One of the gray areas of Medicare Part D coverage is determining when a prescription falls under Part D and when it falls under Part B. Most Part B drug spending is for drugs billed by a physician and provided incident to the physician's services for a Medicare patient. Medicare Part D medications are dispensed via a prescription and are usually self-administered. Here are examples of situational rules that determine whether a patient is covered under Part B or Part D. Many situations exist where a particular drug for a specific patient is covered under both Part B and Part D, albeit with different delivery and cost-sharing aspects. Understanding which applies when is important to gaining access to medically necessary prescriptions for patients. Giving this information to the prescription plan when writing a prescription order will assure that the medication is provided efficiently, rather than having to deal with denials and an appeal process.