Aromatase inhibitors

An aromatase inhibitors is a drug that inhibits the production of estrogen in the ovaries. Commonly, this drug is used in women who have been treated for breast cancer. In some women who have had breast cancer, natural levels of estrogen increases the risk that the disease will return (recur) or worsen.

An aromatase inhibitor can also be used in infertility to stimulate ovulation in women with ovulation disturbances (anovulation). The most common cause of ovulation disturbances is  PCOS.

The commonly used drug is available by prescription only as tablets in the strength 2.5 milligrams. The smallest package size contains 30 tablets.

How does aromatase inhibitors induce ovulation?

Aromatase inhibitors inhibit the production of estrogen in the ovaries. By giving this for a short period at the beginning of the menstrual cycle, estrogen levels are temporarily reduced. This leads to the release of higher levels of follicle stimulating hormone, FSH, from the pituitary gland in the brain. FSH stimulates the follicles in the ovary to grow and mature so ovulation can occur. FSH also stimulates the ovaries to produce estrogen, which is needed for uterine lining (endometrium) to develop. The drug has a short duration and is removed quickly from the body. After stopping with it, estrogen levels quickly return to normal. The endometrium can then develop normally.

If the drug works as intended, ovulation will usually occur around a week after the last tablet is taken. You can check for yourself that ovulation occurs by using ovulation tests available at the pharmacy. In order to become pregnant, it is important to have intercourse at the time around ovulation.

Ovulation stimulation increases the likelihood of having twins or triplets (also called multiple pregnancy). However, the risk of multiple pregnancy with an aromatase inhibitor is low. To reduce the risk of multiple pregnancy, usually the treatment will be monitored to determine how the ovaries react to the medicine to check that only one egg matures.

If you do not get pregnant, menstrual bleeding will usually start within one month after the last tablet. If you do not have any bleeding you should do a pregnancy test. Another reason no bleeding occurs can be that the treatment has not worked and ovulation not occurred.

Individually tailored dosage

A prescription drug has a dosage that is tailored to the person who will be using the medicine. Therefore, it is always very important to follow the instructions printed on the label on the medicine package. This dosage gives you the best possible results of the treatment while reducing the risk of side effects.

The stimulation treatment begins on the third day of menstruation. The dose is usually 1 tablet (2.5 mg) a day for five days (cycle day 3-7).

Has the treatment worked?

To determine how the ovaries react and how many follicles are maturing, an ultrasound examination is usually done on cycle day 12-13. To see if and when ovulation occurs, you can buy ovulation tests at the pharmacy and monitor your ovulation yourself. If no ovulation occurs after the first treatment, one can try again the following month with an increased dosage (usually 2 tablets (5 mg) daily for 5 days). Change in dosage is made in consultation with your physician.

If you ovulate after the treatment cycle but do not get pregnant, you can begin a new cycle using the same dose. If no pregnancy occurs after three to six treatments, you may need to switch to another type of treatment.

Are there risks with aromatase inhibitors?

It is safe and easy to use the aromatase inhibitor you have been prescribed. Since it is an adjuvant treatment for cancer, this may seem unappealing; however, it does not have any effect or side effect associate with such treatment. The only effect of inhibiting aromatase in ovulation stimulation treatment is a quite brief and transient reduction in the level of estrogen. This reduction causes a follicle to develop and ovulation to occur. Common, but generally mild and transient side effects include nausea, sweating and headaches.

Previous studies indicate a possible association of aromatase inhibitors with birth defects but have not been substantiated in further studies.

Because aromatase inhibitors reduces the estrogen levels, this medication should not be take longer than prescribed. It should not be used during pregnancy.

For further information about ovulation stimulation treatment, click here.