United States Patent 4,457,942: Scope, Claim Construction, and U.S. Landscape

What does US 4,457,942 claim in plain scope terms?

US 4,457,942 is directed to a method of treating “waste nitrogen accumulation disease” in patients with impaired urea synthesis or impaired urea excretion, by administering phenylacetate-generating compounds. The core claim family is process-based and centers on dosing a substituted phenylacetate prodrug to enable conversion to an “amino acylation product for urinary discharge.”

The independent claim ties together four technical/legal elements:

Disease/indication definition
- “waste nitrogen accumulation disease” caused by impairment in:
  - normal synthesis of urea from ordinary waste nitrogen, or
  - normal excretion of urea/waste nitrogen in the body.
Therapeutic mechanism requirement
- administration must be sufficient to produce enough phenylacetate to react with waste nitrogen to form an “amino acylation product” that enables urinary discharge.
Active ingredient class
- at least one compound having a structural formula (as provided in the claim), where n is 2, 4, 6, or 8, or a pharmaceutically acceptable salt.
Method/process character
- administering an “effective amount,” with continuation-dependent limitations in dependent claims.

How should the independent claim be construed?

Claim 1 element-by-element

A. “A process for controlling waste nitrogen accumulation disease”

This is a therapeutic treatment claim. In the U.S., infringement is typically assessed based on the act of treating an eligible patient with an eligible compound at an eligible dose to achieve the claimed therapeutic effect.

B. Patient state and causation

The claim anchors “waste nitrogen accumulation disease” to two mechanistic categories:
1. impairment in the normal synthesis of urea
2. impairment in normal excretion of urea from ordinary waste nitrogen.
Practically, this language narrows coverage to disorders where the nitrogen detoxification pathway is dysfunctional, including urea cycle disorders and severe hepatic dysfunction that disrupts ammonia detoxification.

C. Compound structure: “wherein n is 2, 4, 6 or 8”

The claim covers a family of compounds defined by parameter n, allowing multiple members of the same structural genus. Without the actual chemical drawing content of “STR3,” precise mapping to each member is limited. Still, the dependent claims resolve some embodiments as:
- phenylbutyrate (claim 6), and
- calcium and sodium salts (claims 7-8).

D. Mechanism-to-effect requirement: phenylacetate and urinary discharge

The claim does not just recite “an ammonia-lowering agent.” It requires dosing “sufficient to produce enough phenylacetate” so that phenylacetate “react[s] with waste nitrogen” to form an “amino acylation product for urinary discharge.”

This language increases claim strength against “close analogs” that do not produce phenylacetate in vivo or do not route nitrogen toward urinary discharge as contemplated.

Key legal takeaways on construction

Indication and mechanism are integrated: the method is not merely “administer drug”; it is “administer so phenylacetate is generated and waste nitrogen is converted to a urinary-discharge product.”
Dose sufficiency is functional: “effective amount sufficient to produce enough phenylacetate” is a functional limitation. In litigation, it can become a central question of pharmacokinetics, metabolism, and exposure thresholds.
Genus-plus-embodiments: claim 1 is a genus defined by n = 2, 4, 6, 8, while dependent claims lock in specific embodiments (phenylbutyrate, and salts).

What is the practical claim chart across claims 1 to 10?

Claim	Additional limitation beyond claim 1	Scope impact
1	Core method: treat waste nitrogen accumulation disease by administering a compound (n = 2, 4, 6, 8) or salt; dose must generate enough phenylacetate to react with waste nitrogen to form an amino acylation product for urinary discharge	Broadest coverage; requires both eligible patient state and phenylacetate-mediated urinary nitrogen excretion
2	Continue administration until accumulated waste nitrogen is discharged as urinary nitrogen	Adds a duration/endpoint condition; narrows infringement to continued dosing until discharge endpoint
3	Patient has a urea cycle enzymopathy	Narrows to a subgroup with defined underlying enzymatic deficiency
4	Patient has renal failure	Expands clinical relevance but still tied to “waste nitrogen accumulation disease” causation as defined
5	Patient has hepatic failure	Narrows to patients where hepatic dysfunction drives nitrogen accumulation
6	Compound is phenylbutyrate or salt	Captures a specific marketed/known embodiment of the prodrug mechanism
7	Salt is calcium salt	Limits to Ca salt form
8	Salt is sodium salt	Limits to Na salt form
9	Orally administered	Route limitation narrows method to oral dosing
10	Intravenously administered	Route limitation narrows method to IV dosing

Where is the “scope” strongest: patient category, mechanism, or compound?

The strongest anchors for the patent’s scope are:

Mechanism-to-effect tether (“phenylacetate” + “urinary discharge”)
- This is the most distinguishing element. Many nitrogen-modulating approaches exist (e.g., nitrogen scavengers, dialysis, supportive measures). This claim requires in vivo generation of phenylacetate and the contemplated nitrogen-handling chemistry.
Functional dose sufficiency (“enough phenylacetate”)
- The claim does not define an exact mg/kg threshold. It instead requires a pharmacodynamic outcome. That can either broaden the claim (any dose producing enough phenylacetate) or narrow it (requires proof of sufficiency).
Compound genus parameterization (n values) plus specific dependent embodiments
- Claim 6 to 8 reduce ambiguity by explicitly naming phenylbutyrate and salts. Those dependents strengthen enforcement against direct phenylbutyrate products.

What does the patent landscape look like in the U.S. around these claims?

