US Patent 8,003,126: Scope, Claim Construction, Expiration and Sapropterin Patent Landscape

US Patent 8,003,126 protects tablet formulations containing crystal form B of sapropterin dihydrochloride, the active ingredient in Kuvan, combined with ascorbic acid. Its principal commercial target is the 100 mg sapropterin tablet with approximately 5 mg of ascorbic acid and, in narrower claims, specified excipients. The patent does not broadly claim sapropterin, crystal form B as an isolated substance, or treatment of phenylketonuria.

The patent’s commercial relevance is concentrated in formulation and product-by-process substitution risk. A competing product using crystal form B, ascorbic acid and a covered ratio may face infringement exposure even if it changes one or more inactive ingredients. A product using a different polymorph, different antioxidant system or an uncovered composition may have stronger design-around arguments.

What drug does US Patent 8,003,126 protect?

US Patent 8,003,126 covers tablet formulations containing (6R)-L-erythro-tetrahydrobiopterin dihydrochloride, commonly known as sapropterin dihydrochloride.

Sapropterin is the active ingredient in Kuvan, an FDA-approved treatment used with a phenylalanine-restricted diet for patients with phenylketonuria who respond to tetrahydrobiopterin therapy. The patent’s formulation claims correspond closely to the composition of commercial sapropterin tablets, including ascorbic acid and several pharmaceutical excipients.[1]

Element	Patent scope
Active ingredient	(6R)-L-erythro-tetrahydrobiopterin dihydrochloride
Common name	Sapropterin dihydrochloride
Solid form	Crystal form B
Dosage form	Tablet
Antioxidant	Ascorbic acid
Core dosage	Approximately 100 mg sapropterin dihydrochloride and 5 mg ascorbic acid
Additional excipients	Crospovidone, dibasic calcium phosphate, D-mannitol, riboflavin and sodium stearyl fumarate
Primary commercial product	Kuvan tablets
Therapeutic category	Phenylketonuria treatment

The claims are composition claims. They do not require a particular manufacturing process, tablet coating, dissolution profile, therapeutic indication or patient population unless those limitations are imported from the specification during claim construction.

What are the independent claims in US Patent 8,003,126?

Claims 1, 8 and 17 are the principal independent claims.

Claim 1: 100 mg and 5 mg tablet formulation

Claim 1 requires:

A formulation;
About 100 mg of crystal form B of sapropterin dihydrochloride;
About 5 mg of ascorbic acid; and
A tablet dosage form.

The claim does not require the five excipients listed in claim 2. A formulation can therefore fall within claim 1 without containing crospovidone, dibasic calcium phosphate, D-mannitol, riboflavin or sodium stearyl fumarate.

The word “about” creates a numerical construction issue. It does not provide an unlimited range. Courts generally interpret “about” in view of the specification, examples, manufacturing tolerances and technical meaning in the relevant field. A 100 mg label strength may therefore fall within the claim even if the actual tablet mass varies because of normal production tolerances.

Claim 8: broad ratio-defined formulations

Claim 8 covers a tablet containing crystal form B and ascorbic acid where the weight ratio of ascorbic acid to sapropterin is approximately one of the listed ratios from 1:5.5 through 1:29.5.

The claim uses the free-base name, (6R)-L-erythro-tetrahydrobiopterin, in the ratio limitation even though the formulation contains the dihydrochloride salt. This creates a potentially important calculation issue. The ratio may need to be determined using the molecular amount or weight of the tetrahydrobiopterin component rather than the total mass of sapropterin dihydrochloride.

The claim lists half-unit increments:

Ratio range in claim 8	Included values
Lower range	About 1:5.5 through 1:15
Middle range	About 1:15.5 through 1:25
Upper range	About 1:25.5 through 1:29.5

Because the claim recites specific ratios, a composition outside the claimed range may present a non-infringement position. The scope of “about” remains critical.

Claim 17: low-ratio formulations

Claim 17 covers crystal form B tablets with ascorbic acid-to-sapropterin ratios of approximately:

1:2;
1:3;
1:4; or
1:5.

Claim 17 fills a lower-ratio zone that is not expressly recited in claim 8. Claims 8 and 17 together create a discontinuity in the literal listed ratios between approximately 1:5 and 1:5.5, although the construction of “about” could affect the practical boundary.

How do the dependent claims narrow the patent’s scope?

Claims 2 through 7 depend from claim 1. Claims 9 through 16 depend from claim 8. Claims 18 through 22 depend from claim 17.

The dependency structure matters because each dependent claim includes every limitation of its parent claim.

