Classifications: antineoplastic; aromatase inhibitor;
Therapeutic: antineoplastic
; aromatase inhibitor
Prototype: Anastrozole
Pregnancy Category: D


2.5 mg tablets


Nonsteroid competitive inhibitor of aromatase, the enzyme that converts androgens to estrogens. It does not inhibit adrenal steroid synthesis.

Therapeutic Effect

Results in the regression of estrogen-dependent tumors.


Advanced breast cancer in postmenopausal women following antiestrogen therapy, first-line treatment of locally advanced or metastasized breast cancer in postmenopausal women.


Hypersensitivity to letrozole; pregnancy (category D), pregnant women, women of childbearing age, premenopausal females, hormone replacement therapy (HRT).

Cautious Use

Moderate to severe hepatic impairment; lactation. Safety and efficacy in children are not established.

Route & Dosage

Breast Cancer
Adult: PO 2.5 mg q.d.

Hepatic Impairment
Reduce the dose in severe hepatic impairment (Child-Pugh C class) by 50%.


  • Give without regard to food.

Adverse Effects (≥1%)

Body as a Whole: Fatigue, peripheral edema, asthenia, weight increase, musculoskeletal pain, arthralgia. CNS: Headache, somnolence, dizziness. CV: Chest pain, hypertension, hypercholesterolemia. GI: Nausea, vomiting, constipation, diarrhea, abdominal pain, anorexia, dyspepsia. Respiratory: Dyspnea, cough. Skin: Hot flushes, rash, pruritus.


Drug: estrogens, oral contraceptives could interfere with the pharmacologic action of letrozole.


Absorption: Rapidly absorbed from GI tract. Metabolism: In liver by cytochromes P450 3A4 and 2A6. Elimination: 90% in urine. Half-Life: 2 d.

Nursing Implications

Assessment & Drug Effects

  • Lab tests: Periodically monitor serum calcium and CBC with differential.
  • Monitor carefully for S&S of thrombophlebitis or thromboembolism; report immediately.

Patient & Family Education

  • Notify physician immediately if S&S of thrombophlebitis develop (see Appendix F).

Common adverse effects in italic, life-threatening effects underlined; generic names in bold; classifications in SMALL CAPS; Canadian drug name; Prototype drug

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