Evaluation of clinical efficacy and tolerability of azathioprine in adult Chinese atopic dermatitis patients in Hong Kong with pre-treatment thiopurine methyltransferase assessment

Background: Azathioprine (AZA) has been proposed as an off-label option in treating moderateto-severe atopic dermatitis. Pre-treatment thiopurine methyltransferase (TPMT) assessment is commonly used in western countries, but TPMT test is not commonly available locally. Objective: We sought to evaluate the efficacy and tolerability of AZA in adult Chinese atopic dermatitis patients with pre-treatment TPMT assessment. Methods: Patients with atopic dermatitis seen in all government skin clinics in Hong Kong were screened to receive AZA for 12 weeks. The target dose of AZA was 2.5 mg/kg/day. The primary outcome was the change in disease activity as measured by the Sixarea, Six sign Atopic Dermatitis (SASSAD) scores after treatment. Result: Thirty-six patients were recruited. The data were analysed on an intention-to-treat basis. The mean age was 26.9 years (range 18-63) with a male-to-female ratio of 1.4:1. After a treatment duration of 12 weeks, the disease activity was reduced by 52.1% (95%CI 47.6-52.6%) (p<0.05). Twenty-one patients (58. 3%) achieved at least 50% reduction in disease activity (SASSAD50). The reduction in disease activity parallelled a significant improvement of symptoms and quality of life. The overall drug tolerability was good. Two patients discontinued AZA due to neutropaenia but both had a normal TPMT level. Other recognised adverse events such as nausea, rash, and raised liver enzymes were also observed. Conclusion: AZA can be considered as an effective and well-tolerated systemic treatment for patients with moderate-to-severe atopic dermatitis. Close blood monitoring is still warranted despite a normal level of thiopurine methyltransferase.