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Pharmacotherapeutic Group: Antidiabetic agent.
Pharmacology: Metformin is an oral antihyperglycaemic agent used in the management of non-insulin dependent diabetes mellitus (NIDDM). It reduces blood glucose levels, predominantly by improving hepatic and peripheral tissue sensitivity to insulin without affecting the secretion of this hormone. Metformin possesses similar antihyperglycaemic efficacy to sulfonylureas in obese and non-obese patients with NIDDM.
Pharmacokinetics: Metformin has an absolute oral bioavailability of 50-60% and gastrointestinal absorption is apparently complete within 6 hrs of ingestion. Higher oral doses are proportionately less bioavailable than lower doses (observed with doses ranging from 500-1500 mg).
The appearance of metformin in plasma from Diamet SR is slower and more prolonged compared to immediate-release metformin. Distribution studies with Diamet SR have not been conducted. The apparent volume of distribution (V/F) of metformin following single oral doses of immediate-release metformin 850 mg averaged 654±358 L. Metformin is negligibly bound to plasma proteins.
Metformin is partially absorbed from the genitourinary tract. Half-life is 1.5-3 hrs. It is not bound to plasma proteins. It is eliminated by the renal route.
Renal clearance of metformin 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 1st 24 hrs, with a plasma elimination half-life of approximately 6.2 hrs. In the blood, the elimination half-life is approximately 17.6 hrs, suggesting that the erythrocyte mass may be a compartment of distribution.
