Letrozolum Genthon (Letrozole)

Letrozole is employed in hormone‑dependent breast cancer therapy, targeting estrogen‑driven disease processes.

• Estrogen receptor‑positive breast cancer in postmenopausal women: Reduces tumor growth by lowering circulating estrogen levels.
• Adjuvant treatment of early breast cancer: Decreases risk of disease recurrence after surgery when used as part of endocrine therapy.
• Metastatic breast cancer: Helps control disease progression in advanced stages by maintaining low estrogen environment.
• Hormone receptor‑positive breast cancer (any stage): Provides systemic estrogen suppression to improve survival outcomes when combined with other agents.

• Letrozole selectively and competitively inhibits the aromatase enzyme (CYP19A1) in peripheral tissues, blocking the conversion of androstenedione and testosterone to estrone and estradiol. The inhibition is reversible and results in a marked decline in circulating estradiol, the most potent estrogen, leading to decreased activation of estrogen receptors in tumor tissue.

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

Common Side Effects

• Hot flashes: Sudden feeling of warmth, sweating, and flushing that may disrupt daily activities.
• Joint and muscle pain: Arthralgia and myalgia that can limit mobility and cause discomfort.
• Fatigue: Persistent tiredness affecting physical and mental performance.
• Nausea: Mild gastrointestinal upset that may be transient.
• Headache: Persistent head pain that can vary in intensity.
• Insomnia: Difficulty falling or staying asleep, leading to reduced rest.

Serious or Rare Side Effects

• Osteoporosis or bone fractures: Decreased bone mineral density increasing risk of fractures, especially in long‑term use.
• Severe liver dysfunction: Elevated transaminases, hepatitis, or hepatic failure requiring monitoring.
• Cardiovascular events: Thromboembolic disorders, stroke, or myocardial infarction may occur rarely.
• Allergic reactions: Rash, angioedema, or anaphylaxis demanding immediate medical attention.

When prescribing Letrozole, clinicians should consider several safety precautions to minimize risk.

• Assess bone health: Baseline DEXA scan recommended because letrozole can accelerate bone loss.
• Monitor liver function: Periodic liver enzyme tests to detect potential hepatotoxicity.
• Evaluate cardiovascular risk: Use caution in patients with prior thromboembolic events.
• Avoid use in pregnancy: Contraindicated due to teratogenic risk; pregnancy category X.
• Review concomitant medications: Check for drugs that may alter estrogen levels or CYP activity.
• Store at ambient temperature: Keep below 25°C in original packaging, protect from moisture.

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

Major Interactions (Avoid)

• Strong CYP3A4 inducers (e.g., rifampin, carbamazepine): May reduce letrozole plasma concentrations and diminish therapeutic effect.
• Estrogen‑containing therapies (hormone replacement, oral contraceptives): Counteract estrogen suppression, potentially decreasing efficacy.

Moderate Interactions (Monitor Closely)

• CYP2C19 inhibitors (e.g., fluconazole): May increase letrozole levels, requiring observation for toxicity.
• Warfarin: Potential alteration of anticoagulant effect; monitor INR closely.
• Tamoxifen: Combined endocrine therapy may affect outcomes; clinical judgment required.
• SSRIs (e.g., fluoxetine, paroxetine): May inhibit CYP enzymes affecting letrozole metabolism; monitor for increased adverse effects.