Sulphation and glucuronidation of xamoterol in the dog: dose dependence and site of sulphation.

1. Xamoterol has been administered both intravenously and orally over a 100-fold dose range to male beagle dogs. 2. Over the dose range examined, sulphation was not saturable, with the proportion of the dose excreted as the sulphate conjugate remaining constant. 3. Extensive first-pass sulphation of an oral dose of xamoterol occurred in the intestine with approximately 50% of sulphation occurring during absorption. 4. The intestine is not a major site of sulphation for circulating xamoterol. 5. The liver is not believed to play an important role in the first-pass sulphation of xamoterol.