Letrozol Kern Pharma (Letrozole)

• Letrozole is an aromatase inhibitor used in hormone‑dependent breast cancer management.
• Postmenopausal estrogen receptor‑positive breast cancer: reduces risk of disease recurrence and progression in adjuvant therapy.
• Metastatic estrogen receptor‑positive breast cancer: provides hormonal control to delay tumor growth.
• Neoadjuvant treatment of early‑stage disease: lowers tumor size before surgery.

• Letrozole reversibly binds to the aromatase enzyme (CYP19A1) in peripheral tissues, inhibiting the conversion of androstenedione and testosterone to estrone and estradiol. By suppressing estrogen synthesis, circulating estrogen levels fall dramatically, depriving estrogen‑dependent tumor cells of growth stimulus. The inhibition is competitive and dose‑dependent, leading to sustained low estrogen concentrations during chronic therapy. The drug is absorbed orally and undergoes hepatic metabolism, with the majority excreted unchanged in urine.

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

Common Side Effects

• Hot flashes: sudden feeling of warmth and sweating.
• Joint and muscle pain: arthralgia or myalgia.
• Fatigue: persistent tiredness.
• Nausea: mild gastrointestinal upset.
• Headache: transient cranial discomfort.

Serious or Rare Side Effects

• Severe liver injury: elevated transaminases or hepatitis.
• Bone fracture: increased risk of osteoporosis‑related fractures.
• Pulmonary embolism: sudden shortness of breath and chest pain.
• QT interval prolongation: cardiac rhythm disturbances.

When prescribing Letrozole, clinicians should observe several safety considerations.

• Pregnancy contraindication: drug is teratogenic and must not be used in pregnant women (Category X).
• Premenopausal use: ineffective and not recommended in premenopausal patients.
• Bone health monitoring: assess bone mineral density periodically and consider calcium/vitamin D supplementation.
• Liver function: evaluate hepatic enzymes before initiation and monitor during treatment.
• Drug interactions: review concomitant medications that may alter letrozole metabolism.
• Store at ambient temperature: keep below 25 °C, in original container, protected from moisture and light.

Letrozole can interact with other medicines that affect its metabolism or hormonal activity.

Major Interactions (Avoid)

• Combined estrogen therapy: negates aromatase inhibition and reduces efficacy.
• Strong CYP3A4 inducers (e.g., rifampin, carbamazepine): markedly lower plasma concentrations.
• Strong CYP2C19 inhibitors (e.g., fluconazole): may increase exposure and risk of toxicity.

Moderate Interactions (Monitor Closely)

• Warfarin: letrozole may enhance anticoagulant effect; monitor INR.
• Tamoxifen: concurrent use may diminish therapeutic benefit of both agents.
• Selective serotonin reuptake inhibitors (e.g., fluoxetine): possible modest increase in letrozole levels.
• Antacids containing aluminum or magnesium: may reduce absorption if taken simultaneously.