US Patent 5,550,165: Nitisinone Patent Scope, Expiration, Orange Book Status, and Generic Entry Risk

US Patent No. 5,550,165 covers pharmaceutical compositions and therapeutic methods using nitisinone, also known as NTBC, for hereditary tyrosinaemia type 1. The patent does not claim nitisinone as a chemical compound, its manufacture, or every possible HPPD inhibitor. Its enforceable scope is limited to compositions containing nitisinone and treatment methods directed to hereditary tyrosinaemia and associated HPPD-mediated pathology.

The patent was issued on August 27, 1996. Because the underlying U.S. application predates the 1995 patent-term transition, its ordinary statutory term was generally calculated from issuance rather than the later 20-year-from-filing rule. The patent therefore expired on August 27, 2013, absent an effective term adjustment or other extension. No current enforceable exclusivity should be attributed to US 5,550,165.

What drug and disease does US 5,550,165 protect?

The claimed active ingredient is nitisinone:

Attribute	Description
Generic name	Nitisinone
Development code	NTBC
Chemical name in patent	2-(2-nitro-4-trifluoromethylbenzoyl)-1,3-cyclohexanedione
Pharmacologic target	4-hydroxyphenylpyruvate dioxygenase, or HPPD
Principal indication	Hereditary tyrosinaemia type 1
FDA reference product	Orfadin
Later U.S. product	Nityr
Drug class	Small-molecule HPPD inhibitor

Nitisinone inhibits HPPD, an enzyme in tyrosine catabolism. In hereditary tyrosinaemia type 1, HPPD inhibition reduces formation of downstream toxic metabolites, including fumarylacetoacetate-derived compounds. The claims are directed to the therapeutic use of this metabolic intervention rather than to a broad class of HPPD inhibitors.

The patent’s disease language is broader in some claims than the modern FDA indication. Claim 6 refers to “multi-organ symptoms” caused by hereditary tyrosinaemia. Claims 7, 9, and 10 cover treatment of hereditary tyrosinaemia in humans or warm-blooded animals and inhibition of HPPD catalytic activity in patients with the disease.

What are the independent claims of US 5,550,165?

Claims 1, 6, 7, 9, and 10 are the principal independent claims. Their practical scope is as follows:

Claim	Claim category	Core limitation
1	Pharmaceutical composition	Nitisinone or a pharmaceutically acceptable salt, in an effective HPPD-inhibiting amount, with a pharmaceutically acceptable carrier
6	Method of treatment	Administering nitisinone to a human patient with hereditary tyrosinaemia and associated multi-organ symptoms
7	Method of treatment	Administering nitisinone to a warm-blooded animal suffering from hereditary tyrosinaemia
9	Method of enzyme inhibition and treatment	Administering nitisinone to a human patient with hereditary tyrosinaemia and associated symptoms to inhibit HPPD
10	Method of treatment	Treating hereditary tyrosinaemia where HPPD catalytic products are involved or implicated

Claim 1 is the central composition claim. It requires four elements:

A pharmaceutical composition.
Nitisinone or a pharmaceutically acceptable salt.
An effective amount that inhibits HPPD.
A pharmaceutically acceptable diluent or carrier.

The claim does not require a particular dosage strength, release profile, excipient combination, route of administration, patient age, or treatment duration.

How broad is the composition claim?

Claim 1 is chemically narrow but formulation-neutral.

It is chemically narrow because the claim identifies one specific active compound. A composition containing another HPPD inhibitor would not fall within the literal scope of claim 1 merely because it produced the same pharmacologic effect.

It is formulation-neutral because the claim does not limit the composition to capsules, tablets, suspensions, a specific excipient, or a particular manufacturing process. A conventional oral capsule containing nitisinone and a pharmaceutically acceptable carrier could satisfy the claim. The same applies to an injectable or rectal formulation if the remaining limitations are met.

The claim also covers pharmaceutically acceptable salts of nitisinone. Claim 2 reinforces this scope by identifying:

Alkali metal salts.
Alkaline earth metal salts.
Ammonium salts.
Salts with organic bases producing physiologically acceptable cations.

The salt language does not create a separate compound patent. It expands the composition claim to specified salt forms of the claimed active ingredient.

What formulations are protected by claims 3, 4, 5, and 8?

The dependent composition claims provide formulation and route examples but do not materially expand the chemical scope beyond nitisinone-containing compositions.

