-5%
Letrozole is a potent, nonsteroidal aromatase inhibitor that reduces estrogen biosynthesis by competitively inhibiting the aromatase enzyme. This deprives estrogen-dependent breast cancer cells of their growth stimulus.
- In Postmenopausal Women: Estrogens are synthesized by aromatase converting adrenal androgens (androstenedione, testosterone) to estrone (E1) and estradiol (E2). Letrozole effectively suppresses estrogen levels without affecting androgen levels.
- Suppression Rates: Single doses (0.1–2.5 mg) suppress serum estrone and estradiol by 75–78%, achieving maximum suppression within 48–78 hours.
Pharmacokinetics:
- Absorption: Rapid, complete absorption (bioavailability ~99.9%). Food delays absorption slightly without affecting clinical relevance.
- Protein Binding: ~60% (primarily to albumin).
- Metabolism: Converted to an inactive carbinol metabolite primarily by CYP3A4 and CYP2A6.
- Half-Life: ~2 days.
- Steady State: Achieved within 2–6 weeks of daily 2.5 mg administration.
