United States Patent 4,189,469: Claim Scope, Expiration, and Patent Landscape for Pentoxifylline Formulations

U.S. Patent No. 4,189,469 covers orally administered, high-dose xanthine compositions that combine an otherwise gastrointestinally incompatible active ingredient with a swelling agent. The claims specifically encompass pentoxifylline, also known as 1-(5-oxohexyl)-3,7-dimethylxanthine, in unit doses of at least 300 mg and with defined active-to-swelling-agent ratios.

The patent issued on February 19, 1980. Its original U.S. patent term expired no later than February 19, 1997, subject to any term adjustment or disclaimer appearing in the official patent record. The patent therefore does not create current U.S. exclusivity for pentoxifylline, its extended-release tablets, or the claimed excipient combinations. Current commercial competition proceeds through generic-drug pathways, principally abbreviated new drug applications rather than biosimilar applications.

What does U.S. Patent 4,189,469 cover?

The patent has two principal claim groups:

Composition claims covering an active pharmaceutical ingredient combined with a swelling agent.
Preparation-method claims covering admixture of the active ingredient and swelling agent.

The central inventive concept is the use of a swelling agent to reduce gastrointestinal incompatibility sufficiently to permit oral administration of a dose that would otherwise be unsafe.

Claim group	Claims	Primary limitation
Broad composition	1	Any pharmaceutically active component with gastrointestinal incompatibility plus sufficient swelling agent
Xanthine composition	2	Specified xanthine derivatives, at least 300 mg per unit, active-to-swelling-agent ratio of 1:2 to 10:1
Water-soluble form	3	Claim 2 composition in which the xanthine derivative is water-soluble
Higher dose	4	At least 400 mg of xanthine derivative per unit
Oxoalkyl dose	5	Up to 1,200 mg of an oxoalkyl-dimethylxanthine
Pentoxifylline and isomer	6	1-(5-oxohexyl)-3,7-dimethylxanthine or 7-(5-oxohexyl)-1,3-dimethylxanthine
Swelling-agent species	7	Guar, galactomannan, alginate, acrylic-acid powder or cellulose derivative
Additional excipients	8	Povidone, polyvinyl acetate, talc or magnesium stearate
Tablet form	9	Tablet dosage form
Physical admixture	10	Xanthine derivative mixed with swelling agent
Hydroxyhexyl compounds	11-12	1-(5-hydroxyhexyl)- or 7-(5-hydroxyhexyl)-dimethylxanthine
Structural alternatives	13-16	Subclasses (a) through (d) of claim 2
Preparation method	17	Admixing active ingredient with sufficient swelling agent
Higher-dose method	18	Admixing a higher unit dose with sufficient swelling agent

The use of “comprises” makes the composition claims open-ended. A product may contain additional active ingredients, excipients, coatings or processing aids and still fall within the literal scope if all required limitations are present.

How broad is independent claim 1?

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

An orally administrable pharmaceutical composition.
A unit-dosage form.
A pharmaceutically active component having gastrointestinal-tract incompatibility that makes oral administration unsafe.
A sufficient amount of swelling agent that reduces the incompatibility to a safe level.

Claim 1 is not limited to xanthines, pentoxifylline, tablets, a particular swelling agent, a minimum active dose or a defined active-to-excipient ratio.

Its principal breadth comes from the functional language:

“having a degree of gastro-intestinal-tract incompatibility”
“sufficient amount”
“reduce such incompatibility”
“safe for oral administration”

A competing composition could potentially fall within claim 1 even if it uses a different active ingredient, provided the formulation satisfies the functional gastrointestinal-safety limitation. Claims 2 through 16 narrow the scope by adding chemical, dose, excipient and dosage-form limitations.

The principal enforcement issue would be proof. A patent owner would need to establish that the active ingredient is unsafe, or otherwise unsuitable, for oral administration at the relevant dose without the swelling agent and that the swelling agent reduces the problem to a safe level. The claim does not provide a numerical test for “safe” or “incompatible.”

What xanthine derivatives are protected by claim 2?

Claim 2 defines four structural classes.

Class A: Hydroxyalkyl-dialkylxanthines

The hydroxyalkyl substituent contains five to six carbon atoms and is attached at the 1- or 7-position. The other 1- or 7-position contains an alkyl group of one to 12 carbon atoms. The 3-position contains an alkyl group of one to four carbon atoms.

