Medicare Drug Formulary Protection Act - Amends title XVIII (Medicare) of the Social Security Act to prohibit removal of covered part D (Voluntary Prescription Drug Benefit Program) drugs from a prescription drug plan formulary, or imposition of a restriction or limitation on the coverage of such a drug, during the plan year: (1) except at the beginning; or (2) for an individual enrollee, from the date of enrollment until December 31 of the immediately succeeding plan year. Specifies exceptions to such prohibition. Requires an annual notice to enrollees of changes in formulary and other restrictions or limitations on coverage.