Dose emission and aerodynamic characterization of the terbutaline sulphate dose emitted from a Turbuhaler at low inhalation flow

Previously, dose emission below 30 L min(-1) through DPI has not been routinely determined. However, during routine use some patients do not achieve 30 L min(-1) inhalation flows. Hence, the aim of the present study was to determine dose emission characteristics for low inhalation flows from terbutaline sulphate Turbuhaler. Total emitted dose (TED), fine particle dose (FPD) and mass median aerodynamic diameter (MMAD) of terbutaline sulphate Turbuhaler were determined using inhalation flows of 10-60 L min(-1) and inhaled volume of 4 L. TED and FPD increase significantly with the increase of inhalation flows (p < 0.05). Flows had more pronounced effect on FPD than TED, thus, faster inhalation increases respirable amount more than it increases emitted dose. MMAD increases with decrease of inhalation flow until flow of 20L min(-1) then it decreases. In vitro flow dependent dose emission has been demonstrated previously for Turbuhaler for flow rates above 30 L min(-1) but is more pronounced below this flow. Minimal FPD below 30 L min(-1) suggests that during routine use at this flow rate most of emitted dose will impact in mouth. Flow dependent dose emission results suggest that Pharmacopoeias should consider the use variety of inhalation flows rather than one that is equivalent to pressure drop of 4 KPa.