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Systemic absorption of 5-aminosalicylic acid in patients with inactive ulcerative colitis treated with olsalazine and mesalazine

Objective: To compare the systemic load of 5-aminosalicylic acid (5-ASA) as a basis for potential long-term toxicity during treatment in usual dosage with olsalazine (Dipentum) and one controlled-release mesalazine preparation (Salofalk) in patients with inactive ulcerative colitis. Design: Open, randomized, crossover study. Treatment schedule: Olsalazine 500 mg twice daily for 7 days and mesalazine 500 mg thrice daily for 7 days consecutively. Patients: Fifteen patients (12 males/3 females) aged between 18–70 years with ulcerative colitis in endoscopically confirmed remission for at least one month. Methods: A morning predose plasma sample and a 24-h urine collection on days 6 and 7 of each course were obtained from all patients for quantitative determination of 5-ASA and acetyl-5-ASA (Ac-5-ASA) concentrations. High performance liquid chromatography was used and all analyses were performed blindly on coded samples. Results: Treatment with mesalazine compared with olsalazine gave significantly higher levels of 5-ASA and Ac-5-ASA in plasma and urine. Maximum values and ranges of all variables were higher in the mesalazine group than in the olsalazine group. It is noteworthy that there was clear discriminance in the range of urine 5-ASA and Ac-5-ASA concentrations after mesalazine and olsalazine treatment. Conclusion: 1. The mesalazine preparation used, in comparison with olsalazine given in usual dosages, causes significantly higher levels of 5-ASA and Ac-5-ASA in plasma and urine in patients with inactive ulcerative colitis. 2. The lower systemic load of 5-ASA may reduce the potential risk of adverse events and in particular of nephrotoxicity. European Journal of Gastroenterology & Hepatology 1996, 8:1083–1088