Purdue OxyContin Patents Invalid Despite Stemming From Discovery Of Source Of Toxic Impurity

In Purdue Pharma L.P. v. Epic Pharma LLC, the Federal Circuit affirmed the district court decision holding four OxyContin patents invalid as obvious. In so doing, the court rejected Purdue's arguments that its discovery of the source of the toxic impurity that was minimized in the claimed products did not support patentability, because the solution to the problem did not depend on the source of the impurity.

The Perdue OxyContin Patents At Issue

There were four OxyContin® patents at issue, three of which claimed products having a low level of the toxic impurity referred to as “ABUKs” (α,β-unsaturated ketones) (U.S. Patent No. 7,674,799, U.S. Patent No. 7,674,800, and U.S. Patent No. 7,683,072), and one of which related to an abuse-resistant formulation (U.S. Patent No. 8,114,383). This article will focus on the court's treatment of the “low-ABUK patents.”

According to the Federal Circuit decision, prior to the invention at issue oxycodone hydrochloride was made by a three-step process:

oxidizing thebaine to form 14-hydroxycodeinone (referred to in the decision as “14-hydroxy”) converting 14-hydroxy to oxycodone free base by hydrogenation reacting oxycodone free base with hydrochloric acid to form oxycodone hydrochloride However, this process resulted in a final product with “high levels of 14- hydroxy, on the order of 1500 parts per million.” Since that compound was believed to be toxic, Purdue investigated how to make a product with lower levels of 14- hydroxy.

Its investigations led to the discovery that a particular isomer (8α, 14-dihydroxy-7,8- dihydrocodeinone ("8α")) was produced during the first step of the prior art process, and that the isomer was converted to 14-hydroxy during step three of the process. To solve this problem, Purdue added an additional hydrogenation step as a fourth step of the process, such that 14-hydroxy present after step three is converted to oxycodone free base in new step four.

Claim 1 of the '072 patent recites:

1. An oxycodone hydrochloride active pharmaceutical ingredient having less than 25 ppm 14-hydroxycodeinone, wherein at least a portion of the 14:hydroxycodeinone is derived from 8α,14-dihydroxy-7,8-dihydrocodeinone.

   Claim 1 of the '799 patent recites:

1. An oral dosage form comprising particles, the particles comprising from about 5 mg to about 320 mg oxycodone hydrochloride active pharmaceutical ingredient having less than 25 ppm 14-hydroxycodeinone, wherein at least a portion of the...