Glipizide 5 mg, Metformin 500 mg (CR) Tablets

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.

Absorption — Following a single oral dose of 1,000 mg (2x500 mg tablets) metformin hydrochloride extended-release tablets after a meal, the time to reach maximum plasma metformin concentration (T max) is achieved at approximately 7 to 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 C max, 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 to 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 C max and AUCs for the two formulations.

Single oral doses of metformin hydrochloride extended-release tablets from 500 mg to 2,500 mg resulted in less than proportional increase in both AUC and C max.

Effect of food: Low-fat and high-fat meals increased the systemic exposure (as measured by AUC) from metformin hydrochloride extended-release tablets by about 38% and 73%, respectively, relative to fasting. Both meals prolonged metformin T max by approximately 3 hours but C max 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.

Renal Impairment — Following a single-dose administration of metformin hydrochloride extended-release tablets 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 2.36-fold greater in subjects with moderate renal impairment as compared to healthy subjects [see Dosage and Administration (2.2), Contraindications (4), and Warnings and Precautions (5.1)].

Hepatic Impairment — No pharmacokinetic studies of metformin hydrochloride extended-release tablets have been conducted in subjects with hepatic impairment [see Warnings and Precautions (5.1) and Use in Specific Populations (8.7)].

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 C max 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 (2) and Warnings and Precautions (5.1)].

Gender — In the pharmacokinetic studies in healthy volunteers, there were no important differences between male and female subjects with respect to metformin AUC and t 1/2. However, C max 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 C max are unlikely to be clinically important.

Mechanism of Action:The primary mode of action of glipizide in experimental animals appears to be the stimulation of insulin secretion from the beta cells of pancreatic islet tissue and is thus dependent on functioning beta cells in the pancreatic islets. In humans, glipizide appears to lower the blood glucose acutely by stimulating the release of insulin from the pancreas, an effect dependent upon functioning beta cells in the pancreatic islets. The mechanism by which glipizide lowers blood glucose during long-term administration has not been clearly established. In man, stimulation of insulin secretion by glipizide in response to a meal is undoubtedly of major importance. Fasting insulin levels are not elevated even on long-term glipizide administration, but the postprandial insulin response continues to be enhanced after at least 6 months of treatment. The insulinotropic response to a meal occurs within 30 minutes after an oral dose of glipizide in diabetic patients, but elevated insulin levels do not persist beyond the time of the meal challenge. Extrapancreatic effects may play a part in the mechanism of action of oral sulfonylurea hypoglycemic drugs.

Blood sugar control persists in some patients for up to 24 hours after a single dose of glipizide, even though plasma levels have declined to a small fraction of peak levels by that time (see Pharmacokinetics below).

Some patients fail to respond initially, or gradually lose their responsiveness to sulfonylurea drugs, including glipizide. Alternatively, glipizide may be effective in some patients who have not responded or have ceased to respond to other sulfonylureas.

Gastrointestinal absorption of glipizide in man is uniform, rapid, and essentially complete. Peak plasma concentrations occur 1–3 hours after a single oral dose. The half-life of elimination ranges from 2–4 hours in normal subjects, whether given intravenously or orally. The metabolic and excretory patterns are similar with the two routes of administration, indicating that first-pass metabolism is not significant. Glipizide does not accumulate in plasma on repeated oral administration. Total absorption and disposition of an oral dose was unaffected by food in normal volunteers, but absorption was delayed by about 40 minutes. Thus, glipizide was more effective when administered about 30 minutes before, rather than with, a test meal in diabetic patients. Protein binding was studied in serum from volunteers who received either oral or intravenous glipizide and found to be 98–99% one hour after either route of administration. The apparent volume of distribution of glipizide after intravenous administration was 11 liters, indicative of localization within the extracellular fluid compartment. In mice, no glipizide or metabolites were detectable autoradiographically in the brain or spinal cord of males or females, nor in the fetuses of pregnant females. In another study, however, very small amounts of radioactivity were detected in the fetuses of rats given labelled drug.

The metabolism of glipizide is extensive and occurs mainly in the liver. The primary metabolites are inactive hydroxylation products and polar conjugates and are excreted mainly in the urine. Less than 10% unchanged glipizide is found in the urine.