Some categories of beneficiaries are not bound by the lock-in rules and may enroll or disenroll from a PDP plan in other than the AEP. An individual may at any time, during a designated Special Election Period (SEP), discontinue the election of a PDP plan offered by an PDP organization and change his or her election to original Medicare or to a different PDP plan. Examples of situations which may entitle an individual to an SEP include the termination or discontinuation of a plan, a change in residency out of the service area, the organization violating a provision of a contract or misrepresenting the planâ€™s provisions, or the individual meeting other exceptional conditions as CMS may provide. CMS has also designated an SEP for individuals entitled to Medicare A and B and who receive any type of assistance from Title XIX (Medicaid), including full-benefit dual eligible individuals, as well as those eligible only for the Medicare Savings Programs. This SEP lasts from the time the individual becomes dually eligible until such time as they no longer receive Medicaid benefits. Individuals who are eligible for an SEP under the guidance for Part D enrollment and disenrollment may use that SEP to also make an election into or out of an MA-PD plan.
from Medicare.gov, Prescription Drug Coverage (2013), Prescription Drug Coverage: Basic Information (2013)