Claims 11 and 12 identify two specific members:

1-(5-hydroxyhexyl)-3,7-dimethylxanthine
7-(5-hydroxyhexyl)-1,3-dimethylxanthine

Class B: Oxoalkyl-dimethylxanthines

The oxoalkyl group contains five to six carbon atoms and occupies the 1- or 7-position. The other ring nitrogens are methyl-substituted.

Claim 6 expressly identifies:

1-(5-oxohexyl)-3,7-dimethylxanthine
7-(5-oxohexyl)-1,3-dimethylxanthine

The first compound is pentoxifylline. Pentoxifylline is the commercially relevant compound associated with the patent’s formulation claims.

Class C: Higher alkyl dimethylxanthines

These compounds have an additional alkyl group containing four to 12 carbon atoms at the 1- or 7-position.

Class D: Benzyl dimethylxanthines

These compounds have an additional benzyl group at the 1- or 7-position.

Claim 2 also requires:

At least 300 mg of xanthine derivative per dosage unit.
A weight ratio of xanthine derivative to swelling agent from 1:2 to 10:1.

A formulation with 299 mg of the relevant xanthine derivative would not meet the express minimum in claim 2. A formulation containing 400 mg of active and 20 mg of swelling agent would have a 20:1 ratio and would fall outside the stated ratio limitation, assuming no broader claim applied.

What formulations and excipients are protected?

Claim 7 lists the principal swelling-agent categories:

Guar powder
Galactomannan
Alginate
Acrylic-acid powder
Cellulose derivative

Claim 8 adds optional excipients:

Polyvinylpyrrolidone
Polyvinyl acetate
Talc
Magnesium stearate

Claims 9 and 10 add manufacturing or dosage-form limitations:

Tablet form
Physical admixture of the xanthine derivative and swelling agent

The claims do not require an extended-release coating, a particular dissolution profile, a specific tablet hardness, a particular polymer molecular weight or a defined release mechanism. A modern formulation using the same active and swelling-agent concept could therefore be analyzed against the claims without relying on the presence of a conventional sustained-release coating.

The claim set also does not expressly require that the swelling agent be the sole release-controlling excipient. A formulation containing multiple polymers or excipients could still satisfy the claims if the stated swelling-agent limitation is met.

What does claim 6 mean for pentoxifylline?

Claim 6 is the most commercially important claim because it expressly names pentoxifylline and its 7-substituted positional isomer.

Pentoxifylline is a methylxanthine derivative used in extended-release oral tablets, historically marketed under the Trental brand. The patent’s claim structure focuses on high-dose oral administration and gastrointestinal tolerability rather than on the underlying discovery of pentoxifylline as a chemical entity.

A product would need to satisfy all limitations inherited from claim 2, including:

At least 300 mg of the xanthine derivative per unit.
The stated active-to-swelling-agent ratio.
A swelling agent of the type required by claim 2, as narrowed or interpreted through the claim chain.
The pentoxifylline structure identified in claim 6.

A 400 mg pentoxifylline tablet with a qualifying swelling agent is the clearest commercial embodiment within the claim architecture. Claim 5 reaches up to 1,200 mg of an oxoalkyl-dimethylxanthine, but it does not eliminate the other requirements inherited from claim 2.

How do claims 17 and 18 protect manufacturing methods?

Claim 17 covers a method of preparing an oral dosage form by admixing:

A pharmaceutically active component that is unsafe for oral administration because of gastrointestinal incompatibility; and
A sufficient amount of swelling agent to reduce that incompatibility.

Claim 18 is directed to a higher unit dose. It applies where a particular dose is unsafe or incompatible and the formulation uses a higher unit dose together with enough swelling agent to make that higher dose safe.

The method claims are narrower in practical enforcement than the composition claims because they require proof of the preparation process. A finished-product manufacturer could face a process-claim issue if its manufacturing records establish that the active and swelling agent were admixed in the claimed manner. Claims 17 and 18 do not appear to require a tablet specifically, so they can reach other oral unit-dosage forms if the remaining limitations are met.

When did U.S. Patent 4,189,469 lose exclusivity?

