A 28-year-old woman presents to the emergency department 18 hours after unprotected intercourse. She has no contraindications to hormonal methods and is not breastfeeding. What is the drug of choice for emergency contraception in this case?

Explanation

## Emergency Contraception: Levonorgestrel as First-Line ### Mechanism of Action Levonorgestrel is a progestin that acts primarily by: 1. Inhibiting or delaying ovulation 2. Altering cervical mucus to impede sperm transport 3. Most effective when taken within 72 hours of unprotected intercourse ### Dosing & Efficacy **Key Point:** Levonorgestrel 1.5 mg as a single dose is the WHO-recommended first-line emergency contraceptive for non-breastfeeding women. - **Efficacy:** ~60% reduction in pregnancy risk when taken within 72 hours - **Optimal window:** Most effective within 12 hours; efficacy decreases after 72 hours - **No absolute contraindications:** Can be used in most women, including those with relative contraindications to combined oral contraceptives ### Comparison of Emergency Contraceptive Options | Agent | Dosing | Efficacy Window | Mechanism | Special Use | |-------|--------|-----------------|-----------|-------------| | **Levonorgestrel** | 1.5 mg single dose | ≤72 hours | Ovulation inhibition | First-line, non-breastfeeding | | Mifepristone | 10 mg single dose | ≤72 hours | Progesterone antagonist | Effective up to 120 hours; limited availability in India | | Ulipristal acetate | 30 mg single dose | ≤120 hours | Selective progesterone receptor modulator | More effective than levonorgestrel; expensive; limited access | | Copper IUD | Insertion | ≤5 days | Spermicide + endometrial inflammation | Most effective method; invasive; requires insertion expertise | ### High-Yield Facts **High-Yield:** Levonorgestrel is available over-the-counter in most countries and is the most accessible emergency contraceptive globally. It is not effective if ovulation has already occurred. **Clinical Pearl:** Efficacy is inversely related to body weight; women >75 kg may have reduced efficacy with standard levonorgestrel dosing. **Warning:** Levonorgestrel does NOT terminate an established pregnancy—it prevents conception. If pregnancy is already established, it will not be effective. ### Why Levonorgestrel Is Preferred in This Case - Presentation is 18 hours post-intercourse (well within 72-hour window) - No mention of contraindications - Not breastfeeding (eliminates concern about infant exposure) - Cost-effective and widely available - High safety profile with minimal side effects [cite:Park 26e Ch 8]