The Metabolism of Terbutaline in Man

1. The metabolism of terbutaline has been investigated in man after oral, intravenous and subcutaneous administration of the tritium-labelled drug.2. Serum levels and excretion rates were followed for 3–4 days after administration by the three different routes. After oral administration, one-third to one-half of the dose is excreted in the urine whereas after intravenous and subcutaneous administration >90% is eliminated by this route. The remainder is recovered in the faeces.3. A method for determination of [3H]terbutaline using ion pair extraction has been developed. A quantitative separation of unchanged drug from its metabolite is achieved in the range 1–250 ng/ml urine or serum.4. After administration of terbutaline by any of the three routes, high voltage electrophoresis and paper chromatography reveal the presence of only one metabolite. Hydrolysis of urine with β-glucuronidase and/or sulphatase indicates that the major metabolite is a sulphate conjugate of terbutaline.