Clinical effects of Diskus(TM) dry-powder inhaler at low and high inspiratory flow-rates in asthmatic children

Abstract

In vitro studies with the Diskus(TM) inhaler at low and high flow rates show consistent doses of drug as fine particles <4.7 μm. The present study was designed to ascertain whether this in vitro flow independency translates into flow-independent clinical effect when the device is used by patients at low (30 L · min-1) and high (90 L · min-1) flow rates. A pilot study in 129 children aged 3-10 yrs demonstrated that 99% of children of 3 yrs and above can generate a flow ≤30 L · min-1 through the device, while 26% performed ≤90 L · min-1. Eighteen children aged 8-15 yrs with exercise induced asthma inhaled placebo or salmeterol 50 μg at either 30 L · min-1 or 90 L · min-1. Exercise challenges were carried out 1 h and 12 h after dosing. The maximum percentage fall in forced expiratory volume in one second (FEV1) after exercise 12 h after treatment was significantly less after salmeterol at either flow rates as compared to placebo. There was no significant difference in the protection from salmeterol on the day of low-flow inhalation versus the day of high-flow inhalation. Consistent in vitro fine particle dosing from the Diskus(TM) inhaler translates into a consistent clinical effect at low and high flow rates in children.