The patent issued on February 19, 1980. For a pre-June 8, 1995 U.S. application, the governing patent term was generally 17 years from issuance under the law then applicable. On that basis, the ordinary expiration date was February 19, 1997.[2]

Event	Date or status
U.S. patent issued	February 19, 1980
Ordinary pre-1995 patent term	17 years from issuance
Ordinary expiration	February 19, 1997
Current enforceability	Expired
Current Orange Book exclusivity from this patent	None
Current Paragraph IV risk from this patent	None

An expired patent cannot support a current U.S. infringement action. It can remain relevant as prior art, as evidence of technical disclosure, or in the analysis of later patents claiming improved formulations, manufacturing processes or therapeutic uses.

What is the FDA and Orange Book status of pentoxifylline?

Pentoxifylline is a small-molecule prescription drug. Its U.S. regulatory pathway is an NDA for the innovator product and ANDAs for generic products, not the biosimilar pathway.

The commercially relevant dosage form is the 400 mg extended-release oral tablet. FDA labeling identifies pentoxifylline extended-release tablets for the treatment of patients with intermittent claudication caused by chronic occlusive arterial disease.[3]

Regulatory issue	Status
Active ingredient	Pentoxifylline
Dosage form	Extended-release oral tablet
Typical strength	400 mg
Innovator brand	Trental
Regulatory pathway for generics	ANDA
Biosimilar pathway	Not applicable
Patent 4,189,469	Expired
Patent-based U.S. exclusivity from this patent	None

The Orange Book is relevant to listed patents and regulatory exclusivity associated with approved drug products. An expired 1980 patent does not provide a current barrier to ANDA approval. Any current regulatory delay would need to arise from a different listed patent, non-patent exclusivity period, approval issue or product-specific regulatory requirement.[4]

Are there Paragraph IV challenges to this patent?

No current Paragraph IV challenge can create commercial delay based on U.S. Patent 4,189,469 because the patent expired in 1997.

Paragraph IV certifications are relevant when an ANDA applicant asserts that a listed patent is invalid, unenforceable or will not be infringed. A generic applicant seeking approval after expiration would generally have no need to make a Paragraph IV challenge to this patent. The patent’s expiration removes the 30-month-stay mechanism associated with a live listed patent.

Historical ANDA litigation involving pentoxifylline, if any, would not restore enforceability or extend the patent term. The claim set supplied does not establish a historical Paragraph IV filing, litigation docket, settlement agreement or consent judgment.

What patent litigation and settlement risks remain?

Patent 4,189,469 itself presents no current U.S. litigation risk because all claims are expired. There is no basis for a current infringement suit under claims 1 through 18.

The relevant residual risks are separate patent rights covering:

A specific extended-release matrix.
Polymer selection or polymer ratios.
Tablet coating or multiparticulate delivery systems.
Dissolution profiles.
Manufacturing processes.
New therapeutic uses.
Combination therapy.
A different dosage regimen.
Foreign counterparts with later expiration dates.

A later formulation patent could remain enforceable even though the foundational swelling-agent patent has expired. A freedom-to-operate review should therefore distinguish the expired patent from later patents identified in the Orange Book, FDA patent records, USPTO databases and national patent registers.

No settlement agreement can be inferred from the claims or the patent document itself. Any settlement would require separate litigation or docket evidence.

How strong is the patent estate?

The patent had meaningful historical breadth but has no current blocking strength in the United States.

Strength factor	Assessment
Chemical specificity	Moderate; claim 2 covers defined xanthine classes and claim 6 names pentoxifylline
Formulation breadth	Broad in claim 1; narrower in claims 2 and 7
Dose coverage	Strong for units of at least 300 mg, particularly 400 mg products
Excipient coverage	Moderate; claim 7 lists defined swelling-agent categories
Functional limitations	Broad but potentially fact-intensive to prove
Method coverage	Moderate; claims 17 and 18 require proof of admixing and safety effect
Current U.S. enforceability	None
Current competitive barrier	None from this patent
Prior-art value	Potentially significant for later formulation claims

The estate is best characterized as an expired foundational formulation patent, not a live exclusivity estate. Its commercial value now lies in historical technology disclosure and possible prior-art relevance.

How does the patent compare with current generic-entry barriers?

Issue	U.S. Patent 4,189,469	Current pentoxifylline market
Protection type	Composition and preparation method	Generic product competition
Key product	High-dose xanthine formulation, including pentoxifylline	400 mg extended-release tablets
Expiration	1997	No barrier from this patent
Regulatory route	Historical NDA-era patent protection	ANDA approval for generics
Biosimilar exposure	None	Not applicable because pentoxifylline is a small molecule
Formulation risk	Swelling-agent and gastrointestinal-safety concept	Later formulation patents must be separately reviewed
Launch risk	No current delay from this patent	Primarily regulatory, manufacturing and commercial

Generic manufacturers can generally rely on the absence of enforceable rights under this patent. The primary technical barrier is product equivalence, including extended-release performance, tablet manufacture, stability and regulatory compliance.

