Pregnancy mercaptopurine

Metronidazole or methotrexate should not be used during pregnancy. Azathioprine and mercaptopurine may be associated with fetal deformities. 

When chemotherapeutic mercaptopurines are being given concomitantly with allopurinol, their dosage must be reduced by about 75%. Allopurinol may also increase the effect of cyclophosphamide. Allopurinol inhibits the metabolism of probenecid and oral anticoagulants and may increase hepatic iron concentration. Safety in children and during pregnancy has not been established. 

Antineoplastic drugs such as 6-mercaptopurine, methotrexate, cyclophosphamide, and aminopterin administered in early pregnancy have produced various congenital malformations. Cytotoxic drugs also have induced fetal malformation and early abortion of malformed fetuses (4-6). 

Rajapakse RO, Korelitz BI, Zlatanic J, Baiocco PJ, Gleim GW. Outcome of pregnancies when fathers are treated with 6-mercaptopurine for inflammatory bowel disease. Am J Gastroenterol 2000 95(3) 684-8. 

The role of incorporation of thiopurines into cellular DNA with regard to therapeutic or toxic effects remains unknown. The incidence cff pregnancy-related complications, however, was significantly increased when fathers used mercaptopurine within 3 months of conception. These compounds can cause marked inhibition of the coordinated induction of various enzymes required for DNA synthesis, as well as potentially critical alterations in the synthesis of polyadenylate-containing RNA. 

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