Colonic prostaglandin E2 levels and olsalazine metabolism in relapsing ulcerative colitis: implications for controlled trials in the long term.

To examine the tolerance and pharmacokinetics of long-term olsalazine administration, increasing doses of the drug were given to 31 patients with ulcerative colitis. All patients were refractory to or intolerant of sulphasalazine. Complete azo-reduction occurred in most cases. Concentrations of 5-ASA, but not acetyl-5-ASA, in faecal dialysates increased dose-dependently. Estimates of efficacy were more favourable among those intolerant of sulphasalazine. Patients with high prostaglandin E2 levels determined by equilibrium in vivo dialysis of rectum were less likely to benefit from treatment. In conclusion, olsalazine is a highly effective means of delivering 5-ASA to the colonic mucosa. Long-term use of olsalazine in controlled trials may be considered safe, even in high doses.