US Patent 4,259,315: Scope, Claims, Expiration, and Potassium Chloride Patent Landscape

US Patent 4,259,315 covers gelatin capsules containing microencapsulated potassium salt, particularly potassium chloride, combined with a hydrophilic surfactant positioned outside the microcapsules. The patent targets controlled release, improved powder flow, and delivery through a partially obstructed gastrointestinal tract.

The patent issued on March 31, 1981. Because it predates the 1995 change to a patent term measured from the earliest effective nonprovisional filing date, its ordinary term was 17 years from issuance. Its term therefore ended on March 31, 1998, absent an unusual terminal disclaimer or other term adjustment. US Patent 4,259,315 is not an active blocking patent today. [1][2]

What does US Patent 4,259,315 protect?

The patent protects a specific pharmaceutical architecture:

A gelatin capsule.
Microencapsulated potassium salt inside the capsule.
A hydrophilic surfactant external to the microcapsules.
In narrower claims, an ethyl cellulose coating around a potassium chloride core.
In some claims, specified surfactant concentration, HLB value, polymer loading, and therapeutic use.

The invention is not directed to potassium chloride generally. It is directed to the combination of potassium salt microcapsules and external hydrophilic surfactant in a gelatin capsule.

Core technical concept

The microcapsules contain potassium salt in a core surrounded by a polymeric coating. The external surfactant is intended to improve the movement and handling of the microencapsulated material. Claim 5 expressly links the surfactant to improved flowability in a partially obstructed alimentary tract.

Ethyl cellulose is the principal polymer identified in the asserted claim set. Potassium chloride is the principal potassium salt. The claims also contemplate other potassium salts and polymeric materials in their broader forms.

How many independent claims does US 4,259,315 have?

The claim set contains three independent composition or method concepts:

Claim	Independent subject matter	Principal limitation
1	Pharmaceutical composition	Gelatin capsule containing microencapsulated potassium salt and external hydrophilic surfactant
2	Pharmaceutical composition	Microcapsules with polymeric outer layer, potassium salt core, and external surfactant
5	Veterinary pharmaceutical composition	Controlled-release potassium salt, polymer loading, surfactant range, and improved flowability
7	Human treatment method	Administration of potassium in the claimed capsule formulation

Claims 3, 4, 6, 8, 9, and 10 narrow the composition or method claims through concentration, HLB, polymer, salt, species, or treatment limitations.

The claim numbering includes drafting inconsistencies. Claim 9 refers to claim 6 but introduces limitations associated with claim 3. Claim 10 refers to claim 7 while adding polymer and potassium chloride limitations not fully recited in claim 7. Those defects would have affected claim construction and enforceability analysis during the patent term.

What are the broadest claims in US Patent 4,259,315?

Claim 1: broad composition claim

Claim 1 is the broadest composition claim in the supplied set. It requires:

a pharmaceutical composition;
a gelatin capsule;
a mixture inside the capsule;
microencapsulated potassium salt; and
hydrophilic surfactant external to the microencapsulated salt.

Claim 1 does not expressly require potassium chloride, ethyl cellulose, a particular HLB number, a particular surfactant concentration, or a stated controlled-release profile.

Its breadth is limited by the requirement that the surfactant be external to the microencapsulated salt. A formulation in which the surfactant is incorporated inside the microcapsule, chemically bound to the coating, or absent would fall outside the literal wording of claim 1.

Claim 2: structural limitation

Claim 2 adds a defined microcapsule structure:

an outer layer of polymeric material; and
a core containing potassium salt.

This claim is narrower than claim 1 because it requires a polymer-coated core-shell structure. It still does not limit the polymer to ethyl cellulose or the salt to potassium chloride.

Claim 5: functional and quantitative limitation

Claim 5 requires:

treatment of potassium deficiency in monogastric animals;
a gelatin capsule;
controlled-release microencapsulated potassium salt;
external hydrophilic surfactant;
3% to 50% polymeric material in the microencapsulated salt; and
0.05% to 5.0% surfactant based on the weight of the microencapsulated salt.

