• Modeling cardiovascular health outcomes in Medicaid hypertensive patients - Effect of patient adherence

      Gu, Sen; Shaya, Fadia T. (2008)
      Background. Low adherence rates to antihypertensive pharmacotherapy have been documented everywhere, especially among people of lower socioeconomic status such as Medicaid beneficiaries. Existing studies tend to focus on hypertensive patients who received mono-therapy or measure adherence at a fixed point in time, which may generate external validity issues or not be suitable for patients whose survival periods vary considerably. Purpose. To examine the relationship between patient adherence to antihypertensive medication and subsequent risk of cardiovascular events by using a new approach to measure adherence. Methods. A secondary data analysis of a mid-Atlantic Medicaid Managed Care Organization (MCO) data was conducted. We used Ordinary Least Squares (OLS) models and logistic regression models to examine predictors of patients' adherence at one year post index date. We also used Cox's Proportional Hazard models and pooled logistic regressions to investigate the relationship between adherence and subsequent risk of cardiovascular events. Adherence was first measured as a Cumulative Medication Acquisition (CMA) at six months post index date and second as CMA at each month since six months post index date until the date of disenrollment, date of a cardiovascular event, or the end of the study time frame, whichever comes first. We compared the area under Receiver Operating Characteristic (ROC) curves of the time-constant and time-varying approaches in terms of their utility in assessing risk of cardiovascular events. Results. A total of 3091 patients were included for the fist study aim, with an estimated mean annual CMA score of 0.649 (median = 0.652). For other study aims, 7939 patients met the inclusion criteria and 140 cardiovascular events were found after six months post index date. A higher CMA score was found to be protective against cardiovascular events, when controlling for potential confounders. For each 10% increase of CMA score, the hazard of cardiovascular events decreased by approximately 14% and the effect was significant (P = 0.0134). The model with CMA measured with time-varying approach also yielded by similar results and a Mann-Whitney test indicated there was no significant difference in terms of utilities of time-constant and time-varying approach in predicting risk of cardiovascular events. Conclusions. In this Medicaid population, patient adherence to antihypertensive medications is affected by sociodemographic factors and health status. Adherence at six months post index date is a significant predictor of subsequent risk of cardiovascular events. Adherence measured at a fixed point in time and by time varying method are similar in predicting cardiovascular health outcomes.