How Patent Expiration Makes Generic Drugs Possible

Generic drugs are chemically equivalent to their brand-name counterparts but sold at a fraction of the price. They exist because patents expire. Understanding the mechanics of how patent expiration enables generics helps explain both drug pricing and the strategic behavior of pharmaceutical companies.

The basic requirement: no active patents

Before a generic manufacturer can sell a product in the US, it must submit an Abbreviated New Drug Application (ANDA) to the FDA demonstrating that its product is bioequivalent to the reference listed drug.

The ANDA process also requires the applicant to certify, for each patent listed in the FDA's Orange Book, one of the following:

• The patent has expired
• The patent doesn't apply to the generic's formulation
• The patent is invalid or won't be infringed by the generic

A generic manufacturer filing under the third option (known as a Paragraph IV certification) is asserting that an active patent shouldn't block its entry. That typically results in patent litigation, which can delay generic entry for up to 30 months under the Hatch-Waxman statute.

The 30-month stay

If a brand-name company sues a Paragraph IV filer within 45 days of receiving notice, the FDA automatically imposes a 30-month stay on approving the ANDA. This gives the brand-name company time to litigate.

The 30-month stay is a critical feature of the US system. It effectively gives originator companies a litigation window that can extend exclusivity even for patents that might ultimately be invalidated. The generic can win the litigation and still have spent 2.5 years waiting.

The 180-day exclusivity incentive

To encourage generics to challenge questionable patents, Congress created a reward: the first ANDA filer to successfully challenge a patent gets 180 days of generic exclusivity. During that period, no other generic can enter the market.

This 180-day window can be enormously valuable. The first generic typically captures significant market share before additional generics enter and prices fall further.

Why not all patents expire at the same time

As discussed in the post on patent cliffs, a single drug may be protected by dozens of patents with different expiration dates. The compound patent might expire first, but formulation patents, dosing patents and method patents can extend protection further.

Generic manufacturers often enter as soon as the compound patent expires if other patents are weak enough to challenge, rather than waiting for every patent in the portfolio to expire.

The Hatch-Waxman tradeoff

The Drug Price Competition and Patent Term Restoration Act of 1984 (Hatch-Waxman) was designed to balance two interests: encouraging generic entry to lower drug prices and preserving innovator incentives for pharmaceutical R&D.

On the generic side, the ANDA process streamlined approval by accepting bioequivalence data rather than requiring new clinical trials.

On the innovator side, the law enabled PTE (patent term extension) to compensate for regulatory review time and created the 5-year new chemical entity exclusivity period, which is separate from patent protection.

How to find out when a drug's patents expire

The FDA's Orange Book lists patents associated with approved drugs and their expiration dates. The Purple Book covers biologics. These are publicly searchable.

For checking the expiration date of a specific patent number associated with a drug, the Patent Sunset calculator provides a calculated date accounting for PTA, PTE and other adjustments.

Pharmaceutical patent analysis is one of the most common applications for patent expiration tracking, given the direct connection between patent status and generic availability.