Comparison of HIV Virologic Failure Rates Between Patients with Variable Adherence to Three Antiretroviral Regimen Types

Medication adherence is a major determinant of antiretroviral (ARV) treatment success and a significant challenge for HIV-positive patients, yet a well-defined adherence threshold to maintain virologic suppression on current ARV regimens remains unclear. The present study evaluated 1915 Kaiser Permanente Southern California HIV-positive patients on one of three regimen types: (1) emtricitabine-tenofovir-efavirenz (FTC-TDF-EFV); (2) emtricitabine-tenofovir (FTC-TDF) and raltegravir (RAL); and (3) FTC-TDF and a boosted protease inhibitor, either darunavir (DRV) or atazanavir (ATV), to compare virologic failure rates between patients with varying levels of adherence to the regimens. Medication possession ratios (MPRs) were calculated to determine adherence, and HIV RNA PCR levels drawn 12-18 months after the initial pharmacy claim for the measured drug were used to determine virologic failure, which was defined as two consecutive HIV RNA PCR measurements 200 copies/mL. Adherence was inversely related to virologic failure, with an 80-90% MPR threshold resulting in no more than 3.5% virologic failure rate. In comparison, 90% MPR yielded no more that 1.1% virologic failure rate. Although the gold-standard adherence threshold for older ARV regimens has been 95%, an 80-90% MPR appears sufficient to maintain virologic suppression in patients treated with these three ARV regimen types.