Teratogen update: Azathioprine and 6‐mercaptopurine

Azathioprine (AZA) and its active metabolite, 6-mer-captopurine (6-MP), are purine analogues that inter-fere with the synthesis of adenine and guanine ribo-nucleosides. These ribonucleosides are important precursors of DNA and RNA. Because AZA and 6-MP act predominantly on rapidly dividing cells such as the T lymphocytes, these drugs are not only cytotoxic but also immunosuppressive and anti-inflammatory. The effects are dose-related, small doses of either drug are anti-inflammatory, but larger doses are immunosup-pressive and cytotoxic (Goldstein, ’87). 6-MP has been used in cancer chemotherapy, pri-marily in childhood and adult leukemias and usually in combination with other drugs. 6-MP is also used to treat autoimmune diseases, such as inflammatory