· Pharm class: biguanides
· Basic drug actions:
o Decreases hepatic glucose production.
o Decreases intestinal glucose absorption.
o Increases sensitivity to insulin.
· Routes for administration: PO
· Administration techniques:
o Metformin should be temporarily discontinued in patients requiring surgery involving restricted intake of food and fluids. Resume metformin when oral intake has resumed and renal function is normal.
o Withhold metformin before or at the time of studies requiring IV administration of iodinated contrast media and for 48 hr after study.
o PO: Administer metformin with meals to minimize GI effects.
o XR tablets must be swallowed whole; do not crush or chew.
· Drug/drug and drug/food interactions:
o Acute or chronic alcohol ingestion or iodinated contrast media ↑ risk of lactic acidosis.
o Cimetidine and furosemide may ↑ effects of metformin.
o Nifedipine ↑ absorption and effects.
o Glucosamine may worsen blood glucose control.
· Most common side/adverse effects:
o abdominal bloating, diarrhea, nausea, vomiting, unpleasant metallic taste
o hypoglycemia
o LACTIC ACIDOSIS
o decreased vitamin B12 levels
· Lab values to monitor:
o Monitor serum glucose and glycosylated hemoglobin periodically during therapy to evaluate effectiveness of therapy. May cause false-positive results for urine ketones.
o Assess renal function before initiating and at least annually during therapy. Discontinue metformin if renal impairment occurs.
o Monitor serum folic acid and vitamin B12 every 1–2 yr in long-term therapy. Metformin may interfere with absorption.
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