The surfactant must be present in an amount sufficient to increase flowability in a partially obstructed alimentary tract. That functional limitation creates additional proof requirements. An accused product would need to satisfy both the composition ranges and the claimed flowability function.

What formulations are protected by the patent?

The most commercially relevant formulation is the combination identified in claims 4, 8, and 10:

gelatin capsule;
potassium chloride core;
ethyl cellulose outer layer;
hydrophilic surfactant outside the microcapsules.

Claims 3 and 6 specify the surfactant concentration. Claim 3 requires a hydrophilic surfactant with an HLB number above 10 at approximately 0.05% to 5.0% by weight. Claim 6 narrows the amount to 0.05% to 1.0% based on the weight of the microencapsulated salt.

Feature	Broad claims	Narrower claims
Dosage form	Gelatin capsule	Gelatin capsule
Active	Potassium salt	Potassium chloride
Release system	Microencapsulated salt	Ethyl cellulose-coated KCl
Surfactant location	External to microcapsules	External to microcapsules
Surfactant	Hydrophilic	HLB above 10
Surfactant amount	Not always specified	0.05%-5.0% or 0.05%-1.0%
Polymer	Polymeric material	Ethyl cellulose
Use	General composition	Human or animal potassium replacement

The patent does not claim every extended-release potassium chloride product. A tablet, liquid, osmotic system, ion-exchange resin, or capsule lacking the claimed external surfactant arrangement would not fall within the principal claim language solely because it delivers potassium chloride over time.

When did US Patent 4,259,315 lose exclusivity?

US Patent 4,259,315 lost patent exclusivity on March 31, 1998, based on its March 31, 1981 issue date and the pre-1995 17-year term applicable to the patent. [1][2]

Event	Date
Patent issued	March 31, 1981
Ordinary 17-year expiration	March 31, 1998
Current status	Expired
Current enforceability	No prospective patent enforcement right

The patent is therefore relevant as prior art and as historical formulation technology, not as a current barrier to generic or branded commercialization.

Patent expiration does not eliminate other possible barriers. Later patents may cover a particular coating process, particle-size distribution, capsule design, excipient combination, manufacturing method, or commercial product. Those later rights must be analyzed separately.

What is the Orange Book status of US Patent 4,259,315?

US Patent 4,259,315 is not an active Orange Book patent that currently provides exclusivity for potassium chloride products. The patent expired before the modern commercial landscape for many current potassium chloride ANDAs developed.

The Orange Book lists patents submitted by NDA sponsors for approved drug products and does not operate as a general registry of every historical formulation patent. An expired patent may appear in historical or archival records, but its presence would not create a current pediatric, formulation, method-of-use, or patent-term barrier. [3]

Potassium chloride products are approved through several dosage forms and regulatory pathways, including extended-release tablets, capsules, oral solutions, and other potassium replacement products. The relevant Orange Book question is product-specific: a company must identify the reference listed drug, the applicable NDA, and the patents currently listed against that product. [3][4]

What Paragraph IV challenges relate to this patent?

No current Paragraph IV challenge can create a viable litigation risk against US Patent 4,259,315 because the patent expired in 1998.

A Paragraph IV certification historically could have been used against an unexpired patent listed for a reference product. The certification states that the patent is invalid, unenforceable, or will not be infringed. Once a patent expires, the patent no longer supports an injunction or a 30-month stay under the Hatch-Waxman framework. [4][5]

For current potassium chloride products, Paragraph IV risk depends on later-listed patents, not on US 4,259,315. Relevant later patents could cover:

modified-release matrix systems;
microencapsulation processes;
capsule fill compositions;
tablet coatings;
reduced gastrointestinal irritation;
dose-specific formulations;
manufacturing controls;
product-specific methods of use.

How strong was the patent estate for the claimed technology?

The patent had moderate historical strength for a narrow formulation combination but weak breadth against alternative potassium delivery systems.

Strengths

Claim 1 covered a broad combination of microencapsulated potassium salt and external hydrophilic surfactant.
Claims 2 through 4 supplied concrete structural limitations that could be easier to identify analytically.
The ethyl cellulose and potassium chloride combination aligned with a commercially plausible controlled-release formulation.
The patent covered both composition and treatment-method concepts.
Claims 5 and 6 addressed a practical manufacturing and administration problem: flowability of microcapsules.

