Pharmacokinetics of antenatal maternally-administered tadalafil after 5 days of oral administration. Serum tadalafil concentrations were quantified at the fifth treatment (0 hours) and at 2, 4, 6, 8, and 24 hours afterwards in maternal ewes. In fetal lambs, blood was drawn at the fifth treatment (0 hours) and at 4, 8, 12, 16, 20, and 24 hours afterwards. In the maternal ewe, peak concentrations occur between 6–8 hours after administration. In the fetal lamb, there is a steady state of tadalafil, with concentrations comparable to peak levels seen in the maternal ewe. There is a proportional increase in serum tadalafil concentration with increases in tadalafil dosage.