Affordable Prescriptions for Patients Through Promoting Competition Act of 2021 This bill prohibits product hopping by drug manufacturers and authorizes the Federal Trade Commission to sue in court or institute administrative proceedings to enforce this prohibition. Generally, product-hopping describes a situation where, when the patents on a reference drug (or biological product) expire, the manufacturer switches to a follow-on product that is covered by a later-expiring patent. Under this bill, a follow-on product is a changed, modified, or reformulated version of the reference drug that shares an indication (what the drug is used for) with the reference drug. The bill presumes product hopping has occurred when a reference drug manufacturer engages in a hard switch or a soft switch . A hard switch occurs when, after receiving notice of an application for Food and Drug Administration (FDA) approval to market a generic (or biosimilar) version of the reference drug, the manufacturer markets a follow-on product and (1) the FDA withdraws approval of the reference drug at the manufacturer's request, or (2) the manufacturer announces the withdrawal or discontinuance of the reference drug or destroys the drug's inventory in a manner that impedes generic competitors. Furthermore, the bill presumes that a soft switch occurred if a reference drug manufacturer (1) markets a follow-on product, and (2) takes actions that disadvantage the reference drug relative to that follow-on product in a way that impedes competition from a generic drug. A drug manufacturer may rebut these presumptions by demonstrating that its conduct was not intended to limit competition.