A Markov Model of the Cost-Effectiveness of Pharmacist Care for Diabetes in Prevention of Cardiovascular Diseases: Evidence from Kaiser Permanente Northern California
AUTHORS: Junhua Yu, Bijal M. Shah, Eric J. Ip, James Chan
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BACKGROUND: It has been demonstrated in previous studies that pharmacist management of patients with type 2 diabetes mellitus (T2DM) in the outpatient setting not only improves diabetes-related clinical outcomes such as hemoglobin A1c but also blood pressure (BP), total cholesterol (TC), and quality of life. Improved control of BP and TC has been shown to reduce the risks of cardiovascular disease (CVD), which has placed a heavy economic burden on the health care system. However, no study has evaluated the cost-effectiveness of pharmacist intervention programs with respect to the long-term preventive effects on CVD outcomes among T2DM patients.
OBJECTIVES: To (a) quantify the long-term preventive effects of pharmacist intervention on CVD outcomes among T2DM patients using evidence from a matched cohort study in the outpatient primary care setting and (b) assess the relative cost-effectiveness of adding a clinical pharmacist to the primary care team for the management of patients with T2DM based on improvement in CVD risks with the aid of an economic model.
METHODS: Clinical data between the periods of June 2007 to February 2010 were collected from electronic medical records at 2 separate clinics at Kaiser Permanente (KP) Northern California, 1 with primary care physicians only (control group) and the other with the addition of a pharmacist (enhanced care group). Patients in the enhanced care group were matched 1:1 with patients in the control group according to baseline characteristics that included age, gender, A1c, and Charlson comorbidity score. The estimated 10-year CVD risk for both groups was calculated by the United Kingdom Prospective Diabetes Study (UKPDS) Risk Engine (version 2) based on age, sex, race, smoking status, atrial fibrillation, duration of diabetes, levels of A1c, systolic BP (SBP) and TC, and high-density lipoprotein cholesterol (HDL-C)observed at 12 months. There was no statistical difference in the baseline clinical inputs to the Risk Engine (A1c [P = 0.115], SBP [P = 0.184], TC [P = 0.055], and HDL-C [P = 0.475]) between the 2 groups. A Markov model was developed to simulate the estimated CVD outcomes over 10 years and to estimate cost-effectiveness. The final outcomes examined included incremental cost and effectiveness measured by life years and per quality-adjusted life year gained. Both deterministic sensitivity analysis (SA) and probabilistic SA were conducted to examine the robustness of the results.
RESULTS: The estimated risks for coronary heart disease (CHD) and stroke (both nonfatal and fatal) at the end of the follow-up were consistently lower in the enhanced care group compared with the control group, even though baseline risks in both groups were similar. The absolute risk reduction (ARR) between the enhanced care and control groups increased over time. For example, the ARR for nonfatal CHD risk in year 1 was 0.5% (1.2% vs. 0.7%), whereas the ARR increased to 5.5% in year 10 (14.8% vs. 9.3%). Similarly, the ARR between the enhanced care and the control groups was calculated as 0.3% for fatal CHD in year 1 and increased to 4.6% in year 10.
Results from the Markov model suggest that the enhanced care group was shown to be a dominant strategy (less expensive and more effective) compared with the control group in the 10-year evaluation period in the base-case (average or mean results) scenario. Sensitivity analysis that took into account the uncertainty in all important variables, such as wage of pharmacists, utility weight (the degree of preference individuals have for a particular health state or condition), response rate to pharmacists’ care, and uncertainty associated with the estimated 10 years of CVD risk, revealed that the relative value of enhanced care was robust to most of the variations in these parameters. Notably, the level of cost-effectiveness measured by net monetary value depends on the time horizon adopted by the payers and the magnitude of CVD risk reduction. The enhanced care group has a higher chance of being considered as a cost-effective strategy when a longer time horizon such as a minimum of 4 to 5 years is adopted.
CONCLUSIONS: Adding pharmacists to the health care management team for diabetic patients improves the long-term CVD risks. The longer-term CVD risk reductions were shown to be more dramatic than the short-term reduction. A longer time horizon adopted by health plans in managing T2DM patients has a higher probability of making the intervention cost-effective.