Ulipristal acetate (emergency contraceptive) is a selective progesterone receptor modulator (SPRM). It differs from levonorgestrel (Plan B) in its primary mechanism and efficacy window because:

• A Ulipristal acts solely by preventing implantation via endometrial suppression
• B Ulipristal primarily inhibits ovulation and can also delay follicular rupture even after the LH surge has begun, extending efficacy to 120 hours ✓
• C Ulipristal inhibits sperm capacitation at the cervix for up to 5 days
• D Ulipristal is a progesterone agonist that thickens cervical mucus for 120 hours

Explanation

Levonorgestrel (progestogen) prevents or delays ovulation most effectively before the LH surge; it has little effect once the LH surge has started. Ulipristal acetate, as a selective progesterone receptor modulator, can inhibit or delay follicular rupture even after the LH surge has commenced by blocking progesterone's permissive role in follicular rupture. This extends effective use to 120 hours (5 days) post-unprotected intercourse and makes it more effective than levonorgestrel within 72-120 hours. Both agents are NOT abortifacients — neither prevents implantation of an already fertilized egg at recommended doses.

Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.