Continuing from alexandrabuga’s response, a Request for Designation is a written to the Office of Combination Products (OCP) requesting regulatory classification to determine if it is a device, drug, and/or biologic product and which Agency will be assigned. The FDA formally responds to RFD’s by returning a letter of designation. The letter of designation is a binding commitment to the device classification and it’s assigned agency. These terms may only be subjected to change only under the conditions detailed in Section 563 of the FD&C Act and 21 CFR 3.9. A change in classification or the product’s assigned agency typically occurs when the primary mode of action (PMOA) differs from what was originally described in the RFD.
http://www.fda.gov/CombinationProducts/GuidanceRegulatoryInformation/ucm109108.htm