United States Patent 4,762,709: Scope, Claims, Expiration, and Pharmaceutical Patent Landscape

US Patent 4,762,709 protects a liquid oral formulation in which an ionic drug is bound to an ion-exchange resin, the drug-resin particles are treated to reduce swelling and coated with a water-permeable diffusion barrier, and a second same-charge ionic component is separately bound to uncoated resin. The claim architecture is directed principally to controlled-release liquid formulations containing combinations such as hydrocodone or codeine with chlorpheniramine.

The patent issued on August 9, 1988. Assuming no applicable patent-term extension or unusual terminal disclaimer, its 17-year pre-URAA term expired on August 9, 2005. The patent therefore does not create current United States exclusionary rights. Its technical disclosure remains relevant to products using resin-bound controlled-release suspensions, including hydrocodone/chlorpheniramine formulations.

What technology does US Patent 4,762,709 protect?

The patent covers a multipart formulation system with four required technical elements:

An ionic drug is adsorbed onto an ion-exchange resin.
The drug-resin particles are impregnated with a swelling-control agent.
The treated particles are coated with a water-permeable diffusion barrier.
A second ionic component having the same charge is separately bound to uncoated ion-exchange resin and suspended in the same liquid carrier.

The listed impregnants are:

Polyethylene glycol
Propylene glycol
Mannitol
Lactose
Methylcellulose

The invention addresses a formulation problem that arises when multiple ionic ingredients are placed in a liquid suspension. A freely dissolved second ionic component can alter the release rate of the primary drug-resin complex. The patent instead binds the second ionic component to uncoated resin, reducing its effect on the dissolution profile of the coated complex. [1]

The technical distinction is therefore not simply “drug plus ion-exchange resin.” The claims require a controlled-release coated complex and a separately prepared uncoated resin complex for the second same-charge ionic component.

What are the independent claims in US Patent 4,762,709?

The patent has three principal independent claims: claims 1, 9, and 17.

Claim	Core structure	Principal limitations
1	Formulation	Coated drug-resin complex, liquid carrier, second same-charge ionic component on uncoated resin, swelling-control impregnation, diffusion barrier
9	Pharmaceutical composition	Ionic drug on treated and coated resin; second same-charge ionic component on uncoated resin; liquid carrier
17	Narrow combination	Codeine, pseudoephedrine, or hydrocodone on coated resin, with chlorpheniramine on uncoated resin

Claim 1 is the most technically detailed independent claim. It requires that the second ionic component be present in an amount that would disturb the dissolution profile if present in unbound form. It also requires enough uncoated resin to bind that component, but not so much resin that the coated complex’s dissolution profile is disturbed.

Claim 9 omits some of the quantitative or functional language found in claim 1. It focuses on the structural arrangement of the two resin complexes.

Claim 17 is narrower in chemical scope but more commercially specific. It limits the first ionic drug to codeine, pseudoephedrine, or hydrocodone and limits the second ionic component to chlorpheniramine.

How do the claims differ from one another?

Claims 1 through 8

Claims 1 through 8 establish the general formulation architecture and then narrow it by drug identity.

Claim 1 covers the general two-resin system.
Claim 2 specifies that the second ionic component is also a drug.
Claims 3 and 4 identify codeine as the primary drug and chlorpheniramine as the second drug.
Claims 5 and 6 identify pseudoephedrine as the primary drug and chlorpheniramine as the second drug.
Claims 7 and 8 identify hydrocodone as the primary drug and chlorpheniramine as the second drug.

The codeine/chlorpheniramine, pseudoephedrine/chlorpheniramine, and hydrocodone/chlorpheniramine combinations are therefore narrower embodiments of claim 1.

Claims 9 through 16

Claims 9 through 16 restate the invention as a pharmaceutical composition.

Claims 11 and 12 cover codeine with chlorpheniramine. Claims 13 and 14 cover pseudoephedrine with chlorpheniramine. Claims 15 and 16 repeat the pseudoephedrine/chlorpheniramine combination, with claim 16 containing the apparent typographical error “wherin.”

