Placental drug transfer in near-term ewes: acetylsalicylic and salicylic acid.

Abstract

Radiolabelled acetylsalicylic acid (ASA) and salicylic acid (SA) were given intravenously to four near-term ewes and their occurrence in both maternal and fetal plasma was ascertained using a specific thin-layer chromatographic analysis procedure. Findings proved that ASA and SA cross the placental barrier and reach distribution equilibrium about 40 min after salicylate administration. The equilibrium plasma fetal/maternal ratio for both salicylates averaged 0.4. Plasma concentrations of the two compounds in the mother and the fetus accorded with a two-compartment model having unusually large mean estimates (54 and 39 L) for the tissue distribution space of ASA and SA, respectively. Furthermore, the mean SA clearance in the ewe (358 mL X min-1) was much greater than that reported in man, while the mean ASA clearance (764 mL X min-1) was similar. Since ASA is an irreversible inhibitor of arachidonate cyclooxygenase, our findings reassert the need for caution in the use of the drug during pregnancy.