Eva Ann-Christin Trofast

Terbutaline sulphate Turbuhaler: effect of inhaled flow rate on drug deposition and efficacy

The deposition and efficacy of 0.5 mg terhutaline sulphate from Turbuhaler (Astra Pharmaceuticals). a multi-dose powder inhaler, have been measured simultaneously in 10 asthmatic subjects at two inhaled flow rates (fast, mean 57 l/min and slow, mean 28 l/min). At the fast flow rate, a mean (SEM) 16.8 (2.6)% of the dose was deposited in the lungs, compared with 9.1 (1.5)% of the dose at the slow flow rate (P < 0.01). At either flow rate, the majority of the dose was deposited in the oropharynx, and this quantity was significantly higher with slow inhalation (P < 0.01). There was a trend towards a reduced bronchodilator response at the lower flow rate, but this did not reach statistical significance. It is concluded that Turbuhaler works optimally at a fast inhaled flow rate, but functions adequately at a lower flow rate which some patients may find easier to attain.