Claim 17

Claim 17 is a consolidated composition claim. It covers a formulation containing:

Codeine, pseudoephedrine, or hydrocodone on treated and coated ion-exchange resin; and
Chlorpheniramine on uncoated ion-exchange resin; and
A liquid carrier.

Claim 17 does not expressly repeat every functional limitation from claim 1, such as the requirement that the second ionic component would disturb the release profile if unbound. Its enforceability would depend on ordinary claim-construction principles, prosecution history, and the precise meaning of “treated,” “coated,” and “uncoated” in the patent specification.

What formulation components are protected?

The ionic drug

The claims are limited to ionic drugs. The drug must be capable of binding to the ion-exchange resin through ionic interaction. Claims 3, 5, 7, and 17 identify codeine, pseudoephedrine, and hydrocodone as express embodiments.

Neutral drugs would not fall within the literal scope of the claims unless they were present in an ionic form that satisfied the claim language.

The ion-exchange resin

The claims do not identify a single resin chemistry. They use the broader term “ion exchange resin.” This creates potentially broad coverage over cationic or anionic resin systems, depending on the charge of the active ingredient and the interpretation of the specification.

The resin must perform two different roles:

The coated resin carries the primary controlled-release drug.
The uncoated resin binds the second same-charge ionic component.

The claim language therefore distinguishes the two resin populations by treatment and coating status, not necessarily by resin chemistry.

The swelling-control impregnant

The coated drug-resin particles must be treated with one of five listed agents:

Impregnant	Claimed function
Polyethylene glycol	Retards resin swelling in water
Propylene glycol	Retards resin swelling in water
Mannitol	Retards resin swelling in water
Lactose	Retards resin swelling in water
Methylcellulose	Retards resin swelling in water

The amount must be sufficient to retard the rate of swelling in water. A formulation using a different swelling-control agent could fall outside the literal Markush limitation, although doctrine-of-equivalents issues would require a fact-specific analysis.

The diffusion barrier

The coated drug-resin complex must have a water-permeable diffusion barrier. The claims do not expressly identify one polymer or coating material. The coating must allow water penetration and drug diffusion while controlling release.

A product using an uncoated resin, a wholly impermeable coating, or a non-diffusion-based release mechanism would present a stronger noninfringement position against the literal claims.

The second ionic component

Claims 1 and 9 require the second component to bear the same charge as the coated drug-resin complex. Claims 2, 10, and 17 narrow the second component to a drug, and the specific dependent claims identify chlorpheniramine.

The second component must be bound to uncoated resin. It cannot simply be dissolved in the liquid carrier if the product is to satisfy the express composition limitations.

What products are most closely associated with the patent?

The commercial embodiment most closely associated with the claim structure is an extended-release liquid containing hydrocodone polistirex and chlorpheniramine polistirex. Tussionex Pennkinetic Extended-Release Suspension uses hydrocodone polistirex and chlorpheniramine polistirex in a liquid oral suspension. [2]

The product’s technical arrangement is highly similar to claim 17:

Patent claim 17 element	Hydrocodone/chlorpheniramine resin suspension
Ionic drug selected from hydrocodone	Hydrocodone polistirex
Treated ion-exchange resin	Resin-bound hydrocodone complex
Water-permeable diffusion barrier	Controlled-release resin coating
Chlorpheniramine on uncoated resin	Chlorpheniramine polistirex component, subject to product-specific manufacturing details
Liquid carrier	Oral suspension vehicle

The patent’s expired status means that this historical product relationship does not create current patent infringement exposure under the ’709 patent.

When did US Patent 4,762,709 expire?

US Patent 4,762,709 issued August 9, 1988. For a United States patent filed before June 8, 1995, the ordinary term was 17 years from issuance. On that basis, the patent expired August 9, 2005. [1]

Event	Date
Patent issued	August 9, 1988
Ordinary statutory term	17 years from issue
Expected expiration	August 9, 2005
Current status	Expired

The patent is therefore not a current blocking patent for a generic, branded product, reformulation, or new liquid suspension in the United States.

