Biol. Pharm. Bull. 30(1) 162—164 (2007)

Diskhaler (FP-DH), developed for inhalation of corticosteroids, is widely used for the treatment of asthma. A dry powder inhaler (DPI) is a breath controlled drug delivery system, in which a turbulent airstream is created by exploiting the patient’s own inspiratory flow rate and is required to aerosolize particles for inhalation at a satisfactory peak inspiratory flow rate, which can achieve sufficient diffusion of the drug into the lungs. Therefore, it is considered that the inspiratory flow rate of the patient has a significant influence on the effects of drugs administered by an FP-DH. It was reported that 28 of 233 patients who inhaled corticosteroids for asthma could not achieve the optimal flow rate of 60 l/min, of whom 5 were treated for exacerbation of symptoms. Thus, it is very important to clarify the relationship between inspiratory flow rate and amount of drug delivered into the lungs when using a DPI. Although several in vitro studies have shown the delivery of drugs into the lungs at unvaried or slightly varied high flow rates, there is no known examination of the detailed relationship of these factors. In the present study, we investigated the relationship between inspiratory flow rate and amount of drug delivered into the lungs by quantification of FP after inhalation with an FP-DH equipped with a twin impinger at various inspiratory flow rates.