Letrozol Medical Valley (Letrozole)

Letrozole is used in endocrine therapy targeting estrogen‑dependent breast cancer.

• Adjuvant treatment of hormone receptor‑positive breast cancer in postmenopausal women: reduces risk of disease recurrence after surgery.
• Metastatic hormone receptor‑positive breast cancer in postmenopausal women: slows disease progression and prolongs survival.
• Neoadjuvant therapy for locally advanced hormone receptor‑positive breast cancer: facilitates tumor shrinkage before surgery.

• Letrozole selectively binds to the aromatase enzyme, a cytochrome P450 isoform responsible for converting adrenal and ovarian androgens into estrogens. By inhibiting aromatase, the drug markedly lowers circulating estradiol levels, depriving estrogen‑dependent tumor cells of a growth stimulus. The reduction in systemic estrogen is achieved without affecting gonadotropin release, making the effect peripheral and specific to postmenopausal patients.

Letrozole may cause a range of adverse reactions, varying from mild to severe.

Common Side Effects

• Hot flashes
• Joint and muscle pain
• Fatigue
• Nausea
• Headache
• Insomnia

Serious or Rare Side Effects

• Severe osteoporosis or bone fractures
• Venous thromboembolism (deep vein thrombosis, pulmonary embolism)
• Liver function test abnormalities
• Severe skin reactions such as Stevens‑Johnson syndrome
• Interstitial lung disease or pneumonitis

When prescribing Letrozole, several safety considerations should be observed.

• Assess bone health: obtain baseline DEXA scan and monitor bone density during therapy.
• Monitor liver function: perform periodic liver enzyme tests.
• Evaluate cardiovascular risk: review history of thromboembolic events before initiating.
• Contraindicated in pregnancy: avoid use in pregnant women (Category X).
• Use caution in severe renal impairment: adjust dosing or consider alternative therapy.
• Store at ambient temperature below 25°C: keep in original packaging, protect from moisture.

Letrozole can interact with other medicines, requiring careful management.

Major Interactions (Avoid)

• Concurrent estrogen replacement therapy: may diminish letrozole efficacy.
• Strong CYP3A4 inducers (e.g., rifampin, carbamazepine): can lower plasma concentrations.
• Tamoxifen co‑administration: antagonistic effect on estrogen blockade.

Moderate Interactions (Monitor Closely)

• Warfarin: letrozole may increase INR, require coagulation monitoring.
• Selective serotonin reuptake inhibitors (e.g., fluoxetine): may affect metabolism, observe for side effects.
• Antacids containing aluminum or magnesium: may reduce absorption, separate dosing by at least 2 hours.