Evaluation of a physician-pharmacist collaborative intervention for treating hypertension

Quality of care is identified as a major problem in the current health care system. Multidisciplinary teamwork has been proposed to address quality-of-care problems because, theoretically, a health-care team can expand knowledge and follow up patients more efficiently. However, questions about how to successfully implement team-based care in ambulatory settings and its long-term costs are still unanswered.

The first objective of this dissertation is to estimate the marginal effects of process measures including number of counseling sessions about lifestyle modification and number of specified-dose antihypertensive medications provided by a physician-pharmacist collaborative intervention and usual care on blood pressure reduction and direct treatment costs by comparing the results from as-treated and instrumental variable methods. The second objective is to estimate the long-term cost changes attributable to the physician-pharmacist collaborative intervention by considering costs related to coronary heart disease, stroke, and heart failure. To accomplish both objectives, data from two prospective, clustered randomized controlled clinical trials implementing a physician-pharmacist collaborative intervention in the Midwest were used.

In the first study, multiple linear regression models included blood pressure reduction and costs as outcome variables, and the two process measures and other control variables as explanatory variables. As-treated methods revealed insignificant associations between the two process measures and blood pressure reduction outcomes. On the other hand, both process measures were significantly associated with the costs. By using instrumental variable methods, utilizing two instruments of randomization and the trial indicator, the models were unidentified and showed no significant associations between the process measures and all of the outcomes. However, the post-hoc analysis of the instrumental variable models, evaluating one process measure at a time without controlling for the other process measure, showed significant associations between the process measures and all of the outcomes. The estimates from instrumental variable methods were larger than the estimates from the as-treated methods.

The second study used a Markov model cohort simulation in a 10-year timeframe, transition probabilities estimated by several risk estimation systems and published statistics, and published event costs. The reference case employed a sample of patients aged 30 to 74 years from the trials and assumed that blood pressure after the intervention was constant. The total costs of the intervention for hypertension care and the costs related to the vascular diseases in the intervention group were shown to be lower than the usual care group at 6.5 years. However, cost-savings by the intervention were sensitive to patient risk profiles and sustainability of blood pressure after the intervention.

To conclude, from the first study, combining multiple studies and using instrumental variable methods may be useful for evaluating marginal effects of the care process but further research is needed to address under-identification problems. The results of the second study suggested that it was likely that the physician-pharmacist collaborative intervention to treat hypertension was appropriate for high-risk patients.