Siliciano is a professor of medicine at Johns Hopkins University.

“There hasn’t been a lot of theoretical basis of why some combinations should work better than others. [With] what we know about how the virus replicates, it should be possible at least to predict some aspects of treatment outcome, specifically how well the drugs actually inhibit the virus,” he said.

What works, what doesn’t

The study analyzed how well individual drugs and drug combinations inhibit infection. Researchers then fed that data into computers and applied their mathematical formula.

“The standard way to do this is to look at the amount of drug that gives you 50 percent inhibition. That turns out to be a very poor way of doing it because at least some of the drugs are actually extremely good and they cause way, way more than 50 percent inhibition,” he said.

In fact, some drugs are more than 99 percent effective in inhibiting HIV from replicating. Those are the antiretrovirals included in the study.

“Because the virus replicates exponentially,” said Siliciano, “it can increase very, very quickly, and so that’s why you need that extremely high level of inhibition.”

Siliciano and his fellow researchers used 19 drugs and came up with well over 800 treatment combinations. He said while more study of the mathematical formula is needed, he foresees two uses. The first, of course, is treatment.