N-acetyltransferase 1 and 2 genotypes do not predict response or toxicity to treatment with mesalamine and sulfasalazine in patients with ulcerative colitis

OBJECTIVES: 5-Aminosalicylate is metabolized in colonic mucosa by N-acetyltransferase 1 (NAT1), and sulfapyridine is metabolized in the liver by N-acetyltransferase 2 (NAT2). Common genetic polymorphisms in these enzymes result in rapid and slow acetylation. We determined the association between NAT1 genotype and response to mesalamine and sulfasalazine, as well as between NAT2 genotype and toxicity to sulfasalazine, in a population-based cohort of patients with ulcerative colitis. METHODS: DNA was obtained from 77 white patients with ulcerative colitis from Olmsted County, MN. NAT1 and NAT2 genotyping was performed using microelectronic array devices. Phenotypes were deduced from previously published genotype/phenotype correlations. Clinical response to mesalamine and sulfasalazine, and toxicity to sulfasalazine, were determined by medical record review and associated with NAT1 and NAT2 genotypes. RESULTS: The clinical response rates among 52 patients treated with mesalamine were 67% (31 of 46) for rapid acetylators and 83% (five of six) for slow acetylators (odds ratio = 0.4, 95% CI = < 0.1-3.9, P = 0.65). Similarly, the clinical response rates among 64 patients treated with sulfasalazine were 74% (43 of 58) for rapid acetylators and 67% (four of six) for slow acetylators (odds ratio = 1.4, 95% Cl = 0.2-8.6, p = 0.65). The toxicity rates among the 64 patients treated with sulfasalazine were 34% ( 12 of 35) for slow acetylators and 45% ( 13 of 29) for rapid acetylators (odds ratio = 0.6, 95% Cl = 0.2-1.8, p = 0.65). CONCLUSIONS: NAT1 and NAT2 genotypes did not predict response to mesalamine or sulfasalazine, or toxicity to sulfasalazine.