Nonadherence to antiretroviral therapy (ART) jeopardizes good clinical outcome in people living with HIV. In a single-center prospective study, prevalence and correlates of nonadherence were investigated in 43 patients on ART. Nonadherence was assessed using Medication Event Monitoring System (MEMS), self-report and collateral report of treating physicians. Based on MEMS data, median taking adherence, dosing adherence, and timing adherence was 98% (interquartile range [IQR] = 5.3), 91.5% (IQR = 18), and 86% (IQR = 31.5), respectively. The median number of drug holidays per 100 days was 0.8 (IQR = 4.8). The prevalence of nonadherence measured by MEMS was 40%. Self-reported nonadherence and collateral report of nonadherence by physicians varied from 5% to 41% and 24% to 28%, respectively. Patients were categorized as adherent or nonadherent based on a clinically validated algorithm derived from MEMS parameters. Nonadherent patients used significantly more escaping coping strategies (p = 0.003) and planned problem solving strategies (p = 0.049), were prescribed significantly more antiretroviral medications (p = 0.02) and were significantly longer on ART (p = 0.04) than adherent patients. Identified correlates of nonadherence may help clinicians in detecting patients with HIV at risk for nonadherence and can support the development of adherence enhancing interventions.

Adherence to highly active antiretroviral therapy (HAART) is crucial, but which aspects of drug-taking behavior are important remain largely unknown. In a prospective observational study, 43 HIV-1-infected patients taking HAART underwent electronic event monitoring (EEM). Taking adherence was defined as the percentage of doses taken compared with the number prescribed, dosing adherence was defined as the percentage of days on which all doses were taken, and timing adherence was defined as the percentage of doses taken within 1 hr of the time prescribed. Drug holidays were defined as periods of no drug intake for >24 hr. Cluster analysis, including the four EEM parameters, was used and refined to construct an algorithm to discriminate patients. Patients were categorized as nonadherent if they had a taking adherence of <90%, or a dosing adherence of <75% and at least 1 drug holiday, or a timing adherence of <80% and at least 1 drug holiday, or >6 drug holidays per 100 days. All four EEM parameters differed significantly (p < 0.0001) between the two groups. Adherent patients had a better outcome, as shown by a larger drop in viral load (p = 0.011) and rise in CD4+ cell count (p = 0.035), showing that the algorithm-based categorization is clinically relevant.

The relationship between adherence, virological response to highly active antiretroviral therapy (HAART) and the presence and development of genotypic resistance was assessed in 41 HIVinfected patients on HAART. Four adherence parameters (drug taking adherence, dosing adherence, timing adherence and drug holidays) were scored prospectively using electronic event monitoring. Genotypic resistance at baseline and after therapy failure was scored retrospectively and a genotype-based susceptibility score was calculated. Overall median adherence rates were high. All adherence parameters were better in virological responders (n=31) compared to non-responders (n=10), drug taking adherence and number of drug holidays being significantly different. Responders had a significantly higher susceptibility score. Stepwise logistic regression showed that the number of drug holidays and a low susceptibility score were highly predictive for therapy failure. Despite the presence of a limited number of baseline resistance mutations, perfectly adherent patients can control virus replication for a prolonged period.