Combined Phenytoin and Phenobarbital Overdose

Abstract

A 32-year-old female attempted suicide by consuming large quantities of both phenytoin (P) and phenobarbital (Pb). On hospital admission, serum drug concentrations (SDC), measured by immunoassay, were 46 μg/ml for P and 86 μg/ml for Pb. The patient remained unconscious, requiring mechanical ventilation, for the next two weeks. Serial SDC demonstrated: (1) continued P absorption over the next five days; (2) different elimination patterns for the two drugs (Pb exhibited first-order elimination while P elimination represented Michaelis-Menten kinetics); and (3) the limited effectiveness of forced alkaline diuresis in lowering Pb serum concentration, though resulting in an episode of pulmonary edema. The patient's clinical status subsequently improved and correlated well with SDC decline into the usual therapeutic range.