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Metformin

Class
Indications
Administration/Absorption
  • Oral
  • Absorbed over 6 hours
  • Bioavailability is 50 to 60% under fasting conditions.
  • Administration with food decreases and delays absorption
  • Peak action occurs 3 hours after oral administration.
Dosage

Distribution
  • VOD is 654 L for metformin 850 mg administered as a single dose
  • Negligibly bound to plasma proteins
Mechanism
Excretion
  • Half-life 6.2 hours
  • Metformin is not metabolized and is excreted unchanged in the urine
  • Approximately 90% of the drug is eliminated in 24 hours in those with healthy renal function
  • Renal clearance of metformin is approximately 3.5 times that of creatinine clearance
    • Indicates that tubular secretion is the primary mode of metformin elimination.
Side effects
  • Its main side effects are dyspepsia, nausea and diarrhea
    • Dose titration and/or use of smaller divided doses may decrease side effects
Interactions

Contraindications
  • Risk of lactic acidosis means metformin should be avoided in:
    • severely compromised renal function (creatinine clearance < 30 ml/min)
    • acute/decompensated heart failure
    • severe liver disease
    • for 48 hours after the use of iodinated contrast dyes
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