Low-dose azathioprine is effective in maintaining remission in steroid-dependent ulcerative colitis: results from a territory-wide Chinese population-based IBD registry

Background: Whether low-dose azathioprine (AZA) is effective in maintaining remission in patients with steroid-dependent ulcerative colitis (UC) remains unclear. We assessed the efficacy and safety of low-dose AZA in a Chinese population with UC. Methods: We identified steroid-dependent UC patients in clinical remission on AZA maintenance therapy from a territory-wide IBD Registry. Standard- and low-dose AZA were defined as at least 2 mg/kg/day and less than 2 mg/kg/day, respectively. Relapse rates were analyzed by Kaplan-Meier analysis and compared using log-rank test. Results: Among 1226 UC patients, 128 (53% male, median duration on AZA 44 months) were included. Median maintenance AZA dose was 1.3 mg/kg/day. 97.7% of the patients were on concomitant oral 5-aminosalicylic acid. Cumulative relapse-free rates in patients on standard-dose and low-dose AZA were 71.2%, 52.8% and 45.2%, and 71.8%, 55.3% and 46.2% at 12, 24 and 36 months, respectively (p = 0.871). Relapse rate within 12 months was higher in patients who withdrew compared with those who maintained on AZA (52.6% versus 29.4%; p = 0.045). Mean corpuscular volume increased after AZA therapy in both of the low-dose [median (interquartile range, IQR): 88.2 (81.4-92.2) versus 95.1 (90.1-100.9) fl, p < 0.001] and standard-dose subgroups [median (IQR) 86.8 (76.9-89.9) versus 94.7 (85.9-99.7) fl, p < 0.001]. Leukopenia occurred in 21.1% of the patients. Patients on standard dose had a higher risk for leukopenia than those on low-dose AZA [odds ratio (OR) 3.9, 95% CI 1.9-8.2, p < 0.001]. Conclusions: In the Chinese population, low-dose AZA is effective for maintaining remission in steroid-dependent UC patients. Standard-dose AZA was associated with more than threefold increased risk of leukopenia.