Metformin Hydrochloride
Common Brand Names: Glucophage, Glumetza, Riomet
Generic Available
Common Dosage Forms:
Tablets: 500 mg, 850 mg, 1000 mg
Tablets, extended-release (XR): 500 mg, 750 mg, 1000 mg
Oral solution: 500 mg/5 mL (Riomet)
FDA Indications/Dosages:
Used as an adjunct to diet to lower blood glucose in patients with non-insulin dependent diabetes mellitus (NIDDM): Usual starting dose is one 500 mg tablet given twice a day with meals or one 850 mg tablet given with the morning meal. Gradually increase dose by adding one 500 mg tablet every week or one 850 mg tablet every other week until the optimum response is seen. The maximum daily dose is 2550 mg. Metformin XR can be started at 500 mg once a day with the evening meal. Maximum daily dose of Metformin XR is 2000 mg. Patients can be switched from the same daily dose of metformin to metformin XR, up to 2000 mg.
Metformin can be used concomitantly with a sulfonylurea when diet and metformin or a sulfonylurea alone do not result in adequate glycemic control.
No transition period is needed when transferring patients from most other hypoglycemic agents. Due to chlorpropamide’s long half-life, particular care should be exercised during the first 2 weeks when transferring from chlorpropamide therapy.
Monitor: FBG, Hba1C, RFT
Pharmacology/Pharmacokinetics: Metformin is a biguanide which improves glucose tolerance in NIDDM patients. It decreases intestinal absorption of glucose, suppresses hepatic gluconeogenesis, and improves insulin sensitivity. Endogenous insulin must be present for metformin to be effective, although it has no effect on B cells. Unlike sulfonylureas, metformin does not cause hypoglycemia in either diabetic or nondiabetic patients. Steady state plasma levels are reached in 24-48 hours. Metformin is excreted entirely by renal excretion and has a half-life of about 6 hours. There is a lack of dose proportionality with increasing doses for both metformin and metformin XR. Metformin XR comprises a dual-hydrophilic polymer matrix system. Fluid from the GI tract enters the tablet and hydrates polymers causing them to swell. Drug is released through a gel matrix independent of pH. Tablets may be found in the stool as a soft hydrated mass.
Drug Interactions: Furosemide, cimetidine, and nifedipine may increase plasma levels. Alcohol may potentiate the effects of metformin on lactate metabolism. Cationic drugs eliminated by renal tubular secretion may increase metformin plasma levels. Use with drugs which may cause hypoglycemia (corticosteroids, diuretics, phenothiazines, estrogens, phenytoin, sympathomimetics, calcium-channel blockers) may result in loss of glycemic control.
Contraindications/Precautions: Contraindicated in patients with impaired renal functions (serum creatinine ≥1.5 mg/dL [males] or ≥1.4 mg/dL [females]) and impaired hepatic function. Temporarily discontinue therapy when undergoing radiological studies involving parenteral administration of iodinated contrast material because of effects on renal function. Do not use in patients with acute or chronic metabolic acidosis, including diabetic ketoacidosis. METFORMIN MAY CAUSE LACTIC ACIDOSIS RESULTING IN DEATH, HYPOTHERMIA, HYPOTENSION, AND RESISTANT BRADYARRHYTHMIAS. RISK FACTORS INCLUDE ADVANCED AGE, RADIOLOGICAL STUDIES WITH CONTRAST, SURGERY, HYPOXIC STATES, EXCESSIVE ALCOHOL USE, AND HEPATIC IMPAIRMENT. Fatal lactic acidosis may occur in patients with elevated blood levels of metformin (>5 µg/mL) or if the patient is dehydrated. Monitor renal function to avoid drug accumulation. Pregnancy Category B.
Adverse Effects: Decreased vitamin B12 absorption, LACTIC ACIDOSIS, diarrhea, vomiting, nausea, flatulence, anorexia, bloating, and an unpleasant metallic taste. Adverse GI effects are transient and disappear once the patient is stabilized. Lactic acidosis is manifested by unexplained hyperventilation, myalgia, malaise, or unusual somnolence.
Patient Consultation:
Should be taken with meals.
Avoid excessive alcohol consumption during treatment. This includes drinking alcohol all the time or binge drinking for short periods.
Closely follow recommended diet and exercise.
Stop treatment and notify your physician if you experience any of the following symptoms: unexplained hyperventilation, myalgia, malaise, or unusual somnolence.
If a dose is missed by more than a couple of hours, skip it and return to your dosing schedule. Do not double doses.
Contact a physician if the above side effects are severe or persistent.
Keep well hydrated during therapy by drinking plenty of fluids.
