Sequential oxytocin reduces contractile responsiveness, whereas carbetocin preserves it in human pregnant myometrium
Carbetocin appears to preserve uterine contractility after prior exposure to oxytocin, which could be relevant for managing postpartum hemorrhage.
Where it sits
this study against the rest of the carbetocin corpusSummary and findings
This study investigated the in vitro effects of carbetocin and oxytocin on human pregnant myometrium. Myometrial strips from 7 women were exposed to various concentrations of both agents. The results indicated that carbetocin preserved contractile responsiveness, while sequential oxytocin administration reduced contraction frequency.
Abstract
Abstract Purpose Carbetocin and oxytocin are widely used uterotonic agents for postpartum hemorrhage prevention; however, sequential administration may influence uterine contractility. Evidence regarding their combined and sequential effects on human myometrium is limited. This study aimed to investigate the in vitro effects of cumulative and sequential administration of oxytocin and carbetocin on amplitude and frequency of contractions in term pregnant human myometrium. Methods Myometrial strips (n = 28) were obtained from 7 women undergoing elective cesarean section and mounted in organ baths for isometric tension recording. Two baths were exposed to cumulative oxytocin (10⁻¹⁰–10⁻⁶ M) and two to cumulative carbetocin (10⁻¹⁰–10⁻⁵ M). Following a 1-hour washout, sequential single-dose administrations of oxytocin or carbetocin were applied twice under four protocols (OXY + oxy+oxy, OXY+carb+carb, CARB + oxy+oxy, CARB+carb+carb), with a second washout between applications. Contractile amplitude and frequency were recorded and analyzed. Results Carbetocin induced contractions across all concentrations, whereas oxytocin was effective only below 10⁻⁶ M. No significant differences in amplitude or frequency were observed between oxytocin and carbetocin at 10⁻¹⁰–10⁻⁷ M (p > 0.05). Sequential oxytocin administration significantly reduced contraction frequency (p < 0.05) without affecting amplitude. In contrast, sequential carbetocin administration did not significantly alter contractile responses to either drug (p > 0.05). Conclusion Carbetocin preserves myometrial contractile responsiveness after prior exposure to oxytocin or carbetocin. These findings suggest that carbetocin may remain effective for postpartum hemorrhage management even following prophylactic uterotonic administration.