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 31 adult patients with asthma [forced expiratory volume in one second (FEV1), 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 [FEV1, forced vital capacity (FVC), forced expiratory flow at 75% of FVC (FEF75%), 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 FEV1 and serum potassium, respectively. The corresponding relative dose potencies for PEF, FVC, and FEF75% 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.