Prescription Drug Labeling Act -Amends the Federal Food, Drug, and Cosmetic Act to require that in the labeling and advertising of drugs sold by prescription the established name of such drug must appear each time the drug's proprietary name is used.

Allows a pharmacist to fill or refill a prescription for a drug identified by its proprietary name with a substitute drug of the same established name or the same qualitative composition, unless the prescription requires the proprietary name drug exclusively. Requires that such substitute drugs, whether identified in the prescription by proprietary or by established name, be sold at a cost to the patient which is less than the cost of the drug so identified.