Dose potency relationship of terbutaline inhaled via turbuhaler or via a pressurized metered dose inhaler

Objective: The relative dose potency of cumulative doses of terbutaline sulfate inhaled via Turbuhaler and via a pressurized metered dose inhaler was estimated with respect to lung efficacy and systemic effect. Methods: The study was an open, crossover, randomized, multicenter study including 3 1 adult patients with asthma [forced expiratory volume in one second (FEV 1 ), 65% of predicted]. The patients inhaled terbutaline 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 capacity (FVC), forced expiratory flow at 75% of FVC (FEF 75% ), and peak expiratory flow (PEF)], and systemic effect variables (serum potassium, tremor, pulse, blood pressure) were monitored prior to the first inhalation and 15 to 25 minutes after each inhaled dose. Results: The mean relative dose potency of terbutaline inhaled via Turbuhaler compared with 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, and 1.6, respectively, with no statistically significant difference between the two devices. No differences between the devices were evident with regard to blood pressure and pulse. Conclusion: The results suggest that Turbuhaler is more efficient in the delivery of inhaled terbutaline to the lungs compared with the conventional pressurized metered dose inhaler