metformin hydrochloride
Glucophage
Pregnancy Risk Category B
How supplied
Tablets: 500 mg, 850 mg
Action
Decreases hepatic glucose production and intestinal absorption of glucose and improves insulin sensitivity (increases peripheral glucose uptake and utilization).
Indications & dosage
Adjunct to diet to lower blood glucose level in patients with type 2 non-insulin-dependent diabetes mellitus--
Adults: initially, 500 mg P.O. b.i.d. given with morning and evening meals, or 850 mg P.O. once daily given with morning meal. When 500-mg form used, dosage increased 500 mg weekly to maximum dose of 2,500 mg P.O. daily in divided doses, p.r.n. When 850-mg form used, dosage increased 850 mg every other week to maximum dose of 2,550 mg P.O. daily in divided doses, p.r.n.
Elderly: for patients over age 65, dosing should be conservative because of potential decrease in renal function.
Adjust-a-dose: For debilitated patients, dosing should be conservative because of potential decrease in renal function.
Adverse reactions
GI: diarrhea, nausea, vomiting, abdominal bloating, flatulence, anorexia, unpleasant or metallic taste.
Hematologic: megaloblastic anemia.
Other: lactic acidosis.
Interactions
Drug-drug. Calcium channel blockers, corticosteroids, estrogens, isoniazid, nicotinic acid, oral contraceptives, phenothiazines, phenytoin, sympathomimetics, thiazide and other diuretics, thyroid drugs: may produce hyperglycemia. Monitor patient's glycemic control. Metformin dosage may need to be increased.
Cationic drugs (such as amiloride, cimetidine, digoxin, morphine, procainamide, quinidine, quinine, ranitidine, triamterene, trimethoprim, vancomycin): have potential to compete for common renal tubular transport systems, which may increase metformin plasma levels. Monitor patient's blood glucose level.
Nifedipine: increased metformin plasma levels. Monitor patient closely. Metformin dosage may need to be decreased.
Radiologic contrast dye: can result in acute renal failure. Withhold metformin for 24 hours before procedure.
Drug-lifestyle. Alcohol use: potentiated drug's effects. Avoid concurrent use.
Effects on diagnostic tests
None reported.
Contraindications
Contraindicated in patients with hypersensitivity to drug and in those with renal disease or metabolic acidosis. Drug should be temporarily withheld in patients undergoing radiologic studies involving parenteral administration of iodinated contrast materials because use of such products may result in acute renal dysfunction. Drug should be promptly discontinued if patient enters a hypoxic state. Avoid use in patients with hepatic disease.
Nursing considerations
- Use caution when giving drug to elderly, debilitated, or malnourished patients and to those with adrenal or pituitary insufficiency because of increased risk of hypoglycemia.
- Before therapy begins, and at least annually thereafter, patient's renal function should be assessed. If renal impairment is detected, expect doctor to switch patient to a different antidiabetic. This is particularly important in elderly patients.
- Administer with meals; once-daily dosage should be given with breakfast and twice-daily dosage with breakfast and dinner.
- When transferring patients from standard oral hypoglycemics (except chlorpropamide) to metformin, no transition period generally is needed. When switching patients from chlorpropamide to metformin, care should be exercised during the first 2 weeks of metformin therapy because the prolonged retention of chlorpropamide increases risk of hypoglycemia during this time.
- Monitor patient's blood glucose levels regularly to evaluate effectiveness of therapy. Notify doctor if they become elevated despite therapy.
- If patient hasn't responded to 4 weeks of therapy using the maximum dose, doctor may add an oral sulfonylurea while continuing metformin at the maximum dose. If patient still doesn't respond after several months of concomitant therapy at maximum doses, doctor may discontinue both drugs and institute insulin therapy.
- Monitor patient closely during times of increased stress, such as infection, fever, surgery, or trauma. Insulin therapy may be needed in these situations.
- Risk of drug-induced lactic acidosis is very low. Reported cases have occurred primarily in diabetic patients with significant renal insufficiency; in those with multiple, concomitant medical or surgical problems; and in those with multiple, concomitant drug regimens. Risk increases with degree of renal impairment and patient's age.
- Alert:
Discontinue drug immediately and notify doctor if patient develops a condition associated with hypoxemia or dehydration because of risk of lactic acidosis.
- Expect drug therapy to be temporarily suspended for surgical procedures (except minor procedures not associated with restricted intake of food and fluids) and for patients undergoing radiologic studies involving use of contrast media containing iodine. Therapy shouldn't be restarted until patient's oral intake has resumed and renal function has been evaluated as normal by doctor.
- Monitor patient's hematologic status for evidence of megaloblastic anemia. Patients with inadequate vitamin B12 or calcium intake or absorption appear to be predisposed to developing subnormal vitamin B12 levels. These patients should have routine serum vitamin B12 level determinations every 2 to 3 years.
Patient teaching
- Alert:
Instruct patient about nature of diabetes, importance of following therapeutic regimen, adhering to specific diet, weight reduction, exercise, personal hygiene programs, and avoiding infection. Explain how and when to perform self-monitoring of blood glucose level; teach signs and symptoms of hypoglycemia and hyperglycemia, and emergency measures.
- Instruct patient to discontinue drug and notify doctor immediately if unexplained hyperventilation, myalgia, malaise, unusual somnolence, or other nonspecific symptoms of early lactic acidosis occur.
- Warn patient not to consume excessive alcohol while taking drug.
- Tell patient not to change drug dosage without doctor's consent. Encourage patient to report abnormal blood glucose level test results.
- Advise patient not to take other drugs, including OTC drugs, without first checking with doctor.
- Instruct patient to carry medical identification at all times.
*Liquid contains alcohol. **May contain tartrazine. †Canada ‡Australia §U.K. OTCOver the counter
Reactions may be common, uncommon, life-threatening, or COMMON AND LIFE-THREATENING