Medicare prescription drug plan formulary restrictions after postmarket FDA black box warnings

BACKGROUND: The boxed warning (also known as”black box warning”) is one of the FDA's strongest safety actions for pharmaceuticals. After the FDA issues black box warnings for drugs, prescribing changes have been inconsistent. Formulary management may provide an opportunity to restrict access to drugs with serious safety concerns. OBJECTIVE: To examine Medicare prescription drug plan formulary changes after new FDA postmarket black box warnings and major updates to preexisting black box warnings. METHODS: In this cohort study, we identified each drug that received a new FDA postmarket black box warning or a major update to a preexisting black box warning from January 2008 through June 2015 and examined its formulary coverage. The main outcome measure was the proportion of Medicare prescription drug plan formularies providing unrestrictive coverage immediately before the black box warning, at least 1 year after the warning and at least 2 years after the warning. Unrestrictive formulary coverage was defined as coverage of a drug without prior authorization or step-therapy requirements. RESULTS: Of 101 new black box warnings and major updates to preexisting warnings affecting 68 unique drug formulations, the mean percentage of formularies providing unrestrictive coverage changed from 65.4% (95% CI=59.6%-71.2%) prewarning; 62.6% (95% CI=56.3%-68.9%, P=0.04) at least 1 year postwarning; and 61.9% (95% CI=55.4%-68.5%, P=0.10) at least 2 years postwarning. CONCLUSIONS: The mean percentage of Medicare prescription drug plan formularies providing unrestrictive coverage decreased modestly by approximately 3 percentage points after drugs received postmarket FDA black box warnings. Formulary restrictions may present an underused mechanism to reduce use of potentially unsafe medications.