Diphenhydramine disposition in the sheep maternal–Placental–Fetal unit: Determinants of plasma drug concentrations in the mother and the fetus††Abbreviations: DPHM, diphenhydramine; [2H10]DPHM, deuteriumlabeled diphenhydramine; CLmm, maternal total body clearance; CLff, fetal total body clearance; CLmf, maternal to fetal placental clearance; CLfm, fetal to maternal placental clearance; CLmo, maternal nonplacental clearance; CLfo, fetal nonplacental clearance; Cm, maternal plasma steady-state DPHM concentration after maternal administration; Cf, fetal plasma steady-state DPHM concentration after maternal administration; Cm′, maternal plasma steady-state DPHM (or [2H10]-DPHM) concentration after fetal administration; Cf′, fetal plasma steady-state DPHM (or [2H10]DPHM) concentration after fetal administration; ko, maternal drug infusion rate; ko′, fetal drug infusion rate; M-UF, maternal steady-state plasma unbound fraction of the drug; F-UF, fetal steady-state plasma unbound fraction of the drug; r, Pearson correlation coefficient