To the Editors:
Antiretroviral adherence is central to HIV treatment success.1-3 Many patient and system barriers to adherence have been identified and serve as targets for intervention studies.4-9 Disruption of daily routine is thought to be an important barrier to adherence. Although they are commonly periods of more leisurely activity, weekends represent a change in routine from the more structured activity of weekdays. If disruption of routines on weekends results in missed doses, intervention designers could target this time for particular attention. However, if weekends are not particularly high risk, more attention could be paid to established barriers. Unfortunately, little research has been done to determine the effect of day of the week on medication adherence. Therefore, we examined differences in adherence on weekends compared with weekdays in HIV-infected individuals on stable antiretroviral regimens.
We conducted an observational cohort study of HIV-infected participants with HIV RNA <75 copies per milliliter on standard regimens including efavirenz.10 Adherence was measured using microelectronic monitors (Aardex, Zug, Switzerland) for the 90 days before a censoring event of either viral load >1000 copies per milliliter or 12 months, whichever came first. Weekends were defined as Friday 5 pm to Sunday 5 pm and weekdays as the rest of the week. Percent adherence was calculated separately for weekends and weekdays for each participant using the following formula: 100 × (number of doses taken/number of doses prescribed). The paired data were compared using the Wilcoxon signed-rank test. The study was approved by the study site Institutional Review Boards; all participants provided written informed consent.
The cohort consisted of 116 participants with 94 (81%) males, 76 (66%) African-American, 30 (26%) white, 32 (28%) with a history of injection drug use, and a median CD4 count of 433 cells per cubic millimeter. Median adherence on weekdays was statistically significantly higher than on weekends (95.3% vs. 93.2%; P = 0.012) with a median absolute difference 0.9% (interquartile range: −2.9%, +9.9%). Adherence was better for 63 participants (54%) on weekdays, 46 (40%) on weekends, and was the same for 7 (6%).
Weekends were associated with slightly lower antiretroviral adherence. Although statistically significant, the absolute difference was small. Although strict adherence is particularly important for antiretroviral therapy, the clinical implication of this small difference is likely to be marginal even the HIV setting where the treatment is relatively unforgiving.
Previously published studies of medication adherence on weekends are few. In contrast to our findings, 2 small studies, one of antihypertensives11 and the other of topical treatment for psoriasis,12 noted a disproportionately high number of missed doses on weekends. In the context of HIV, a cross-sectional study of adherence to HAART noted that 22.1% of participants reported missing a dose of medication the previous weekend.13 Our results might have differed from those because we studied individuals with prior treatment success who may have had relatively high levels of adherence before enrolling.
Our study highlights the importance of tailoring adherence interventions to patients' needs rather than on widely assumed risk factors. Although a majority of participants had better adherence on weekdays as might be expected, a significant number had better adherence on weekends. One possible explanation is that we used a fixed “weekend” period, whereas participants may have had a more regular routine on Saturday and Sunday rather than the traditional Monday to Friday workweek. For many participants, however, the “weekend” may still have entailed a different routine even if the participant was working because any children cared for by the participant were not in school and other household members may have been off work. Therefore, given the observed difference, albeit slight, we recommend that clinicians query patients regarding their “weekends” and other periods with disrupted routines, such as vacations, so as to develop plans for ensuring adherence on those days. For designers of adherence interventions, weekend and weekday differences warrant exploration with participants, but should not be “de facto” considered a time at particularly high risk for nonadherence.
We are grateful for the support of the National Institutes of Health, which supported this research through the University of Pennsylvania Center for AIDS Research Clinical Core (P30-AI45008), Career Development Award K08MH01584 (R.G.), and an Agency for Healthcare Research and Quality (AHRQ) Centers for Education and Research on Therapeutics cooperative agreement (HS10399). Additional support was provided via a contract with Bristol-Myers Squibb and a Young Investigator award from GlaxoSmithKline.
Marcus Bachhuber, BS*
Warren B. Bilker, PhD*†
Hao Wang, MS*
Jennifer Chapman, MPH*
Robert Gross, MD, MSCE*†‡
*Center for Clinical Epidemiology and Biostatistics, University of Pennsylvania School of Medicine, Philadelphia, PA
†Center for Education and Research on Therapeutics, University of Pennsylvania School of Medicine, Philadelphia, PA
‡Division of Infectious Diseases/Department of Medicine, University of Pennsylvania School of Medicine, Philadelphia, PA
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