We were told by FDA CDER last June, after a fairly extensive interaction in which we outlined some technology that we had in mind, that if a material is "antimicrobial" and its function is to protect or benefit the patient or the user, it is a drug and the product is a combination device.
If OTOH the anti-microbial functionality is justified to FDA's satisfaction as being primarily intended to protect the product itself from deterioration, and if the material is shown via testing to be non-leaching/non-migratory/non-sacrificial/not chemically interactive with the patient in the intended use, the FDA may choose to regard the product as just a device.
Also note that any such material must have an EPA pesticide registration in order to make any antimicrobial-functionality claim or statement at all. The EPA has taken big-time enforcement action against shoe makers for anti-microbial claims based on use of unregistered materials. Do a Google search on "EPA VF North Face".
And, note that other nations have differing stances. Japan, for instance, applies their standard Z2801.