Topical Microbicides
The Develompent Process
The development process ensures that a microbicide candidate is safe and non-irritating to the genital and anorectal tract while demonstrating effectiveness in preventing HIV infection. Following identification of an active component that can prevent HIV infection from in vitro assays designed for specific transmission routes, further studies to assess potential toxicities are conducted. After studies show high potency and lack of toxicity and predetermined criteria have been satisfied, the physical properties of the active component are exploited to generate a compatible formulation for its delivery. Additional in vitro, ex vivo, and in vivo studies are undertaken to further characterize the properties of the newly developed topical microbicide prior to testing in clinical trials.
Ultimately, the effectiveness of a microbicide is directly related to behavioral patterns of use and any social or cultural factors that might influence its use, which must also be taken into account during its development. A summary of these issues, in addition to characteristics that may enhance the potential candidacy of a newly developed topical microbicide are summarized in Table 2 below.
Ideally, topical microbicides should also reduce the infectivity of other sexually transmitted infections (STI), because many have been associated with increased risk of HIV infection or a poor prognosis. Some of the STIs or clinical conditions that increase the risk for HIV infection include:
Characteristics of Topical Microbicides
|
Acceptable |
Unacceptable |
Safety
- Administration up to six or more times daily or continuous delivery
- Extended periods of use
- Lack of reproductive toxicities
|
- Cause epithelial disruption
- Induce inflammation
- Absorbed systemically
|
Effect
- Fast
- Long duration
- Irreversible
|
- Unstable
- Interval of efficacy between application and coitus brief (before or after)
|
Acceptability
- Formulation stability
- Acceptable to the user and user’s sex partner
- Unobtrusive/pleasurable
|
- Messy, leaky
- Burning, itching
- Cumbersome
- Odor/taste/color/texture
- Delivery vehicle trauma/discomfort
|
Availability
- Contraceptive/non-contraceptive formulations
- Low cost
- Unlimited access
- Ease of scale-up and GMP production
|
- Costly for use and/or manufacturing
- Regulated distribution (MD or health care provider)
- Requires special storage/transport
|
Uses
- Vaginal and/or rectal
- Unlimited use
- Compatible with condoms and other STI prevention methods
|
|
Activity
- Affect STIs in ejaculate and cervicovaginal secretions
- Broadly active: HIV + other STIs
|
- Affect normal vaginal (rectal) microbial ecology
- Enhance growth of STIs or secondary pathogens
|
Other Applications
After the vaginal microbicide has been tested and shown to prevent transmission in clinical trials, and approval from appropriate regulatory bodies has been obtained, the product will be made available to consumers. In light of studies documenting the routine practice of anal intercourse among a considerable number of heterosexuals and the fact that men who have sex with men (MSM) constitute a significant portion of the HIV-infected population in selected regions of the world, it is anticipated that off-label or unintended use will occur. Thus, products developed as vaginal microbicides also need to be safe for rectal use. Development of safe, effective, and acceptable microbicides specifically for rectal use, while not as far advanced, is proceeding in parallel with vaginal microbicides.
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