The Embryotoxic effects of 5‐fluoro‐2′‐deoxyuridine in mice

The embryolethal and teratogenic dose‐response relations of 5‐fluoro‐2′‐deoxyuridine (FUdR) were tested in mice at day VIII of pregnancy. FUdR was embryotoxic at dosages above 5 mg/kg maternal body weight. Types of resorptions and malformations were similar to those produced by 5‐fluoro‐2′‐deoxycytidine (FCdR) at day VIII (Degenhardt et al., '68; Kleinebrecht et al., '70). To produce the same frequency of resorptions or malformations the dosage of FUdR had to be about 2–4 times that of FCdR. These findings compared with data in rats (Chaube and Murphy, '69a) indicate a differential response to FUdR and FCdR in the two species.