Introduction: Several new derivatives of sulphasalazine that make use of its active moiety, 5-aminosalicylic acid (5-ASA), have been introduced for the treatment of inflammatory bowel disease (IBD). In rats short term intravenous administration of 5-ASA has been associated with nephrotoxicity. A number of cases of nephrotoxicity have been reported recently in IBD patients taking oral maintenance treatment with 5-ASA compounds.
Objective: To study the urinary and serum levels of acetylated 5-ASA (Ac-5-ASA) and the unacetylated 5-ASA (5-ASA) in patients with IBD maintained on sulphasalazine, olsalazine and mesalazine (pH dependent release form). We also sought correlation between levels of 5-ASA, clinical disease activity and extent of disease.
Methods: We studied 79 patients (male, n = 30; female, n = 49) with established IBD [ulcerative colitis (UC), n = 48; Crohn's disease (CD), n = 31], 72 maintained on 5-ASA compounds (sulphasalazine = 27; olsalazine = 28; mesalazine = 17) and 7 patients were receiving no medication. Urinary and serum analysis of 5-ASA was performed by high performance liquid chromatography (HPLC). Clinical disease activity was quantified using simple index of Harvey and Bradshaw.
Results: Patients receiving mesalazine had significantly higher levels of serum free 5-ASA compared to those who were receiving olsalazine and sulphasalazine (mesalazine mean +/- SEM; range; 2.84 +/- 1.21 (0.00-16.00) vs olsalazine 0.45 +/- 0.18 (0.00-16.20); mumol/L; p < 0.04; sulphasalazine 0.37 +/- 0.25 (0.00-3.74); p < 0.03). Similarly levels of urinary free 5-ASA were significantly higher in patients maintained on mesalazine compared to those on olsalazine or sulphasalazine (mesalazine 219 +/- 80.43 (0.00-1050) vs olsalazine 33.3 +/- 17.23 (0.00-317) mumol/L; p < 0.01; and sulphasalazine 15 +/- 8.86 (0.00-192); p < 0.05). However, no significant difference was observed in the levels of urinary free 5-ASA between olsalazine and sulphasalazine. No significant difference was observed in the levels of free-5-ASA in UC patients with left sided disease and those with extensive disease. Furthermore, no significant difference was observed in the levels of serum and urinary 5-ASA in CD patients with ileo-colic disease and colonic disease. Urinary and serum free-5-ASA did not correlate with the clinical disease activity.
Conclusion: Systemic absorption of 5-ASA from sulphasalazine and olsalazine is relatively low. However, pH-dependent mesalazine formulations may release their contents rapidly in the small intestine and proximal colon resulting in higher plasma and urinary concentrations of free 5-ASA. The effects of free 5-ASA on renal function in the human require further evaluation.