Prospectief multicentrisch farmacokinetisch onderzoek: Invloed van mesalazine op het thiopurinemetabolisme bij patiënten met inflammatoire darmziekten

Objective: To determine the influence of mesalazine (5-ASA) on thiopurine metabolism in inflammatory bowel disease (IBD) patients. Design: A prospective multicenter pharmacokinetic study of two different mesalazine dosages was performed in IBD patients using azathioprine (AZA) or mercaptopurine (6-MP). Methods: IBD patients on stable maintenance therapy (AZA or 6-MP for at least 8 weeks) with normal laboratory parameters were included in our study. Patients received consecutively per protocol two different dosages of mesalazine (2 g/day and 4 g/day). Laboratory parameters and levels of 6-thioguanine nucleotides (6-TGN), N-methylmercaptopurine ribonucleotides (6-MMPR), 5-ASA and N-acetyl-5-mesalazine (N-Ac-5-ASA) were determined before initiation and after 4, 8, 12 weeks. Adverse events were recorded. Results: 26 IBD patients were included. 4 weeks use of 2 g/day mesalazine, followed by a 4 week period of 4 g/day mesalazine, led to statistically significant increases (40% and 70%, respectively) in the mean 6-TGN levels. The rise of the active 6-TGN metabolite levels correlated with the mesalazine dosage, but not with mesalazine and N-Ac-5-ASA serum levels. 6-TGN levels significantly increased in a mesalazine dose-dependent manner; mesalazine had no significant influence on the hepatotoxic 6-MMPR metabolite levels during the entire study. 2 patients developed a temporary leucopenia. Conclusion: IBD patients who are unresponsive or refractory to standard thiopurine therapy, may benefit from the co-administration of mesalazine, due to an increase in 6-TGN metabolites.