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

center dot The relative bioavailability of salbutamol to the lung and body following inhalation can be identified by a urinary pharmacokinetic method. WHAT THIS STUDY ADDS center dot The amount of terbutaline excreted in the urine during the first 30 min and over the 24 h period post inhalation represents the relative bioavailability of terbutaline to the lung and the body following an inhalation. center dot Terbutaline study doses can replace a routine salbutamol dose during studies in patients when comparing different inhalation methods. AIMS The aim of the study was to determine the relative lung and systemic bioavailability of terbutaline. METHODS On separate days healthy volunteers received 500 mu g 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 0.5 h 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) mu g. I and IC were similar and both significantly greater than O (P < 0.001). Urinary 24 h 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.