Claim	Protected subject matter
3	Oral, parenteral, or rectal dosage forms
4	Tablets, lozenges, hard capsules, soft capsules, aqueous suspensions, oily suspensions, emulsions, dispersible powders, dispersible granules, syrups, and elixirs
5	Sterile aqueous and oily parenteral solutions
8	A composition using lactose, croscarmellose sodium, maize starch, polyvinylpyrrolidone, or magnesium stearate as carrier or excipient

Claim 4 is a dosage-form list. It is not limited to the exact commercial Orfadin capsule formulation. A product may infringe claim 4 if it contains nitisinone and is presented in one of the listed palatable oral forms, subject to the other limitations inherited from claim 1 or claim 2.

Claim 8 is narrower than claim 1 because it identifies specific excipients. It may be relevant to a formulation that uses one or more of the listed excipients, but it does not establish ownership over those excipients or over the general concept of a nitisinone tablet or capsule.

The claims do not expressly cover:

Enteric coatings.
Specific particle sizes.
Polymorphs.
Amorphous dispersions.
Nanoparticle formulations.
Controlled-release systems.
Particular dissolution specifications.
Specific nitisinone concentrations.
A defined tablet hardness or manufacturing process.

Those features would require support from other claims or separate patents.

What method-of-use patents does US 5,550,165 contain?

The patent includes overlapping method claims directed to hereditary tyrosinaemia and HPPD inhibition.

Claim 6 is focused on multi-organ symptoms in human patients. Claim 7 is broader as to the treated animal population because it refers to a “warm blooded animal,” but it remains limited to hereditary tyrosinaemia. Claim 9 combines treatment of human patients with inhibition of HPPD catalytic activity. Claim 10 addresses disease conditions in which products of HPPD catalysis are involved or implicated.

The method claims have several important limits:

They require administration of nitisinone or a pharmaceutically acceptable salt.
They require an effective or therapeutically effective amount.
Most claims require hereditary tyrosinaemia.
Claims 6 and 9 are directed to human patients.
Claim 7 includes animals but remains disease-specific.
The claims do not state a precise dose or dosing interval.

The claims are therefore not broad claims to treating every metabolic disease involving tyrosine, nor are they claims to HPPD inhibition in agriculture. Nitisinone’s herbicidal and other nonmedical applications would not fall within these treatment claims absent the required disease and pharmaceutical limitations.

When did US Patent 5,550,165 expire?

Milestone	Date or status
Priority and foreign-family development	Approximately early 1990s family originating in the Astra/Zెనeca group
U.S. patent issue	August 27, 1996
Nominal pre-URAA term	17 years from issue
Nominal expiration	August 27, 2013
Current enforceability	Expired
Patent-term extension relevance	No current extension-based exclusivity is generally associated with this patent

The patent’s expiration removed the principal composition and method-of-use barrier created by US 5,550,165. A later applicant could still face separate patents covering a formulation, salt, dosage regimen, manufacturing process, or newly approved indication. Those rights would need independent analysis and cannot be inferred from the expired patent.

What was the Orange Book status of US 5,550,165?

US 5,550,165 was associated with the U.S. Orfadin product and was relevant to the Orange Book patent listing for nitisinone capsules. The patent listed the foundational nitisinone composition and treatment technology rather than a narrow commercial package configuration.

The Orange Book distinction is important:

An Orange Book listing identifies patents submitted by an NDA holder for a drug product.
It does not make an expired patent enforceable.
It does not establish that every listed claim covers every later nitisinone product.
It does not eliminate the need to analyze later formulation or use patents.

For Orfadin, the more important non-patent exclusivity was orphan-drug exclusivity. FDA approved Orfadin for hereditary tyrosinaemia type 1 in 2002, and the orphan exclusivity period generally ran for seven years from approval, through approximately January 2009. Orphan exclusivity and patent protection are separate rights. Orphan exclusivity restricted approval of the same drug for the same indication during its statutory period, while the patent restricted conduct falling within valid, unexpired claims.

Which products competed with Orfadin after patent expiration?

The main U.S. competitive products are Orfadin and Nityr.

Product	Active ingredient	Sponsor or manufacturer	Regulatory route or status
Orfadin capsules	Nitisinone	Swedish Orphan Biovitrum, or Sobi, through the Orfadin franchise	Original FDA-approved product
Orfadin oral suspension	Nitisinone	Sobi	FDA-approved liquid formulation
Nityr tablets	Nitisinone	Cycle Pharmaceuticals	FDA-approved competing product
Compounded nitisinone	Nitisinone	Pharmacies or specialty providers	Not equivalent to an FDA-approved finished product

Nityr entered the U.S. market after the core US 5,550,165 patent had expired. Its commercial differentiation has included tablet presentation, patient access, and competition in a rare-disease market rather than reliance on a continuing monopoly under the 1996 patent.

