Femara, brand name for letrozole, inhibits aromatase, an enzyme essential for estrogen production. Femara is FDA-approved to block estrogen production in estrogen-sensitive cancers but is also prescribed off-label to stimulate the ovaries for fertility treatments. Reducing estrogen levels with aromatase-inhibitors prevents the negative feedback from rising estradiol that normally blocks follicle stimulating hormones. Because production of follicle stimulating hormone is sustained, ovarian stimulation is increased. Femara's episodic use in fertility treatment results in short duration side effects.
Hot Flashes
Hot flashes are one possible side effect when Femara is used for infertility. Hot flashes are experienced as a brief sensation of heat on the upper body. It can also occur all over the body. Hot flashes can last between 30 seconds and 10 minutes and can cause skin to become flushed and red-looking. The hot sensation can be followed by sweating and chills and can occur at night or during the day. These menopause-like symptoms are likely caused by the reduction in estrogen levels from the aromatase-inhibiting action of Femara.
Headaches
Headaches are another common symptom reported by patients using Femara for fertility treatments. According to WomensHealth.gov, changes in hormonal levels such as lowered estrogen levels can cause blood vessels in the brain to become inflamed. The inflammation may cause blood vessels in the brain to swell and press on nearby nerves, causing severe headaches or migraines.
Breast Tenderness
Femara used for fertility treatments can cause premenstrual or menopausal-like symptoms due to Femara's action of lowering estrogen levels relative to progesterone. Breast tenderness is a common side effect of hormonal fluctuations experienced monthly or during menopause and can be temporarily induced by the use of aromatase inhibitors, including Femara. Breast tenderness can be experienced as any combination of symptoms including swollen breasts, sore breasts, increased sensitivity to touch and pressure, dull, heavy or aching sensation in the breasts, discomfort with movement and pain and aches while sleeping.
Controversial Side Effect
Novartis, the manufacturer of Femara came out with a warning that Femara should not be used during pregnancy because of concerns that it could cause birth defects. Some physicians have interpreted this warning to mean that Femara should not be used for fertility treatments. According to Dr. Randy Morris, MD, of IVF1 fertility program, a distinction must be made between using Femara for fertility treatments prior to establishing a pregnancy and using Femara once a pregnancy is established. There are no reports of birth defects occurring from the use of Femara for fertility treatments.
As of 2010, Serono, a competing pharmaceutical company, began conducting clinical trials specifically on fertility treatments using another aromatase inhibitor to submit and win FDA approval for the use of aromatose inhibitors in fertility treatments.
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