CLINICAL PHARMACOLOGY
Mechanism Of Action
Metformin is a biguanide that improves glucose tolerance in patients with type 2 diabetes, lowering both basal and postprandial plasma glucose. Metformin decreases hepatic glucose production, decreases intestinal absorption of glucose, and improves insulin sensitivity by increasing peripheral glucose uptake and utilization. With metformin therapy, insulin secretion remains unchanged while fasting insulin levels and day-long plasma insulin response may decrease.
Pharmacokinetics
Absorption
Following a single oral dose of 1,000 mg (2x500 mg tablets) GLUMETZA after a meal, the time to reach maximum plasma metformin concentration (Tmax) is achieved at approximately 7-8 hours. In both single-and multiple-dose studies in healthy subjects, once daily 1,000 mg (2x500 mg tablets) dosing provides equivalent systemic exposure, as measured by area under the curve (AUC), and up to 35% higher Cmax, of metformin relative to the immediate-release given as 500 mg twice daily. At usual clinical doses and dosing schedules of metformin, steady state plasma concentrations of metformin are reached within 24-48 hours and are generally <1 mcg/mL.
In a two-way, single-dose, crossover study in healthy volunteers, the 1,000 mg tablet was found to be similar to two 500 mg tablets under fed conditions based on equivalent Cmax and AUCs for the two formulations.
Single oral doses of GLUMETZA from 500 mg to 2,500 mg resulted in less than proportional increase in both AUC and Cmax.
Effect of food
Low-fat and high-fat meals increased the systemic exposure (as measured by AUC) from GLUMETZA tablets by about 38% and 73%, respectively, relative to fasting. Both meals prolonged metformin Tmax by approximately 3 hours but Cmax was not affected.
Distribution
The apparent volume of distribution (V/F) of metformin following single oral doses of 850 mg metformin HCl averaged 654±358 L. Metformin is negligibly bound to plasma proteins. Metformin partitions into erythrocytes, most likely as a function of time.
Metabolism
Intravenous, single-dose studies in healthy 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.
Excretion
Renal clearance 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
Renal Impairment
Following a single-dose administration of GLUMETZA 500 mg in subjects with mild and moderate renal impairment, the oral and renal clearance of metformin were decreased by 33% and 50% and 16% and 53%, respectively. Metformin peak and systemic exposure was 27% and 61% greater, respectively in subjects with mild renal impairment and 74% and 2.36fold greater in subjects with moderate renal impairment as compared to healthy subjects. [see DOSAGE AND ADMINISTRATION , CONTRAINDICATIONS , and WARNINGS AND PRECAUTIONS]
Hepatic Impairment
No pharmacokinetic studies of GLUMETZA have been conducted in subjects with hepatic impairment, [see WARNINGS AND PRECAUTIONS and Use In Specific Populations]
Geriatrics
Limited data from controlled pharmacokinetic studies of metformin HCl in healthy elderly subjects suggest that total plasma clearance of metformin is decreased by 35%, the half-life is prolonged by 64% and Cmax is increased by 76%, 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 DOSAGE AND ADMINISTRATION and WARNINGS AND PRECAUTIONS]
Gender
In the pharmacokinetic studies in healthy volunteers, there were no important differences between male and female subjects with respect to metformin AUC and t1/2. However, Cmax for metformin was 40% higher in female subjects as compared to males. In controlled clinical studies in patients with type 2 diabetes, the antihyperglycemic effect of metformin HCl tablets was comparable in males and females. The gender differences for Cmax are unlikely to be clinically important.
Race
A trend towards 10% higher metformin Cmax and AUC values for metformin are obtained in Asian subjects when compared to Caucasian, Hispanic and Black subjects. The differences between the Asian and Caucasian groups are unlikely to be clinically important. In controlled clinical studies of metformin HCl in patients with type 2 diabetes, the antihyperglycemic effect was comparable in whites (n=249), blacks (n=51) and Hispanics (n=24).
Pediatrics
There are no available pharmacokinetic data with GLUMETZA in pediatric patients.
Drug Interactions
Specific pharmacokinetic drug interaction studies with GLUMETZA have not been performed except for one with glyburide. However, such studies have been performed on metformin HCl tablets.
