Letrozol Normon (Letrozole)

• Letrozole is an aromatase inhibitor used in the management of estrogen‑dependent breast cancer.
• Postmenopausal hormone‑receptor positive breast cancer: reduces estrogen levels to inhibit tumor growth.
• Adjuvant therapy after surgery: helps prevent disease recurrence in eligible patients.
• Metastatic breast cancer: provides systemic control of disease progression in postmenopausal women.
• Neoadjuvant therapy: may be employed to shrink tumors prior to surgery in postmenopausal patients.

• Letrozole acts by reversibly binding to the aromatase enzyme, a cytochrome P450 isoform responsible for converting adrenal and peripheral androstenedione and testosterone into estrone and estradiol. By inhibiting this conversion, systemic estrogen concentrations fall markedly, depriving estrogen‑dependent tumor cells of a growth stimulus. The inhibition is dose‑dependent and persists for the duration of drug exposure, allowing sustained suppression of estrogen production in postmenopausal patients.

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

Common Side Effects

• Hot flashes: sudden feeling of warmth and sweating.
• Joint and muscle pain: arthralgia or myalgia.
• Fatigue: persistent tiredness.
• Nausea: mild to moderate upset stomach.
• Headache: occasional throbbing pain.
• Insomnia: difficulty sleeping.

Serious or Rare Side Effects

• Severe bone loss: increased risk of osteoporosis and fractures.
• Cardiovascular events: rare cases of thromboembolic disease.
• Liver function abnormalities: elevated transaminases.
• Allergic reactions: rash, angioedema, or anaphylaxis.

• When prescribing Letrozole, clinicians should observe several precautionary measures to ensure patient safety.
• Assess bone health: evaluate baseline bone mineral density and consider calcium/vitamin D supplementation.
• Monitor liver function: perform periodic hepatic enzyme tests during therapy.
• Check cardiovascular risk: review history of thromboembolic disease before initiation.
• Avoid use in pregnancy: drug is contraindicated in pregnant women (Category X).
• Drug interactions: review concomitant medications for potential CYP2A6 substrates.
• Store at ambient temperature: keep below 25 °C, in original packaging, protected from moisture.

Letrozole can affect the pharmacokinetics of other medicines; relevant interactions are categorized by clinical significance.

Major Interactions (Avoid)

• Strong CYP2A6 inhibitors (e.g., ketoconazole): may increase letrozole plasma levels, raising toxicity risk.
• Estrogen‑containing therapies (e.g., hormone replacement): counteract letrozole’s estrogen suppression, reducing efficacy.

Moderate Interactions (Monitor Closely)

• Tamoxifen: combined use may alter hormonal balance; monitor patient response.
• Anticoagulants (e.g., warfarin): letrozole may enhance anticoagulant effect; check INR regularly.
• CYP2A6 inducers (e.g., rifampicin): may lower letrozole concentrations, potentially decreasing effectiveness.