Mifepristone

2347

Summary

Antiprogestins are drugs that inhibit progestin to antagonize progesterone receptors at the uterus. The main anti-progestin drug we need to know for test day is mifepristone. Since signaling at progesterone receptors is needed to maintain the uterine lining during implanation and pregnancy, antiprogestins cause sloughing of the uterine lining and may be used for emergency contraception and abortions. A major side effect of antiprogestins is heavy vaginal bleeding.

Key Points

  • Antiprogestins (Mifepristone, Ulipristal)
    • Mechanism
      • Inhibits progestin at progesterone receptors in the uterus
        • Progesterone is necessary for uterine growth and implantation
    • Indications
      • Emergency Contraception (ulipristal)
        • Must be taken within 5 days of unprotected intercourse
      • Abortion/Termination of Pregnancy
        • combined with misoprostol for maximum efficacy
      • Contraception at high doses (delay ovulation) and low doses (change endometrial morphology)
      • Endometriosis
      • Uterine fibroids
    • Adverse Effects
      • Heavy vaginal bleeding
        • Due to decidual necrosis and expulsion of products of conception
      • GI effects (cramping,  nausea)
        • Blocking progesterone sensitizes uterine muscle to the effect of hormone, causing cramping and nausea.