Comparison of three methods to calculate adherence in patients receiving antiretroviral treatment

INTRODUCTION. Knowledge of the patient's adherence to antiretroviral treatment is extremely useful for monitoring HIV infection. Several methods have been proposed to calculate adherence, but they all have certain problems at application. The aim of this study was to compare three of the available methods for assessing medication adherence in order to determine their accuracy for this purpose. PATIENTS AND METHODS. Three methods for evaluating medication adherence were prospectively studied: 1. Remaining pill count (RPC), 2. Structured interview (SI), and 3. Pharmacy registry of drug refills (DR). The RPC was considered the gold standard and sensitivity and specificity of the other methods was calculated according to the RPC. The study included 100 consecutive patients and had a follow-up of one year. RESULTS. We were able to assess all three methods in 69 cases. The percentages of patients taking 95% or more of the prescribed dose according to the three methods were 72.5% (RPC), 85.5% (SI) and 81.2% (DR). Taking the RPC as gold standard, there was 75.1% concordance with the DR and 75.1% with the SI method. The sensitivities of the DM and SI were 52.6% and 42.1%, respectively. After one year of follow-up, patients with > 90% adherence (RPC) had a 1.29-times higher probability of achieving good virological response (CI 95% 1.04-1.62, p = 0.0138). CONCLUSION. Although concordance among the methods was acceptable, the SI and DR overestimated adherence as compared to the RPC. Since there is currently no ideal method for determining treatment adherence, it is important to combine several methods to minimize errors and provide results that are as close to the true situation as possible.