Bioavailability using cold labels: studies on a novel antidiarrhoeal agent SC-27166

Abstract

The use of simultaneous administration of a compound to an animal or man by two routes where one route is distinguished by a stable-isotope-labelled derivative has been described in a study of the absolute availability of procainamide in man (Strong et al., 1975; Dutcher et al., 1975). Generally the method has a number of advantages, not least being the necessity to take only one set of blood samples. Also, in the usual crossover study the assumption is made that the kinetics of drug absorption, distribution, metabolism and elimination remain unchanged between doses. However, problems associated with the technique of simultaneous administration could arise if a high circulating plasma concentration of the compound interferes with the absorption of an orally administered dose or if extensive biliary excretion of free drug should take place, thereby making a high percentage of the intravenously administered drug available for intestinal re-absorption.