Bioavailability of single and multiple doses of enteric-coated mesalamine and sulphasalazine

The bioavailibity of mesalamine from enteric-coated mesalamine and sulphasalazine was determined following a single dose and at steady state in healthy subjects in crossover studies. Plasma concentrations and urinary excretion of mesalamine and its major metabolite, N-acetyl-5-aminosalicylic acid, were measured. After a single dose of enteric-coated mesalamine, about 10 h elapsed before the onset of measurable plasma drug concentrations, probably representing gastro-intestinal transit prior to drug release near the ileocaecal junction. The elimination kinetics were similar for a single oral dose and steady state using enteric-coated mesalamine, but after both single and multiple administration of enteric-coated mesalamine only about 20% of the mesalamine given was absorbed, with about 80% estimated to remain for colon therapeutic activity. It is concluded that, despite different mechanisms of mesalamine release, enteric-coated mesalamine and sulphasalazine produced similar mesalamine absorption.