The ex vivo transfer of the anti-HIV nucleoside compound d4T in the human placenta.

The purpose of this study was to determine the ex vivo maternal-fetal placental transfer of 2',3'-didehydro-3'-deoxythymidine (d4T) and to compare it to the perfusion characteristics of 3'-azido-2',3-dideoxythymidine (AZT). This study used the single cotyledon perfusion system and antipyrine to determine the clearance index of this thymidine-containing anti-human immunodeficiency virus (HIV) compound. The endogenous base thymidine and the inhibitor dipyridamole were used to determine if this anti-HIV compound crossed the placenta by simple diffusion. The clearance index of d4T was 0.24 +/- 0.07 at 1.0 micrograms/ml and 0.235 +/- 0.045 at 10.0 micrograms/ml. These data suggest that the clearance index of d4T is 77-81% of AZT. The presence of high concentrations of dipyridamole and endogenous thymidine did not alter the clearance of d4T. In studies in which both the maternal and fetal circulations were closed, the accumulation in the fetal circulation was linear when the maternal concentration was in the range of 1-100 micrograms/ml. These data suggest that d4T crosses the human placenta by simple diffusion, and has similar perfusion characteristics to that of AZT.