Thiopurine Methyltransferase Levels and Azathioprine Outcomes in Thai Patients with Cutaneous Autoimmune Diseases

Background: Thiopurine methyltransferase (TPMT) is responsible for the inactivation of azathioprine, and is widely used to treat cutaneous autoimmune diseases. TPMT activity is inherited as an autosomal codominant trait and ranges from high to undetectable levels in different individuals. Low TPMT activity may result in a higher risk of adverse effects (AEs), whereas high TPMT activity may result in potential treatment failure. Objective: To assess TPMT levels in patients with cutaneous autoimmune diseases and evaluate the correlation between TPMT levels and AEs of azathioprine and clinical response in patients with pemphigus. Methods: genotype was performed. Results: (wild-type) in all 10 patients with the lowest TPMT levels. In the pemphigus group, the TPMT level did not correlate with clinical response (p = 0.363). Conclusion: Alcohol consumption resulted in lower TPMT levels. TPMT levels did not correlate with clinical response in the pemphigus group and AEs. These findings provide real-world clinical insight in Thai patients, where routine TPMT screening is not universally implemented, highlighting the need for alternative predictors of azathioprine toxicity.