M1 and M2 increased as renal function decreased. Mean urinary excretion of M1 plus M2 as a percentage of dose decreased from 44.4% for Group I to 21.9% for Group II and 9.3% for Group III.
Hepatic Impairment: It is unknown whether there is an effect of hepatic impairment on AMARYL pharmacokinetics because the pharmacokinetics of AMARYL has not been adequately evaluated in patients with hepatic impairment.
Obese Patients: The pharmacokinetics of glimepiride and its metabolites were measured in a single-dose study involving 28 patients with type 2 diabetes who either had normal body weight or were morbidly obese. While the tmax, clearance, and volume of distribution of glimepiride in the morbidly obese patients were similar to those in the normal weight group, the morbidly obese had lower Cmax and AUC than those of normal body weight. The mean Cmax, AUC0–24, AUC0–∞ values of glimepiride in normal vs. morbidly obese patients were 547 ± 218 ng/mL vs. 410 ± 124 ng/mL, 3210 ± 1030 hours∙ng/mL vs. 2820 ± 1110 hours∙ng/mL and 4000 ± 1320 hours∙ng/mL vs. 3280 ± 1360 hours∙ng/mL, respectively.
Aspirin: In a randomized, double-blind, two-period, crossover study, healthy subjects were given either placebo or aspirin 1 gram three times daily for a total treatment period of 5 days. On Day 4 of each study period, a single 1 mg dose of AMARYL was administered. The AMARYL doses were separated by a 14-day washout period. Co-administration of aspirin and AMARYL resulted in a 34% decrease in the mean glimepiride AUC and a 4% decrease in the mean glimepiride Cmax.
Colesevelam: Concomitant administration of colesevelam and glimepiride resulted in reductions in glimepiride AUC0–∞ and Cmax of 18% and 8%, respectively. When glimepiride was administered 4 hours prior to colesevelam, there was no significant change in glimepiride AUC0–∞ or Cmax, -6% and 3%, respectively [see Dosage and Administration and Drug Interactions].
Cimetidine and Ranitidine: In a randomized, open-label, 3-way crossover study, healthy subjects received either a single 4 mg dose of AMARYL alone, AMARYL with ranitidine (150 mg twice daily for 4 days; AMARYL was administered on Day 3), or AMARYL with cimetidine (800 mg daily for 4 days; AMARYL was administered on Day 3). Co-administration of cimetidine or ranitidine with a single 4 mg oral dose of AMARYL did not significantly alter the absorption and disposition of glimepiride.
Propranolol: In a randomized, double-blind, two-period, crossover study, healthy subjects were given either placebo or propranolol 40 mg three times daily for a total treatment period of 5 days. On Day 4 or each study period, a single 2 mg dose of AMARYL was administered. The AMARYL doses were separated by a 14-day washout period. Concomitant administration of propranolol and AMARYL significantly increased glimepiride Cmax, AUC, and T 1/2 by 23%, 22%, and 15%, respectively, and decreased glimepiride CL/f by 18%. The recovery of M1 and M2 from urine was not changed.
Warfarin: In an open-label, two-way, crossover study, healthy subjects received 4 mg of AMARYL daily for 10 days. Single 25 mg doses of warfarin were administered 6 days before starting AMARYL and on Day 4 of AMARYL administration. The concomitant administration of AMARYL did not alter the pharmacokinetics of R- and S-warfarin enantiomers. No changes were observed in warfarin plasma protein binding. AMARYL resulted in a statistically significant decrease in the pharmacodynamic response to warfarin. The reductions in mean area under the prothrombin time (PT) curve and maximum PT values during AMARYL treatment were 3.3% and 9.9%, respectively, and are unlikely to be clinically relevant.
Carcinogenesis, Mutagenesis, and Impairment of Fertility
Studies in rats at doses of up to 5000 parts per million (ppm) in complete feed (approximately 340 times the maximum recommended human dose, based on surface area) for 30 months showed no evidence of carcinogenesis. In mice, administration of glimepiride for 24 months resulted in an increase in benign pancreatic adenoma formation that was dose-related and was thought to be the result of chronic pancreatic stimulation. No adenoma formation in mice was observed at a dose of 320 ppm in complete feed, or 46–54 mg/kg body weight/day. This is about 35 times the maximum human recommended dose of 8 mg once daily based on surface area.
Glimepiride was non-mutagenic in a battery of in vitro and in vivo mutagenicity studies (Ames test, somatic cell mutation, chromosomal aberration, unscheduled DNA synthesis, and mouse micronucleus test).
There was no effect of glimepiride on male mouse fertility in animals exposed up to 2500 mg/kg body weight (>1,700 times the maximum recommended human dose based on surface area). Glimepiride had no effect on the fertility of male and female rats administered up to 4000 mg/kg body weight (approximately 4,000 times the maximum recommended human dose based on surface area).