Evaluation of "toxic" serum theophylline concentrations.

The relationships between excessively high theophylline doses, the incidence of theophylline toxicity, and toxic serum theophylline concentrations in hospitalized patients were investigated. During a 24-month period, the medical records of patients whose serum theophylline content was above 20 micrograms/ml were studied. Demographic and medical information was recorded, including symptoms attributable to theophylline toxicity, and concurrent disease states and medications. A total of 3112 serum theophylline determinations were made during the study (January 1978 through December 1979); 17% were above 20 micrograms/ml. The medical records of 128 patients were available; 87 of these were studied. The patients were divided into three groups: Group 1--serum theophylline concentrations between 20 and 29.9 micrograms/ml (42 patients); Group 2--30-39.9 micrograms/ml (26 patients); Group 3--above 40 micrograms/ml (19 patients). In Group 1, 81% of the patients had at least one symptom of toxicity. In the other groups, all patients had one or more symptoms of toxicity. Tachycardia was the most common symptom. Four patients had seizures attributable to theophylline toxicity; all four had serum theophylline concentrations above 40 micrograms/ml. Of the 87 study patients, 77 (89%) had received theophylline doses above recommended guidelines. It is concluded that serum theophylline concentrations above 20 micrograms/ml result in a high incidence of toxic symptoms. Serum theophylline determinations should be obtained when treating patients with theophylline.