Letrozole Zentiva (Letrozole)

Letrozole acts on estrogen‑dependent pathways in breast cancer and is indicated for several therapeutic settings.

• Postmenopausal hormone‑receptor‑positive breast cancer: reduces tumor growth by lowering circulating estrogen levels.
• Adjuvant therapy for early‑stage breast cancer: helps prevent disease recurrence after surgery.
• Metastatic breast cancer in postmenopausal women: provides disease control when other endocrine therapies are insufficient.

• Letrozole acts as a selective, reversible inhibitor of the aromatase enzyme (CYP19A1) that converts adrenal and peripheral androgens into estrogens. By binding to the enzyme’s active site, it blocks estrogen synthesis, leading to markedly reduced circulating estradiol concentrations. The resulting hypo‑estrogenic state diminishes estrogen‑driven proliferation of hormone‑sensitive breast cancer cells, thereby slowing tumor progression.

Letrozole may be associated with a range of adverse reactions, which are categorized by frequency and severity.

Common Side Effects

• Hot flashes: transient episodes of increased skin temperature and sweating.
• Joint and muscle pain: arthralgia or myalgia affecting mobility.
• Fatigue: persistent tiredness not relieved by rest.
• Nausea: mild gastrointestinal upset.

Serious or Rare Side Effects

• Severe liver injury: marked elevation of transaminases or hepatic failure.
• Bone fracture: increased risk of osteoporosis‑related fractures.
• Pulmonary embolism: sudden shortness of breath and chest pain.
• Severe allergic reaction: anaphylaxis with rash, swelling, or airway compromise.

When prescribing Letrozole, clinicians should consider several safety measures.

• Monitor bone density: assess risk of osteoporosis and consider calcium/vitamin D supplementation.
• Assess liver function: obtain baseline tests and repeat periodically during therapy.
• Check lipid profile: monitor cholesterol levels as they may rise.
• Avoid use in pregnancy: Letrozole is contraindicated in pregnant women.
• Store at ambient temperature: keep below 25°C in the original container, protect from moisture.

Letrozole can interact with other medicines, requiring attention to avoid reduced efficacy or increased toxicity.

Major Interactions (Avoid)

• Strong CYP3A4 inhibitors (e.g., ketoconazole, itraconazole): may increase letrozole plasma concentrations.
• Estrogen replacement therapy: antagonizes the intended estrogen‑lowering effect.

Moderate Interactions (Monitor Closely)

• Moderate CYP3A4 inducers (e.g., rifampin, carbamazepine): may lower letrozole levels and reduce effectiveness.
• Anticoagulants (e.g., warfarin): letrozole may alter INR, requiring closer monitoring.
• Selective serotonin reuptake inhibitors (e.g., fluoxetine): may increase risk of QT prolongation when combined with other QT‑affecting agents.