What is the Orange Book status of US Patent 4,762,709?

The ’709 patent should not be treated as a current Orange Book barrier. Even if it was historically submitted in connection with an approved drug product, its expiration removes it as a live patent obstacle.

Orange Book relevance depends on three separate questions:

Whether the patent was submitted to FDA by the NDA holder.
Whether FDA accepted the patent for listing.
Whether the listing remains unexpired and relevant to the approved drug substance, drug product, or method of use.

A formulation patent can exist without being listed in the Orange Book. FDA listing does not determine the patent’s validity, claim scope, or enforceability. The FDA Orange Book identifies approved products, patent listings, and regulatory exclusivity, but it does not replace a patent-law analysis. [3]

For a current ANDA applicant, the practical result is that the ’709 patent should not require a Paragraph IV certification because the patent’s statutory term has ended.

How do Paragraph IV challenges apply to this patent?

A Paragraph IV certification is relevant only to an unexpired patent listed for an approved reference product. The ’709 patent expired in 2005, so it cannot presently support a new Paragraph IV challenge.

Historical litigation involving a product associated with this patent could have included:

A patent infringement action based on an ANDA filing.
A Paragraph IV notice letter.
A 30-month stay under Hatch-Waxman.
A settlement providing a licensed or delayed generic entry date.

Those mechanisms have no current prospective effect from the ’709 patent itself. Any present generic challenge would need to address later, unexpired patents, regulatory exclusivity, controlled-substance requirements, manufacturing know-how, or other product-specific rights.

What patent landscape surrounds resin-bound liquid drug formulations?

The relevant landscape has four layers.

Foundational ion-exchange resin technology

Older patents cover the use of ion-exchange resins to bind drugs, improve taste, and modify release. These patents generally concern resin selection, drug loading, particle size, and ion-exchange conditions.

Coated drug-resin particles

A separate group of patents addresses coating resin particles with water-permeable polymers or diffusion barriers. These patents can claim coating composition, coating thickness, permeability, curing conditions, or release-rate testing.

Swelling-control treatment

The ’709 patent’s distinctive contribution is the combination of resin impregnation with a listed swelling-control agent and subsequent coating. Later patents could potentially claim different impregnants, coating systems, resin treatments, or manufacturing parameters.

Combination liquid suspensions

Later patent families may claim particular combinations of active ingredients, dosage strengths, preservative systems, suspending agents, particle-size distributions, or release profiles. Those claims would need to be reviewed independently. Expiration of the ’709 patent does not eliminate later patents covering a specific commercial product.

How strong is the patent estate for this technology?

The ’709 patent was commercially meaningful when unexpired because it combined composition limitations with functional release-control limitations. Its strongest features were:

The two-population resin system.
The same-charge requirement.
The swelling-control impregnation step.
The water-permeable diffusion coating.
The specific hydrocodone/chlorpheniramine embodiment.

Its principal weaknesses from a modern enforcement perspective are:

Expiration in 2005.
Dependence on broad terms such as “ion exchange resin.”
Potential factual disputes over the identity and function of the coating.
Potential prosecution-history limits on broad claim interpretation.
Narrow listed impregnant classes.
Lack of current exclusionary effect.

The patent has no current standalone patent strength because expired claims cannot support prospective infringement relief.

What generic launch risks exist today?

The ’709 patent presents no current generic launch risk. A developer of an oral liquid containing hydrocodone, chlorpheniramine, codeine, or pseudoephedrine can no longer be blocked by this patent alone.

Current launch risks are more likely to arise from:

Later formulation patents.
Product-specific patents listed for the reference product.
Controlled-substance scheduling and DEA requirements.
FDA requirements for bioequivalence of extended-release suspensions.
Manufacturing consistency for resin loading and coating.
Drug-drug interaction or dose-dumping concerns.
Trade secrets covering resin treatment, coating, and particle-size control.
Trademark and regulatory exclusivity issues unrelated to the ’709 patent.

For a hydrocodone/chlorpheniramine product, the principal technical hurdle is likely demonstrating equivalent release performance rather than avoiding the expired claim set.

