Postpartum hemorrhage is the leading cause of maternal morbidity and mortality worldwide, with uterine atony estimated to account for 70% to 80% of cases, thereby remaining the single most common cause. Pharmacotherapy remains the first-line preventative therapy for postpartum hemorrhage. These therapies may be single (oxytocin, carbetocin, methylergonovine, ergometrine, misoprostol, prostaglandin analogs, or tranexamic acid) or combination therapies, acting in an additive, infra-additive, or synergistic fashion to prevent postpartum hemorrhage. Evidence is strong for the use of oxytocin, the first-line uterotonic agent in the United States for prevention of postpartum hemorrhage. Although carbetocin, a long-acting analog of oxytocin, is not yet available for use in the United States, it is likely the most effective single pharmacologic therapy for prevention of postpartum hemorrhage and need for additional uterotonics. Use of second-line uterotonics such as methylergonovine, misoprostol, and carboprost in combination with oxytocin has an additive or synergistic effect and a greater risk reduction for postpartum hemorrhage prevention compared with oxytocin alone. Therefore, combined therapy rather than oxytocin alone should be advised for preventing postpartum hemorrhage. Tranexamic acid has been found to be both effective and safe for decreasing maternal mortality in women with postpartum hemorrhage, and prophylactic use of tranexamic acid may decrease the need for packed red blood cell transfusions and/or uterotonics. The WOMAN-2 Trial, designed to assess if tranexamic acid prevents postpartum hemorrhage in women with moderate to severe anemia undergoing vaginal delivery, is currently recruiting participants. The additive, infra-additive, or synergistic action of oxytocin in combination with other second-line therapies deserves further study.
Keywords: drug–drug interactions; pharmacotherapy; postpartum hemorrhage; prevention; uterotonics.
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