Alternative venlafaxine kinetics in overdose

The pharmacokinetics of venlafaxine in therapeutic doses is well established. It is metabolized by the cytochrome P450 enzymes including CYP2D6. The toxicokinetics in overdose is less well known.

A 33-year-old Caucasian female who ingested 3.0 g venlafaxine, and 210 mg zolpidem. The patient remained symptomatic for the following 24 h. Plasma pharmacokinetic analysis demonstrated a prolonged elimination half-life of venlafaxine, estimated to be 15.3 h. We postulate that the patient was a slow metabolizer of substrates for CYP2D6, an enzyme known to exhibit polymorphism.