Protease inhibitors (PIs) are potent antiretroviral agents that in combination regimens have dramatically changed the natural history of HIV disease. However, therapy with many PIs at standard doses may be limited by inconvenient dosing regimens, high tablet volumes, and variable drug exposure. Booster agents, such as low doses of ritonavir (RTV) are increasingly used to maintain high PI trough exposures. 1 The advantages of the boosted PI approach include raising trough drug concentrations, diminishing interpatient variability, prolonging drug half-life to allow twice-daily and possibly once-daily dosing, and diminishing food requirements and tablet volume. In addition, increases in drug exposure may potentially enable inhibition of the virus in the presence of reduced sensitivity to PIs. The administration of RTV in independent tablets is associated with disadvantages, including lack of achievement of optimal efficacy of the PI regimen, increased number of tablets, and the fact that RTV tablets have size, flavor, and storage characteristics that are poorly accepted by patients, which may adversely affect adherence and compromise the efficacy of highly active antiretroviral therapy (HAART). 2 Moreover, the number of tablets in the RTV container complicates the coordination of drug collection with the remaining antiretroviral agents, a circumstance that can also favor missed or skipped doses. Although RTV-booster regimens do not require the strict >95% adherence of traditional PI-based regimens, less than that percentage is strongly associated with increased mortality over time. 3 Medication event monitoring systems (MEMS) and selfreported questionnaires are common methods to measure adherence. MEMS can be time-consuming and expensive, whereas self-reported questionnaires are subject to measurement bias, such as recall and response bias. 4 Another method to assess compliance is the use of pharmacy records. The refill records of computerized pharmacy systems are used increasingly as a source of compliance information. Because refill compliance data only give information about whether or not the medication is collected by the patient, it provides an upper bound for medication consumption, and allows identification of those patients that cannot be compliant simply because they do not obtain enough medication. 5,6 Moreover, incorporating refill-based measures of adherence into clinical practice facilitates early identification of subjects who may experience virologic failure because of poor adherence, and may be useful in real time to determine whether an individual is exhibiting incomplete adherence. 7 We compared refill data for RTV and the PI boosted with RTV tablets in patients with good adherence to PI medication (pharmacy refill rate >80%) and examined the possible effect of poor selective adherence to RTV on the efficacy of antiretroviral treatment.Between April 1 and April 30, 2009, a cross-sectional study of all HIV-1-infected adult patients treated with antiretroviral drugs that included a PI boosted with R...
