Azathioprine in dermatology.

Azathioprine is a synthetic purine analog derived from 6-mercaptopurine. It is a purine antagonist and its active metabolites act by disrupting the function of endogenous purines. It has a cytotoxic and immunosuppressive mechanism of action. It is used in dermatology for treatment of immunobullous diseases, generalized eczematous disorders and photodermatoses. There is an enzyme in the metabolism of azathioprine called thiopurine s-methyltransferase (TPMT). It is very important to measure the TPMT activity before initiating therapy so that proper dosing of azathioprine can be achieved.