Weaknesses

The claims required a gelatin capsule.
The surfactant had to be external to the microcapsules.
The narrower claims imposed concentration and HLB limitations.
Claim 5 included a difficult functional limitation tied to flowability in a partially obstructed alimentary tract.
The claim dependencies contain apparent drafting errors.
The patent did not broadly cover potassium chloride independent of the delivery architecture.
Alternative tablets, matrices, liquids, coated granules, and non-gelatin dosage forms could avoid the literal claims.

The estate also appears to have been concentrated in one US patent rather than a long chain of continuation, divisional, and improvement patents. That reduced the duration and geographic reach of exclusivity.

What patent litigation affected US 4,259,315?

The supplied information does not establish a reported infringement action involving US Patent 4,259,315. Because the patent has been expired for more than two decades, it does not present a current litigation threat.

Any historical litigation search should distinguish:

cases naming US 4,259,315 directly;
cases involving a product that practiced the claimed formulation;
later patents covering potassium chloride products;
regulatory litigation involving ANDA certifications; and
post-expiration patent disputes involving related formulation technology.

A citation to the patent in later patents does not establish litigation, ownership, licensing, or infringement.

Which companies challenged or licensed the patent?

The supplied claim text does not identify the patent owner, later assignees, licensees, or challengers. No current licensing obligation can arise from the expired patent itself.

During the patent term, commercial rights could have been transferred or licensed through private agreements that do not appear in the claim language. Assignment records and SEC filings are required to establish ownership history. A product label or ANDA reference alone does not prove a license to US 4,259,315.

For current commercial diligence, the important counterparties are manufacturers of potassium chloride extended-release products, including NDA sponsors, ANDA applicants, contract manufacturers, and suppliers of coated potassium chloride particles. Their relevant rights are likely to arise from later patents, formulation know-how, process controls, and regulatory approvals.

How does US 4,259,315 compare with later potassium chloride patents?

Issue	US 4,259,315	Later potassium chloride patent strategies
Core technology	Microencapsulated potassium salt	Matrix tablets, coated particles, osmotic or multiparticulate systems
Dosage form	Gelatin capsule	Tablets, capsules, liquids, granules
Polymer	Broad polymeric material; narrower ethyl cellulose	Product-specific coating and release polymers
Surfactant	External hydrophilic surfactant	Excipient systems tailored to dissolution or handling
Main objective	Controlled release and flowability	Release control, tolerability, manufacturability, or dose uniformity
Legal status	Expired	Must be reviewed patent by patent
Current blocking value	None	Potentially material if unexpired and product-specific

The key distinction is that US 4,259,315 claims a formulation arrangement, while later patent portfolios may divide protection across composition, process, particle engineering, dosage form, and manufacturing claims.

What generic entry risks exist for potassium chloride products?

US 4,259,315 creates no current generic-entry risk. Generic entry depends on:

the reference listed drug’s current Orange Book patents;
regulatory exclusivity;
formulation differences;
manufacturing-process patents;
supply of coated potassium chloride or other controlled-release intermediates;
product-specific labeling and therapeutic equivalence requirements.

A generic applicant using ethyl cellulose-coated potassium chloride in a gelatin capsule with an external hydrophilic surfactant would not infringe this patent because the patent is expired. The same formulation could, however, implicate later patents if the later claims cover the product or manufacturing process.

What are the manufacturing and intellectual-property barriers?

The principal technical barriers associated with the patented concept are:

producing uniform potassium chloride cores;
applying a consistent ethyl cellulose coating;
controlling release across gastrointestinal conditions;
maintaining capsule-fill flow;
preventing segregation of microcapsules and surfactant;
achieving dose uniformity;
controlling residual solvent and coating defects;
demonstrating dissolution and stability;
meeting current good manufacturing practice requirements.

These are commercial and regulatory barriers, not continuing rights under US 4,259,315. The patent's disclosure may remain useful as prior-art technical knowledge, but it does not prevent independent manufacture after expiration.

