At a recent forum, researchers discussed the use of existing antiviral drugs to prevent HIV infection.

“Pre-exposure prophylaxis [PrEP] is the most important concept in the [HIV] prevention field today,” Robert Grant, a University at California San Francisco researcher, told the Infectious Disease Society of America at its annual meeting in San Diego Oct. 5.

The forum was a “debate” between Grant and Ward Cates, president of Family Health International. Both support the concept of using antiviral drugs to prevent HIV and are conducting research to demonstrate its viability, but they drew straws to see who would take the pro and con sides of the argument.

Grant said his argument was based on two key points: “First, that HIV infection is the cause of AIDS. It is not sex. It is not drugs. It is not antiviral drugs. It is HIV infection. My second point is that people like sex. People are sex connoisseurs, they like their sex just so. Other prevention concepts have not worked because people don’t use them, because they alter sex in some ways that people care about.”

His kids call abstinence “proof of adult stupidity,” Grant said. “Condoms are like showering with your sox on. Diaphragms plus condoms are like showering with your shoes and your sox on. Microbicides are messy. Male circumcision – it has been pointed out that in the adult male it means removing a 3-by-5-inch surface area of the penis – so it is no wonder that women are more interested in male circumcision than are men.”

The prognosis for a vaccine remains problematic.

“Anti-HIV drugs, in contrast, inhibit HIV without altering sex. They are already formulated and mass produced and prescribed now to prevent mother to child transmission.” They also are prescribed for use after occupational exposure through a needle stick and for possible sexual exposure after the fact. “They are at least as female controlled as a microbicide, and more easily concealed.”

Grant said the two drugs combined in Truvada have demonstrated success in preventing infections in monkeys, in mother to child transmission, and in couples trying to conceive where the male is positive and the woman is negative.

He would prescribe PrEP to “people, but not all people; it should be people who like sex and do not want HIV.”

Cates used a “Top 10 Reasons” why people should not use PrEP. He said the monkey data may not be applicable to humans, and the data in humans is very limited. “Our knowledge of toxicity, while somewhat encouraging, is less than one year old and we really need to look at that over five years.”

He feared a possible increase in risky behavior and pointed out that “sporadic pill taking is the rule. It’s hard to take pills for prevention, even in a clinical trial setting.” In a recent trial in West Africa that provided such pills and counseling, adherence was only 70 percent. That may lead to the emergence of drug resistant virus.

Gilead Sciences is selling Truvada at cost in sub-Saharan Africa, about $20 a month, “which is still out of the range of acceptability in resource poor settings,” even for high-risk groups such as sex workers. Cates said, “PrEP is the wrong idea at the wrong time.”

During the discussion period Grant acknowledged that three-drug combination therapy is the gold standard for treating HIV infection. “Theoretically one or two drugs might be enough to prevent drug resistance in the prevention setting,” primarily “because the amount of viral load is very different. On average, viral loads in genital secretions are 50-fold less than in blood.”

He also downplayed the likelihood that PrEP would lead to an increase in risky behavior. That has not proven to be the case in clinical trials in the U.S. and Africa.

Cates said a lot of it comes down to money. “How can we possibly afford [drugs for prevention] in resource-poor settings where we have not gotten treatment to those who need to be kept alive?” Less than 1 in 5 who should be on therapy are receiving drugs, “so why are we trying to find even more unusable methods?”

A few score members of the audience had interactive devices that allowed them to vote on questions put to them. It found that 65 percent would discuss PrEP with a hypothetical oil company executive who would be working in Africa for several months but they would not prescribe it for him. In their own practice, only 5 percent of physicians have prescribed PrEP, but 9 percent are aware of patients who have used the drugs in that way.

A modeling study published in the online journal PLoS ONE on Oct. 19, by researchers at the University of Pittsburgh School of Medicine, found that PrEP could potentially cut new HIV infections by 74 percent in sub-Saharan Africa, if used consistently for 10 years.

More limited use of the prevention strategy, targeting those at highest behavioral risk, could prevent 3.2 million new HIV infections over that same period.