During the last Medicare Annual Open Enrollment Period (AOEP), you might have made changes to your Medicare Prescription Drug Plan (Part D) or your Medicare Advantage Plan (Part C) without realizing that one of your drugs was not covered. If a drug you are taking is no longer covered because Part D plan changed its formulary or if you changed to a new plan that does not cover the drug, you may need a transition fill. This gives you time to switch to another drug that is in the formulary or to request a formulary exception. Plans are required to provide a one-time "transition fill" (up to a 30-day supply) within the first 90 days after your plan or its formulary changes. Transition fills also apply if your plan covers the drug but quantity limits or prior authorization prevent you from getting the prescription filled. If you are eligible for a transition fill, the pharmacy will fill your prescription and will receive an electronic notice from your plan that this is a transition fill. In some cases, the pharmacist may need to call the drug plan to get permission to dispense the drug. You will receive a letter from the plan that includes instructions on how to find an appropriate substitute, how to file an exception request or how to manage quantity limits. If you have a problem getting a transition fill, your first step should be to contact your drug plan.