Above all others, though, the question of effectiveness is perhaps the most important.
Though more than a dozen microbicides are currently in development, not one has yet been proven to deliver the efficacy afforded by other prophylactic methods, such as condoms.
Kiser says microbicides of the future could approach the effectiveness seen with barrier contraception.
"It is imminently doable to build a microbicide that has 90-percent effectiveness," Kiser said. "That is our hope."
But many say that when dealing with a virus like HIV, it is far better to be safe than sorry.
"I, however, think we should still use with condoms when possible," said Dr. Kristin Ries, professor of internal medicine at the University of Utah. "I would not discourage condoms at all as they have shown to be very effective in prevention of HIV spread in many studies."
"We need large, controlled studies, even to be sure it is safe, then to see if [it's] effective. These will be difficult to do as ethically, as I think we must not recommend [microbicides] without condoms," Ries said.
Experts still see microbicides as a potentially important tool in the fight against HIV.
"Microbicides are not going to be the ultimate solution for the HIV pandemic," Kiser said. "But I think the idea is that between this and condoms and testing and education, we can kind of cut the top off of the expansion of the pandemic and get it more under control."
"None have been approved as none have proven safe and effective yet; however, developing one would be great in the fight against HIV," Ries said. "Also, it would put the prevention in the hands of women who do not have choices in many cultures."
Feinberg says a lack of interest on the part of pharmaceutical companies is also slowing the development of microbicides. However, she says such chemicals could be useful.
"Microbicides have great potential, I think, to slow the spread of the epidemic," Feinberg said. "An option for protection against HIV and other STDs that would be under the woman's control would be significant."
"Right now women are dependent on their partners' willingness to access and use a condom, and convincing men to do this has not proven to be easy," she said.