METHODS: Regulatory data were derived from the FDA. Average wholesale prices (AWP) and national average drug acquisition costs (NADAC) were derived from the RedBook (Truven Health Analytics) and the Centers for Medicare and Medicaid Services, respectively. Prices were adjusted to 2014 dollars using the consumer price index (CPI) and converted to prices per 30-day supply using defined daily dose (DDD). The AWP compounded annual growth rate (CAGR) was estimated for each drug. A multivariate regression model was conducted to examine factors associated with antidiabetic drug prices at market entry.

RESULTS: In the period 1980-2014, there were 88 antidiabetic drugs (86 NDAs, 2 BLAs) marketed in the US, including 37 insulins and analogues and 51 non-insulin antidiabetic drugs. Animal-sourced insulins were excluded from analysis. The CPI-adjusted AWP CAGR from approval to December 2014, or to drug discontinuation date, was positive for antidiabetic drugs except for two inhaled insulins (one discontinued from the market), troglitazone (discontinued) and metformin/rosiglitazone. The average of NADAC per unit, as percentage of the AWP per unit on December 31, 2014, was 80.95% (n=42; range:79.50%-82.09%).

The year of market entry of insulins and analogues was associated with the CPI-adjusted AWP 30-days at market entry (p<0.001). The FDA approval date (p<0.001) and priority review process (p=0.005) of oral non-insulin antidiabetic drugs were associated with an increase in the AWP-30 days; whereas a FDA-labeled boxed warning was associated with a decrease in the AWP-30 days (p<0.001).

CONCLUSIONS: In the study period, antidiabetic drug prices increased above the inflation rate. The year of approval is significantly associated with antidiabetic drugs prices. The FDA priority review and FDA-labeled boxed warning are associated with prices of oral antidiabetic drugs.