Final answer:
The Durham-Humphrey Amendment of 1951 created the two separate drug classes of prescription (RX) and over-the-counter (OTC) and mandated that drugs be safe for use. This legislation made a clear distinction between drugs that required a doctor's prescription and those that could be purchased over the counter.
Step-by-step explanation:
The FDCA amendment that created two different drug classes, prescription (RX) and over-the-counter (OTC), and required drugs to be safe, is the Durham-Humphrey Amendment of 1951. This amendment is a significant piece of pharmaceutical legislation that distinguished between drugs that could be sold with or without a prescription.
Before the amendment, the distinction between prescription and OTC drugs was not as clear. The Durham-Humphrey Amendment clarified the need for a prescription for certain drugs, partly to ensure they were used safely under medical supervision. It also permitted verbal prescriptions via telephone and refills on prescriptions, simplifying the process for both patients and healthcare providers.
The safety requirement stemmed from the need to protect consumers from potential harm due to the consumption of medicines without proper oversight. The amendment also provided the framework for FDA's later decisions to allow certain drugs initially approved as prescription medications to be reclassified as OTC under conditions deemed safe for self-medication by the public.