Longterm olsalazine treatment: pharmacokinetics, tolerance and effects on local eicosanoid formation in ulcerative colitis and Crohn's colitis.

To examine pharmacokinetics and tolerance of long term administration of olsalazine (azodisalicylate), increasing doses of the drug were given for one year to 31 patients with ulcerative colitis (UC) and nine patients with Crohn's colitis (CC), refractory to, or intolerant of sulphasalazine, until sustained remission was obtained or a maximum of 4 g/day was reached. Colonic drug metabolism was studied by equilibrium in vivo dialysis of faeces. Complete azoreduction occurred in most cases. Concentrations of 5-aminosalicylic acid, but not N-acetyl-5-aminosalicylic acid, in faecal dialysates increased dose dependently. Serum concentrations disclosed no cumulation in the long term and olsalazine was well tolerated, although loose stools occurred transiently in some patients with extensive disease: this was associated with a larger proportion of unsplit olsalazine in the faecal dialysates. Patients with ulcerative colitis having a high prostaglandin E2 concentration (greater than ng/ml) determined by equilibrium dialysis of rectum, were less likely to benefit from treatment. Olsalazine is a very effective means of delivery of 5-aminosalicylic acid to the colonic mucosa in active disease. Use of the drug in controlled trials may be considered safe even in prolonged high dosage.