Combined phenytoin and phenobarbital overdose

Area of Science:

• Pharmacology
• Clinical Toxicology

Background:

• This report details a case of severe poisoning from a combined overdose of phenytoin and phenobarbital.
• Such co-ingestions present unique challenges in clinical management due to differing drug pharmacokinetics.

Observation:

• A 32-year-old female presented with a massive overdose of phenytoin and phenobarbital following a suicide attempt.
• Initial serum drug concentrations were significantly elevated (Phenytoin: 46 µg/ml, Phenobarbital: 86 µg/ml).
• The patient required prolonged mechanical ventilation due to unconsciousness.

Findings:

• Continued phenytoin absorption was observed for five days post-ingestion.
• Phenobarbital exhibited first-order elimination, while phenytoin followed Michaelis-Menten kinetics.
• Forced alkaline diuresis showed limited efficacy for phenobarbital and precipitated pulmonary edema.

Implications:

• Understanding distinct drug elimination kinetics is crucial for managing mixed overdoses.
• This case underscores the limitations of forced alkaline diuresis in phenobarbital toxicity.
• Clinical recovery correlated with the decline of serum drug concentrations into therapeutic ranges.