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

Abstract

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 µg 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) µg. 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.