Femara (letrozole), marketed by Novartis, is a medication primarily used to treat breast cancer in postmenopausal women.

It can also be used in endometriosis to inhibit the growth of endometriotic lesions and to reduce endometriosis-related pain.

How Femara works

During the menstrual cycle, estrogen promotes the thickening of the endometriotic lining in the uterus. Similarly, the hormone also stimulates the growth of endometriotic lesions outside the uterus.

Enzymes called aromatases convert estrogen precursor hormones called androgens into active estrogen. Femara inhibits aromatases and thereby decreases the level of estrogen.

Femara in clinical trials for endometriosis

In a randomized controlled clinical trial, 51 women with endometriosis who had undergone laparoscopic surgery were treated for four months with either Femara in addition to an oral contraceptive pill (OCP) or with an OCP alone. The OCP contained 0.15 mg levonorgestrel and 0.03 mg ethinyl estradiol and was taken daily. Femara was dosed at 2.5 mg per day. Both groups also received 400 IU Vitamin D and 1 g calcium per day.

Dyspareunia (painful intercourse), dysmenorrhea (pain during menstruation), and pelvic pain improved significantly in both groups after four months of treatment. OCP in combination with Femara was, however, not more effective in treating endometriosis-related pain than an OCP alone.

In another randomized clinical trial, 105 endometriosis patients were randomly assigned to receive either 2.5 mg oral Femara, 600 mg oral danazol, another medication used to treat endometriosis, or a placebo. All three groups also received 1,000 mg calcium and 800 IU vitamin D per day.

Out of 31 patients in the placebo group, 22 did not complete the study because of pelvic pain and dysmenorrhea. After five months of treatment, participants in the Femara and danazol group had lower chronic pelvic pain, dyspareunia, and dysmenorrhea than the placebo group. Chronic pelvic pain and dyspareunia were lowest in patients who had received Femara.

In a randomized study, 144 infertile women with endometriosis underwent laparoscopic surgery during which endometriotic lesions in the pelvis were removed. Following the surgery, the women were allocated 2.5 mg of Femara per day for two months, intramuscular injections of 3.75 mg triptorelin at an interval of four weeks, or no treatment.

After a treatment period of two months, the participants were followed up at three-month intervals for one year to evaluate their rate of pregnancy and endometriosis recurrence. Recurrence was defined as the return of dyspareunia, dysmenorrhea, and pelvic pain.

The recurrence rate was 6.4 percent in the Femara group, 5 percent in the triptorelin group, and 5.3 percent in the group without treatment. The pregnancy rate was 23.4 percent in the Femara group, 27.5 percent in the triptorelin group, and 28.1 percent in the group with no treatment. The differences were not statistically significant.

In a randomized trial including 35 women with endometriosis, all participants were treated with 2.5 mg of Famara per day for six months. They were randomized to receive either 2.5 mg oral norethisterone acetate (an inhibitor of ovulation) or intramuscular injections of 11.25 mg triptorelin every three months in addition to Femara.

In the norethisterone acetate group, 64.7 percent of women rated the treatment as satisfactory or very satisfactory, compared to 22.2 percent in the triptorelin group. Non-menstrual pelvic pain and dyspareunia significantly decreased in both groups, but there was no significant difference between the groups. The reduction in the volume of endometriotic lesions was significantly greater in the triptorelin group than in the norethisterone acetate group. Adverse events were reported in 77.8 percent of women in the triptorelin group and 35.3 percent in the norethisterone acetate group. In the triptorelin group, 44.4 percent interrupted treatment due to adverse events, compared to 5.9 percent in the norethisterone acetate group. The differences were statistically significant.

Additional information

Common side effects of Femara include fatigue, hypertension, sleeping difficulties, pain in the joints and muscles, and depression.


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