Vaginal Rings Silastic vaginal rings releasing either progestin or progestin–estrogen combinations were studied for years. The NuvaRing contains both estrogen and progestin, must be changed monthly, and has the same safety concerns as the other estrogen-containing hormonal methods. A new reusable ring, Nestorone, contains a nonandrogenic progestin that is inactive orally, and ethinyl estradiol. It can be worn for 3 weeks, removed for 1 week, and then reinserted for a total of 13 months of use (375). The advantage of this method is the use of a less androgenic progestin and the elimination of regular trips to the pharmacy. Progering contains natural progesterone and no estrogen. It is approved in some countries in Latin America and Asia. It was developed for up to 3 months use by breastfeeding women (376).
Barrier Methods The Ovaprene ring is a nonhormonal “one-size-fits-all” intravaginal organic silicone ring that continuously releases spermiostatic and spermicidal agents over a 4-week period. The phase I trial demonstrated patient acceptability and safety and the product is in phase II trials (377). Under investigation is the SILCS diaphragm, a single-size reusable device with a contoured rim. This device is nonlatex and is available over the counter with no requirement for a pelvic examination (378). Another potential new barrier method under development is a female condom with a dissolvable capsule to ease insertion, a polyurethane vaginal pouch, and a soft outer ring.
Fit and concerns over slippage are improved by urethane foam that allows the condom to cling to the vaginal walls (38).
The Invisible Condom™ is a novel barrier/germicide/spermicide combination in human trials. It is a polymer gel that adheres to the vaginal and cervical mucosa when inserted into the vagina through a special applicator, forming a nondetectable physical barrier. One version has sodium laurel sulfate (SLS) incorporated in to the polymer film. The gel by itself blocks entry of HIV and of herpes virus into target cells in vitro. Daily vaginal application of the polymer plus SLS prevents pregnancy in rabbits (379).
Contraceptive Vaccines Immunologic contraception–sterilization with vaccination against human chorionic gonadotropin was pursued for many years in India but appears to be abandoned (380). Zona pellucida glycoproteins are another target for a potential vaccine, but application in humans appears blocked by the ovarian dysfunction observed in animal studies (381). More promising are efforts that target sperm. Because of the large number of antigens associated with sperm, some of which are found on somatic cells, the challenge lies in choosing the correct antigen (382). The search continues for target proteins unique to reproduction to which a vaccine could be employed without adversely affecting other functions.
Male Contraception As described earlier, considerable progress was made in hormonal contraception for men based on long-acting androgens in combination with progestins or GnRH antagonists. Nonhormonal male methods are being investigated. These include efforts to target and specifically interfere with spermatogenesis, epididymal sperm maturation, and sperm function (383). The majority of the targets being explored involve inhibiting sperm motility (384). Chinese researchers developed a method of percutaneous occlusion of the vas that was used in more than 100,000 men; it is effective and appears to be reversible. Polyurethane elastomer is injected into the vas, where it solidifies and forms a plug, providing an effective block to sperm. The plugs are removed using local anesthesia, and fertility returns in most cases after as long as 4 years with the plugs in situ (385).