Because nitisinone is a small molecule, biosimilar analysis is not applicable. The relevant regulatory pathways are abbreviated or hybrid small-molecule pathways, including ANDA and 505(b)(2) mechanisms, not the biosimilar pathway under the Public Health Service Act.

Which companies challenged Orfadin exclusivity?

Publicly visible market entry has involved competing nitisinone products, including Nityr, rather than a biosimilar challenge. A Paragraph IV certification would be relevant if an ANDA applicant challenged an unexpired Orange Book patent. That issue became less significant for US 5,550,165 after its 2013 expiration.

The record should be separated into three periods:

Period	Entry barrier
2002 to approximately 2009	FDA orphan-drug exclusivity for the approved hereditary tyrosinaemia indication
Before August 27, 2013	Orphan exclusivity had ended, but the patent remained within its nominal term
After August 27, 2013	US 5,550,165 no longer created a live patent barrier

No current Paragraph IV risk should be assigned to this patent itself. A present-day applicant would instead assess any later-listed patents and regulatory exclusivity associated with the specific reference product and dosage form.

What litigation and settlement agreements affect this patent?

US 5,550,165 is an expired patent. Its litigation value is therefore historical rather than prospective. A patent-infringement action based solely on the patent cannot create future market exclusivity after expiration, although historical damages and litigation records may remain relevant where a suit was filed during the patent term.

No reliable current basis exists to treat this patent as an active litigation obstacle for Orfadin, Nityr, or another nitisinone product. The commercial competition between Sobi and Cycle Pharmaceuticals should be analyzed through product approvals, pricing, distribution, orphan-drug strategy, and any later patents, not through US 5,550,165 alone.

A settlement agreement involving a later nitisinone patent would not revive the expired rights in US 5,550,165. Any settlement would have to be tied to a separate enforceable patent, regulatory exclusivity, contract right, or commercial arrangement.

How strong is the patent estate for nitisinone?

The foundational estate was strong during its term because US 5,550,165 combined composition claims with disease-specific treatment claims. Its strength had three principal characteristics:

The active ingredient was precisely identified.
The composition claims covered ordinary pharmaceutical presentations.
The method claims targeted the core hereditary tyrosinaemia use.

Its current strength is zero as an exclusionary patent right because the patent has expired.

Patent-estate factor	Assessment for US 5,550,165
Chemical compound claim	Not present as an independent claim
Composition protection	Broad across carriers and dosage forms, but limited to nitisinone
Salt protection	Expressly included
Oral formulation protection	Included
Parenteral formulation protection	Included
Method-of-use protection	Included for hereditary tyrosinaemia
Dose-specific protection	Not expressly claimed
Manufacturing protection	Not claimed
Current enforceability	None after expiration
Biosimilar relevance	None
Generic relevance	Historical and freedom-to-operate relevance only

The absence of a compound claim matters. A competitor that made or supplied nitisinone outside the claimed pharmaceutical composition or therapeutic-use context would not automatically infringe the patent. In practice, however, a commercial drug product for hereditary tyrosinaemia would have been exposed to both the composition and method claims during the patent term.

What generic launch risks exist for nitisinone?

The core patent does not create a current generic-launch risk because it has expired. Current risks are commercial and regulatory:

FDA approval requirements for bioequivalence or a suitable 505(b)(2) showing.
Orphan-disease market size and patient concentration.
Limited manufacturing capacity.
Supply continuity for a rare-disease population.
Potential later formulation patents.
Labeling constraints for hereditary tyrosinaemia type 1.
Distribution through specialty pharmacies and metabolic-disease centers.
Pricing pressure from tablets, capsules, and oral suspension products.

A conventional nitisinone product would generally have a stronger freedom-to-operate position against US 5,550,165 after August 27, 2013. The remaining patent risk would depend on later patents covering a specific dosage form, formulation, salt, manufacturing method, or treatment regimen.

What geographic coverage does the patent provide?

US 5,550,165 provides rights only in the United States. Corresponding foreign applications or patents may have existed in Europe and other jurisdictions, but U.S. expiration does not determine foreign status.

