<p>Fluorouracil is contraindicated throughout pregnancy. The literature pertaining to pregnancy and cytotoxic drugs is necessarily limited but it appears in general that risk of teratogenesis diminishes with the advancement of pregnancy. Therefore most cytotoxic drugs are absolutely contraindicated in the first trimester and 5-fluorouracil, used in the first trimester has been reported to cause multiple congenital abnormalities. There are many case reports, however, of pregnancy being conducted successfully with combination chemotherapy being given to the mother during the second and third trimesters. Because of the age of the population and the natural history of the tumors treated, most of the data on long-term follow-up pertain to therapy for leukemias. More data need to be accrued on the subsequent development of neonates before it is certain that any of these compounds are free of late effects.<br />
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It is not known whether fluorouracil is excreted in human milk. Because fluorouracil inhibits DNA, RNA and protein synthesis, mothers should not nurse while receiving this drug.</p>