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Impact of continuity of care and provider factors on medication adherence in patients with hypertension

Baltimore, MD, USA: Johns Hopkins University (doctoral dissertation).

Johns Hopkins University, Baltimore, MD, USA

STATEMENT OF THE PROBLEM: Hypertension is one of the most common and deadly chronic diseases in the United States today. Approximately 65 million Americans currently have the disease, which was responsible for over 57,000 deaths in 2003. Despite the fact that medications are readily available that can control high blood pressure and reduce the associated morbidity and mortality, less than 25% of people who are diagnosed have adequate control of blood pressure. Nonadherence to prescribed antihypertensive medication regimens plays a major role in this avoidable morbidity and mortality. The etiology of this nonadherence to prescribed regimens is multifactorial, but previous studies have focused on primarily on patient-related factors. The primary goal of this dissertation is to assess understudied factors that may be related to adherence to antihypertensive medications. The results of this study could be used to identify patients who are at a high risk for nonadherence and provide valuable information for the design of programs to enhance adherence to antihypertensive regimens.

OBJECTIVES: This study assessed the relationship between continuity of care, the mix of provider types involved in care, and morbidity burden on adherence to antihypertensive regimens.

METHODS: This was a retrospective observational study using longitudinal medical and pharmaceutical claims data from the PharMetrics Integrated Outcomes Database. Patients included in this analysis had a medical claim with a diagnosis of hypertension in 2001 or 2002 and received at least one prescription for an antihypertensive medication in 2001. The relationship between adherence and the dependent and control variables was assessed using multivariate proportional odds models.

RESULTS: A total of 2,432 patients were included in the analysis. The average adherence level, measured by the medication possession ratio (MPR), was 0.75. Fifty four percent of the study population had an MPR above 0.8. There was no significant relationship detected between continuity of care and adherence. Compared to patients who only saw specialist providers, patients had higher odds of poor adherence if they only saw primary care providers (OR: 1.5, 95% CI: 1.0 – 2.2) or if they saw both types of providers (OR: 1.4, 95% CI: 1.1 – 1.9). Patients with the highest level of morbidity had decreased odds of having good adherence (OR: 0.7, 95% CI: 0.5 -0.9).

CONCLUSIONS: The results suggest there is no relationship between continuity of care and adherence and patients with a primary care provider or a higher morbidity burden experience worse adherence. However, the results should be interpreted with caution. The measure of continuity of care used in this study does not assess the quality of the relationship between patient and provider. Additionally, details about the managed care plans and enrollees within the PharMetrics dataset, such as level or type of managed care services, the extent of automatic refills or refill reminders as part of disease state management programs, or racial and socioeconomic status of the patients are not included. These variables, if available, might help to explain the unexpected results observed in this study. Future studies should be designed to overcome these limitations.