Thanks to Viagra, Cialis and Levitra, men with erectile dysfunction can get on board the Food and Drug Administration-approved love train. But women who experience a different sexual problem — sagging libido — have been left at the station. That may be changing.

BioSante Pharmaceuticals Inc. is testing the safety and effectiveness of LibiGel, a testosterone gel for women designed to combat declines in sexual arousal in menopause.

The Lincolnshire, Ill.,-based company is conducting two trials, comprising 1,000 women, to test the effectiveness of the gel, which is applied to the upper arm. If the trials go well, the drug could be available by prescription by 2011.

A testosterone gel for menopausal women makes sense medically, says Dr. Richard Paulson, professor of reproductive medicine and chief of reproductive endocrinology at the University of Southern California’s Keck School of Medicine.

Both men and women produce the female hormone estradiol and the male hormone testosterone, but in different quantities. Women in menopause lose almost all of their estradiol production and most of their testosterone production.

Estrogen ( taken orally or topically applied) helps keep the vaginal tissue strong and elastic, but it doesn’t enhance libido.