Oral theophylline intoxication. A serious error of patient and physician understanding.

Twenty-two episodes of hospitalization for patients with inadvertent oral theophylline intoxication were reviewed to determine the mechanism of toxicity as well as clinical features and pharmacokinetic values. Toxic effects occurred in older subjects with poorly reversible airflow obstruction and evidence of reduced theophylline clearance. Maximum serum theophylline levels ranged from 22.4 to 104.8 mg/L. Gastrointestinal tract disturbances were the most common toxic effects; three patients had grand mal seizures. Serum theophylline levels were a poor predictor of serious toxic effects. Causes of theophylline intoxication included excessive drug ingestion by the patient, excessive dose prescription by the physician, and unrecognized drug interactions. With appropriate patient selection and education, as well as better understanding of theophylline kinetics and potential drug interactions, inadvertent oral theophylline intoxication can be minimized.