Azathioprine in dermatological practice. An overview with special emphasis on its use in non-bullous inflammatory dermatoses.

Azathioprine is employed for its immunosuppressive properties, as a steroid-sparing agent or as monotherapy. Its most traditional clinical indications are connective tissue diseases, vasculitis, post-transplant, and immunobullous dermatoses. The main disadvantages of azathioprine therapy are a delayed onset of action (6-8 weeks), and rare profound bone marrow toxicity. Susceptibility to bone marrow toxicity is due to a genetically determined metabolic defect (1 in 300). Patients at risk of such toxicity may be identified by a Thiopurine methyltransferase enzyme assay. We have undertaken a retrospective study, looking at the use of azathioprine as monotherapy for non-bullous inflammatory dermatoses. We studied a total of 24 patients (10 male, 14 female). The dermatoses comprised: atopic eczema (10), pompholyx (6), plaque psoriasis (6), and chronic actinic dermatitis (2). All patients had severe refractory disease warranting systemic second line therapy. The mean age was 49.4 years (range 17-86 years). The starting dose of azathioprine was 100-150 mg/day, and the maintenance dose 50-100 mg/day. The mean duration of treatment was 33.5 months(range 1-132 months). Eighteen patients (75%) showed a good to excellent sustained clinical response to azathioprine. This response rate was evenly represented in the 4 dermatoses studied. The adverse reactions encountered were raised MCV (6), leucopenia (2), raised hepatic enzymes (6), and dyspepsia (4). Azathioprine had to be discontinued due to adverse reactions in 2 patients (dyspepsia, raised hepatic enzymes) followed by normalization. Other factors that potentially contributed to the observed adverse events were present in 5 patients: alcoholism (2), erythromycin toxicity (1), and malabsorption (2). Our study demonstrates the efficacy of azathioprine monotherapy for severe atopic eczema, pompholyx, plaque psoriasis, and chronic actinic dermatitis. Furthermore, azathioprine is a low cost and generally well tolerated drug.