Geographic variation in pharmacotherapy decisions for U.S. Medicare enrollees with diabetes

Prescription rates for diabetic drugs vary considerably across the United States for Medicare beneficiaries. The goal of this study was to determine if non-clinical factors (patient race, ethnicity, gender, income) are associated with regional variation in pharmacotherapy decisions for diabetic patients enrolled in Medicare.

We performed a spatially-weighted, linear regression analysis of the entire diabetic population enrolled in Medicare Parts A, B, and D for the years 2006 through 2009. Our outcomes of interest were the percentage of diabetic patients being treated with metformin, a sulfonylurea, a thiazolidinedione, or insulin within a hospital referral region (HRR).

Prescription rates for metformin, sulfonylureas, thiazolidinediones, and insulin varied more than two-fold between hospital referral region. Metformin prescription rates were increased in western states while prescription rates for sulfonylureas and insulins were highest in the South and Midwest. In contrast with these other diabetic drug classes, members of the thiazolidinedione drug class were prescribed more frequently in the Central United States (Great Plains, Colorado Rockies, Northern Texas, Oklahoma). Prescription rates for each drug class were increased in hospital referral regions with a lower household income. Referral regions with larger African American populations were associated with higher prescription rates for insulin (p<0.001) and lower prescription rates for metformin (p<0.001). Gender and Hispanic ethnicity were not associated with regional variation in prescription rates for the four major diabetic drug classes.

Geographic differences exist in the management of type 2 diabetes for Medicare enrollees. Prescription patterns were associated with household income and African American race. Further studies are necessary to identify local, unidentified factors that might be influencing provider management styles.