Young HIV-Infected Adults Are at Greater Risk for Medication Nonadherence

Stephen L. Becker, MD; Christopher M. Dezii, RN, MBA; Beth Burtcel, PharmD; Hugh Kawabata, MA; Sally Hodder, MD

Disclosures
In This Article

Methods

We reviewed administrative pharmaceutical claims data of the California Medicaid (Medi-Cal) population from July 1995 to June 1999. Patients were required to be eligible for benefits for at least 26 months in order to minimize an adverse impact of disenrollment or death on the adherence results. This required time horizon enabled us to identify patients who did not receive antiretrovirals during a screening period of 12 months, and for the purposes of this study these individuals were assumed to be antiretroviral-naive. Patients were then monitored for 12 months to assess adherence, and for 14 months to assess persistence with therapy.[3] Individuals younger than 18 years of age were not included in the analysis. Individuals with less than a 30-day supply of NRTI therapy during the entire observation period were excluded, in an effort to account for individuals who received therapy only in the context of postexposure prophylaxis. Individuals who died during the observation period were excluded.

The NRTI class was selected as the observed agent based on the assumption that once patients initiated NRTI therapy, they would continue on NRTI therapy as part of their antiretroviral regimen for at least 1 year. Greater regimen variation was expected for the nonnucleoside reverse transcriptase inhibitor (NNRTI) or protease inhibitor (PI) classes. Recent literature has suggested that there is only limited variability in the rates at which patients adhere to the agents from the various antiretroviral classes, indicating that assessment of adherence to NRTIs may serve as a reasonable proxy for overall regimen adherence.[4]

The first identified NRTI claim served as the index date for examination, and adherence was estimated during the next year. The adherence rate was defined as the proportion of days on therapy as evidenced by the days of therapy supplied compared with the total number of observed days (365 days or 1 year).[5,6] The analysis considered each day with regard to whether exposure to any NRTI therapy could have occurred, regardless of the number of NRTIs in the regimen. Thus, for an individual whose regimen contained a single NRTI and who received a 183-day supply of that agent, the adherence rate was expressed as a proportion of 183 day/365 day, or 50% adherent. In simple terms, exposure to NRTI therapy was defined as adherence. Adherence rates were determined and patients were stratified by age and sex.

Persistence with therapy was calculated using the NRTI prescription refill data and was monitored over time.[7] Individuals were required to refill a prescription within 60 days of the exhaustion of the preceding prescription. Patients who failed to refill within this period were identified as not persistent with therapy. The proportion of patients who were not persistent with therapy during the 12-month period was then plotted as a curve against time. Statistical analysis was performed by use of SAS, version 8.1 (SAS Institute Inc; Cary, North Carolina). Univariate analysis of adherence, persistence, and sex was performed by the chi-square test ( 2), while adherence by sex and age were examined using a General Linear Model analysis of variance (ANOVA). A P value of < .05 was considered statistically significant.

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