Individualization of Theophylline Dosage Using a Single Serum Sample Following a Test Dose

¹ Department of Pediatrics, University of Washington School of Medicine, Seattle

Because formulas for theophylline requirement based on weight alone carry the risk of overdosing and toxicity, this study was designed to test a clearance nomogram for determining daily theophylline requirement after a known initial dose of theophylline. Twenty asthmatic children who had not taken theophylline for at least 36 hours fasted and were given one dose of anhydrous theophylline (5 mg/kg). Six hours later the serum level was measured and the appropriate dosage of sustained-release theophylline to achieve a serum level of 10 µg/ml was selected from the clearance nomogram. Three to seven days later a six-hour theophylline level was obtained. Of 20 patients, therapeutic levels of 10 to 20 µg/ml were achieved in 15, and the remaining five patients had levels close to this (range 6.2 to 16.0 µg/ml). The dosage requirement per 24 hours ranged from 10 to 32 mg/kg/24 hr. This method of determining theophylline requirements for children required measurement of the serum theophylline level only once for the determination of a safe and effective daily dose. It is especially valuable when follow-up is difficult and is a safe way to avoid serious overdosing while being certain of effective dosing.

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