Last updated: August 31, 2026
Mallinckrodt Hospital Products IP Ltd. lost its patent dispute against Praxair Distribution Inc. after the Federal Circuit held that the asserted inhaled-nitric-oxide treatment claims were directed to a natural law and lacked an inventive concept under 35 U.S.C. § 101. The case involved Mallinckrodt’s patents covering treatment of premature infants at risk of developing bronchopulmonary dysplasia, a complication associated with premature birth. The decision materially weakened patent protection around Mallinckrodt’s INOmax nitric oxide franchise.
What was Mallinckrodt v. Praxair about?
Mallinckrodt sued Praxair in the U.S. District Court for the District of Delaware after Praxair filed an abbreviated new drug application seeking approval for a generic inhaled nitric oxide product. The action was filed under the Hatch-Waxman framework, including 35 U.S.C. § 271(e)(2), which treats submission of a drug application as an artificial act of patent infringement.
The dispute concerned two Mallinckrodt patents:
| Patent |
Subject matter |
Litigation significance |
| U.S. Patent No. 8,795,741 |
Methods of treating premature infants with inhaled nitric oxide |
Asserted against Praxair’s proposed generic product |
| U.S. Patent No. 8,776,505 |
Related nitric-oxide treatment methods |
Asserted in the same ANDA litigation |
Mallinckrodt’s commercial product, INOmax, is inhaled nitric oxide approved for use in certain neonatal patients with hypoxic respiratory failure. The asserted patents focused on patient selection and treatment protocols intended to reduce the risk of bronchopulmonary dysplasia.
Which companies were involved in the patent litigation?
Mallinckrodt Hospital Products IP Ltd. was the patent owner and plaintiff. Praxair Distribution Inc. was the defendant and generic-drug applicant. Praxair was associated with the Linde group, which marketed medical gases and pursued competition in inhaled nitric oxide.
The case was filed in the District of Delaware under Civil Action No. 1:15-cv-00170. Judge Leonard P. Stark presided at the district-court stage. The Federal Circuit later reviewed the case in Mallinckrodt Hospital Products IP Ltd. v. Praxair Distribution Inc., 903 F.3d 1360 (Fed. Cir. 2018).
What patents protected Mallinckrodt’s inhaled nitric oxide treatment?
The asserted patents protected treatment regimens rather than the basic chemical identity of nitric oxide.
The claimed treatment framework generally involved:
- identifying premature infants at risk of developing bronchopulmonary dysplasia;
- administering inhaled nitric oxide;
- monitoring the patient’s oxygenation status; and
- adjusting or discontinuing treatment based on specified clinical conditions.
Mallinckrodt argued that the claims covered a specific clinical protocol and therefore recited patent-eligible applications of medical knowledge. Praxair argued that the claims merely instructed physicians to apply a natural relationship between nitric oxide treatment, oxygen saturation, and the risk of bronchopulmonary dysplasia.
The dispute did not primarily concern a new nitric oxide molecule, a novel device, or a manufacturing process. The patent estate was concentrated in method-of-treatment claims.
When did the district court invalidate the Mallinckrodt patents?
The District of Delaware granted summary judgment against Mallinckrodt on patent-eligibility grounds. The court concluded that the asserted claims were directed to a natural law and did not contain an inventive concept sufficient to transform that natural law into patent-eligible subject matter.
The relevant statutory framework was 35 U.S.C. § 101. Under the Supreme Court’s two-step framework, courts first determine whether a claim is directed to a law of nature, natural phenomenon, or abstract idea. If so, the court examines the claim elements individually and as an ordered combination to determine whether they add an inventive concept.
The district court treated the claims as directed to the discovery that inhaled nitric oxide could affect the risk of bronchopulmonary dysplasia in a particular population of premature infants. It found that the additional treatment and monitoring steps were conventional medical activity.
How did the Federal Circuit rule in Mallinckrodt v. Praxair?
The Federal Circuit affirmed the judgment that the asserted claims were invalid under § 101. The court held that the claims were directed to a natural law concerning the relationship between inhaled nitric oxide and the risk of bronchopulmonary dysplasia.
The court’s analysis focused on the practical substance of the claims. Although the claims contained multiple steps, the Federal Circuit concluded that the steps did not materially change the natural relationship identified by Mallinckrodt. Patient identification, nitric oxide administration, and monitoring were viewed as routine activities that implemented the natural law.
The Federal Circuit stated that a claim does not become patent-eligible merely because it recites a specific patient population or requires administration of a known therapy. The claim must include additional features that represent more than conventional application of the underlying biological relationship. Mallinckrodt, 903 F.3d at 1371-74.
Why did the court find the treatment claims ineligible?
The Federal Circuit’s reasoning had three central components.
