*2.3.1 Azathioprine*

Azathioprine is a purine analogue. It inhibits DNA synthesis by acting on proliferating cells [37]. It acts on the DNA [38]. Azathioprine is metabolized to 6-mercaptopurine through reduction by glutathione and other sulfhydryl-containing compounds and then enzymatically converted into 6-thiouric acid, 6-methyl-mercaptopurine, and 6-thioguanine [38]. Ultimately, azathioprine is incorporated into replicating DNA and can block the de novo pathway of purine synthesis. It is this action that is thought to contribute to its relative specificity to lymphocytes due to lack of a salvage pathway. The inhibition of purine synthesis, leads to less DNA and RNA available for the synthesis of white blood cells, including cells of the immune system. Actively replicating cells, such as T cells and B cells of the immune system, which actively synthesize purine to make new DNA are strongly affected [39, 40]. Thus, immunosuppression ensues. It has been used successfully in SLE as steroid sparing agent and in cases of lupus flares. It can be used safely during pregnancy [41]. It can be used as maintenance treatment in lupus nephritis [42].
