Letrozol Viatris (Letrozole)

Letrozole is used in the management of hormone‑dependent breast cancer, acting on estrogen synthesis pathways.

• Hormone receptor‑positive breast cancer (adjuvant): Reduces risk of disease recurrence after surgery.
• Hormone receptor‑positive breast cancer (metastatic): Delays disease progression in advanced disease.
• Postmenopausal estrogen‑dependent tumors: Lowers circulating estrogen levels to inhibit tumor growth.

• Letrozole selectively and non‑steroidally inhibits the aromatase enzyme, which converts androstenedione and testosterone to estrone and estradiol in peripheral tissues. By blocking this conversion, systemic estrogen concentrations fall, limiting estrogen‑driven proliferation of hormone‑sensitive breast cancer cells.

Letrozole may cause a range of adverse reactions that vary in frequency and severity.

Common Side Effects

• Hot flashes: Sudden feeling of warmth and sweating.
• Arthralgia: Joint pain or stiffness.
• Fatigue: Persistent tiredness not relieved by rest.
• Nausea: Mild to moderate upset stomach.
• Headache: Tension‑type or migraine‑like pain.
• Bone loss: Decreased bone mineral density over time.

Serious or Rare Side Effects

• Venous thromboembolism: Deep vein thrombosis or pulmonary embolism.
• Severe liver injury: Elevated transaminases or hepatitis.
• Cardiovascular events: Myocardial infarction or stroke.
• Severe hypersensitivity: Rash, angioedema, or anaphylaxis.
• Osteoporotic fracture: Pathologic bone break due to weakened bone.

Before initiating Letrozole therapy, consider the following safety measures.

• Cardiovascular assessment: Evaluate history of heart disease or clotting disorders.
• Bone health monitoring: Perform baseline bone mineral density testing and consider calcium/vitamin D supplementation.
• Liver function: Check hepatic enzymes periodically, especially in patients with pre‑existing liver disease.
• Drug interactions: Review concomitant medications that may affect estrogen metabolism.
• Pregnancy and lactation: Avoid use in pregnant or breastfeeding women; contraception is required for women of child‑bearing potential.
• Store at ambient temperature: Keep below 25°C in the original container, protect from moisture and direct sunlight.

Letrozole can interact with other medicines, altering its efficacy or safety profile.

Major Interactions (Avoid)

• Strong CYP3A4 inducers (e.g., rifampin, carbamazepine): May reduce Letrozole plasma levels and effectiveness.
• Tamoxifen: Concurrent use can antagonize aromatase inhibition and diminish therapeutic benefit.

Moderate Interactions (Monitor Closely)

• Anticoagulants (warfarin): May increase bleeding risk; monitor INR.
• SSRIs/ SNRIs (e.g., fluoxetine, venlafaxine): Potential to affect hormone metabolism; observe for side‑effect changes.
• Cholesterol‑lowering agents (statins): May increase risk of musculoskeletal complaints; assess patient tolerance.