CLINICAL PHARMACOLOGY
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.
Pharmacodynamics
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].
Pharmacokinetics
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 HbA 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
(T½) 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 singledose 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.
Drug Interactions
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-∞
and 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 T½ 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.
Clinical Studies
Monotherapy
A total of 304 patients with type 2 diabetes already
treated with sulfonylurea therapy participated in a 14-week, multicenter,
randomized, double-blind, placebo-controlled trial evaluating the safety and efficacy
of AMARYL monotherapy. Patients discontinued their sulfonylurea therapy then
entered a 3- week placebo washout period followed by randomization into 1 of 4
treatment groups: placebo (n=74), AMARYL 1 mg (n=78), AMARYL 4 mg (n=76) and
AMARYL 8 mg (n=76). All patients randomized to AMARYL started 1 mg daily.
Patients randomized to AMARYL 4 mg or 8 mg had blinded, forced titration of the
AMARYL dose at weekly intervals, first to 4 mg and then to 8 mg, as long as the
dose was tolerated, until the randomized dose was reached. Patients randomized
to the 4 mg dose reached the assigned dose at Week 2. Patients randomized to
the 8 mg dose reached the assigned dose at Week 3. Once the randomized dose
level was reached, patients were to be maintained at that dose until Week 14. Approximately
66% of the placebo-treated patients completed the trial compared to 81% of
patients treated with glimepiride 1 mg and 92% of patients treated with
glimepiride 4 mg or 8 mg. Compared to placebo, treatment with AMARYL 1 mg, 4 mg
and 8 mg daily provided statistically significant improvements in HbA1c
compared to placebo (Table 3).
Table 3: 14-week Monotherapy Trial Comparing AMARYL to
Placebo in Patients Previously Treated With Sulfonylurea Therapy*
|
Placebo
(N=74) |
AMARYL |
1 mg
(N=78) |
4 mg
(N=76) |
8 mg
(N=76) |
HbA1C (%) |
|
n=59 |
n=65 |
n=65 |
n=68 |
Baseline (mean) |
8.0 |
7.9 |
7.9 |
8.0 |
Change from Baseline (adjusted mean†) |
1.5 |
0.3 |
-0.3 |
-0.4 |
Difference from Placebo (adjusted mean†) 95% confidence interval |
|
-1.2*
(-1.5, -0.8) |
-1.8*
(-2.1, -1.4) |
-1.8*
(-2.2, -1.5) |
Mean Baseline Weight (kg) |
|
n=67 |
n=76 |
n=75 |
n=73 |
Baseline (mean) |
85.7 |
84.3 |
86.1 |
85.5 |
Change from Baseline (adjusted mean†) |
-2.3 |
-0.2 |
0.5 |
1.0 |
Difference from Placebo (adjusted mean†) 95% confidence interval |
|
2.0‡
(1.4, 2.7) |
2.8‡
(2.1, 3.5) |
3.2‡
(2.5, 4.0) |
*Intent-to-treat population using last observation on
study
†Least squares mean adjusted for baseline value
‡p ≤ 0.001 |
A total of 249 patients who were treatment-naive or
who had received limited treatment with antidiabetic therapy in the past were
randomized to receive 22 weeks of treatment with either AMARYL (n=123) or placebo
(n=126) in a multicenter, randomized, double-blind, placebo-controlled,
dose-titration trial. The starting dose of AMARYL was 1 mg daily and was
titrated upward or downward at 2-week intervals to a goal FPG of 90-150 mg/dL.
Blood glucose levels for both FPG and PPG were analyzed in the laboratory.
Following 10 weeks of dose adjustment, patients were maintained at their
optimal dose (1, 2, 3, 4, 6 or 8 mg) for the remaining 12 weeks of the trial.
Treatment with AMARYL provided statistically significant improvements in HbA1c
and FPG compared to placebo (Table 4).
Table 4: 22-Week Monotherapy Trial Comparing AMARYL to
Placebo in Patients Who Were Treatment-Naïve or Who Had No Recent Treatment
with Antidiabetic Therapy*
|
Placebo
(N=126) |
AMARYL
(N=123) |
HbA1C (%) |
n=97 |
n=106 |
Baseline (mean) |
9.1 |
9.3 |
Change from Baseline (adjusted meant) |
-1.1* |
-2.2* |
Difference from Placebo (adjusted meant) |
-1.1* |
95% confidence interval |
(-1.5,-0.8) |
Body Weight (kg) |
n=122 |
n=119 |
Baseline (mean) |
86.5 |
87.1 |
Change from Baseline (adjusted meant) |
-0.9 |
1.8 |
Difference from Placebo (adjusted meant) |
2.7 |
95% confidence interval |
(1.9, 3.6) |
* Intent to treat population using last observation on
study
† Least squares mean adjusted for baseline value
‡ p ≤ 0.0001 |