With little explanation, CMS has proposed several changes to Medicare Part D that could hamstring what by all accounts has been an almost unqualified success. If the proposed rule changes take effect, they not only would limit patient access to drugs for some diseases, but also remove incentives to negotiate pharmacy discounts, and could have unforeseen knock-on effects on drug companies.

The changes aren't due to take effect until calendar 2015 and 2016. But under current rulemaking deadlines, CMS has precious little time to incorporate public feedback in the short time between the end of the comment period and the due date for the agency's annual letter informing insurers of plan requirements for 2015.