Personalized medicine considers factors unique and specific to each patient to make clinical decisions, including selecting pharmacotherapy. Drug formularies, including those available to enrollees in Medicare Part D, are based on group characteristics and financial considerations. Consequently, an appeal of a formulary's preferred drug selection may be necessary to ensure the best care of the patient. Consideration of basic principles of clinical pharmacology can be used to decide whether an exemption should be considered and to document specific reasons for the request.