Letrozole effective for ovulation induction: Higher pregnancy rates than clomiphene. (Decreased Multiples Risk?).

ORLANDO, FLA. -- Letrozole, an aromatase inhibitor approved for treating advanced breast cancer, may soon replace clomiphene citrate as first-line therapy for ovulation induction, Canadian experts predicted.

Compared with clomiphene citrate, letrozole produces both higher pregnancy rates and fewer side effects. Importantly, letrozole also rarely stimulates more than one follicle, decreasing the risk of multiple gestations, Dr. Marinko Biljan said at the annual meeting of the American Society for Reproductive Medicine.

In a prospective, double-blind, randomized study, 25 women were randomized to receive letrozole (2.5 mg for 5 days, starting on day 3) and 24 to clomiphene citrate (100 mg for 5 days, starting on day 3). The letrozole group had a much higher pregnancy rate (16.7% vs. 5.6%), said Dr. Biljan of McGill University, Montreal, an investigator in the study.

In addition, on the day of HCG administration, the letrozole patients had a thicker endometrium (8.6 mm vs. 6.9 mm), which may have been the result of a more favorable hormonal environment, Dr. Biljan suggested.

"In patients treated with letrozole there are a number of small follicles [that are] not large enough to ovulate but large enough to contribute to estrogen production, which probably corrects the hormonal environment and increases pregnancy rates," he said.

Another advantage of letrozole is that patients experience fewer side effects while on it. "Most patients on clomiphene citrate suffer from mood swings, vaginal dryness, and hot flushes, but none of these symptoms were present in our letrozole patients. The only side effect we noticed is tiredness," he said.

In addition, letrozole rarely stimulates more than one follicle to ovulate. "This is perhaps one of the most important elements in favor of letrozole. While with clomiphene there are an increased number of eggs produced--and therefore the risk of multiple pregnancy is increased--in the letrozole group there is usually only one mature follicle, rarely two, and therefore the risk of multiple pregnancy is practically zero," Dr. Biljan ...