Likarda (Letrozole)

Letrozole is used in breast‑cancer management by reducing estrogen production, a key driver of hormone‑dependent tumors.

• Postmenopausal hormone receptor‑positive breast cancer: decreases recurrence risk and improves survival.
• Adjuvant treatment of early‑stage breast cancer: lowers the chance of disease return after surgery.
• Metastatic breast cancer: slows disease progression and extends overall survival.

• Letrozole reversibly binds to the aromatase enzyme, blocking the conversion of androgens to estrogens in peripheral tissues. This inhibition markedly reduces circulating estrogen levels, depriving estrogen‑dependent tumor cells of a growth stimulus and thereby limiting tumor proliferation.

Adverse reactions may vary in frequency and severity.

Common Side Effects

• Hot flashes
• Joint and muscle pain
• Fatigue
• Nausea
• Headache
• Dizziness

Serious or Rare Side Effects

• Liver toxicity (elevated transaminases)
• Severe bone loss leading to fractures
• Pulmonary embolism
• Myocardial infarction or other cardiovascular events
• Anaphylactic or severe allergic reactions
• QT interval prolongation on ECG

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

• Bone health monitoring: assess bone mineral density regularly.
• Liver function assessment: check hepatic enzymes prior to initiation and periodically thereafter.
• Cardiovascular evaluation: review history of thromboembolic disease or cardiac risk factors.
• Pregnancy avoidance: contraindicated in pregnancy; ensure effective contraception.
• Drug interaction review: evaluate concomitant medications that affect CYP2C19 or CYP3A4.
• Store at room temperature: keep in the original container, protect from moisture and direct sunlight.

Letrozole may interact with other medicines that influence its metabolism or hormonal effects.

Major Interactions (Avoid)

• Estrogen replacement therapy: may counteract letrozole’s aromatase inhibition.
• Strong CYP2C19 inhibitors (e.g., fluconazole): can increase letrozole plasma levels.
• Strong CYP3A4 inhibitors (e.g., ketoconazole): may raise exposure and toxicity risk.

Moderate Interactions (Monitor Closely)

• CYP2C19 inducers (e.g., rifampin): may reduce therapeutic effectiveness.
• Warfarin: letrozole can alter INR, requiring closer coagulation monitoring.
• Statins metabolized by CYP3A4: monitor for increased statin-related adverse effects.