Virtual Inhibitory Quotient (VIQ) Predicts Response to Protease Inhibitors in HIV Patients

By David Douglas

A parameter that encompasses viral resistance and plasma drug exposure, the "virtual inhibitory quotient" (VIQ), is helpful in determining the virological response to therapy with protease inhibitors (PIs) in HIV-infected patients, researchers report in the December issue of Antimicrobial Agents and Chemotherapy.

As lead investigator Dr. Nancy Shulman told Reuters Health, the study "shows that a certain amount of resistance can be overcome by optimizing drug levels and that the variable that contained pharmacokinetics and resistance (VIQ) was superior to either variable by itself when looking at predictors of response."

Dr. Shulman of Stanford University School of Medicine, California, and colleagues came to these conclusions after studying 37 patients with chronic detectable viremia who initially were receiving 800 mg of indinavir 3 times a day.

They were switched to indinavir 400 mg twice daily along with ritonavir 400 mg twice daily for a total of 48 weeks.

Although 16 patients eventually dropped out due to adverse events "enhanced viral suppression was demonstrated in more than half of the subjects...and one-third maintained improved responses over 48 weeks."

The VIQ, say the investigators, "a ratio which takes into consideration both the baseline resistance and the indinavir trough concentrations achieved with combination therapy, was the best predictor of a virologic response."

However, Dr. Shulman pointed out that "we are not at the stage where a specific VIQ can be used to predict outcome based on a level, as there are controversies on how protein binding adjustment is performed--methods vary from study to study and company to company."

1/03/03

Antimicrob Agents Chemother 2002; 46:3907-3916.