Letrozol Viatris (Letrozole)

Letrozole is indicated for the endocrine management of hormone‑dependent breast cancer in postmenopausal patients.

• Hormone receptor‑positive early‑stage breast cancer: used as adjuvant therapy to reduce recurrence after surgery.
• Hormone receptor‑positive metastatic breast cancer: employed to control disease progression in advanced stages.
• Locally advanced breast cancer: given to shrink tumors before surgery or radiation.

• Letrozole reversibly binds to the aromatase enzyme’s heme site, blocking the conversion of androstenedione and testosterone into estrone and estradiol. By reducing peripheral estrogen synthesis, circulating estrogen concentrations fall, depriving estrogen‑dependent tumor cells of growth stimulation and thereby inhibiting tumor proliferation. The inhibition is dose‑dependent and persists for several days after the last dose, allowing sustained estrogen suppression during chronic therapy.

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

Common Side Effects

• Hot flashes: sudden feeling of warmth and sweating.
• Joint and muscle pain: arthralgia or myalgia.
• Fatigue: persistent tiredness.
• Nausea: mild stomach upset.
• Headache: mild to moderate intensity.
• Insomnia: difficulty sleeping.

Serious or Rare Side Effects

• Osteoporosis: decreased bone mineral density leading to fractures.
• Severe liver injury: elevated transaminases or hepatitis.
• Cardiovascular events: thromboembolic disorders.
• Allergic reactions: rash, angioedema, anaphylaxis.
• Severe bone pain: may indicate pathological fracture.
• Vision changes: rare ocular disturbances.

When prescribing Letrozole, clinicians should consider several safety precautions.

• Pregnancy contraindication: drug is teratogenic and must not be used in pregnant women.
• Menopause status: only indicated for postmenopausal patients; assess menopausal state before initiating.
• Bone health monitoring: evaluate bone mineral density and consider calcium/vitamin D supplementation.
• Liver function: monitor hepatic enzymes regularly during therapy.
• Drug interactions: review concomitant medications for potential interactions.
• Store at ambient temperature: keep below 25 °C in original packaging, protect from moisture.

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

Major Interactions (Avoid)

• Strong CYP3A4 inducers (e.g., rifampin, carbamazepine): may markedly reduce letrozole plasma levels.
• Estrogen‑containing hormone therapy: antagonizes therapeutic effect and should be avoided.

Moderate Interactions (Monitor Closely)

• Anticoagulants (warfarin): may increase bleeding risk; monitor INR.
• SSRIs/SNRIs (e.g., fluoxetine): may affect metabolism; observe for side effects.
• Tamoxifen: concurrent use may diminish efficacy of both agents; assess clinical need.