Background
Prozac — the brand name for fluoxetine hydrochloride — was the blockbuster antidepressant of the 1990s and one of the best-selling prescription drugs in the world. Eli Lilly owned a portfolio of patents protecting Prozac, including the ‘081 patent covering the compound fluoxetine hydrochloride itself, and the ‘549 patent covering the method of administering fluoxetine to inhibit serotonin uptake in an animal’s brain neurons. Blocking serotonin reuptake is the mechanism by which fluoxetine treats depression.
In December 1995, Barr Laboratories filed an Abbreviated New Drug Application (ANDA) under the Hatch-Waxman Act seeking FDA approval to sell generic fluoxetine, certifying that Lilly’s patents were either invalid or would not be infringed by Barr’s proposed product. Lilly sued Barr in the Eastern District of Indiana. After an eight-day bench trial, the district court found the ‘081 patent valid and the ‘549 patent invalid for obviousness-type double patenting. Both sides appealed portions of the ruling.
The case turned on whether Lilly’s ‘549 patent — covering the method of administering fluoxetine to inhibit serotonin uptake — was obvious in light of Lilly’s earlier ‘213 patent, which covered a method of treating anxiety in humans with fluoxetine hydrochloride. If the ‘549 patent was merely an obvious variation of the ‘213 patent, it could not be used to extend patent protection beyond the term of the ‘213 patent.
The Court’s Holding
The Federal Circuit affirmed the district court’s invalidation of claim 7 of the ‘549 patent for obviousness-type double patenting. The doctrine of obviousness-type double patenting prevents a patentee from extending the life of a patent by obtaining a second patent on an obvious variation of the first. The court found that the only difference between the ‘213 patent’s method claim (treating anxiety with fluoxetine) and the ‘549 patent’s method claim (using fluoxetine to inhibit serotonin uptake) was that serotonin uptake inhibition is an inherent property of fluoxetine when administered. In other words, anyone practicing the ‘213 patent’s method (treating anxiety with fluoxetine) necessarily also performs the ‘549 patent’s claimed method (inhibiting serotonin uptake), because serotonin inhibition is how fluoxetine works.
On the best mode requirement, the court affirmed the district court’s finding that the ‘081 patent satisfied the requirement. Lilly had disclosed its best method of making and using fluoxetine hydrochloride at the time of filing, even if subsequent manufacturing improvements were not included — inventors need only disclose their best mode at the time of filing.
The practical effect of invalidating the ‘549 patent was significant: with that patent gone, generic manufacturers could potentially enter the Prozac market earlier than Lilly had hoped, since the ‘081 patent’s term was shorter than the ‘549 patent’s would have been.
Key Takeaways
- Obviousness-type double patenting prevents a patentee from extending patent protection by obtaining a second patent on a method that is merely an obvious variation of an earlier patent.
- If a claimed method is an inherent consequence of practicing an earlier patented method, it cannot be separately patented to extend the patent term.
- Pharmaceutical companies cannot use method-of-use patents to extend protection beyond the expiration of their compound patents when the method is inherent to the compound’s known pharmacological mechanism.
- The best mode requirement is assessed at the time of patent filing, not at the time of trial — later-developed improvements need not be disclosed.
- Hatch-Waxman ANDA litigation can result in generic entry years before expected, with major commercial consequences for brand-name pharmaceutical companies.
Why It Matters
The Eli Lilly v. Barr case had immediate and enormous commercial implications: Prozac was generating roughly $2.6 billion in annual U.S. sales at the time of the decision. When the Federal Circuit affirmed the invalidation of a key patent, Barr and other generic manufacturers were able to begin selling generic fluoxetine, rapidly eroding Lilly’s dominant market position. Within months of generic entry, Prozac’s market share collapsed — a textbook illustration of the competitive effects of patent expiration in the pharmaceutical industry.
The case is a landmark in Hatch-Waxman patent litigation and remains a leading precedent on obviousness-type double patenting in the pharmaceutical context. It established that pharmaceutical companies cannot manipulate their patent portfolios to extend exclusivity by patenting the known pharmacological mechanism underlying a patented drug’s therapeutic use. The decision influenced how pharmaceutical companies structure their patent strategies and how courts analyze double patenting claims in ANDA litigation.