Does biosimilar risk apply to this patent?

No. The claimed products are small-molecule drug formulations, not biologics. Biosimilar approval under the Public Health Service Act is not the relevant pathway.

A follow-on product would generally proceed through an ANDA if it can demonstrate pharmaceutical equivalence and bioequivalence, or through an NDA under a different regulatory strategy if the formulation or route does not qualify for an ANDA. The patent does not create a biologic exclusivity period.

What manufacturing and intellectual-property barriers remain?

Although the claims are expired, manufacturing know-how can remain commercially valuable. A developer may need to reproduce:

Drug loading onto the resin.
Resin particle-size distribution.
Impregnation level.
Coating thickness and permeability.
Coating uniformity.
Suspension stability.
Drug release under multiple pH conditions.
Resistance to dose dumping.
Uniformity of delivered dose over the product’s shelf life.

These parameters may be protected by trade secrets, later patents, or regulatory know-how even when the original patent is expired.

Geographic protection is also exhausted in the United States for the ’709 patent. Foreign counterparts, if any, would have had separate national terms and should not be assumed to have expired on the same date without country-specific review. The US patent itself provides no current protection outside the United States.

Key Takeaways

US Patent 4,762,709 covers liquid suspensions using a coated, swelling-controlled drug-resin complex and an uncoated resin complex carrying a second same-charge ionic component.
The express drug combinations include codeine/chlorpheniramine, pseudoephedrine/chlorpheniramine, and hydrocodone/chlorpheniramine.
Claim 17 is the most commercially focused claim because it specifically names hydrocodone, codeine, pseudoephedrine, and chlorpheniramine.
The patent issued August 9, 1988 and ordinarily expired August 9, 2005.
It is not a current US blocking patent and cannot support a present Paragraph IV challenge.
The patent is relevant to the technical history of hydrocodone/chlorpheniramine extended-release suspensions, including Tussionex-type products.
Current launch analysis must focus on later patents, Orange Book listings, FDA requirements, controlled-substance regulation, and manufacturing know-how.
Biosimilar analysis is inapplicable because the products are small-molecule formulations.

FAQs About US Patent 4,762,709

Is US Patent 4,762,709 still enforceable?

No. Its ordinary US patent term expired in 2005.

Does the patent cover hydrocodone polistirex?

Claim 17 expressly covers hydrocodone as the ionic drug when it is bound to treated, coated ion-exchange resin and used with chlorpheniramine bound to uncoated resin in a liquid carrier.

Can a generic manufacturer rely on the expired patent?

The expired patent cannot be asserted as a current infringement barrier. A generic manufacturer may still need to address later patents, FDA requirements, controlled-substance rules, and product-specific manufacturing issues.

Is chlorpheniramine required in every claim?

No. Claims 1 and 9 broadly refer to a second same-charge ionic component. Chlorpheniramine is required only in narrower dependent claims and claim 17.

Does the patent cover an immediate-release liquid drug product?

Generally, no. The claims require a coated drug-resin complex with a water-permeable diffusion barrier and swelling-control treatment. A conventional freely dissolved immediate-release liquid would not satisfy those limitations.

References

United States Patent No. 4,762,709. (1988). Pharmaceutical compositions containing ion exchange resins. United States Patent and Trademark Office.
UCB, Inc. (n.d.). Tussionex Pennkinetic extended-release suspension: Prescribing information. DailyMed, National Library of Medicine.
U.S. Food and Drug Administration. (n.d.). Approved drug products with therapeutic equivalence evaluations. FDA, Center for Drug Evaluation and Research.

Country	Patent Number	Estimated Expiration	Supplementary Protection Certificate	SPC Country	SPC Expiration
Austria	42894	⤷ Start Trial
Australia	2789184	⤷ Start Trial
Australia	565487	⤷ Start Trial
>Country	>Patent Number	>Estimated Expiration	>Supplementary Protection Certificate	>SPC Country	>SPC Expiration

Details for Patent: 4,762,709

Summary for Patent: 4,762,709