Letrozole
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| Trade names | Femara |
| AHFS/Drugs.com | Monograph |
| MedlinePlus | a698004 |
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| Routes of administration |
By mouth (tablets) |
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| Pharmacokinetic data | |
| Bioavailability | 99.9% |
| Protein binding | 60%, mainly to albumin |
| Metabolism | pharmacologically-inactive carbinol metabolite (4,4΄-methanol-bisbenzonitrile) |
| Biological half-life | 2 days |
| Excretion | Kidneys |
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| ECHA InfoCard | 100.200.357 |
| Chemical and physical data | |
| Formula | C17H11N5 |
| Molar mass | 285.303 g/mol |
| 3D model (Jmol) | |
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Letrozole (INN, trade name Femara) is an oral non-steroidal aromatase inhibitor for the treatment of hormonally-responsive breast cancer after surgery.
Letrozole is approved by the United States Food and Drug Administration (FDA) for the treatment of local or metastatic breast cancer that is hormone receptor positive or has an unknown receptor status in postmenopausal women.
Letrozole has been used for ovarian stimulation by fertility doctors since 2001 because it has fewer side-effects than clomiphene (Clomid) and less chance of multiple gestation. A study of 150 babies following treatment with letrozole or letrozole and gonadotropins presented at the American Society of Reproductive Medicine 2005 Conference found no difference in overall abnormalities but did find a significantly higher rate of locomotor and cardiac abnormalities among the group having taken letrozole compared to natural conception. A larger, follow-up study with 911 babies compared those born following treatment with letrozole to those born following treatment with clomiphene. That study also found no significant difference in the rate of overall abnormalities, but found that congenital cardiac anomalies was significantly higher in the clomiphene group compared to the letrozole group. Despite this, India banned the usage of letrozole in 2011, citing potential risks to infants. In 2012, an Indian parliamentary committee said that the drug controller office colluded with letrozole's makers to approve the drug for infertility in India and also stated that letrozole's use for infertility was illegal worldwide; however, such off-label uses are legal in many countries such as the US and UK.
The anti-estrogen action of letrozole has been shown to be useful in pretreatment for termination of pregnancy, in combination with misoprostol. It can be used in place of mifepristone, which is expensive and unavailable in many countries.
Letrozole is sometimes used as a treatment for gynecomastia, although it is probably most effective at this if caught in an early stage (such as in users of anabolic steroids).
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Wikipedia