Theophylline Toxicity due to Impaired Theophylline Degradation1, 2

A 72-year-old man with severe chronic obstructive pulmonary disease and normal liver function had convulsions at a time when his serum theophylline level was 86 µg per ml. The day before convulsing he had received 960 mg of theophylline (17.5 mg per kg). After discontinuation of the drug, the serum level of theophylline declined with a half-time of approximately 28 hours. The patient was also markedly sensitive to the anticoagulant effects of warfarin. This report illustrates that severe toxicity to theophylline may occur during administration of the ordinary recommended dosage. Measurement of serum theophylline permitted recognition of this complication. The value of this measurement is to avoid or to identify overdosage.