Is there biosimilar risk for this patent?

No. Biosimilar risk is not applicable to US 4,259,315 because the patent covers a small-molecule potassium salt formulation, not a biologic drug. The relevant competitors are generic and authorized-generic manufacturers, not biosimilar applicants.

Potassium chloride is an inorganic active ingredient. The principal regulatory pathway is ANDA or, depending on product characteristics, another FDA drug approval pathway rather than a biologics license application. [4][6]

What is the revenue exposure from this patent?

There is no current revenue exposure attributable to US 4,259,315 as an enforceable right. Any historical product revenue protected by the patent ended with patent expiration in 1998.

Current revenue exposure must be assessed against:

sales of extended-release potassium chloride capsules and tablets;
product-level Orange Book listings;
later formulation patents;
market exclusivity;
manufacturing concentration;
substitution by generic potassium chloride products;
reimbursement and pricing pressure.

The patent should be assigned zero current exclusivity value in a standard patent valuation model. It may retain historical citation value, freedom-to-operate relevance as expired prior art, and technical value for formulation benchmarking.

Key Takeaways

US Patent 4,259,315 covers gelatin capsules containing microencapsulated potassium salt and external hydrophilic surfactant.
The narrow commercial embodiment is an ethyl cellulose-coated potassium chloride core in a gelatin capsule with external surfactant.
Claims 3, 5, and 6 impose HLB, concentration, polymer-loading, and flowability limitations.
Claims 7 through 10 cover human potassium replacement methods and narrowed formulation embodiments.
The patent expired on March 31, 1998.
It does not create current Orange Book, Paragraph IV, generic-entry, or litigation risk.
No biosimilar analysis applies because the technology concerns a small-molecule potassium salt.
Current freedom to operate depends on later potassium chloride patents, product-specific listings, manufacturing patents, and regulatory exclusivity.

FAQs

Does US Patent 4,259,315 cover all extended-release potassium chloride products?

No. It covers a gelatin capsule containing microencapsulated potassium salt and an external hydrophilic surfactant. Tablets, liquids, matrix systems, and other products may fall outside the claims.

Can an expired patent still block an ANDA?

No. An expired patent cannot support a current Paragraph IV stay or injunction. It can remain relevant as prior art or as evidence in a historical patent analysis.

Is ethyl cellulose required by every claim?

No. Ethyl cellulose is required only in narrower claims, including claims 4, 8, and 10. The broader claims refer to polymeric material or do not specify a particular polymer.

Does the patent claim the surfactant inside the microcapsule?

No. The claims require the hydrophilic surfactant to be external to the microencapsulated potassium salt or microcapsules.

Does US 4,259,315 protect a specific commercial potassium chloride brand?

The claims do not identify a brand. Commercial-product coverage would require comparison of the product's capsule, coating, potassium salt, surfactant, and manufacturing details with the claim limitations.

References

United States Patent and Trademark Office. (1981). U.S. Patent No. 4,259,315.
United States Code, 35 U.S.C. § 154. Patent term and grant of patents.
U.S. Food and Drug Administration. (2024). Approved drug products with therapeutic equivalence evaluations, commonly known as the Orange Book.
U.S. Food and Drug Administration. (2024). Abbreviated new drug application process.
United States Code, 21 U.S.C. § 355(j). Abbreviated applications and patent certifications.
U.S. Food and Drug Administration. (2023). Potassium chloride extended-release oral dosage forms: Prescribing information.

Country	Patent Number	Estimated Expiration	Supplementary Protection Certificate	SPC Country	SPC Expiration
Australia	544965	⤷ Start Trial
Australia	6589880	⤷ Start Trial
Belgium	886973	⤷ Start Trial
Canada	1135624	⤷ Start Trial
Switzerland	648206	⤷ Start Trial
Germany	3100808	⤷ Start Trial
France	2484254	⤷ Start Trial
>Country	>Patent Number	>Estimated Expiration	>Supplementary Protection Certificate	>SPC Country	>SPC Expiration

Details for Patent: 4,259,315

Summary for Patent: 4,259,315