Unsuspected caffeine toxicity complicating theophylline therapy.

A 58-year-old man with a history of alcoholic liver disease and chronic airflow obstruction presented with heart failure and acute bronchitis. Plasma methylxanthines were estimated as a guide to further theophylline therapy and serious caffeine accumulation was noted in the presence of a subtherapeutic concentration of theophylline. After 3 weeks on a caffeine-free diet theophylline and caffeine challenge tests were performed which demonstrated the ease with which caffeine could accumulate. The importance of caffeine accumulation during theophylline therapy is discussed.