Understanding protease inhibitor potency: the intersection of exposure, efficacy, and resistance

Prescribing antiretrovirals has become increasingly complex, not only because of the expanding armamentarium but also because the tools available to measure different aspects of drug efficacy are complicated and interrelated. Potency cannot be viewed as a single unit of data, such as inhibitory concentration, and viral susceptibility to a drug cannot be viewed as a binary choice between "sensitive" and "resistant." Rather, both potency and resistance are continums, and attempts to quantify them in simple terms are often misleading. At the same time, potency and resistance must be considered pieces of a more complex puzzle that also involves drug exposure, metabolism, and pharmacokinetics. Appraising all of these factors simultaneously is difficult but necessary for the optimal care of people with HIV infection.