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Pharmacogenomic studies have suggested that metabolic breakdown of azathioprine in an individual is genetically determined. Coupled with the fact that certain thiopurine metabolites, notably 6\u2010thioguanine nucleotide and 6\u2010methylmercaptopurine, are associated with antiinflammatory effects and adverse effects, respectively, some investigators have examined intentionally shunting the metabolism of azathioprine toward increasing 6\u2010thioguanine nucleotide levels by using low doses of the xanthine oxidoreductase inhibitor allopurinol to improve efficacy and decrease toxicity of azathioprine in patients with inflammatory bowel disease. We performed a search of the MEDLINE and Embase databases for basic and clinical research reports of this modality. Pertinent articles were retrieved, reviewed, and assessed by the authors. Case series, cohort studies, and one randomized trial have investigated adding allopurinol to azathioprine therapy in patients with inflammatory bowel disease. Most reports primarily examined metabolite levels in these patients. In general, the literature suggests that this modality was successful at significantly increasing 6\u2010thioguanine nucleotide levels while decreasing 6\u2010methylmercaptopurine levels. Several small reports have suggested that patients with increased 6\u2010thioguanine nucleotide levels had improved symptoms or symptom remission. Adverse effects and discontinuation rates remained similar or were improved in patients who were taking a thiopurine and started allopurinol. In conclusion, the addition of allopurinol may be an option for optimizing thiopurine metabolite production in select patients with low 6\u2010thioguanine nucleotide levels. Appropriate care and monitoring of these patients are mandatory to prevent neutropenia or other adverse effects.<\/jats:p>","DOI":"10.1002\/phar.2067","type":"journal-article","created":{"date-parts":[[2017,12,1]],"date-time":"2017-12-01T22:46:37Z","timestamp":1512168397000},"page":"259-270","update-policy":"https:\/\/doi.org\/10.1002\/crossmark_policy","source":"Crossref","is-referenced-by-count":12,"title":["Addition of Allopurinol for Altering Thiopurine Metabolism to Optimize Therapy in Patients with Inflammatory Bowel Disease"],"prefix":"10.1002","volume":"38","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-8668-9966","authenticated-orcid":false,"given":"Geoffrey C.","family":"Wall","sequence":"first","affiliation":[{"name":"Drake University College of Pharmacy and Health Sciences Des Moines Iowa"},{"name":"Iowa Methodist Medical Center\u2010University of Iowa Medical Residency Program Des Moines Iowa"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Hamid","family":"Muktar","sequence":"additional","affiliation":[{"name":"Iowa Methodist Medical Center\u2010University of Iowa Medical Residency Program Des Moines Iowa"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Cassandra","family":"Effken","sequence":"additional","affiliation":[{"name":"Drake University College of Pharmacy and Health Sciences Des Moines Iowa"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Pramod B.","family":"Mahajan","sequence":"additional","affiliation":[{"name":"Drake University College of Pharmacy and Health Sciences Des Moines Iowa"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"311","published-online":{"date-parts":[[2018,1,10]]},"reference":[{"key":"e_1_2_7_2_1","doi-asserted-by":"publisher","DOI":"10.1038\/nature10209"},{"key":"e_1_2_7_3_1","doi-asserted-by":"crossref","first-page":"200","DOI":"10.1097\/MPG.0000000000001455","article-title":"Extraintestinal manifestations of pediatric inflammatory bowel disease: prevalence, presentation, and anti\u2010TNF treatment","volume":"65","author":"Greuter T","year":"2011","journal-title":"J Pediatr Gastroenterol Nutr"},{"key":"e_1_2_7_4_1","doi-asserted-by":"publisher","DOI":"10.15585\/mmwr.mm6542a3"},{"key":"e_1_2_7_5_1","doi-asserted-by":"publisher","DOI":"10.1053\/j.gastro.2011.10.001"},{"key":"e_1_2_7_6_1","doi-asserted-by":"publisher","DOI":"10.3748\/wjg.v23.i6.1067"},{"key":"e_1_2_7_7_1","doi-asserted-by":"publisher","DOI":"10.1016\/j.mayocp.2017.04.010"},{"key":"e_1_2_7_8_1","doi-asserted-by":"publisher","DOI":"10.1053\/j.gastro.2013.10.047"},{"key":"e_1_2_7_9_1","doi-asserted-by":"publisher","DOI":"10.1038\/ajg.2011.64"},{"key":"e_1_2_7_10_1","doi-asserted-by":"publisher","DOI":"10.1002\/ibd.21221"},{"key":"e_1_2_7_11_1","first-page":"1078","article-title":"Metabolism of thiopyrimidines and thiopurines. 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