Metformin Oral: Dosing and Precautions

Therapeutic action

Biguanide antidiabetic.

Indications

First-line treatment of type 2 diabetes when diet and lifestyle measures alone are insufficient, as monotherapy or in combination with another antidiabetic.

Forms and strengths

• 500 mg and 1 g tablets.

Dose and duration

Adult:

• Week 1: 500 mg once daily in the morning.
• Week 2: 500 mg 2 times daily, morning and evening.
• Increase if necessary in increments of 500 mg per week according to blood glucose levels and as long as the drug is well tolerated, without exceeding 2 g daily.

Contra-indications, adverse effects, precautions

• Do not administer to patients with ketoacidosis or cardiac, respiratory, hepatic, or severe renal impairment.
• May commonly cause dose-related gastrointestinal disturbances, loss of appetite, and metallic taste in the mouth.
• Rarely, may cause lactic acidosis and decreased absorption of vitamin B12.
• Reduce dose to a maximum of 1 g daily in moderate renal impairment.
• Monitor combination with diuretics, ACE inhibitors, NSAIDs, and drugs increasing blood glucose levels.
• Stop metformin before surgery or injection of iodinated contrast agents, and resume 48 hours later after checking renal function.
• Pregnancy: insulin is the drug of choice, but metformin is not contraindicated.
• Breast-feeding: no contra-indication.