The claims were directed to a natural relationship
The court viewed the asserted claims as centered on the relationship between nitric oxide treatment and reduced risk of bronchopulmonary dysplasia in premature infants. That relationship existed independently of the patent and was therefore treated as a natural law.
The treatment steps were conventional
The claims required actions such as administering inhaled nitric oxide and monitoring a patient. The court found those actions to be conventional in the relevant clinical setting. Conventional treatment activity cannot supply the inventive concept required under § 101 when the claim is directed to a natural law.
The claims did not require a new device or treatment technology
The asserted claims did not require a new nitric oxide formulation, a new delivery apparatus, or a previously unknown manufacturing technique. The court considered the claims to be directed to the selection and management of patients receiving an existing therapy.
This distinction matters for pharmaceutical patent strategy. A treatment patent may survive § 101 when it claims a genuinely unconventional dosing regimen, a new delivery technology, or a specific technical improvement. The Mallinckrodt claims were vulnerable because the court characterized their limitations as clinical instructions rather than technical advances.
What was the Federal Circuit’s final outcome?
The Federal Circuit affirmed the district court’s § 101 judgment. The ruling eliminated the asserted patent claims as enforceable barriers against Praxair’s proposed generic nitric oxide product.
The decision is reported at:
- Mallinckrodt Hospital Products IP Ltd. v. Praxair Distribution Inc., 903 F.3d 1360 (Fed. Cir. 2018).
- District of Delaware Civil Action No. 1:15-cv-00170.
The Federal Circuit’s decision resolved the central patent-eligibility issue. The court did not convert the case into a narrower claim-construction or infringement dispute. Once the claims were held ineligible, Mallinckrodt could not use them to block the ANDA pathway.
Did Mallinckrodt have an Orange Book patent listing?
The litigation arose from a generic-drug application for inhaled nitric oxide and therefore implicated the Orange Book and Hatch-Waxman certification process. The relevant patents were asserted against Praxair through an ANDA litigation framework.
The record and appellate opinion establish the patent litigation and the ANDA context. They do not provide a complete, current listing history for every INOmax-related patent or every regulatory exclusivity period. The Orange Book status of a patent can change through expiration, delisting, correction, or FDA administrative action.
The practical result was that the asserted method patents did not remain effective barriers after the Federal Circuit’s ruling.
What Paragraph IV issues affected Praxair’s generic launch?
Praxair’s ANDA filing triggered a patent dispute under the Hatch-Waxman Act. The filing was treated as an artificial act of infringement, allowing Mallinckrodt to sue before commercial launch.
The case illustrates the risk profile of Paragraph IV litigation involving hospital products:
| Issue |
Impact |
| ANDA filing |
Created jurisdiction for an infringement action before launch |
| Method-of-use claims |
Required Mallinckrodt to rely on clinical-treatment patents |
| § 101 challenge |
Allowed Praxair to attack the patent estate before a full infringement trial |
| Generic nitric oxide |
Created potential competition with INOmax |
| Invalidity judgment |
Removed the asserted claims as launch barriers |
Praxair’s strategy was effective because § 101 offered a threshold invalidity route. The company did not need to establish that every clinical step was noninfringing if the claims themselves were legally invalid.
Did the case involve formulation patents or manufacturing patents?
The principal patents at issue were method-of-treatment patents. The Federal Circuit decision did not invalidate a new nitric oxide molecule, a pharmaceutical composition claim, or a manufacturing process claim.
That limitation is commercially important. Invalidity of the ’741 and ’505 patents did not necessarily eliminate every possible patent right associated with INOmax, nitric oxide delivery systems, packaging, oxygen-control systems, or other product attributes. It eliminated the specific asserted claims at issue in the action.
For generic competitors, remaining barriers could include:
- device or delivery-system patents;
- formulation or container patents;
- manufacturing-process patents;
- later-filed method-of-use patents;
- regulatory exclusivity;
- contractual supply arrangements;
- hospital purchasing restrictions.
The decision therefore weakened one part of the estate but did not establish that every INOmax-related right was invalid.
What was the patent-strength assessment after the Federal Circuit decision?
The asserted patent estate was weak against a § 101 challenge because the claims combined a natural law with conventional medical steps.
| Patent-strength factor |
Assessment |
| Claim type |
Method of treatment |
| Technical novelty |
Limited in the asserted claim structure |
| Dependence on clinical observations |
High |
| Conventional administration steps |
High |
| Exposure to § 101 challenge |
High |
| Manufacturing protection |
Not central to the case |
| Device protection |
Not central to the case |
| Litigation outcome |
Claims held invalid |
| Generic-entry barrier |
Substantially reduced |
The decision also created drafting risks for future pharmaceutical patents. Claims that identify a patient subgroup and direct clinicians to administer a known drug may be vulnerable if the asserted benefit is characterized as a natural law. Patent applicants generally need technical claim limitations that demonstrate how the treatment is carried out, not merely what biological result is expected.
