Massive Theophylline Dosing in a Heavy Smoker Receiving Both Phenytoin and Phenobarbital

Abstract

OBJECTIVE:

To report unusually high theophylline dosing requirements in a smoker receiving concomitant therapy with phenytoin and phenobarbital.

DESIGN:

Single case report.

SETTING:

517-bed, university teaching hospital.

PATIENT:

29-year-old woman with newly diagnosed asthma, heavy smoking history, and a seizure disorder.

RESULTS:

The additive influence of smoking, phenytoin, and phenobarbital greatly increased the theophylline dosing requirements. Doses of up to 4 g/d (59 mg/kg/d) were required to achieve adequate symptomatic relief of her asthma as well as to provide therapeutic serum theophylline concentrations.

CONCLUSIONS:

Multiple polymorphisms may additively influence theophylline metabolism and exceptionally large theophylline doses may be required in some patients who smoke and are comedicated with phenytoin and phenobarbital.