Letrozole

# Letrozole ## Overview - **Classification**: Aromatase inhibitor (Non-steroidal) - **Mechanism**: Selectively inhibits the aromatase enzyme, which catalyzes the conversion of androgens to estrogens. This reduces estrogen levels, primarily in postmenopausal women, suppressing estrogen-dependent tumor growth. ## Primary Indications 1. **Adjuvant Breast Cancer**: Adjuvant treatment of early hormone receptor (HR)-positive invasive breast cancer in postmenopausal women. 2. **Extended Adjuvant Breast Cancer**: Extended adjuvant treatment of HR-positive early breast cancer in postmenopausal women who have completed 5 years of adjuvant tamoxifen therapy. 3. **Advanced Breast Cancer**: First-line treatment of HR-positive or unknown advanced breast cancer in postmenopausal women. 4. **Advanced Breast Cancer (2nd-line)**: Second-line treatment of advanced breast cancer in postmenopausal women with disease progression following anti-estrogen therapy. 5. **Ovulation Induction (Off-label)**: For anovulatory infertility. ## Adult Dosing ### Standard Dosing **Adjuvant/Extended Adjuvant/Advanced Breast Cancer** - **Dose**: **2.5 mg** - **Frequency**: Once daily (QD) - **Route**: Oral (PO) - **Duration**: Adjuvant: Typically 5 years. Extended adjuvant: Up to 5 years after tamoxifen. **Ovulation Induction (Off-label)** - **Dose**: **2.5 mg** or **5 mg** - **Frequency**: Once daily (QD) - **Route**: Oral (PO) - **Duration**: For 5 days, starting on cycle day 2, 3, 4, or 5. ### Dose Adjustments - **Renal Impairment**: No adjustment needed for mild to moderate impairment (CrCl ≥10 mL/min). No data for severe impairment (CrCl <10 mL/min). - **Hepatic Impairment**: No adjustment for mild to moderate (Child-Pugh A or B). For severe (Child-Pugh C), reduce dose to **2.5 mg every other day**. - **Elderly Patients**: No specific dose adjustment required based on age. ## Pediatric Dosing Letrozole is **not FDA-approved for pediatric use**. Any use is off-label and should be under strict specialist guidance. ### Neonates (0-28 days) - **Not indicated** for this age group. ### Infants (1-12 months) - **Not indicated** for this age group. ### Children (1-12 years) - **Indication**: Investigational for conditions like precocious puberty, growth failure, or McCune-Albright syndrome. - **Dose**: Typically **0.5 mg** to **2.5 mg** - **Frequency**: Once daily (QD) - **Maximum**: **2.5 mg/day** (based on studied doses) - **Special Notes**: Use only under expert endocrine supervision. Monitor bone age, growth velocity, and pubertal development. Potential for premature epiphyseal closure. ### Adolescents (13-18 years) - **Indication**: Investigational for conditions like precocious puberty, short stature, or gynecomastia. - **Dose**: Typically **2.5 mg** - **Frequency**: Once daily (QD) - **Maximum**: **2.5 mg/day** - **Special Notes**: Use only under expert endocrine supervision. Monitor for bone age progression and potential impact on final adult height. ## Safety Information ### Contraindications - **Absolute**: Pregnancy (known to cause fetal harm/death). - **Absolute**: Premenopausal women (unless ovarian function is suppressed). - **Absolute**: Hypersensitivity to letrozole or any excipients. ### Common Adverse Effects - **Very Common (>10%)**: Hot flushes, arthralgia (joint pain), fatigue, sweating increased. - **Common (1-10%)**: Headache, nausea, dizziness, bone pain, peripheral edema, hypercholesterolemia, alopecia. - **Serious but Rare**: Thromboembolic events (DVT, PE, stroke, MI), osteoporosis and fractures, hepatotoxicity, acute kidney injury. ### Key Drug Interactions - **Tamoxifen, Estrogen-containing medications**: Avoid concurrent use; may significantly reduce letrozole efficacy. - **CYP3A4 inducers (e.g., Rifampin, Phenytoin)**: May decrease letrozole plasma concentrations. Monitor for reduced efficacy. - **CYP3A4 inhibitors (e.g., Ketoconazole, Ritonavir)**: May increase letrozole plasma concentrations. Monitor for increased adverse effects. - **Drugs metabolized by CYP2C19 (e.g., Phenytoin, Clopidogrel)**: Letrozole is a weak inhibitor; potential for altered drug levels. Monitor closely. ## Monitoring & Follow-up - **Before Treatment**: Liver function tests (LFTs), renal function, baseline bone mineral density (BMD) scan (DEXA). Confirm postmenopausal status. - **During Treatment**: BMD (every 1-2 years), lipid panel (periodically), LFTs (periodically). Monitor for signs of bone pain, fractures. - **Clinical Signs**: Watch for symptoms of thromboembolic events (chest pain, shortness of breath, leg swelling), jaundice, or unexplained fatigue. ## Clinical Pearls - 💡 **Tip 1**: Letrozole can be taken with or without food. Administer at the same time each day for consistency. - 💡 **Tip 2**: Advise patients on adequate calcium and vitamin D intake to help mitigate bone density loss. - 💡 **Tip 3**: Counsel patients on common side effects like hot flashes, joint pain, and fatigue. Suggest strategies for management. - 💡 **Tip 4**: Confirm postmenopausal status (e.g., FSH, LH, estradiol levels) before initiating treatment in women with unclear menstrual status. > **⚠️ Important**: This information is for educational purposes only. Always consult current prescribing information, local guidelines, and clinical judgment before prescribing.