DOSE POTENCY RELATIONSHIP OF TERBUTALINE INHALED VIA TURBUHALER OR VIA A PRESSURIZED METERED-DOSE INHALER

Objective: The relative dose potency of cumulative doses of terbutalin e sulfate inhaled via Turbuhaler and via a pressurized metered dose in haler was estimated with respect to lung efficacy and systemic effect. Methods: The study was an open, crossover, randomized, multicenter st udy including 31 adult patients with asthma [forced expiratory volume in one second (FEV(1)), 65% of predicted]. The patients inhaled terbut aline doses of 0.125, 0.125, 0.25, 0.5, 1.0, and 2.0 mg (a total of 4 mg) at 30-minute intervals. Lung function [FEV(1), forced vital capaci ty (FVC), forced expiratory flow at 75% of FVC (FEF(75%)), and peak ex piratory flow (PEF)], and systemic effect variables (serum potassium, tremor, pulse, blood pressure) were monitored prior to the first inhal ation and 15 to 25 minutes after each inhaled dose. Results: The mean relative dose potency of terbutaline inhaled via Turbuhaler compared w ith pressurized metered dose inhaler was 1.5 (95% confidence interval: 1.2 to 1.8) with respect to FEV(1) and serum potassium, respectively. The corresponding relative dose potencies for PEF, FVC, and FEF(75%) were 1.0, 1.2, 1.6, respectively, with no statistically significant di fference between the two devices. No differences between the devices w ere evident with regard to blood pressure and pulse. Conclusion: The r esults suggest that Turbuhaler is more efficient in the delivery of in haled terbutaline to the lungs compared with the conventional pressuri zed metered dose inhaler.