Background: Inflammatory bowel disease (IBD) is commonly treated with immunomodulators such as azathioprine and 6-mercaptopurine (6-MP). Studies examining lymphoma risk in IBD patients treated with these medications have been underpowered and have yielded conflicting conclusions. Aims: The purpose of this meta-analysis was to provide a more precise estimate of the relative risk of lymphoma among IBD patients treated with azathioprine or 6-MP. Methods: Studies were included if they were English language, full article, cohort studies specifically designed to evaluate cancer as an adverse outcome of treatment with azathioprine or 6-MP. Pooled standardised incidence ratios were calculated to estimate the relative risk of lymphoma associated with therapy. Heterogeneity was assessed using Poisson regression. Sensitivity analyses examined the influence of individual studies on risk estimate and heterogeneity statistics. Results: Six studies were identified that met our inclusion criteria. When the data were combined across all studies, the pooled relative risk was 4.18 (95% confidence interval 2.07-7.51; 11 observed cases, 2.63 expected). Sensitivity analysis showed that exclusion of any one study had a relatively small effect on the pooled relative risk estimate (range 3.49-5.21) but excluding either the study with the highest or lowest estimated relative risk eliminated the statistically significant heterogeneity. Conclusions: Our data suggest an approximate fourfold increased risk of lymphoma in IBD patients treated with azathioprine/6-MP. The increased risk of lymphoma could be a result of the medications, the severity of the underlying disease, or a combination of the two.

We assess toxicity related to 6-mercaptopurine in the treatment of inflammatory bowel disease by reporting our experience with 396 patients (120 patients with ulcerative colitis, 276 with Crohn disease) observed over 18 years. Follow-up data for a mean period of 60.3 months were obtained for 90% of the patients. Toxicity directly induced by 6-mercaptopurine included pancreatitis in 13 patients (3.3%), bone marrow depression in 8 (2%), allergic reactions in 8 (2%), and drug hepatitis in 1 (0.3%). These complications were reversible in all cases with no mortality. Most cases of marrow depression occurred earlier in our experience, when the initial drug doses used were higher. Infectious complications were seen in 29 patients (7.4%), of which 7 (1.8%) were severe, including one instance of herpes zoster encephalitis. All infections were reversible with no deaths. Twelve neoplasms (3.1%) were observed, but only 1 (0.3%), a diffuse histiocytic lymphoma of the brain, had a probable association with the use of 6-mercaptopurine. Our data, showing a low incidence of toxicity in 396 patients, coupled with the previously demonstrated efficacy of 6-mercaptopurine in the treatment of inflammatory bowel disease, indicate that the drug is a reasonable alternative in the management of patients with intractable inflammatory bowel disease.

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To test the effectiveness of 6-mercaptopurine (6-MP) in the treatment of Crohn's disease, we entered 83 chronically ill patients into a two-year double-blind study comparing 6-MP with placebo. Crossover data showed that improvement occurred in 26 of 39 courses of 6-MP (67%) as compared with three of 39 courses of placebo (8%) (P less than 0.001). Non-crossover data likewise confirmed the superiority of 6-MP. The drug was more effective than placebo in closing fistulas (31 vs 6%) and in permitting discontinuation or reduction of steroid dosage (75 vs. 36%) (P less than 0.001). The onset of response to 6-MP was often delayed, with 32% of patients taking longer than three months to respond, and 19% taking longer than four months. Adverse side effects to 6-MP occurred in 10% of patients and were uniformly reversible. We conclude that 6-MP is an effective and useful agent in the management of Crohn's disease.

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