The Metabolism of Terbutaline in Dog and Rat

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Abstract
1. The metabolic fate of [3H]terbutaline has been studied in dog after oral, intravenous and subcutaneous administration and in rat after oral and intravenous administration. In 3–4 days the dog excreted 75% of the dose in the urine after oral administration and more than 90% after intravenous or subcutaneous administration; the remainder was in the faeces. The rat in 24 h excreted about 13% in the urine and 61% in the faeces after oral administration and 48% in the urine and 35% in the faeces after intravenous administration. 2. After oral administration of [3H]terbutaline, the time course of radioactivity concentration was the same in lung, heart and serum; low levels of unchanged drug were found in all tissues. After intravenous administration, the concentration of unchanged drug was higher in lung and heart than in serum. 3. In dog, 1·7% of an intravenous dose was excreted into bile in 6 h. In rat, about 37% of the dose was recovered in the bile during 12 h. 4. Enzymic hydrolysis of urine showed that terbutaline is metabolized by conjugation, forming a glucuronide in rat but probably a sulphate in dog.