Glipizide and Metformin Hydrochloride

GLIPIZIDE AND METFORMIN HYDROCHLORIDE- glipizide and metformin hydrochloride tablet, film coated
A-S Medication Solutions

DESCRIPTION

Glipizide and metformin hydrochloride tablets contain two oral antihyperglycemic drugs used in the management of type 2 diabetes, glipizide and metformin hydrochloride.

Glipizide is an oral antihyperglycemic drug of the sulfonylurea class. The chemical name for glipizide is 1-cyclohexyl-3-[[p -[2-(5-methylpyrazinecarboxamido)ethyl]phenyl] sulfonyl]urea. Glipizide, USP is a white to almost white; crystalline powder with a molecular formula of C21 H27 N5 O4 S, a molecular weight of 445.55 and a pKa of 5.9. The structural formula is represented below.

structuaral formula 01
(click image for full-size original)

Metformin hydrochloride, USP is an oral antihyperglycemic drug used in the management of type 2 diabetes. Metformin hydrochloride (N,N -dimethylimidodicarbonimidic diamide monohydrochloride) is not chemically or pharmacologically related to sulfonylureas, thiazolidinediones, or α-glucosidase inhibitors. It is white crystalline compound with a molecular formula of C4 H12 ClN5 (monohydrochloride) and a molecular weight of 165.63. Metformin hydrochloride is freely soluble in water, slightly soluble in alcohol, practically insoluble in acetone and in methylene chloride. The pKa of metformin is 12.4. The pH of a 1% aqueous solution of metformin hydrochloride is 6.68. The structural formula is as shown:

structural formula 02

Each glipizide and metformin hydrochloride tablet intended for oral administration contains glipizide, 2.5 mg or 5 mg and metformin hydrochloride, 250 mg or 500 mg. In addition, each tablet contains the following inactive ingredients: croscarmellose sodium, hydroxypropyl methylcellulose, magnesium stearate, microcrystalline cellulose, polyethylene glycol, povidone and titanium dioxide. Additionally each 2.5 mg/250 mg and 5 mg/500 mg tablet contains iron oxide red and each 2.5 mg/500 mg tablet contains polysorbate 80.

CLINICAL PHARMACOLOGY

Mechanism of Action:

Glipizide and metformin hydrochloride tablet combines glipizide and metformin hydrochloride, two antihyperglycemic agents with complementary mechanisms of action, to improve glycemic control in patients with type 2 diabetes.

Glipizide appears to lower blood glucose acutely by stimulating the release of insulin from the pancreas, an effect dependent upon functioning beta cells in the pancreatic islets. Extrapancreatic effects may play a part in the mechanism of action of oral sulfonylurea hypoglycemic drugs. 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 post prandial insulin response continues to be enhanced after at least 6 months of treatment.

Metformin hydrochloride is an antihyperglycemic agent that improves glucose tolerance in patients with type 2 diabetes, lowering both basal and postprandial plasma glucose. Metformin hydrochloride decreases hepatic glucose production, decreases intestinal absorption of glucose, and improves insulin sensitivity by increasing peripheral glucose uptake and utilization.

Pharmacokinetics:

Absorption and Bioavailability:

Glipizide and Metformin Hydrochloride Tablets:

In a single dose study in healthy subjects, the glipizide and metformin components of glipizide and metformin hydrochloride tablets 5 mg/500 mg were bioequivalent to co-administered glipizide and metformin hydrochloride. Following administration of a single glipizide and metformin hydrochloride 5 mg/500 mg tablet in healthy subjects with either a 20% glucose solution or a 20% glucose solution with food, there was a small effect of food on peak plasma concentration (Cmax ) and no effect of food on area under the curve (AUC) of the glipizide component. Time to peak plasma concentration (Tmax ) for the glipizide component was delayed 1 hour with food relative to the same tablet strength administered fasting with a 20% glucose solution. Cmax for the metformin component was reduced approximately 14% by food whereas AUC was not affected. Tmax for the metformin component was delayed 1 hour after food.

Glipizide:

Gastrointestinal absorption of glipizide is uniform, rapid, and essentially complete. Peak plasma concentrations occur 1 to 3 hours after a single oral dose. 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.

Metformin Hydrochloride:

The absolute bioavailability of a 500 mg metformin hydrochloride tablet given under fasting conditions is approximately 50% to 60%. Studies using single oral doses of metformin tablets of 500 mg and 1500 mg, and 850 mg to 2550 mg, indicate that there is a lack of dose proportionality with increasing doses, which is due to decreased absorption rather than an alteration in elimination. Food decreases the extent of and slightly delays the absorption of metformin, as shown by approximately a 40% lower peak concentration and a 25% lower AUC in plasma and a 35-minute prolongation of time to peak plasma concentration following administration of a single 850 mg tablet of metformin with food, compared to the same tablet strength administered fasting. The clinical relevance of these decreases is unknown.

Distribution:

Glipizide:

Protein binding was studied in serum from volunteers who received either oral or intravenous glipizide and found to be 98% to 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 labeled drug.

Metformin Hydrochloride:

The apparent volume of distribution (V/F) of metformin following single oral doses of 850 mg averaged 654±358 L. Metformin is negligibly bound to plasma proteins. Metformin partitions into erythrocytes, most likely as a function of time. 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 µg/mL. During controlled clinical trials, maximum metformin plasma levels did not exceed 5 µg/mL, even at maximum doses.

Metabolism and Elimination:

Glipizide:

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. The half-life of elimination ranges from 2 to 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.

Metformin Hydrochloride:

Intravenous single-dose studies in normal 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. Renal clearance (see Table 1) 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.

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