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Abstract
1. The effects of dose and route of administration on the metabolic fate of terbutaline were studied in normal rats and in rats with ligated bile ducts. Unchanged terbutaline and its glucuronide were quantitively determined in the 0–24 h urine after oral doses ranging from 0.15 to 1000 mg/kg and after intra-peritoneal and subcutaneous doses covering a smaller range.
2. Only 2.2–13.5% of orally administered drug, but about 25% of that administered parenterally, was eliminated unchanged in urine, indicating a very large capacity for conjugation of phenols in the intestinal wall.
3. Only the glucuronide conjugate was eliminated in bile.
4. The ratio of unchanged drug to glucuronide conjugate decreased as the dose was increased from 0.15 to 10 mg/kg and then increased at higher doses. This is consistent with increasing saturation of the conjugating capacity of the liver and the intestinal wall at higher doses.