Relative bioavailability of terbutaline to the lung following inhalation, using urinary excretion

AIMS The aim of the study was to determine the relative lung and systemic bioavailability of terbutaline. METHODS On separate days healthy volunteers received 500μg terbutaline study doses either inhaled from a metered dose inhaler or swallowed as a solution with and without oral charcoal. Urine samples were provided at timed intervals post dosing. RESULTS Mean (SD) urinary terbutaline 0.5h post inhalation, in 12 volunteers, with (IC) and without (I) oral charcoal and oral (O) dosing was 7.4 (2.2), 6.5 (2.1) and 0.2 (0.2)μg. I and IC were similar and both significantly greater than O (P<0.001). Urinary 24h terbutaline post I was similar to IC+O. The method was linear and reproducible, similar to that of the urinary salbutamol method. CONCLUSIONS The urinary salbutamol pharmacokinetic method post inhalation applies to terbutaline. Terbutaline study doses can replace routine salbutamol during these studies when patients are studied. © 2011 The Authors. British Journal of Clinical Pharmacology © 2011 The British Pharmacological Society.