Letrozol Bluefish (Letrozole)

Letrozole is an aromatase inhibitor indicated for hormone‑driven breast cancer.

• Hormone receptor‑positive breast cancer (postmenopausal): reduces estrogen production to inhibit tumor growth.
• Adjuvant therapy for early‑stage disease (postmenopausal): lowers risk of cancer recurrence after surgery.
• Metastatic breast cancer (postmenopausal): helps control disease progression by sustaining low estrogen levels.
• Neoadjuvant treatment (postmenopausal): shrinks tumor size before surgical resection by suppressing estrogen.

• Letrozole selectively binds to the aromatase enzyme, which converts androstenedione and testosterone into estrone and estradiol in peripheral tissues. By competitively inhibiting this cytochrome P450‑dependent enzyme, the drug markedly reduces circulating estrogen levels. The resulting hypo‑estrogenic state deprives estrogen‑dependent breast cancer cells of a growth stimulus, thereby slowing proliferation and inducing apoptosis. The inhibition is dose‑dependent and persists for several days after the last dose, providing sustained estrogen suppression.

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

Common Side Effects

• Hot flashes: transient episodes of warmth, sweating, and reddening of the skin.
• Joint and muscle pain: arthralgia and myalgia that may limit mobility.
• Fatigue: persistent tiredness not relieved by rest, affecting daily activities.
• Nausea: mild to moderate upset stomach, sometimes accompanied by loss of appetite.

Serious or Rare Side Effects

• Deep vein thrombosis: formation of blood clots in deep veins, usually in the legs.
• Pulmonary embolism: blockage of lung arteries by a clot, causing sudden shortness of breath.
• Severe liver injury: marked elevation of liver enzymes, hepatitis, or liver failure.

When prescribing Letrozole, several safety considerations should be observed to minimize risk.

• Assess bone health: evaluate baseline bone mineral density and consider calcium/vitamin D supplementation.
• Monitor lipid profile: check cholesterol levels periodically during therapy.
• Check liver function: perform baseline and periodic liver enzyme tests.
• Avoid use in pregnancy: contraindicated due to teratogenic risk; ensure effective contraception in women of childbearing potential.
• Review drug interactions: assess concomitant medications that may affect estrogen metabolism.
• Store at ambient temperature: keep below 25 °C in original packaging, protect from moisture and light.

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

Major Interactions (Avoid)

• Strong CYP3A4 inducers (e.g., rifampin, carbamazepine): may reduce plasma concentrations of Letrozole.
• Estrogen‑containing hormone therapy: antagonizes Letrozole’s estrogen‑lowering effect.
• Tamoxifen: combined use may increase risk of thromboembolic events.

Moderate Interactions (Monitor Closely)

• CYP2C19 inhibitors (e.g., fluoxetine, fluvoxamine): may increase Letrozole exposure.
• Anticoagulants (e.g., warfarin): enhanced anticoagulant effect, monitor INR.
• Cholesterol‑lowering agents (e.g., statins): possible additive effect on lipid profile.