Retosiban (GSK-221,149-A) is an oral drug which acts as a selective, sub-nanomolar (Ki = 0.65 nM) oxytocin receptor antagonist with >1400-fold selectivity[3] over the related vasopressin receptors
L-371,257 is an orally bioavailable, non-blood-brain barrier penetrant, selective and competitive antagonist of oxytocin receptor (pA2=8.4) with high affinity at both the oxytocin receptor (Ki=19 nM) and vasopressin V1a receptor (Ki=3.7 nM).