Pharmacokinetics of olsalazine and its metabolites.

After a single dose of olsalazine, the maximum serum concentration of the intact compound is much lower than after an equivalent dose of sulphasalazine. In both compounds the diazo bond is largely split by colonic bacteria and comparable amounts of the metabolites 5-ASA and acetyl-5-ASA are recovered in the faeces. During long-term ingestion of olsalazine, 1-4 weeks are required to reach a steady state, and serum concentrations of the parent drug are low. It is demonstrated that olsalazine is rapidly sulphated into the metabolite, olsalazine-O-sulphate, which has a long half-life. Acetyl-5-ASA is more stable and more soluble than 5-ASA; however, the therapeutic efficacy of acetyl-5-ASA in inflammatory bowel disease is not proven.