Optimizing Thiopurine Therapy with a Xanthine Oxidase Inhibitor in Patients with Systemic Autoimmune Diseases: A Single-Centre Experience

• Published in: Canadian journal of hospital pharmacy Vol. 74; no. 4; pp. 361 - 369
• Main Authors: Belhocine, Mériem, Mourad, Alissar, Chapdelaine, Aurélie, Mansour, Anne-Marie, Troyanov, Yves, Doré, Maxime
• Format: Journal Article
• Language: English
• Published: Canada Canadian Society of Hospital Pharmacists 01.01.2021
• Subjects: Original Research; xanthine oxidase inhibitors; azathioprine; febuxostat; 6-mercaptopurine; allopurinol; thiopurines
• ISSN: 0008-4123; 1920-2903
• DOI: 10.4212/cjhp.v74i4.3199

Thiopurines are a mainstay of therapy for autoimmune diseases. However, up to 20% to 30% of patients experience overproduction of the methylated metabolites, known as 6-MMP, to the detriment of the active metabolite, 6-thioguanine nucleotide (6-TGN). These patients, commonly referred to as "shunters", are predisposed to thiopurine resistance and hepatotoxicity. In patients with inflammatory bowel diseases, the combination of thiopurine with a xanthine oxidase inhibitor (XOI) is used to reverse this skewed metabolism and to prevent treatment failure or hepatotoxicity. Data on the use of this strategy for patients with other diseases are limited. To investigate and describe the use of thiopurine-XOI combination therapy in shunters with systemic autoimmune diseases. Shunters treated in the study hospital between January 1, 2005, and December 31, 2015, were identified using the hospital's laboratory database, and clinical data were collected retrospectively. For each patient with optimization of thiopurine therapy, clinical and laboratory data were assessed over a 6-month period. Thirty-four patients were identified as shunters; for 14 of these patients, thiopurine therapy was optimized with an XOI. In these 14 patients, the median dose of azathioprine was reduced from 1.95 to 0.78 mg/kg with combination therapy. In addition, median 6-TGN level increased from 135 to 385 pmol/8 × 10 erythrocytes ( = 0.001); furthermore, 6-TGN levels rose to above 235 pmol/8 ×10 erythrocytes for 11 of the 14 patients. Conversely, the median 6-MMP level decreased from 6267 to 271 pmol/8 × 10 erythrocytes ( = 0.001). Except for a 12% increase in mean corpuscular volume, no clinically significant changes in blood count were recorded. Notable infections were reported in 3 patients, and 1 patient had to discontinue treatment because of cytopenia. After 6 months, median prednisone daily dose was reduced by 74%, from 16.7 mg to 4.4 mg ( = 0.005), and 4 patients had been weaned off corticosteroids. Of the 14 patients, 11 (79%) were in full remission, and 2 (14%) were in partial remission. Optimizing thiopurine therapy with an XOI may be a safe and effective strategy for patients with systemic autoimmune diseases.