What Factors Affect a Sufficient Letrozole Dose?

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  • Written By: Canaan Downs
  • Edited By: Kaci Lane Hindman
  • Last Modified Date: 21 November 2019
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The non-steroidal aromatase inhibitor letrozole is a post-operative medication used to treat hormonally-responsive breast cancers. Sometimes known as Femara®, this medication works by blocking the production of estrogens through interfering with a binding site on the aromatase molecules that are necessary for its manufacture. Due to its low incidence of side effects, it is also occasionally used off-label to increase fertility in women by stimulating ovulation. When used to treat ovulation or for people with a dysfunctional liver, a significantly lower letrozole dose is needed. Other off-label uses for letrozole include treating endometriosis, increasing sperm count in men, treating breast growth in men, and improving the development of children with growth disorders. As of 2011, however, no official dosage recommendation exists for these unapproved uses.

Letrozole is often used as a therapeutic adjunct after five years of tamoxifen treatment, particularly in the treatment of early breast cancer in post-menopausal women. For this application, a letrozole dose of just 2.5 mg administered orally once a day is recommended. In 2011, there is currently no conclusive research as to how long this drug regimen must be continued for it to prevent relapse. If a relapse occurs, letrozole use should be discontinued.


In cases where the breast cancer diagnosis is of a hormone receptor positive, hormone receptor unknown metastatic, or locally advanced cancer, letrozole may be indicated as a first-line therapy. A letrozole dose of 2.5 mg administered orally once every 24-hour period is considered to be standard for this application. It is also recommended in the treatment of advanced cancer in patients with disease progression post anti-estrogenic therapy. Use of this medication should be discontinued thought if tumor development is discovered.

Patients with with cirrhosis and severe hepatic dysfunction should be given a lower letrozole dose since the liver may not process the drug as efficiently as in other patients. Instead, a letrozole dose of 2.5 mg should be given every other day. Hormone levels should then be closely monitored to determine the efficacy of the drug. No dosage adjustments are required, however, for patients with reduced kidney function.

The use of this medication does carry some risks. Some of the potential side effects of letrozole use are night sweats, hot flashes, muscle and joint pain, weakness and fatigue, nausea, vomiting, rashes, dizziness, swelling of the extremities, constipation, diarrhea, loss of appetite, or vaginal bleeding. Other side effects include irritation, sleep disturbance, difficulty staying awake, breast pain, difficult or painful urination, cough and flu-like symptoms, and stomach pain. The use of letrozole may affect bone density and increase the risk of osteoporosis. If chest pain or difficulty breathing devlop, patients should discontinue use immediately, as this may indicate a more serious condition.


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