Did Mallinckrodt and Praxair enter a settlement agreement?
The Federal Circuit opinion reports the invalidity judgment and does not disclose a settlement resolving the appeal. No settlement terms are identified in the cited appellate decision.
The reported result is therefore a judicial invalidity decision rather than a publicly described launch settlement. Any commercial launch date would also depend on FDA approval, regulatory exclusivity, manufacturing readiness, and other unreported commercial arrangements.
What was the commercial impact on INOmax?
INOmax was Mallinckrodt’s established inhaled nitric oxide product for neonatal care. A successful generic entrant could pressure price, hospital contracting, and market share.
The litigation exposed revenue associated with:
- neonatal intensive-care-unit use;
- hospital nitric oxide supply contracts;
- proprietary delivery equipment;
- refill and cylinder logistics;
- clinical protocols tied to INOmax use.
The invalidity ruling increased generic-entry risk for the treatment indication covered by the asserted claims. It did not by itself establish the timing or scale of commercial substitution. FDA approval, product quality, gas-delivery compatibility, and hospital purchasing decisions remained relevant.
How does Mallinckrodt v. Praxair compare with other pharmaceutical patent cases?
The case is frequently cited with Mayo Collaborative Services v. Prometheus Laboratories Inc. and later Federal Circuit decisions involving diagnostic and treatment claims.
Its importance lies in the court’s treatment of a medical protocol as an application of a natural law. Compared with a patent claiming a new active ingredient or a technical formulation, Mallinckrodt’s claims had fewer structural limitations. Compared with a conventional dosing patent, the claims contained patient-selection and monitoring steps, but the court found those steps insufficient.
The decision is a warning that clinical specificity alone does not guarantee patent eligibility. A claim can be detailed, patient-specific, and commercially valuable yet remain ineligible if its central teaching is a natural relationship implemented through routine medical practice.
What are the key takeaways from Mallinckrodt v. Praxair?
- Mallinckrodt asserted U.S. Patent Nos. 8,795,741 and 8,776,505 against Praxair’s ANDA for inhaled nitric oxide.
- The patents covered treatment methods for premature infants at risk of bronchopulmonary dysplasia.
- The District of Delaware invalidated the asserted claims under 35 U.S.C. § 101.
- The Federal Circuit affirmed in 2018.
- The court characterized the claims as directed to a natural law concerning nitric oxide treatment and bronchopulmonary dysplasia.
- Conventional administration, monitoring, and patient-identification steps did not provide an inventive concept.
- The ruling reduced the patent barrier to generic competition with Mallinckrodt’s INOmax product.
- The decision did not establish that every INOmax-related formulation, device, manufacturing, or regulatory right was invalid.
- No settlement terms are disclosed in the reported appellate decision.
- The case remains a leading example of § 101 risk for method-of-treatment claims based on natural biological relationships.
FAQs about Mallinckrodt v. Praxair
What drug was involved in Mallinckrodt v. Praxair?
The case involved inhaled nitric oxide, including Mallinckrodt’s INOmax product used in neonatal patients with hypoxic respiratory failure.
Which federal statute did Praxair use to challenge the patents?
Praxair challenged the patents through the Hatch-Waxman ANDA process, with the infringement action proceeding under 35 U.S.C. § 271(e)(2). The principal invalidity ruling relied on 35 U.S.C. § 101.
Were the Mallinckrodt patents invalidated for obviousness?
The reported Federal Circuit decision affirmed invalidity under § 101. The central appellate holding was patent ineligibility based on a natural-law analysis, not an obviousness determination.
Can a method-of-treatment patent on nitric oxide still be valid after this case?
Yes. The decision concerned the specific asserted claims. A different claim directed to a new formulation, delivery system, dosing technology, manufacturing process, or technically unconventional treatment protocol could receive a different analysis.
What precedent is most closely associated with the Mallinckrodt decision?
The decision is closely associated with Mayo Collaborative Services v. Prometheus Laboratories Inc., 566 U.S. 66 (2012), because both cases examine whether medical-treatment steps add enough to a natural biological relationship to satisfy § 101.
References
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Mallinckrodt Hospital Products IP Ltd. v. Praxair Distribution Inc., 903 F.3d 1360 (Fed. Cir. 2018).
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Mallinckrodt Hospital Products IP Ltd. v. Praxair Distribution Inc., No. 1:15-cv-00170, U.S. District Court for the District of Delaware.
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Mayo Collaborative Services v. Prometheus Laboratories Inc., 566 U.S. 66 (2012).
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U.S. Food and Drug Administration. (2024). Orange Book: Approved drug products with therapeutic equivalence evaluations. FDA.
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U.S. Patent and Trademark Office. (n.d.). Patent Center: U.S. Patent Nos. 8,795,741 and 8,776,505. USPTO.
