|
What is Letrozole?
The new aromatase inhibitor, Letrozole, reversibly, inhibits the enzyme responsible
for estrogen biosynthesis. By decreasing the estrogen levels in the body it may release the hypothalamus and/or pituitary
from the negative feed back of estrogen on the release of gonadotropins. This will result in an increase in endogenous FSH
and LH, which stimulate the development of ovarian follicles. This is similar to the proposed mechanism of action of clomiphene
citrate. However, Letrozole may have another peripheral mechanism of action directly in the ovaries. Letrozole is eliminated
from the body in a few days after last administration (in contrast to CC which may last up to few months). Also, it does not
have a direct antiestrogen action by itself as in CC. So there should be no unwanted peripheral antiestrogen effects on the
endometrium, the cervix…etc.
The commercial name of Letrozole is Femara. It is available in 2.5 & 5 mg tablets.
It is a drug that was developed to inhibit the estrogen production in postmenopausal women with breast cancer. We are not
using it as a chemotherapy drug. It has been tested and tolerated very well when administered continuously for several months.
Who is a candidate for Letrozole?
Patients who meet one or more of the following criteria may be offered the
option of trying Letrozole for induction of ovulation:
• Failure to ovulate on clomiphene citrate.
•
Ovulation with clomiphene citrate but with very thin endometrium (less than 0.5 cm)
• Ovulation with clomiphene
citrate with failure to achieve pregnancy after 6 cycles.
• Severe side effects with clomiphene citrate.
The
classical alternative in the above-mentioned conditions would be FSH injections. This option will be discussed with the patient
first. Considering the higher expenses and inconvenience of daily injections with possible severe hyperstimulation, Letrozole
may be a safe and acceptable drug to try.
What are the possible side effects?
Usually mild in the form of headache,
mild gastrointestinal upsets, hot flushes and easy fatigue.
|
 |
|