A global nitisinone freedom-to-operate review should separately examine:

European Patent Office family members.
United Kingdom rights.
Canada.
Japan.
Australia.
Countries where Orfadin or Nityr is marketed.
National patent-term extensions or supplementary protection certificates.
Local regulatory exclusivity.

The U.S. patent cannot be used to block manufacture, sale, or use occurring entirely outside the United States.

What manufacturing and intellectual-property barriers remain?

US 5,550,165 does not claim a process for manufacturing nitisinone. It therefore does not directly block an alternative synthesis, crystallization process, purification method, or dosage-form manufacturing process after expiration.

Potential residual barriers may arise from:

Process patents.
Polymorph or crystalline-form patents.
Stable liquid formulations.
Taste-masked or pediatric formulations.
Tablet manufacturing methods.
Dosing regimens.
Combination treatment with dietary tyrosine or phenylalanine restriction.
Patents directed to additional indications, including alkaptonuria.
Trade secrets concerning scale-up, impurity control, and supply.

These rights should be treated as separate from the expired foundational patent.

Key Takeaways

US 5,550,165 covers nitisinone pharmaceutical compositions and treatment of hereditary tyrosinaemia.
Claims 1 through 5 and 8 cover compositions, salts, routes, dosage forms, and listed excipients.
Claims 6, 7, 9, and 10 cover disease-specific treatment and HPPD inhibition.
The patent does not claim nitisinone as a standalone chemical compound or its manufacturing process.
The patent issued August 27, 1996, and its nominal 17-year term ended August 27, 2013.
Orfadin’s seven-year orphan-drug exclusivity was separate from the patent and generally ended in 2009.
Nityr and other nitisinone products compete in a post-expiration market.
Biosimilar risk is irrelevant because nitisinone is a small molecule.
Current freedom-to-operate analysis must focus on later patents, regulatory exclusivity, formulations, manufacturing methods, and jurisdiction-specific rights.

FAQs

Is US Patent 5,550,165 a compound patent for nitisinone?

No. It claims compositions containing nitisinone and methods of treating hereditary tyrosinaemia. It does not contain an independent claim to nitisinone as a chemical compound.

Did US 5,550,165 cover Orfadin capsules?

Yes. Its composition claims were broad enough to cover pharmaceutical nitisinone compositions, including oral dosage forms such as capsules, subject to the claim limitations.

Can a company launch nitisinone after the expiration of US 5,550,165?

The patent itself does not block launch after its expiration. The applicant must still address FDA approval requirements and any later patents or regulatory exclusivity affecting the selected product and indication.

Does US 5,550,165 cover nitisinone treatment for alkaptonuria?

The claims are directed to hereditary tyrosinaemia and related HPPD-mediated pathology. They should not be assumed to cover alkaptonuria without a separate claim-construction and indication-specific analysis.

Are nitisinone products subject to biosimilar approval?

No. Nitisinone is a small-molecule drug. Competing products generally proceed through small-molecule regulatory pathways rather than the biosimilar pathway.

References

U.S. Patent No. 5,550,165. (1996). Pharmaceutical compositions. United States Patent and Trademark Office.
U.S. Food and Drug Administration. (2002). Orfadin (nitisinone) prescribing information. FDA.
U.S. Food and Drug Administration. (2024). Approved drug products with therapeutic equivalence evaluations. FDA.
U.S. Food and Drug Administration. (2024). Drugs@FDA: FDA-approved drugs database. FDA.
U.S. Food and Drug Administration. (2024). Orange Book: Approved drug products with therapeutic equivalence evaluations. FDA.
National Library of Medicine. (2024). DailyMed: Nitisinone drug labeling. U.S. National Library of Medicine.

Foriegn Application Priority Data
Foreign Country	Foreign Patent Number	Foreign Patent Date
United Kingdom	9113622	Jun 24, 1991
United Kingdom	9206412	Mar 24, 1992

Country	Patent Number	Estimated Expiration	Supplementary Protection Certificate	SPC Country	SPC Expiration
European Patent Office	0591275	⤷ Start Trial	CA 2005 00029	Denmark	⤷ Start Trial
European Patent Office	0591275	⤷ Start Trial	91180	Luxembourg	⤷ Start Trial
European Patent Office	0591275	⤷ Start Trial	SPC/GB05/030	United Kingdom	⤷ Start Trial
>Country	>Patent Number	>Estimated Expiration	>Supplementary Protection Certificate	>SPC Country	>SPC Expiration

Details for Patent: 5,550,165

Summary for Patent: 5,550,165