Clinical practice guidelines recommend the use of statins and ACE inhibitors or ARBs for most elders with DM. Despite the dissemination of these guidelines before the first year of the present investigation, we found that only one-third of high-risk older adults with DM received both statins and an ACE/ARB by 2003. We also demonstrate that the use of recommended therapies was strongly associated with possession of VA, state-sponsored and employer-sponsored drug benefits, but not generous coverage from Medicaid. Our findings are similar to results showing greater statin use among older adults with CVD and drug benefits in a 1997 sample of Medicare beneficiaries.7
We believe our findings suggest that a combination of drug benefit generosity and other factors contribute to the use of guideline recommended medications.
We expected to find that having the most generous types of drug coverage (i.e. Medicaid and VA) would be associated with a higher likelihood of the combined use of both statins and ACE/ARB compared to having no drug coverage. Instead, we observed variation in the strength of the association between drug benefits and recommended drug use among drug plans, with the VA having the strongest association followed by employer-sponsored plans. This may be explained by taking a closer look at the VA system. A recent study comparing diabetes care quality between VA and commercial managed care found that diabetes process of care was better for VA patients.21
This difference is attributed to well-described reengineering efforts in the VA system to improve the efficiency and effectiveness of clinical services through care integration, promotion of practice guidelines, performance monitoring, payment incentives and information technology.21
These authors suggest that similar outcomes may be achieved in other healthcare plans by implementing similar changes.
Disease management programs are similarly motivated efforts to improve chronic disease management using coordinated and proactive efforts to enhance and support patient care.22
Our finding that employer-sponsored drug benefits were also associated with use of combined ACE/ARB and statin use may be explained by the use of disease management programs in many employer health insurance plans. By 2005, over half of employer health plans offered at least one disease management program, many of them for diabetes.22
The difference in the strength of the association between VA or other public benefits and combined use of ACE/ARB and statins (RRR 4.83) compared to employer-sponsored benefits (RRR 2.60) might be explained by systematic differences in care-delivery structure (e.g. the extent of information technology integration) offered by the two groups. This is outside the scope of our investigation, but deserves further study.
Although Medicaid offers generous drug benefits, we failed to observe a statistically significant association with combined ACE/ARB and statin use. The interpretation of this finding is not straightforward, but may, in part, be explained by our exclusion managed care enrollees, including Medicaid managed care patients. Although over 30 states offered disease management in their Medicaid program by 2004,23
these were usually limited to enrollees of Medicaid managed care organizations. The exclusion of the managed care population from our study may have affected our findings. Additionally, other studies report underuse of effective medications among Medicaid enrollees and this may also be a factor in our study.7, 24
Previous studies have shown a significant relationship between lower annual income and underuse of recommended DM drug therapy among a Medicare managed care population who had the same pharmacy benefit.6
Our study did not demonstrate a relationship between income and drug therapy, but this may be explained by the strong relationship between income and possession of drug benefits. We also found that patients who received subspecialty care were more likely to receive combined ACE/ARB and statin treatment, and this finding is consistent with other studies.25 26
We acknowledge that despite the publication of NCEP III guidelines expanding indications for statins to many older adults with DM in 20012
, delays in the dissemination and uptake of clinical guidelines also contribute to the low prevalence of recommended medication use in other studies27
and was likely a factor in our study. However, our findings of low use of combined statin and ACE/ARB therapy among the oldest-old (age ≥ 85 years) is consistent with other studies demonstrating lower statin and ACE/ARB use among high-risk older adults.4, 5
Other unmeasured, non-economic, confounders may also explain the underuse of recommended therapies, such as patient preference and adherence behavior, and physician's usual practice, all factors described in a survey of qualitative and quantitative factors influencing hypoglycemic choice in DM management.28
The limitations of this study deserve comment. First, medication use was based on self-report and did not include aspirin use. Previous MCBS reports suggest underreporting is on the order of 5% of filled prescriptions.13
However, because measures were based on actual medication containers and receipts, and not only self-report or claims, this measurement bias is non-differential by drug coverage thereby minimizing bias of our results. Second, it is possible that beneficiaries with drug benefits were sicker and had greater need for pharmacotherapy than those without benefits. To account for this, we risk adjusted by including the presence of chronic conditions in our study that contribute to greater medication use and health service use. Further, by including receipt of subspecialist care in our analysis, we adjusted for other potential unmeasured severity of illness confounders since patients with DM who receive subspecialty care usually have more severe disease and poorer glycemic control.29
Previous studies examining adverse selection in prescription drug benefits demonstrate that risk adjustment reduces bias caused by insurance selection on drug utilization.30
We also excluded managed care enrollees from our study population, limiting the generalizability of our findings to this population, including Medicaid managed care enrollees. Finally, we were unable to determine whether medications were not received because of a previous history of adverse drug reaction to the medication (e.g. cough in ACE inhibitor), patient preference or physician assessment of limited benefit due to limited life-expectancy.
We conclude that prescription drug benefits from VA and state-sponsored drug programs and from employer-sponsored plans are associated with the use of recommended DM therapy for older adults. Moreover, the VA's drug benefit is most strongly associated with combined ACE/ARB and statin use in their management of type 2 diabetes. We believe this suggests that the VA system, with generous drug benefits combined with strong disease management and information technology integration, contributes to better quality of medication use in DM. This also suggests that generosity of drug coverage alone is insufficient to promote quality of medication management for type 2 DM. The implication for Medicare beneficiaries in the post-Part D era is that the gains in access made by expanding drug coverage may not be realized without coordinated promotion of clinical practice guidelines or disease management programs.