Metformin (Glucophage) - Uses, Side Effects

Glucophage Interactions

Pharmacokinetic Interactions

1. Renal Transport Inhibition

Drugs competing with metformin's tubular secretion increase plasma concentrations by 40-60%:

Interacting Drug Mechanism Clinical Effect Management
Cimetidine OCT2 inhibition ↑ Metformin AUC by 60% Avoid combination or reduce metformin dose
Dolutegravir MATE1 inhibition ↑ Metformin Cmax by 79% Limit metformin to 1000mg/day

2. Nephrotoxic Agents

  • NSAIDs: Reduce renal perfusion → 30% higher metformin levels
  • Vancomycin: Additive tubular toxicity
  • Aminoglycosides: Synergistic nephrotoxicity

High-Risk Category X Interactions

Iodinated Contrast Media

Intravenous contrast increases lactic acidosis risk through:

  • Acute kidney injury (incidence 5-15%)
  • Impaired metformin excretion
  • Dehydration effects

Protocol: Withhold metformin 48 hours pre-procedure in patients with eGFR 30-60

Ethanol Interactions

Alcohol Consumption Effect Recommendation
Acute binge (>4 drinks) ↑ Lactate production 300% Absolute avoidance
Chronic use ↓ Hepatic lactate clearance Limit to 1 drink/day

Interaction Monitoring Guidelines

Pre-Interaction Screening

  • Renal function (eGFR, creatinine)
  • Hepatic enzymes
  • Acid-base status if symptomatic