ATLANTA — Novel contraceptives currently being developed include norprogesterone-derived progestins, new barrier methods, and combination spermicides-microbicides, reported Dr. Michelle Fox at a conference on contraceptive technology sponsored by Contemporary Forums.
“We've made a lot of progress in contraception, but we are still far from the ideal,” said Dr. Fox, who is director of family planning at the University of Maryland, Baltimore.
The only contraceptive that Dr. Fox predicted would be approved within the next year is a continuous combined oral contraceptive pill that contains 90 mcg of levonorgestrel and 20 mcg of ethinyl estradiol, to be taken daily.
The product, named Lybrel by Wyeth Pharmaceuticals, has no hormone-free period and has demonstrated favorable bleeding patterns in clinical trials.
In contrast with today's testosterone-based progestins, new progestins under development are being derived from 19-norprogesterone, a compound that is not androgenic and may better inhibit ovulation.
One such norprogesterone-based product is Nestorone, which is being developed by the Population Council. A limitation of Nestorone is its inactivity when delivered orally. Because the compound is readily absorbed through the vaginal mucosa and skin, Nestorone-based combined hormonal vaginal rings and spray-on contraceptives are being developed.
New barrier methods being evaluated include a one-size silicone diaphragm that would not require individual fitting and a female condom that is more comfortable and easier to use.
A hot topic of research is the quest to develop a spermicide alternative to nonoxynol-9. Currently, all spermicidal products in the United States contain nonoxynol-9. While the compound is considered safe for most users, it is a detergent that disrupts epithelial surfaces. A recent study suggested that frequent use of nonoxynol-9 by sex workers could increase the risk of HIV transmission in high-risk women.
Several buffer-based spermicides are currently under development. These compounds inhibit sperm by maintaining the acidic environment of the vagina.
They have also been shown to inhibit multiple sexually transmitted infections in animal models.
One product, Acidform, forms a protective bioadhesive coating over the cervix and vagina. A 2004 study showed that Acidform can be applied up to 10 hours before anticipated intercourse.
Finally, a new surfactant product has demonstrated less irritation than nonoxynol-9 and has potent activity against both sperm and a range of pathogens in vitro. The contraceptive efficacy of the product is currently being evaluated in a phase III trial.