Effect of low-dose troleandomycin on theophylline clearance: implications for therapeutic drug monitoring

Abstract

Troleandomycin (TAO) is an alternative agent used in the treatment of severe, steroid-requiring asthma. Its mechanism of action, once thought to be inhibition of theophylline clearance, remains unclear. Twenty-four-hour theophylline profiles were obtained in 11 children with severe asthma prior to and after 2 and 12 weeks of low-dose TAO therapy. Theophylline dosages were adjusted by blinded investigators to maintain serum theophylline concentrations (STCs) between 10 and 20 micrograms/ml. Dosages were decreased from 877 +/- 60 mg/day (mean +/- SEM) before TAO to 811 +/- 56 mg/day (NS) after 2 weeks and 764 +/- 56 mg/day (p less than 0.05) after 12 weeks. Because of the dosage adjustments, STCs did not increase significantly. Theophylline clearance was reduced from 65.7 +/- 9.8 ml/kg/hour at baseline to 50.2 +/- 4.1 ml/kg/hour (p less than 0.05) after 2 weeks and 50.1 +/- 6.2 ml/kg/hour (p less than 0.05) after 12 weeks of TAO therapy. We conclude that TAO can significantly reduce theophylline clearance, resulting in increased STCs if dosages are not titrated. We recommend an empiric 25% reduction of daily theophylline dose with the initiation of TAO. We also recommend monitoring STCs 4 hours after the morning dose (with twice-daily dosing of sustained-release products) after 3, 7, 14, and 30 days of TAO therapy, then periodically as indicated.