US Drug Patent 4,863,743: Claim Scope, Expiration, K-Dur Patent Landscape and Generic Entry Risk

US Patent 4,863,743 covered an extended-release potassium chloride tablet made from individually coated potassium chloride crystals. Its core limitation was a specific multipart formulation: potassium chloride crystals coated with high-viscosity ethylcellulose plus hydroxypropylcellulose or polyethylene glycol, then compressed into a tablet.

The patent issued on September 5, 1989, and its original 17-year patent term would have expired in 2006, absent an extension or adjustment. It therefore presents no current US patent barrier to generic potassium chloride products. Its historical commercial relevance was greatest for extended-release products such as K-Dur 20 and related microencapsulated potassium chloride tablets.

What does US Patent 4,863,743 protect?

The patent protects a pharmaceutical dosage unit, rather than potassium chloride as an active ingredient. Its principal protected subject matter is the combination of:

Limitation	Claim 1 requirement
Dosage form	Oral tablet
Active ingredient	Potassium chloride
Potassium chloride content	About 64% to about 86.5% of total dosage-unit weight
Physical form	Multiple individual potassium chloride crystals
Crystal coating	Ethylcellulose plus hydroxypropylcellulose or polyethylene glycol
Ethylcellulose amount	About 9% to about 15% of coated-crystal weight
HPC or PEG amount	About 0.5% to about 3% of coated-crystal weight
Ethylcellulose viscosity	Greater than 40 centipoise

The patent does not broadly cover every sustained-release potassium chloride formulation. A competing product would need to satisfy each limitation of an asserted claim for literal infringement. A formulation using a different release-control polymer, a matrix rather than individually coated crystals, or a non-tablet dosage form would fall outside the literal scope of claim 1.

The term “comprising” makes the claims open-ended. Additional excipients or processing steps do not avoid infringement if all required limitations remain present.

How does claim 1 define the patent’s core scope?

Claim 1 is the broadest independent composition claim. It combines four technically important limitations.

Individually coated potassium chloride crystals

The potassium chloride must be present as crystals that are individually coated. This is narrower than a tablet containing potassium chloride dispersed in a polymer matrix. The coating must be applied to the individual crystals before tablet compression.

This limitation creates a structural distinction between:

coated-crystal systems;
matrix tablets;
wax-matrix potassium chloride systems;
osmotic systems;
tablets containing uncoated potassium chloride particles; and
multilayer tablets in which release is controlled by a separate tablet layer.

A generic manufacturer could therefore design around the patent by using a matrix system or by changing the release-control architecture, subject to separate patent rights and regulatory requirements.

Ethylcellulose concentration

The ethylcellulose must represent approximately 9% to 15% of the weight of the coated crystals. The claim does not express this percentage as a percentage of the entire tablet. That distinction is material.

For example, the patent does not require that ethylcellulose constitute 9% to 15% of the total dosage unit. The calculation is based on the coated-crystal fraction. A formulation can therefore satisfy the ethylcellulose limitation even when ethylcellulose is a materially smaller percentage of the complete tablet.

Hydroxypropylcellulose or polyethylene glycol

Claim 1 requires at least one of two specified materials:

hydroxypropylcellulose; or
polyethylene glycol.

Claims 8 and 9 separately narrow the alternative to hydroxypropylcellulose or polyethylene glycol. A formulation containing ethylcellulose with another hydrophilic polymer, but neither hydroxypropylcellulose nor polyethylene glycol, would not literally satisfy this limitation.

The phrase “at least one member selected from” permits the use of both hydroxypropylcellulose and polyethylene glycol, provided the other limitations are met.

Ethylcellulose viscosity

The independent claim requires ethylcellulose with a viscosity greater than 40 centipoise. Claim 7 narrows this to 85 to 110 centipoise.

