Likarda (Letrozole)

Letrozole is used in the management of estrogen‑dependent breast cancer, targeting hormone‑responsive disease states.

• Early‑stage hormone receptor‑positive breast cancer: reduces risk of recurrence when given as adjuvant therapy.
• Metastatic estrogen‑dependent breast cancer: slows disease progression in post‑menopausal patients.
• Neoadjuvant therapy for locally advanced breast cancer: decreases tumor size before surgery.

• Letrozole selectively inhibits the aromatase enzyme (CYP19A1), which converts adrenal and peripheral androgens into estrone and estradiol. By blocking this conversion, systemic estrogen concentrations fall markedly, depriving estrogen‑dependent tumor cells of growth stimulus. The inhibition is reversible and dose‑dependent, leading to sustained suppression of estrogen synthesis while preserving other steroid pathways.

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

Common Side Effects

• Hot flashes: sudden feeling of warmth, often with sweating and reddening of the skin.
• Joint and muscle pain: aching or stiffness in joints and muscles, commonly reported as arthralgia or myalgia.
• Fatigue: persistent sense of tiredness that is not relieved by rest.
• Nausea: mild to moderate upset stomach, sometimes accompanied by loss of appetite.

Serious or Rare Side Effects

• Osteoporosis: significant loss of bone mineral density increasing fracture susceptibility.
• Severe cardiovascular events: occurrence of blood clots, heart attack, or stroke.
• Liver dysfunction: elevated liver enzymes, hepatitis, or jaundice indicating hepatic injury.

When prescribing Letrozole, clinicians should consider several precautionary measures to ensure patient safety.

• Bone health monitoring: assess baseline bone mineral density and consider calcium/vitamin D supplementation.
• Cardiovascular assessment: evaluate risk factors for thrombosis and heart disease before initiation.
• Liver function testing: perform baseline and periodic liver enzyme tests.
• Drug interactions: review concomitant medications that may affect estrogen levels.
• Pregnancy and lactation: avoid use in pregnant or breastfeeding women due to unknown risks.
• Store at ambient temperature: keep tablets below 25 °C in the original container, protected from moisture.

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

Major Interactions (Avoid)

• Tamoxifen: concurrent use may reduce therapeutic benefit of both agents.
• Estrogen‑containing hormone therapy: antagonizes letrozole’s estrogen‑lowering effect.
• Strong CYP3A4 inducers (e.g., rifampin, carbamazepine): may decrease letrozole plasma concentrations.

Moderate Interactions (Monitor Closely)

• Anticoagulants (warfarin): increased bleeding risk; monitor INR.
• SSRIs/SNRIs (e.g., fluoxetine): may affect hormone metabolism; observe for side effects.
• Cholesterol‑lowering agents (statins): potential for altered metabolism; check liver function.