Potent, high affinity human oxytocin (OT) receptor antagonist (Ki = 4.6 nM) that displays > 800-fold selectivity over human arginine vasopressin receptors V1a and V2. Antagonizes oxytocin-induced contractions in isolated rat uterine tissue (pA2 = 8.44) and in anesthetised rats following intravenous and intraduodenal administration. Orally active.