Cyclooxygenase-2 inhibitors constrict the fetal lamb ductus arteriosus both in vitro and in vivo

Nonselective cyclooxygenase (COX) inhibitors are potent tocolytic agents; h owever, they also have adverse fetal effects such as constriction of the fe tal ductus arteriosus. Recently, selective COX-2 inhibitors have been used in the management of preterm labor in the hope of avoiding fetal complicati ons. However, both COX-1 and -2 are expressed by cells of the ductus arteri osus. We used fetal lambs (0.88 gestation) to assess the ability of selecti ve COX-2 inhibitors celecoxib and NS398 to affect the ductus arteriosus. Bo th selective COX-2 inhibitors decreased PGE(2) and 6ketoPGF(1 alpha) produc tion in vitro; both inhibitors constricted the isolated ductus in vitro. Th e nonselective COX-1/COX-2 inhibitor indomethacin produced a further reduct ion in PG release and an additional increase in ductus tension in vitro. We used a prodrug of celecoxib to achieve 1.4 +/- 0.6 mu g/ml, mean +/- stand ard deviation, of the active drug in vivo. This concentration of celecoxib produced both an increase in pressure gradient and resistance across the du ctus; celecoxib also decreased fetal plasma concentrations of PGE(2) and 6k etoPGF(1 alpha). Indomethacin (0.7 +/- 0.2 mu g/ml) produced a significantl y greater fall in ductus blood flow than celecoxib and tended to have a gre ater effect on ductus resistence in vivo. We conclude that caution should b e used when recommending COX-2 inhibitors for use in pregnant women, becaus e COX-2 appears to play a significant role in maintaining patency of the fe tal ductus arteriosus.