Inherent Disclosures in Prior Art in the United States

By: Emily Marie Boggs


A patent claim may be rejected under 35 USC § 102 as being anticipated by a prior art reference if each and every element of the claim is disclosed by the prior art reference, either expressly or inherently.  According to the inherency doctrine, a prior art reference inherently discloses a claim limitation when “the limitation at issue necessarily must be present, or [is] the natural result of the combination of elements explicitly disclosed by the prior art.” In a recent case[2] from the U.S. Court of Appeals for the Federal Circuit, the Court found the inherency doctrine could not be used to fill in a component of a composition when the prior art includes only an incomplete description of the composition which would not allow skilled artisans to have access to the components of the composition.  The claims in suit were not invalidated because the prior art did not expressly or inherently disclose each and every element of the claims.

Endo Pharmaceuticals Solutions, Inc. (Endo) and Bayer Intellectual Property GmbH and Payer Pharma AG (Bayer) sued Custopharm Inc. (Custopharm) for infringement of various claims of two patents.  The patents relate generally to a formulation and injection regimen for Aveed®, a long-acting injectable testosterone replacement therapy.  Custopharm stipulated to infringement and asserted the claims in suit were invalid.  The district court concluded that Custopharm had not proven the claims were invalid and Custopharm appealed.  The Federal Circuit upheld the District Court decision.

The claims in suit were directed towards three key elements: (1) 750 mg testosterone undecanoate (TU); (2) a vehicle consisting of castor oil and a co-solvent (specifically benzyl benzoate in one claim); and (3) an injection schedule.  Custopharm asserted all three elements were obvious in view of the prior art.  The court addressed each element separately, and found that none of them were obvious in view of the prior art.  The court addressed the inherency doctrine in its treatment of element (2) as discussed below.

The prior art in suit included Behre[3], Nieschlag[4], and von Eckardstein[5], scientific articles (Articles) which described clinical trials involving TU injections using a composition of TU in castor oil.  The Articles do not disclose or describe the use of benzyl benzoate or any co-solvent.  Saad[6], an article published after the priority dates of the patents in suit, disclosed that the vehicle used in the Articles was 40% castor oil and 60% benzyl benzoate.  Because Saad was published after the priority dates of the patents in suit, the information disclosed therein was not available to a skilled artisan before the priority dates, and Saad was not available as prior art.

Custopharm argued that the vehicle formulation consisting of castor oil and benzyl benzoate was “necessarily present” in the Articles because Saad later disclosed that it was used in the studies described by the Articles.  The court disagreed based on the following reasoning.

Custopharm argued that the Articles inherently disclosed the vehicle formulation, including benzyl benzoate, because the Articles provide a detailed recitation of the injection composition’s pharmacokinetic performance, and that a skilled artisan could determine the composition included a vehicle consisting of 40% castor oil and 60% benzyl benzoate based on the reported pharmacokinetic performance.  The court disagreed and found that Custopharm failed to demonstrate that a skilled artisan could determine the vehicle composition based only on the reported pharmacokinetic performance, because the prior art included numerous potential co-solvents other than benzyl benzoate that could potentially produce similar performances.  The court noted that inherency “may not be established by probabilities or possibilities” and that “the mere fact that a certain thing may result from a given set of circumstances is not sufficient.”

The court found that two cases cited by Custopharm did not apply to the situation in suit.  In re Omeprazole[7] addressed patent claims directed towards a pharmaceutical composition including an in situ separating layer, which was a natural result of using the ingredients described in the patent.  The in situ separating layer was inherent because it would result each and every time the ingredients described in the patent were assembled using the method described in the patent.  The court found that Custopharm did not demonstrate that pharmacokinetic profile defined in the prior art would only arise from a mixture of 40% castor oil and 60% benzyl benzoate.  Accordingly, the facts of the present case could not be analogized to In re Omeprazole.

In re Crish[8] addressed patent claims directed towards a human involucrin gene promoter sequence and a prior art publication which disclosed the structure of the human involucrin gene, including the approximate size of the promoter region, but did not disclose the sequence of the promoter region.  The prior art publication made it clear that the human involucrin gene promoter region was known and that the sequence in the patent was necessarily contained in the prior art sequence.  The court found that the prior art in the present suit did not include any evidence that only the claimed vehicle formulation could give rise to the pharmacokinetic performance recited in the prior art.

The court explained:

Crish and Omeprazole were about inherently present properties or characteristics for a “known” prior art product. But here, the TU injection composition recounted in the Articles cannot be said to be “known” in the same way; the Articles failed to disclose that the composition’s vehicle formulation included another, key ingredient, benzyl benzoate, let alone the ratio of benzyl benzoate to castor oil. And there was no evidence in the record that a skilled artisan could determine the nondisclosed vehicle formulation based on the reported pharmacokinetic performance profile, or that the non-disclosed vehicle formulation was necessarily a feature of the TU injection studied in the Articles. Under the circumstances of this case, the incomplete description of the TU injection composition elements denied skilled artisans from having access to that composition, thereby precluding use of the inherency doctrine to fill in disclosure about the product missing from the Articles.

The court found that although the vehicle formulation of 40% castor oil and 60% benzyl benzoate was actually used in the prior art, it was not inherent therein.

In view of this decision, patent practitioners should keep in mind that a prior art disclosure inherently discloses an element only if the element must necessarily be present in the prior art, as taught by the disclosure.  The actual presence of the element at issue in the prior art is not part of the analysis of whether or not the element is inherent in the disclosure of the prior art.  Accordingly, patent practitioners should not automatically treat elements of the prior art which were not explicitly disclosed as being inherently disclosed.  Rather, these elements must be carefully analyzed in view of the case law on inherency to determine whether or not they are inherently disclosed.


[1]  Par Pharmaceutical v. TWI Pharmaceuticals, Inc., 2014-1391 (Fed. Cir., December 3, 2014)

[2]  Endo Pharmaceuticals Solutions v. Custopharm Inc., 2017-1719 (Fed. Cir., July 13, 2018)

[3] H.M. Behre et al., Intramuscular injection of testosterone undecanoate for the treatment of male hypogonadism: phase I studies, 140 Eur. J. Endocrinol. 414 (1999). Behre compared the half-life of a single dose of 1000 mg TU in castor oil with a single dose of 1000 mg TU in tea seed oil.

[4] E. Nieschlag et al., Repeated intramuscular injections of testosterone undecanoate for substitution therapy in hypogonadal men, 51 Clin. Endocrinol. 757 (1999). Nieschlag studied the suitability of using four intramuscular injections of 1000 mg TU in castor oil at six week intervals.

[5] S. von Eckardstein & E. Nieschlag, Treatment of Male Hypogonadism with Testosterone Undecanoate Injected at Extended Intervals of 12 Weeks: A Phase II Study, 23(3) J. Androl. 419 (2002). von Eckardstein studied the efficacy and safety of prolonged TU treatment at extended injection intervals—starting at injections every six weeks followed by a gradual increase in the interval to every twelve weeks after the tenth injection— over a 3.2 year period

[6] F. Saad, et al., More than eight years’ hands-on experience with the novel long-acting parenteral testosterone undecanoate, 9(3) Asian J. Androl 291 (2007).

[7]  In re Omeprazole Patent Litigation, 2007-1414 (Fed. Cir., August 20, 2008).

[8] In re Crish, 2004-1075 (Fed. Cir., December 21, 2004).