Comparison of rates of potentially inappropriate medication use according to the Zhan criteria for VA versus private sector Medicare HMOs

BACKGROUND: Inappropriate prescribing in the elderly is common, but rates across different health care systems and the impact of formulary restrictions are not well described. OBJECTIVE: To determine if rates of inappropriate medication use in the elderly differ between the Veterans Affairs (VA) health care system and the private sector Medicare health maintenance organization (HMO) patients. METHODS: A cross-sectional study design compared administrative pharmacy claims from 10 distinct geographic regions in the United States in the VA health care system and 10 analogous regions for patients enrolled in Medicare HMOs. The cohorts included 123,633 VA and 157,517 Medicare HMO patients aged 65 years and older. Inappropriate medication use was identified using the Zhan modification of the Beers criteria, which categorizes 33 potentially inappropriate drugs into 3 major classifications: "always avoid rarely appropriate," and "some indications." Comparisons between the VA health care system and the private sector Medicare HMO were performed for overall differences and stratified by gender and age. The drug formulary status of the Zhan-criteria drugs was known for the VA health system but not for the Medicare HMO patients. RESULTS: Compared with private sector patients, VA patients were less likely to receive any inappropriate medication (21% vs. 29%, P<0.001), and in each classification: always avoid (2% vs. 5%, P<0.001), rarely appropriate (8% vs. 13%, P<0.001), and some indications (15% vs. 17%, P <0.001). The rate of inappropriate drug use was lower in the VA compared with the private sector for males (21% vs. 24%, P <0.001) and females (28% vs. 32%, P <0.001). Differences were consistent when stratified by age. CONCLUSION: Compared with private sector Medicare HMOs, elderly VA patients were less likely to receive medications defined by the Zhan criteria as potentially inappropriate. A restrictive formulary that excludes 12 of the 33 Zhan criteria drugs may be a factor in the reduction of undesired prescribing patterns in elderly populations.