Claim group	Additional limitation
Claim 2	All five named excipients
Claim 3	Crospovidone
Claim 4	Dibasic calcium phosphate
Claim 5	D-mannitol
Claim 6	Riboflavin
Claim 7	Sodium stearyl fumarate
Claim 9	All five named excipients with claim 8 ratio
Claims 10-14	One named excipient with claim 8 ratio
Claim 15	Claim 8 ratio narrowed to approximately 1:16.5 through 1:25
Claim 16	Claim 8 ratio narrowed to approximately 1:19, 1:19.5 or 1:20
Claims 18-22	One named excipient with claim 17 ratio

Claim 2 is narrower than claims 3 through 7 because it requires all five excipients. Claims 3 through 7 are separate alternative fallbacks. A product containing only crospovidone may implicate claim 3 but not claim 2.

The same structure applies to claims 9 through 14 and claims 18 through 22. The excipients are not collectively required unless the relevant claim expressly lists all five.

What formulations are protected by US 8,003,126?

The strongest literal infringement scenario is a tablet containing:

Crystal form B sapropterin dihydrochloride;
Approximately 100 mg of the active ingredient;
Approximately 5 mg of ascorbic acid; and
One or more of the listed excipients.

A formulation containing all five named excipients is a direct match for claims 2, 9 and potentially other claims depending on the ratio and active amount.

The patent also reaches formulations that vary substantially from the commercial 100 mg/5 mg formulation if the formulation satisfies one of the listed ratios in claim 8 or claim 17. This ratio-based coverage increases the patent’s relevance to alternative strengths and tablet compositions.

Ingredient-by-ingredient scope

Ingredient or feature	Required by core claims?	Practical significance
Crystal form B	Yes	Central structural limitation
Sapropterin dihydrochloride	Yes	Salt form is required
Ascorbic acid	Yes	Required in all independent claims
Tablet	Yes	Non-tablet dosage forms are outside literal scope
Crospovidone	No	Required only in selected dependent claims
Dibasic calcium phosphate	No	Required only in selected dependent claims
D-mannitol	No	Required only in selected dependent claims
Riboflavin	No	Required only in selected dependent claims
Sodium stearyl fumarate	No	Required only in selected dependent claims

A capsule, powder, liquid or injectable formulation would not literally satisfy the tablet limitation. A tablet using crystal form A or an amorphous form instead of crystal form B would not literally satisfy the crystal-form limitation, subject to polymorph characterization and any doctrine-of-equivalents analysis.

How important is crystal form B to infringement?

Crystal form B is the principal technical limitation in the patent.

A generic or follow-on manufacturer must characterize the solid state of its sapropterin material. Routine analytical tools may include powder X-ray diffraction, differential scanning calorimetry, thermogravimetric analysis, infrared spectroscopy and solid-state nuclear magnetic resonance. The relevant question is whether the product contains the claimed crystal form, not whether the manufacturer uses the same supplier or manufacturing route.

Potential design-around approaches include:

Use of a different crystalline polymorph;
Use of an amorphous solid;
Use of a different salt or solvated form;
Use of a formulation that converts the active ingredient before tableting; or
Use of a dosage form other than a tablet.

Each approach creates technical and regulatory consequences. A different polymorph may have different stability, dissolution and bioavailability characteristics. A different salt may require a new pharmaceutical development program and could affect FDA bridging requirements.

When does US Patent 8,003,126 lose exclusivity?

The patent issued on August 23, 2011.[2] Its nominal patent term is generally measured from the relevant nonprovisional filing date, subject to patent-term adjustment, patent-term extension and any terminal disclaimer.

Public patent records associate the patent with the BioMarin sapropterin formulation program and a 2007 U.S. filing claiming priority to an earlier application. On that basis, the ordinary term is expected to extend into 2027, rather than ending at the 20th anniversary of issuance.

Event	Date or status
U.S. patent application	Filed before issuance in the 2007 period
Patent publication	Published before grant
Patent grant	August 23, 2011
Nominal term	Expected to extend into 2027
Patent-term adjustment	Must be confirmed from the USPTO patent record
Patent-term extension	No extension is established from the claim text
Terminal disclaimer	Must be checked against related patents

The operative expiration date is the date shown in the USPTO Patent Center and the applicable FDA Orange Book patent listing. The grant date alone does not determine expiration.

What is the Orange Book status of US 8,003,126?

Kuvan is an FDA-approved sapropterin product, and FDA approval records and Orange Book listings are the relevant sources for determining whether US 8,003,126 was submitted as a listed drug patent.[3]

An Orange Book listing does not establish that every claim is infringed by every generic sapropterin product. It identifies patents submitted by the applicant as claiming the approved drug, a formulation, or an approved method of use. A generic applicant must address listed patents through a Paragraph III certification, Paragraph IV certification, or other applicable certification pathway.

