This study characterizes price increases exceeding inflation between 2012 and 2017 for protected-class drugs (antineoplastics, antiretrovirals, antidepressants, antipsychotics, anticonvulsants, and immunosuppressants for transplant patients) that would lead to their exclusion from Medicare Part D coverage based on excessive cost under a 2018 CMS rule intended to facilitate more effective price negotiations.