Letrozol Sun (Letrozole)

Letrozole is an aromatase inhibitor used in the management of estrogen‑dependent breast cancer.

• Hormone receptor‑positive early‑stage breast cancer: improves disease‑free survival as adjuvant therapy.
• Hormone receptor‑positive metastatic breast cancer: delays disease progression in postmenopausal patients.
• Hormone receptor‑positive breast cancer after surgery: reduces risk of recurrence.

• Letrozole reversibly binds to the aromatase enzyme, a cytochrome P450 isoform responsible for converting androstenedione and testosterone into estrone and estradiol. By non‑steroidal inhibition of this enzyme, the drug markedly lowers circulating estrogen levels in peripheral tissues, depriving estrogen‑dependent tumor cells of a growth stimulus. The reduction in estrogen is sustained throughout the dosing interval, providing continuous hormonal suppression throughout therapy.

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

Common Side Effects

• Hot flashes: transient episodes of increased skin temperature.
• Arthralgia: joint pain or stiffness.
• Fatigue: generalized tiredness.
• Nausea: mild to moderate upset stomach.
• Headache: occasional mild headache.
• Sweating: increased perspiration.

Serious or Rare Side Effects

• Bone fracture: increased risk of osteoporosis‑related fractures.
• Deep vein thrombosis: formation of blood clots in deep veins.
• Liver enzyme elevation: signs of hepatic dysfunction.
• Severe allergic reaction: rash, swelling, or anaphylaxis.
• QT interval prolongation: potential cardiac arrhythmia.

When prescribing Letrozole, clinicians should observe several safety considerations.

• Pregnancy contraindication: avoid use in pregnant women; drug is teratogenic (Category X).
• Bone health monitoring: assess baseline bone mineral density and consider calcium/vitamin D supplementation.
• Liver function: evaluate hepatic enzymes before initiation and periodically during therapy.
• Cardiovascular risk: review patient history for thromboembolic events and monitor accordingly.
• Drug interactions: avoid concurrent estrogen therapy or strong CYP inducers without adjustment.
• Store at ambient temperature below 25°C: keep in the original pack, protect from moisture and light.

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.
• Concurrent estrogen therapy (e.g., hormone replacement): antagonizes the aromatase inhibition effect.
• Certain antifungal agents (e.g., ketoconazole): can increase exposure and risk of toxicity.

Moderate Interactions (Monitor Closely)

• Warfarin: letrozole may enhance anticoagulant effect; monitor INR.
• Tamoxifen: combined use may alter hormonal balance; assess clinical response.
• Selective serotonin reuptake inhibitors (e.g., fluoxetine): may affect metabolism; observe for side‑effects.
• Thyroid hormone replacement: monitor thyroid function tests as estrogen changes can influence dosage.