Objective: To assess the contribution of the determination of concentrations of indinavir (IND) in plasma to the assessment of self-reported adherence and keeping of appointments to withdraw drugs from the hospital pharmacy.
Patients and methods: Adherence was assessed using three criteria: questionnaires, punctuality at appointments to withdraw drugs, and plasma concentrations of IND. Blood samples were obtained from 106 HIV-infected patients who had been receiving IND in combination with two nucleoside reverse transcriptase inhibitors for longer than 6 months. Logistic regression analysis was carried out, and receiver operating characteristic curves were drawn.
Results: The kappa index showed a low concordance for the three measures. When pharmacy appointments and self-report are used together, the nondetection of drug levels is more reliably predicted (AUC = 0.75). With the viral load as the gold standard, plasma levels contribute nothing to the information given by the other two measures combined (AUC = 0.63, AUC = 0.64).
Conclusion: Measurement of adherence to highly active antiretroviral therapy is complex. Because there is no gold standard for it, we demonstrated that each of three common adherence measures has shortcomings that can be minimized in a combined measurement system. Indinavir plasma levels appear to provide no additional information, so further studies are undoubtedly necessary.