Controversy hits letrozole warning.(News)

Letrozole safely and effectively induces ovulation, according to the findings of a retrospective study of data from five Canadian fertility centers.

The recent findings contradict an earlier report presented at last year's conjoint annual meeting of the American Society for Reproductive Medicine and the Canadian Fertility and Andrology Society suggesting that the aromatase inhibitor could cause serious fetal anomalies when used off-label for ovulation induction.

As a result, Novartis, which markets the drug as Femara for the treatment of breast cancer, issued global warnings to health care professionals about the potential for letrozole to cause embryo and fetus toxicity.

"The concern that letrozole use for ovulation induction could be teratogenic is unfounded based on our data," wrote Dr. Togas Tulandi and Dr. Robert F. Casper, professors of obstetrics and gynecology at McGill University in Montreal and the University of Toronto, respectively.

Both physicians pioneered the use of the drug for ovulation induction.

The Canadian team examined the rates of congenital malformations among 911 newborns of women who conceived using either clomiphene citrate (n = 397) or letrozole (n = 514) and compared them with known malformation rates in the general population (Fertil. Steril. 2006;doi: 10.1016/j.fertnstert.2006.03.014).

There were no significant differences among the malformation rates in the letrozole group (2.4%), the clomiphene citrate group (4.8%), and the general population (2%-3%).