Table 3: Effect of Coadministered Drug on Plasma Metformin Systemic Exposure
Coadministered Drug |
Dose of Coadministered Drug1 |
Dose of Metformin HCl1 |
Geometric Mean Ratio (ratio with/ without coadministered drug) No Effect=1.00 |
AUC2 |
Cmax |
No dosing adjustments required for the following: |
Glyburide |
5 mg |
500 mg4 |
0.983 |
0.993 |
Furosemide |
40 mg |
850 mg |
1.093 |
1.223 |
Nifedipine |
10 mg |
850 mg |
1.16 |
1.21 |
Propranolol |
40 mg |
850 mg |
0.90 |
0.94 |
Ibuprofen |
400 mg |
850 mg |
1.053 |
1.073 |
Cationic drugs that are eliminated by renal tubular secretion may increase the accumulation of metformin:
[see WARNINGS AND PRECAUTIONS and DRUG INTERACTIONS]. |
Cimetidine |
400 mg |
850 mg |
1.40 |
1.61 |
Carbonic anhydrase inhibitors may cause metabolic acidosis:
[see WARNINGS AND PRECAUTIONS and DRUG INTERACTIONS]. |
Topiramate |
100 mg5 |
500 mg5 |
1.255 |
1.17 |
1 All metformin HCl and coadministered drugs were given as single doses.
2 AUC=AUC0−inf
3 Ratio of arithmetic means
4 GLUMETZA (metformin HCl extended-release tablets) 500 mg
5 At steady state with topiramate 100 mg every 12 hours and metformin 500 mg every 12 hours; AUC=AUC0-12h |
Table 4: Effect of Metformin on Coadministered Drug Systemic Exposure
Coadministered Drug |
Dose of Coadministered Drug1 |
Dose of Metformin HCl1 |
Geometric Mean Ratio (ratio with/ without coadministered drug) No effect=1.00 |
AUC2 |
Cmax |
No dosing adjustments required for the following: |
Glyburide |
5 mg |
500 mg4 |
0.783 |
0.633 |
Furosemide |
40 mg |
850 mg |
0.873 |
0.693 |
Nifedipine |
10 mg |
850 mg |
1.104 |
1.08 |
Propranolol |
40 mg |
850 mg |
1.014 |
0.94 |
Ibuprofen |
400 mg |
850 mg |
0.975 |
1.015 |
Cimetidine |
400 mg |
850 mg |
0.954 |
1.01 |
1 All metformin HCl and coadministered drugs were given as single doses.
2 AUC=AUC0–inf unless otherwise noted
3 Ratio of arithmetic means, p-value of difference <0.05
4 AUC0-24 hr reported
5 Ratio of arithmetic means |
Clinical Studies
In a multicenter, randomized, double-blind, active-controlled, dose-ranging, parallel group study conducted in patients type 2 diabetes mellitus, GLUMETZA 1,500 mg once daily, GLUMETZA 1,500 per day in divided doses (500 mg in the morning and 1,000 mg in the evening), and GLUMETZA 2,000 mg once daily were compared to immediate-release metformin HCl tablets 1,500 mg per day in divided doses (500 mg in the morning and 1,000 mg in the evening). This study included patients (n=338) who were newly diagnosed with diabetes, patients treated only with diet and exercise, patients treated with a single antidiabetic medication (sulfonylureas, alpha-glucosidase inhibitors, thiazolidinediones, or meglitinides), and patients (n=368) receiving metformin HCl tablets up to 1,500 mg/day plus a sulfonylurea at a dose equal to or less than one-half the maximum dose. Patients who were enrolled on monotherapy or combination antidiabetic therapy underwent a 6-week washout. Patients randomized to GLUMETZA began titration from 1,000 mg/day up to their assigned treatment dose over 3 weeks. Patients randomized to immediate-release metformin initiated 500 mg twice daily for 1 week followed by 500 mg with breakfast and 1,000 mg with dinner for the second week. The 3-week treatment period was followed by an additional 21-week period at the randomized dose. The results are presented in Table 4.
