Letrozin (Letrozole)

Letrozin, an aromatase inhibitor, is indicated for conditions driven by estrogen signaling in breast cancer.

• Estrogen receptor‑positive breast cancer in postmenopausal women: lowers estrogen production to inhibit tumor growth.
• Adjuvant treatment of early breast cancer: reduces risk of disease recurrence after surgery.
• Metastatic breast cancer: helps control disease progression in advanced cases.

• Letrozole reversibly binds to the aromatase enzyme, a non‑steroidal inhibitor that blocks the conversion of androgens to estrogens in peripheral tissues. By reducing circulating estrogen levels, it deprives estrogen‑dependent tumor cells of a growth stimulus, thereby slowing or halting cancer progression.

Adverse reactions may vary in frequency and severity.

Common Side Effects

• Hot flashes: sudden feeling of warmth.
• Joint pain: aching or stiffness in joints.
• Fatigue: persistent tiredness.
• Nausea: mild to moderate upset stomach.
• Headache: tension or throbbing pain.
• Dizziness: light‑headed sensation.

Serious or Rare Side Effects

• Severe liver injury: elevated enzymes or jaundice.
• Pulmonary embolism: sudden shortness of breath.
• Deep vein thrombosis: leg swelling and pain.
• Bone fracture: increased risk due to reduced estrogen.
• Allergic reaction: rash, swelling, or anaphylaxis.
• Elevated cholesterol: changes in lipid profile.

Patients should be monitored for specific safety considerations before and during therapy.

• Bone health: assess bone mineral density regularly.
• Liver function: perform baseline and periodic liver enzyme tests.
• Cardiovascular risk: evaluate history of thrombosis or clotting disorders.
• Hot flashes: counsel on lifestyle measures to mitigate.
• Premenopausal status: avoid use in women who are not postmenopausal.
• Store at room temperature: keep in the original container, protect from moisture and direct sunlight.

Letrozin may interact with other medicines, requiring attention to avoid reduced efficacy or increased toxicity.

Major Interactions (Avoid)

• Tamoxifen: antagonistic effect on estrogen blockade.
• Strong CYP3A4 inducers (e.g., rifampin, carbamazepine): may lower letrozole levels.
• Estrogen‑containing hormone therapy: counteracts intended estrogen suppression.
• Certain anticonvulsants (e.g., phenytoin): reduce drug exposure.
• Antifungal agents that inhibit CYP3A4 (e.g., ketoconazole): may increase exposure.

Moderate Interactions (Monitor Closely)

• Warfarin: potential alteration of anticoagulant effect.
• SSRIs (e.g., fluoxetine): may affect metabolism.
• NSAIDs: increased risk of gastrointestinal irritation.
• Cholesterol‑lowering statins: monitor lipid changes.
• Thyroid hormone replacement: assess thyroid function periodically.