Question

Which drug is commonly used as an emergency oral contraceptive?

• A. Ethinyl estradiol
• B. Oxytocin
• C. Progesterone
• D. Levonorgestrel

Hint:

To work as emergency contraception, Levonorgestrel must be taken prior to ovulation. Once the LH surge has reached its peak or implantation has occurred, levonorgestrel loses its preventive efficacy.

Answer 1

The Correct Option is D

Understanding the Concept: Emergency contraception is intended to prevent pregnancy following unprotected sexual intercourse or contraceptive failure. To be highly effective, the drug must act quickly to inhibit or delay ovulation by disrupting the gonadotropin surges controlled by the hypothalamic-pituitary-ovarian axis.

Step 1: Mechanism of action of Levonorgestrel Levonorgestrel is a highly potent synthetic second-generation progestin. When administered in a single large dose (typically 1.5 mg) within 72 hours of unprotected intercourse, it exerts a strong negative feedback loop on the hypothalamus and anterior pituitary. This action suppresses the surge of Luteinizing Hormone (LH). Without the LH surge, follicular rupture is arrested, and ovulation is prevented or significantly delayed. It also alters cervical mucus thickness to block sperm transport.

Step 2: Evaluation of alternatives
• Ethinyl estradiol: This is a synthetic estrogen component used primarily in chronic, daily combined oral contraceptive pills to stabilize the endometrium, rather than as a monotherapy for emergency intervention.
• Oxytocin: A peptide hormone that stimulates uterine contractions during labor and promotes milk ejection; it has no contraceptive properties.
• Progesterone: Natural progesterone has a short half-life and poor oral bioavailability, rendering it unsuitable for acute, high-potency emergency single-dose administration. Consequently, Levonorgestrel is the designated agent commonly formulated for oral emergency contraception.