Letrozole Arrow Lab (Letrozole)

• Letrozole acts on estrogen‑dependent breast cancer pathways, providing therapeutic benefit in hormone‑responsive disease.
• Postmenopausal estrogen receptor‑positive breast cancer (adjuvant): reduces risk of recurrence and improves disease‑free survival.
• Metastatic hormone‑receptor positive breast cancer: slows disease progression and prolongs overall survival.
• Neoadjuvant therapy for locally advanced breast cancer: facilitates tumor shrinkage before surgery.

• Letrozole selectively binds to and inhibits the aromatase enzyme, which converts androstenedione and testosterone into estrone and estradiol, respectively. By blocking this conversion, systemic estrogen levels decline markedly, depriving estrogen‑dependent tumor cells of a growth stimulus. The inhibition is reversible and dose‑dependent, leading to sustained suppression of estrogen synthesis throughout treatment. The drug’s high affinity for the enzyme’s active site ensures effective inhibition even at low plasma concentrations, and its oral bioavailability allows convenient daily dosing.

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

Common Side Effects

• Hot flashes: transient warmth and sweating.
• Joint pain: arthralgia or stiffness.
• Fatigue: persistent tiredness.
• Nausea: mild gastrointestinal upset.
• Headache: mild to moderate intensity.
• Dizziness: occasional light‑headedness.

Serious or Rare Side Effects

• Severe liver injury: elevated transaminases or hepatitis.
• Bone fracture: increased risk of osteoporosis‑related breaks.
• Deep vein thrombosis: clot formation in veins.
• Pulmonary embolism: blockage of pulmonary arteries.
• Allergic reaction: rash, angioedema or anaphylaxis.
• QT prolongation: cardiac rhythm disturbance.

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

• Bone health monitoring: assess baseline bone mineral density and consider calcium/vitamin D supplementation.
• Liver function monitoring: check hepatic enzymes before initiation and periodically during therapy.
• Cardiovascular assessment: evaluate risk factors for thrombosis and monitor for signs of clotting.
• Premenopausal use avoidance: contraindicated in women with active ovarian function.
• Hypersensitivity caution: discontinue if severe allergic reactions occur.
• Store at ambient temperature: keep below 25 °C in original packaging, protect from moisture and light.

Letrozole interacts with several medicines; awareness of these interactions helps maintain therapeutic effectiveness.

Major Interactions (Avoid)

• Strong CYP3A4 inducers: rifampin, carbamazepine, phenytoin may markedly reduce letrozole exposure.
• Estrogen‑containing hormone therapy: concurrent use antagonizes letrozole’s anti‑estrogen effect.
• Live vaccines: reduced efficacy when administered during letrozole therapy.

Moderate Interactions (Monitor Closely)

• CYP2C19 inhibitors: fluconazole or omeprazole can increase letrozole plasma levels.
• Anticoagulants: warfarin may have enhanced anticoagulant effect; monitor INR.
• Diuretics: may alter electrolyte balance; observe renal function.
• Antidepressants (SSRIs): potential for modest increase in side‑effect profile; assess tolerability.