What geographic coverage does the patent provide?

U.S. Patent 4,189,469 provides U.S. rights only. Any foreign protection would depend on separately issued national patents or regional patent rights. U.S. expiration does not establish the status of European, Japanese, Canadian or other corresponding patents.

For commercial planning, geographic analysis should separate:

U.S. patent expiration.
Foreign counterpart expiration.
Supplementary protection certificates or equivalent extensions.
National regulatory exclusivity.
Local generic-registration requirements.

The U.S. patent cannot block manufacture, sale or importation in another country, and a foreign counterpart cannot create current U.S. rights.

Key Takeaways

U.S. Patent 4,189,469 claims oral unit-dose compositions using swelling agents to reduce gastrointestinal incompatibility.
Claim 1 is broad and functionally drafted; claim 2 supplies the principal xanthine, dose and ratio limitations.
Claim 6 expressly covers pentoxifylline and its 7-substituted positional isomer.
The core quantitative limitation is at least 300 mg of xanthine derivative per dosage unit and an active-to-swelling-agent ratio of 1:2 to 10:1.
Claims 7 through 10 address swelling-agent identity, optional excipients, tablets and physical admixture.
Claims 17 and 18 cover preparation methods, including higher-dose formulations.
The patent issued in 1980 and ordinarily expired in 1997.
It provides no current U.S. patent exclusivity, Paragraph IV leverage or biosimilar barrier.
Pentoxifylline is a small molecule marketed primarily as a 400 mg extended-release tablet, with generic competition proceeding through ANDAs.
Later patents covering release systems, polymer technologies, manufacturing processes or new uses require separate review.
The patent remains potentially relevant as prior art but has no current blocking force.

FAQs About U.S. Patent 4,189,469

Does U.S. Patent 4,189,469 cover all pentoxifylline tablets?

No. The most specific claims require additional limitations, including a qualifying swelling agent, a minimum dose and, for claim 6, the identified pentoxifylline structure. The patent is also expired.

Is pentoxifylline protected by a biosimilar patent strategy?

No. Pentoxifylline is a chemically synthesized small molecule. Generic versions use the ANDA pathway rather than the biosimilar pathway under the Biologics Price Competition and Innovation Act.

Can a generic manufacturer use guar, alginate or cellulose in a pentoxifylline tablet?

The expired patent identified those materials as swelling agents. Because the patent is expired, it does not prevent current use. Separate later patents and regulatory requirements would remain distinct issues.

Does the patent cover injectable pentoxifylline?

The claims are directed to orally administrable compositions and oral dosage-form preparation methods. They do not cover injectable products as such.

Can this expired patent invalidate a later formulation patent?

It may be prior art relevant to novelty or obviousness, but the legal effect depends on the later patent’s claims, priority date, disclosure and prosecution history. Expiration and invalidity are separate questions.

References

U.S. Patent No. 4,189,469. (1980). Pharmaceutical compositions containing xanthine derivatives. United States Patent and Trademark Office.
35 U.S.C. § 154. Patent term provisions applicable to pre-June 8, 1995 applications.
National Library of Medicine. (n.d.). Pentoxifylline extended-release tablet: Prescribing information. DailyMed.
U.S. Food and Drug Administration. (n.d.). Approved drug products with therapeutic equivalence evaluations. Center for Drug Evaluation and Research.

Foriegn Application Priority Data
Foreign Country	Foreign Patent Number	Foreign Patent Date
Germany	2520978	May 10, 1975

Country	Patent Number	Estimated Expiration	Supplementary Protection Certificate	SPC Country	SPC Expiration
Australia	1376576	⤷ Start Trial
Australia	502644	⤷ Start Trial
Belgium	841617	⤷ Start Trial
Cyprus	1153	⤷ Start Trial
Germany	2520978	⤷ Start Trial
Denmark	153918	⤷ Start Trial
Denmark	205376	⤷ Start Trial
>Country	>Patent Number	>Estimated Expiration	>Supplementary Protection Certificate	>SPC Country	>SPC Expiration

Details for Patent: 4,189,469

Summary for Patent: 4,189,469