Massive theophylline dosing in a heavy smoker receiving both phenytoin and phenobarbital

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

Single case report.

517-bed, university teaching hospital.

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

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.

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.