Table 5: Mean Changes from Baseline in HbA1c and Fasting Plasma Glucose at Week 24 ComparingGLUMETZA versus Metformin HCl Tablets* in Patients with Type 2 Diabetes Mellitus
|
GLUMETZA |
Metformin HCl Tablets* 1,500 mg in Divided Doses (n=174) |
1,500 mg Once Daily (n=178) |
1,500 mg in Divided Doses (n=182) |
2,000 mg Once Daily (n=172) |
HbA1c (%), N |
169 |
175 |
159 |
170 |
Baseline |
8.2 |
8.5 |
8.3 |
8.7 |
Mean Change at Final Visit |
-0.7 |
-0.7 |
-1.1 |
-0.7 |
Mean Difference from Metformin HCl Tablets* (98.4% CI) |
0 (-0.3, 0.3) |
0 (-0.3, 0.3) |
-0.4 (-0,7, -0.1) |
N/A |
Fasting Plasma Glucose (mg/dL), N |
175 |
179 |
170 |
172 |
Baseline |
190 |
192.3 |
184 |
197 |
Mean Change at Final Visit |
-39 |
-32 |
-42 |
-32 |
Mean Difference from Metformin HCl Tablets* (95% CI) |
-6 (-15, 2) |
0 (-8, 9) |
-10 (-19, -1) |
N/A |
*Immediate-release metformin HCl tablets |
Mean baseline body weight was 88.2 kg, 90.5 kg, 87.7 kg and 88.7 kg in the GLUMETZA 1,500 mg once daily, GLUMETZA 1,500 mg in divided doses, GLUMETZA 2,000 mg once daily and metformin HCl tablets 1,500 mg in divided doses arms, respectively. Mean change in body weight from baseline to week 24 was -0.9 kg, -0.7 kg, -1.1 kg, and -0.9 kg in the GLUMETZA 1,500 mg once daily, GLUMETZA 1,500 mg in divided doses, GLUMETZA 2,000 mg once daily and metformin HCl tablets 1,500 mg in divided doses arms, respectively.
A double-blind, randomized, placebo-controlled (glyburide add-on) multicenter study enrolled patients with type 2 diabetes mellitus who were newly diagnosed or treated with diet and exercise (n=144), or who were receiving monotherapy with metformin, sulfonylureas, alpha-glucosidase inhibitors, thiazolidinediones, or meglitinides, or treated with combination therapy consisting of metformin HCl/glyburide at doses up to 1,000 mg metformin + 10 mg glyburide per day (or equivalent doses of glipizide or glimepiride up to half the maximum therapeutic dose) (n=431). All patients were stabilized on glyburide for a 6-week run-in period, and then randomized to 1 of 4 treatments: placebo + glyburide (glyburide alone); GLUMETZA 1,500 mg once a day + glyburide, GLUMETZA 2,000 mg once a day + glyburide, or GLUMETZA 1,000 mg twice a day + glyburide. A 3-week GLUMETZA titration period was followed by a 21-week maintenance treatment period. Use of insulin and oral hypoglycemic agents other than the study drugs were prohibited. The results are presented in Table 5.
Table 6: Mean Changes from Baseline in HbA1c and Fasting Plasma Glucose at Week 24 for the GLUMETZA + Glyburide Groups and Placebo+ Glyburide Treatment Group in Patients with Type 2 Diabetes Mellitus
|
GLUMETZA + Glyburide* |
Placebo + Glyburide*
(n=144) |
1,500 mg Once Daily (n=144) |
1,500 mg Once Daily (n=144) |
2,000 mg Once Daily (n=146) |
HbA1c (%), N |
136 |
136 |
144 |
141 |
Baseline |
7.9 |
7.8 |
7.7 |
8.1 |
Mean Change at Final Visit |
-0.7 |
-0.8 |
-0.7 |
-0.1 |
Mean Difference from Glyburide Alone (95% CI) |
-0.8a
(-1.0, -0.6) |
-0.9a
(-1.1, -0.7) |
-0.8a
(-1.0, -0.6) |
N/A |
Fasting Plasma Glucose (mg/dL), N |
143 |
141 |
145 |
144 |
Baseline |
163 |
163 |
159 |
164 |
Mean Change at Final Visit |
-14 |
-16 |
-9 |
16 |
Mean Difference from Glyburide Alone (95% CI) |
-29.2a
(-39, -20) |
-31.2a
(-41, -22) |
-24.9a
(-35, -15) |
N/A |
*Glyburide was administered as 10 mg at breakfast and 5 mg at dinner.
a p-value for pairwise comparison <0.001 |
Mean baseline body weight was 89.4 kg, 103.7 kg, 102.9 kg and 95.6 kg in the GLUMETZA 1,500 mg once daily, GLUMETZA 1,500 mg in divided doses, GLUMETZA 2,000 mg once daily and metformin HCl tablets 1,500 mg in divided doses arms, respectively. Mean change in body weight from baseline to week 24 was 0.3 kg, 0.1 kg, 0 kg, and 0.7 kg in the GLUMETZA 1,500 mg once daily, GLUMETZA 1,500 mg in divided doses, GLUMETZA 2,000 mg once daily and metformin HCl tablets 1,500 mg in divided doses arms, respectively.