The reason you carry two Aspirin around is not for a risk of acquiring HIV. It's for heart disease. I think Aspirin is a good example. These drugs are very complex and have many different mechanisms. The mechanism Aspirin uses to prevent stroke or a heart attack is different from the mechanism that prevents the cell that HIV infects from getting to the genital tract.
There are different approaches, and we need to understand how these drugs are working. It's two different mechanisms in one drug.