Mechanism of Action of Ulipristal Acetate for Emergency Contraception: A Systematic Review

Abstract

Ulipristal acetate (UPA) is now recommended as first choice hormonal emergency contraception (EC), due to its higher efficacy and similar safety compared to Levonorgestrel – EC. Even though all trials demonstrated that the first mechanism of action is inhibition of ovulation, some authors still postulate that a post fertilization effect is also possible, raising the alert on medication and fostering the ethical debate. A Medline database search was performed in order to find recent articles related to UPA’s effects on ovulation, on fallopian tube and on endometrium. We also analyzed the effects on sperm function and pregnancy. All studies conclude that UPA is effective in inhibition of ovulation even when administered shortly before LH peak. The effects on fallopian tube are unclear: according to some authors UPA inhibits ciliar beat through an agonistic effect on progesterone receptors, according to others it antagonizes the progesterone-induced ciliar beat decrease. Concerning the action on endometrium and on embryo implantation most of the studies concluded that low dose UPA used for EC has no significant effect on the decrease of endometrial thickness and on embryo’s attachment, but these results are still matter of debate. Finally recent evidence suggests that UPA modulates human sperm functions while it has no effect on established pregnancy. To date the majority of the evidence concurs in excluding a post-fertilization effect of UPA, even though more studies are needed to clarify its mechanism of action.

The Quality of Counselling for Oral Emergency Contraceptive Pills—A Simulated Patient Study in German Community Pharmacies

“…Of the oral hormonal methods, the Yuzpe method (oestrogen–progesterone combination comprising two doses of 50 µg ethinylestradiol and 0.25 mg levonorgestrel) is also no longer recommended in Germany for post-coital contraception [ 7 ] because it is less effective than other EC methods and is also associated with more adverse events [ 1 , 6 , 7 ]. Because mifepristone is not available in Germany for this indication [ 7 , 8 ]—unlike some other countries [ 5 , 9 ]—the oral hormonal methods are concentrated on emergency contraceptive pills (or “morning after pills”) containing the active substances levonorgestrel (LNG) and ulipristal acetate (UPA).…”

Ulipristal Acetate and Extracellular Matrix Production in Human Leiomyomas In Vivo: A Laboratory Analysis of a Randomized Placebo Controlled Trial

“…Depending on serum levels of progesterone, UPA can demonstrate both agonistic and antagonistic activity. 14 This factor may also partially explain the differences in response to treatment as observed in clinical trials. [6][7][8] Screening microarray experiments conducted in the early 2000s confirmed that the extracellular membrane (ECM) plays a critical role in the pathogenesis of leiomyomas.…”

Ulipristal Acetate Interferes With Actin Remodeling Induced by 17β-Estradiol and Progesterone in Human Endometrial Stromal Cells

“…Its administration is associated with development of a rapid and stable amenorrhea, which can be in part explained by interference with the hypothalamus-pituitary-ovarian axis. Currently, UPA has two major indications in several countries: emergency contraception ( 4 , 5 ) and treatment of symptomatic fibroids ( 6 – 8 ).…”