Out of all the women who are treated with these drugs, 60-80% will ovulate, but only half of those will become pregnant.
The fertility drugs Clomiphene Citrate (Clomid) and Letrozole (Femara) are both used by women with cycle abnormalities and are prescribed to help the pituitary gland improve stimulation of developing follicles, or eggs, in the ovaries. Both these drugs are pills that stimulate the release of FSH and LH, which are crucial hormones to egg production.
“Both these drugs have decent success rates, and there are reasons to use both,” said Dr. Randall R. Odem, Division Chief of Reproductive Endocrinology at Washington University School of Medicine in St. Louis. “The results are not dramatically different.”
History
Clomid has been used over 40 years to restore ovulation and correct fertility problems and is known as “the fertility pill.” Clomid fools the body into thinking its estrogen levels are low. As opposed to Femera, the drug has a consistent success rate and longstanding history.
Femara is much newer and was developed primarily for the treatment of women with post-menopausal breast cancer, not fertility issues, and blocks estrogen production. Femara is considered an aromatase inhibitor that reduces the production of estrogen, which causes the brain to secrete FSH and LH. Femara is not FDA approved to use for fertility, but its generic, Letrozole, has been used successfully for it quite often.
“I don't foresee Femara being FDA approved for fertility use because approval is so expensive and the money spent on it would be lost income because people already use it in its off-brand for fertility,” explained Dr. Odem.
Out of all the women who are treated with these drugs, 60-80% will ovulate, but only half of those will become pregnant. If a pregnancy doesn't happen by three to four cycles, additional testing is suggested for other factors that would contribute to the infertility.
Between 10-20% of women have potential side effects to these drugs such as hot flashes, blurred vision, bloating sensation, nausea, headache, or mood disturbances.
“Typically, there are not many side effects for many women, but I have seen more from Clomid,” said Dr. Odem. “Some have reported pretty bothersome mood changes in the second half of a cycle. Hot flashes are another common complaint but are seen more often in Clomid.”
There is no clinically significant increased risk of birth defects or miscarriage for women on these drugs unless they have polycystic ovary syndrome, and then their risk for miscarriage may increase.
Multiple Births
The multiple pregnancy rate for both drugs is as high as 10%, with triplets being 1/400 and quads 1/800.
Since there is only a 20-25% chance of conception occurring each cycle during the first three to four cycles, four to six cycles are needed to consider it an adequate trial.
“The high incidence of multiple births is very real,” said Dr. Odem. “With Clomid, it's 8% for twins and 1% percent for triplets. There's not a lot of data yet on Letrozole, but it's probably similar. That rate is three times higher with injectables though.”
There is no clinically significant increased risk of birth defects or miscarriage for women on these drugs unless they have polycystic ovary syndrome, and then their risk for miscarriage may increase.
“It's not a big concern with this; their chances are the same as a woman not on these drugs,” confirmed Dr. Odem. “Birth defects are really hard to sort out—what's attributed to the drugs, what's attributed to the patient's health, etc. The rates aren't enough to scare people.”
Other Risks
Clomid and Letrozole have been associated with the occasional development of ovarian cysts, but they usually are not serious and resolve on their own. There has been talk of the drugs having adverse effects such as ovarian cancer with long-term (more than 12 cycles) use, but this may be due to older data sources.
“I don't even include this factor in my discussions with patients because the data doesn't support it,” assured Dr. Odem. “It is not as worrisome as old data suggests.”
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