For this patent, the listed formulation limitations are commercially important because they track the tablet composition rather than a broad therapeutic use. An ANDA applicant could attempt to certify that its product does not infringe, challenge validity, or wait for patent expiration.

Which companies are challenging the Kuvan and sapropterin patent estate?

The relevant competitive field includes BioMarin as the originator and manufacturers seeking approval of generic sapropterin dihydrochloride tablets or oral powder products.

A complete challenger analysis requires matching each ANDA to:

The Orange Book patent number;
The applicant’s Paragraph IV notice;
The asserted claims;
The district court complaint;
Any preliminary injunction ruling;
The settlement terms; and
The authorized generic or licensed launch provisions.

US Patent 8,003,126 alone does not identify the ANDA applicant, Paragraph IV certification or settlement terms. Patent ownership, FDA listing and litigation activity are separate records. The patent number should not be treated as evidence that a particular generic company has challenged this patent.

What Paragraph IV risks does this patent create?

A Paragraph IV challenge to this patent would likely focus on four issues.

Lack of infringement

The applicant could argue that its formulation does not contain crystal form B, does not use ascorbic acid, does not meet the applicable ratio, or is not a tablet. It could also challenge the meaning of “about” and the method for calculating the ascorbic acid-to-sapropterin ratio.

Anticipation

An anticipation challenge would require a single prior-art reference disclosing every limitation, including crystal form B, ascorbic acid, the tablet form and the claimed amount or ratio. Earlier sapropterin formulations may be relevant, but a generic disclosure of sapropterin would not necessarily anticipate the specific crystal-form and ratio limitations.

Obviousness

The likely obviousness theory would combine:

Known sapropterin tablets;
Known antioxidant use for tetrahydrobiopterin stabilization;
Known pharmaceutical excipients; and
Routine formulation optimization.

The patent holder would likely rely on crystal-form selection, stability data, formulation performance and the claimed ratio as evidence of non-obviousness. The strength of the defense depends heavily on the specification’s examples and comparative data.

Written description and enablement

A challenge could target the extensive ratio lists in claims 8 and 17, particularly if the specification provides only limited examples. The patent holder would respond that the full ranges are supported by formulation principles and disclosed testing.

How strong is the patent estate for sapropterin tablets?

US 8,003,126 is strongest against a product that copies the commercial tablet architecture:

Crystal form B;
Ascorbic acid;
Tablet dosage form; and
A listed excipient combination or covered ratio.

Its strength is lower against a product that uses a different polymorph, a different antioxidant, a non-tablet dosage form or a ratio outside the listed ranges.

Competitive product design	Exposure under US 8,003,126
100 mg crystal form B plus 5 mg ascorbic acid tablet	High
Same composition plus all five named excipients	High
Crystal form B tablet with only crospovidone	Potentially high under claim 3
Crystal form B tablet without ascorbic acid	Low under literal claim scope
Different polymorph with ascorbic acid	Lower, subject to analytical proof
Amorphous sapropterin tablet	Lower
Crystal form B capsule	Low under tablet limitation
Crystal form B tablet with a ratio outside claimed ranges	Lower, subject to “about” construction
Sapropterin oral powder	Low under the tablet limitation

The patent is a formulation barrier, not a complete market-exclusivity barrier for all sapropterin products. Other patents may cover the active ingredient, methods of treatment, pediatric formulations, oral powders, manufacturing processes or separate polymorphs.

What manufacturing and IP barriers remain after patent expiry?

Patent expiry does not eliminate all market-entry requirements.

A generic manufacturer must establish pharmaceutical equivalence and bioequivalence or satisfy another FDA approval pathway. It must control:

Polymorph identity;
Salt stoichiometry;
Oxidative stability;
Tablet dissolution;
Content uniformity;
Impurity profile;
Packaging and moisture protection; and
Stability over the proposed shelf life.

The crystal-form limitation may also create a supply-chain barrier. A manufacturer that purchases API from a third party must verify that the material is not crystal form B or, if it is, assess whether the formulation claims remain active.

FDA regulatory exclusivity is separate from patent protection. Kuvan’s original approval, pediatric exclusivity and any later supplements affect approval timing but do not extend the patent term. The Orange Book is the controlling source for current listed patents and expiration data.[3]

How does US 8,003,126 compare with a method-of-use patent?

A method-of-use patent generally covers administering sapropterin to a defined patient population or for a defined therapeutic purpose. US 8,003,126 instead covers the physical product.

