How protected classes in Medicare Part D influence U.S. drug sales, utilization, and price

When the Medicare Part D prescription drug benefit was implemented in 2006, six drug classes were designated "protected classes." Because responsibility for obtaining favorable drug prices depends on private insurers' abilities to negotiate with pharmaceutical manufacturers using the threat of formulary exclusion, the protected class designation could undermine the insurers' ability to control spending and utilization of drugs in these six classes. I estimate the effect of the protected class policy on U.S. national drug sales, utilization, and price using 2001-2010 IMS Health National Sales Perspectives data and Verispan Vector One: National data and controlling for drug and year fixed effects. I find that protected status beginning in 2006 led to $112-121 million per drug per year higher U.S. sales for drugs in protected classes relative to unprotected drugs. Greater sales were driven by the antidepressant, antipsychotic, anticonvulsant, and antineoplastic classes. Subsequent analyses on a subset of drugs reveal that increases in both price and quantity are responsible for the growth of sales in protected class drugs. These results are important for informing the recent and ongoing deliberation by the Medicare program over whether to remove several classes from protection.