At a high level, the landscape for this therapeutic concept has two layers:

Early method-of-use and prodrug/phenylacetate chemistry patents tied to controlling nitrogen accumulation through phenylacetate generation.
Later improvements that can include:
- different formulations (oral/IV),
- different salt forms,
- different dosing regimens,
- and distinct chemical analogs or salt/prodrug derivatives.

Given the claim language you provided, the “most directly mapped” U.S. competitive overlap in practice is other claims that also administer phenylbutyrate (or a compound that generates phenylacetate) to treat hyperammonemia/urea cycle disorders, either as:

method-of-treatment claims, or
claims to formulations and dosing regimens that are used to practice those methods.

How to map likely landscape pressure points to this patent

Because the independent claim is a process claim, the risk surface typically comes from:

label-directed practice: if a competitor’s product is used in a manner that generates phenylacetate and discharges nitrogen as claimed, the product can drive method infringement even without the competitor explicitly asserting a “waste nitrogen” claim.
prodrug metabolism: if a competitor uses a prodrug that yields phenylacetate, the mechanism limitation can be satisfied.
subclass variations (salt form and route): dependent claims 7-8 (calcium/sodium salts) and 9-10 (oral/IV) can be triggered depending on dosage form and route.

What are the likely design-around paths, based on claim structure?

Design-around is assessed by breaking at least one essential limitation. In this claim set, the easiest conceptual levers are:

Avoid phenylacetate generation: if a candidate does not produce enough phenylacetate in vivo, it can miss the mechanism limitation.
Use a non-urinary discharge nitrogen pathway: if the metabolic route does not yield the claimed amino acylation product for urinary discharge (as described), it can miss the functional chemistry requirement.
Avoid the compound genus: claim 1 requires compounds where n is 2, 4, 6, or 8. A different chemical family may avoid the structural limitation.

Route (oral vs IV) and salt form can be varied, but those are dependent limitations. A competitor that practices claim 1 without infringing dependents may still face exposure from claim 1.

Claim strength profile: where does the patent look vulnerable vs. robust?

Robust areas

Specific mechanistic linkage: “phenylacetate to react with waste nitrogen … for urinary discharge” is narrower than a generic ammonia-reducing statement.
Specific embodiment dependence: phenylbutyrate plus calcium/sodium salt dependents reduce the need to rely on interpreting the “n” genus alone.

Potential vulnerability areas (based on claim language, not case law)

Functional dose sufficiency: “effective amount sufficient to produce enough phenylacetate” can require complex evidence. If a product’s phenylacetate exposure differs or is argued as insufficient for the claimed transformation, it can narrow infringement.
Definition of “waste nitrogen accumulation disease”: the phrase is broad, but the causation is specific (urea synthesis or excretion impairment). If a competitor’s target indication is framed outside those causation parameters, it could affect infringement.

What competitive molecules and regimens are most likely to overlap this scope?

Based strictly on your provided claims, the most direct overlap comes from:

phenylbutyrate (including its salts),
calcium and sodium salts used to treat urea cycle enzymopathies and hyperammonemia arising from hepatic dysfunction, and
both oral and IV administrations that are used to achieve phenylacetate-mediated urinary nitrogen excretion.

Competitors using alternative nitrogen scavengers (not described in the claim) may still overlap indirectly if their mechanism converges on phenylacetate production, but the explicit requirement for phenylacetate conversion is a strong discriminator.

Key Takeaways

US 4,457,942 is a method-of-treatment patent for “waste nitrogen accumulation disease” driven by impaired urea synthesis or excretion.
The independent claim requires administering a defined phenylacetate-generating compound class (n = 2, 4, 6, or 8) or a pharmaceutically acceptable salt, in an amount sufficient to produce phenylacetate that reacts with waste nitrogen to form an amino acylation product for urinary discharge.
The claim set is reinforced by dependents specifying phenylbutyrate and calcium/sodium salts, plus oral and intravenous routes, and by narrower patient subsets (urea cycle enzymopathy, renal failure, hepatic failure).
The most direct enforcement and overlap risk in the U.S. comes from products and regimens that generate phenylacetate in vivo and are used to drive urinary nitrogen excretion consistent with the claim mechanism.

FAQs

Is US 4,457,942 a composition patent or a method patent?
It is a process/method patent: “a process for controlling waste nitrogen accumulation disease,” defined by administering a compound and achieving a phenylacetate-mediated urinary discharge outcome.
What is the central mechanistic requirement in claim 1?
The administered amount must be sufficient to produce phenylacetate, which then reacts with waste nitrogen to form an amino acylation product for urinary discharge.
Does the patent cover phenylbutyrate specifically?
Yes. Claim 6 limits the compound to phenylbutyrate (or a salt).
Do salt form and route matter?
They appear in dependent claims: calcium salt (claim 7), sodium salt (claim 8), oral administration (claim 9), and intravenous administration (claim 10). Claim 1 is broader than those dependents.
What patient categories are explicitly called out?
Dependent claims specify a urea cycle enzymopathy (claim 3) and patients suffering from renal failure (claim 4) or hepatic failure (claim 5).

References

[1] United States Patent 4,457,942. “Process for controlling waste nitrogen accumulation disease.” Claims 1-10 (as provided in the prompt).

Country	Patent Number	Estimated Expiration	Supplementary Protection Certificate	SPC Country	SPC Expiration
European Patent Office	0177499	⤷ Start Trial
World Intellectual Property Organization (WIPO)	8504805	⤷ Start Trial
>Country	>Patent Number	>Estimated Expiration	>Supplementary Protection Certificate	>SPC Country	>SPC Expiration

Details for Patent: 4,457,942

Summary for Patent: 4,457,942