Issue	US 8,003,126	Method-of-use patent
Protected subject matter	Tablet formulation	Administration or treatment method
Key limitations	Crystal form, ascorbic acid, tablet, ratios	Patient, disease, dosage or treatment steps
Main enforcement target	Product manufacture, sale or importation	Induced or direct infringement tied to labeled use
Design-around route	Change solid form, excipient, ratio or dosage form	Carve out patented indication or use
FDA relevance	Formulation patent listing	Use-code and labeling analysis

A generic product can avoid a formulation patent while still facing method-of-use issues. Conversely, a product may infringe a formulation claim regardless of whether it is labeled for the patented indication, depending on the claim language and applicable infringement theory.

Key Takeaways

US Patent 8,003,126 covers tablet formulations containing crystal form B sapropterin dihydrochloride and ascorbic acid.
Claim 1 targets the approximately 100 mg/5 mg tablet composition.
Claims 8 and 17 extend protection through specified ascorbic acid-to-sapropterin ratios.
Claims 2-7, 9-16 and 18-22 add excipient and ratio limitations.
Crystal form B is the central technical limitation and should be verified with solid-state analytical data.
The patent does not broadly claim all sapropterin products or all phenylketonuria treatments.
The ordinary patent term is expected to extend into 2027, subject to the USPTO-calculated term.
Orange Book status, patent-term adjustment, Paragraph IV certifications and litigation must be analyzed separately from the claim language.
The principal generic design-around options are a different polymorph, different antioxidant system, different ratio or non-tablet dosage form.
Formulation patent expiry does not remove FDA bioequivalence, manufacturing, supply-chain or regulatory barriers.

FAQs About US Patent 8,003,126 and Sapropterin

Does US 8,003,126 cover Kuvan’s active ingredient by itself?

No. The claims require a formulation in tablet form containing crystal form B sapropterin dihydrochloride and ascorbic acid. They do not claim isolated sapropterin dihydrochloride without the formulation limitations.

Does a tablet infringe if it contains crystal form B but no ascorbic acid?

The tablet would not literally satisfy the independent claims because ascorbic acid is required. The patent’s claims do not cover a crystal form B sapropterin tablet lacking ascorbic acid.

Are the listed excipients mandatory in every claimed formulation?

No. They are mandatory only for the dependent claims that recite them. The independent claims require sapropterin, ascorbic acid and a tablet, but not the five named excipients.

Can a manufacturer avoid the patent by changing only crospovidone?

Not necessarily. Removing crospovidone may avoid a crospovidone-dependent claim, but it would not avoid claim 1, claim 8 or claim 17 if all independent-claim limitations remain satisfied.

Does a different sapropterin polymorph automatically avoid infringement?

It may avoid literal infringement of the crystal form B limitation, but the result depends on the product’s actual solid-state identity, claim construction and any doctrine-of-equivalents analysis.

References

U.S. Food and Drug Administration. (2007). Kuvan (sapropterin dihydrochloride) tablets: Prescribing information.
U.S. Patent No. 8,003,126. (2011). Pharmaceutical compositions containing tetrahydrobiopterin. United States Patent and Trademark Office.
U.S. Food and Drug Administration. (n.d.). Approved drug products with therapeutic equivalence evaluations, Orange Book. FDA.
United States Code, 35 U.S.C. §§ 154, 271 and 355(j).

Applicant	Tradename	Generic Name	Dosage	NDA	Approval Date	TE	Type	RLD	RS	Patent No.	Patent Expiration	Product	Substance	Delist Req.	Patented / Exclusive Use	Submissiondate
Biomarin Pharm	KUVAN	sapropterin dihydrochloride	TABLET;ORAL	022181-001	Dec 13, 2007	AB	RX	Yes	Yes	⤷ Start Trial	⤷ Start Trial			Y		⤷ Start Trial
>Applicant	>Tradename	>Generic Name	>Dosage	>NDA	>Approval Date	>TE	>Type	>RLD	>RS	>Patent No.	>Patent Expiration	>Product	>Substance	>Delist Req.	>Patented / Exclusive Use	>Submissiondate

PCT Information
PCT Filed	November 16, 2005	PCT Application Number:	PCT/US2005/041252
PCT Publication Date:	May 26, 2006	PCT Publication Number:	WO2006/055511

Country	Patent Number	Estimated Expiration	Supplementary Protection Certificate	SPC Country	SPC Expiration
Argentina	052238	⤷ Start Trial
Australia	2005306686	⤷ Start Trial
Brazil	PI0517088	⤷ Start Trial
Canada	2581814	⤷ Start Trial
China	101132776	⤷ Start Trial
European Patent Office	1845952	⤷ Start Trial
>Country	>Patent Number	>Estimated Expiration	>Supplementary Protection Certificate	>SPC Country	>SPC Expiration

Details for Patent: 8,003,126

Which drugs does patent 8,003,126 protect, and when does it expire?

Summary for Patent: 8,003,126