A 28-year-old woman with a 3-year history of primary infertility is found to have polycystic ovary syndrome (PCOS) on ultrasound and elevated androgen levels. She has regular menstrual cycles but anovulation confirmed by progesterone levels. What is the drug of choice for ovulation induction in this patient?

Explanation

## First-Line Ovulation Induction in PCOS **Key Point:** Letrozole (an aromatase inhibitor) is the **drug of choice** for ovulation induction in anovulatory women with PCOS, superseding clomiphene citrate based on superior live birth rates demonstrated in landmark trials and endorsed by current international guidelines. ### Evidence Base The pivotal **NEJM 2014 RCT (Legro et al.)** — the largest randomized trial comparing letrozole vs. clomiphene citrate in PCOS — demonstrated: - **Live birth rate:** Letrozole 27.5% vs. Clomiphene 19.1% (p = 0.007) - **Ovulation rate:** Letrozole 61.7% vs. Clomiphene 48.3% - Benefit was most pronounced in **obese women** but present across all BMI groups This evidence led to updated guidelines from **ASRM (2023)**, **ESHRE (2023)**, and **WHO** recommending letrozole as the **first-line agent** for ovulation induction in PCOS. ### Mechanism of Action Letrozole is a **third-generation aromatase inhibitor** that: 1. Blocks conversion of androgens to estrogens in peripheral tissues and the ovary 2. Reduces negative estrogen feedback at the hypothalamus/pituitary → increases endogenous FSH secretion 3. Promotes **mono-follicular development** (lower multiple pregnancy risk compared to clomiphene) 4. Does NOT block endometrial estrogen receptors → preserves endometrial thickness ### Dosing - **Standard dose:** 2.5–7.5 mg/day for 5 days (days 3–7 of cycle) - Titrated upward if no ovulation at lower doses ### Advantages Over Clomiphene Citrate in PCOS | Parameter | Letrozole | Clomiphene Citrate | |-----------|-----------|-------------------| | Live birth rate | Higher | Lower | | Endometrial thickness | Preserved | Often thinned | | Multiple pregnancy risk | Lower | Higher | | Anti-estrogenic side effects | Absent | Present | | Mechanism | Peripheral aromatase inhibition | Central ER blockade | ### Why Other Options Are Incorrect - **Clomiphene citrate (B):** Previously considered first-line but now classified as **second-line** per ASRM 2023 and ESHRE 2023 guidelines; demonstrates inferior live birth rates vs. letrozole in PCOS; also thins endometrium due to anti-estrogenic effects - **Gonadotropins (C):** Reserved for clomiphene/letrozole-resistant cases; higher risk of OHSS and multiple gestation; requires intensive monitoring - **Metformin (A):** Useful adjunct for insulin resistance in PCOS; not a primary ovulation induction agent; inferior to letrozole as monotherapy for achieving live birth **High-Yield:** Per ASRM 2023 and ESHRE 2023 PCOS guidelines, **letrozole is the first-line drug of choice** for ovulation induction in anovulatory PCOS. Clomiphene citrate is now considered second-line. (Reference: Legro RS et al., NEJM 2014; ASRM Practice Committee 2023; ESHRE PCOS Guidelines 2023)