Safety and Efficacy of Split-Dose Thiopurine vs Low-Dose Thiopurine-Allopurinol Cotherapy in Pediatric Inflammatory Bowel Disease

Split-dose thiopurine and allopurinol-thiopurine cotherapy strategies have been suggested as rescue therapeutic options for children with inflammatory bowel disease (IBD) and impaired thiopurine metabolism. We compared the efficacy and safety of these regimens in patients who previously failed conventional thiopurine treatment. METHODS: Children with IBD treated with split-dose thiopurine or low-dose thiopurine-allopurinol cotherapy were retrospectively identified. Medical records were reviewed for demographics, treatment regimen, reason for thiopurine failure, side effects, and discontinuation of treatment. Laboratory findings were evaluated at different time points. RESULTS: After prior therapeutic failure, 42 patients were on split-dose regimen (group A) and 20 patients were on thiopurine-allopurinol cotherapy (group B). Twelve patients crossed from group A to group B because of treatment failure, 1 patient was lost at follow-up, and 1 patient discontinued the treatment. The final cotherapy group comprised 29 children (group C), while the split-dose group (group D) included 31 children. Intention-to-treat analysis showed significant differences between split-dose regimen and thiopurine-allopurinol cotherapy for 6-thioguanine nucleotide (6-TGN)/6-methyl mercaptopurine (6-MeMP) ratio (P < 0.001), 6-TGN (P < 0.05), and 6-MeMP (P < 0.001) at 1–3 months. As per protocol analysis, there was a significant difference between group C and group D at 6 months for 6-MeMP (P < 0.05) and 6-TGN/6-MeMP ratio (P < 0.05) and at 12 months for 6-MeMP (P < 0.05) and 6-TGN/6-MeMP ratio (P < 0.001). Side effects were more frequent in allopurinol-thiopurine cotherapy (P < 0.05). DISCUSSION: In children with IBD and impaired thiopurine metabolism, split-dose thiopurine and low-dose thiopurine-allopurinol cotherapy are both effective therapeutic strategies. The latter shows higher efficacy but a higher side effect rate, suggesting the use of split-dose regimen as the first-line approach.