DW-116 is a newly developed fluoroquinolone antibacterial with a broad spectrum against both gram-positive and gram-negative bacteria. Recently, we have reported that DW-116 induces a significant developmental toxicity in rat. The present study was undertaken to characterize the placental transfer and pharmacokinetics of DW-116 in Sprague-Dawley rats. Pregnant females were given a single oral dose of 500-mg [14C]DW-116/kg on gestational day 18. Maternal and fetal tissues were collected at 0.17, 0.5, 1, 2, 4, 8 and 24 h after dosing. The [14C]DW-116-derived radioactivity was rapidly distributed to the fetus and slowly eliminated from the tissue. The radioactivity in both maternal plasma and fetal tissue reached its peak within 1 h and maintained the level of radioactivity up to 16-28% of the peak level until 24 h after dosing. Radioactivity in whole fetus was higher than those in the maternal plasma and placenta. The T(1/2)abs, T(1/2)beta, AUC, Tmax and Cmax in the maternal plasma were approximately 6 min, 13.3 h, 1620 microg h/ml, 0.5 h and 136 microg/ml, respectively. Those in the placenta were approximately 20 min, 12.3 h, 2150 microg h/ml, 1.0 h and 172 microg/ml, respectively. Those in the whole fetus were 13 min, 12.8 h, 2549 microg h/ml, 1 h and 191 microg/ml, respectively. In the amniotic fluid of maternal uterus, the T(1/2)abs, T(1/2)beta, AUC, Tmax and Cmax were approximately 1.3 h, 9.3 h, 2508 microg h/ml, 4.4 h, and 135 microg/ ml, respectively. While DW-116 disappeared biphasically from maternal plasma, whole fetus and placenta, it was eliminated monophasically from amniotic fluid. These results indicate that (1) total radioactivity appeared rapidly in maternal plasma and fetuses; (2) the elimination of total radioactivity is slow; and (3) DW-116 or relevant metabolites could cross the blood-placenta barrier in pregnant rats.