Emitted dose and lung deposition of inhaled terbutaline from Turbuhaler at different conditions

Turbuhaler has a very high resistance hence patient inhalation flow when using it would be low. The total emitted dose (TED) of 500microg terbutaline sulphate from a Bricanyl Turbuhaler was determined using a range of inhalation flows (10-60L min(-1)) with inhalation volume of 2 and 4L using a DPI sampling apparatus after one and two inhalations. The relative lung and systemic bioavailability of terbutaline from Bricanyl Turbuhaler when used by healthy subjects and COPD patients were determined after one and two inhalations at slow and fast inhalation flows using a novel urinary terbutaline pharmacokinetic method. The TED resulted from the one and two inhalations increased significantly (p<0.05) with the increase of the inhalation flow at both 2 and 4L inhalation volumes. The relative lung and systemic bioavailability after one inhalation at fast inhalation flow were significantly higher (p<0.01) than at slow inhalation flow in both healthy subjects and patients. Also the healthy subjects results were significantly higher (p<0.05) than the COPD patients after one inhalation. However after two inhalations there was no significant difference between slow and fast inhalation flow or healthy subjects and COPD patients. Hence it is essential to inhale twice and as deep and hard as possible from each dose of Turbuhaler for patients with low inspiratory flow and limited inhalation volume as they may not receive much benefit from one inhalation.