Viscosity is a potentially significant infringement issue because the applicable measurement method, concentration, solvent, temperature and commercial grade can affect the reported value. The patent claim itself, as presented, does not specify the testing protocol. Product testing and the patent specification would be important in any dispute involving a borderline viscosity.

What do claims 2 through 9 add?

Claims 2 through 9 are dependent formulation and particle-size claims.

Claim	Added limitation	Commercial or legal effect
2	Magnesium stearate at 0.5% to 2.0% of tablet weight	Covers a conventional lubricant level
3	Microcrystalline cellulose at 3% to 10%	Narrows the tablet excipient profile
4	Cross-linked polyvinylpyrrolidone at 0.5% to 2.0%	Adds a superdisintegrant limitation
5	Potassium chloride crystal size of 30 to 50 mesh	Narrows particle-size distribution
6	Approximately 40-mesh crystals	Preferred particle-size embodiment
7	Ethylcellulose viscosity of 85 to 110 centipoise	Preferred coating-polymer grade
8	Hydroxypropylcellulose is the selected hydrophilic additive	Excludes PEG-only embodiments
9	Polyethylene glycol is the selected hydrophilic additive	Excludes HPC-only embodiments

A product that falls outside a dependent claim can still infringe claim 1. For example, a tablet using 60-mesh crystals may avoid claims 5 and 6 but remain within claim 1 if the remaining claim 1 limitations are present.

Claims 2 through 4 also create a cumulative formulation chain. Claim 4 requires the limitations of claims 1, 2 and 3, plus cross-linked polyvinylpyrrolidone.

What is the scope of method claims 10 and 11?

Claim 10 covers administering a therapeutically useful amount of potassium chloride in a dosage unit meeting claim 1. It is a method-of-treatment claim tied to the claimed dosage form.

Claim 11 adds disintegration in water or on an aqueous food before administration. This language is directed to administration conditions rather than a new chemical composition.

The method claims have narrower practical value than the composition claim because they require use of the patented dosage unit. They could be relevant to induced-infringement allegations if labeling instructs patients or healthcare providers to disintegrate the tablet in water or on aqueous food. They do not independently cover administration of every potassium chloride product.

How should claim 12 be interpreted?

Claim 12 appears to be a narrower combination claim, but its drafting contains internal inconsistencies.

It recites:

68% to 86.5% coated potassium chloride crystals;
0.5% to 3% magnesium stearate;
3% to 15% microcrystalline cellulose;
0.5% to 2.0% cross-linked polyvinylpyrrolidone;
9% to 15% ethylcellulose based on coated-crystal weight; and
0.5% to 3% hydroxypropylcellulose or polyethylene glycol based on coated-crystal weight.

The apparent inconsistencies are:

Claim 12 depends on claim 2 but recites a magnesium stearate range of 0.5% to 3%, while claim 2 recites 0.5% to 2.0%.
It recites microcrystalline cellulose at 3% to 15%, while claim 3 recites 3% to 10%.
It uses typographical variants such as “magnesuim,” “polyvinyl pyrrolidone,” and “polyethlene glycol.”
The phrase “the pharmaceutical dosage unit in tablet form of claim 2 comprising” may incorporate claim 2’s narrower limitations while also restating broader ranges.

Under normal dependency rules, a dependent claim includes all limitations of the parent claim. The broader repeated ranges in claim 12 would not necessarily eliminate the narrower limitations inherited from claims 2 and 3. The prosecution history and issued patent text would control the final interpretation.

When did US Patent 4,863,743 lose exclusivity?

The patent issued September 5, 1989. For a pre-1995 US application, the ordinary term was generally 17 years from issuance. On that basis, the expected expiration date was September 5, 2006.

Milestone	Date or status
Patent issued	September 5, 1989
Ordinary patent term	17 years from issuance
Expected expiration	September 5, 2006
Current status	Expired
Current generic-blocking effect	None

The patent’s expiration eliminated ordinary infringement risk based solely on US Patent 4,863,743. It also eliminated the commercial value of any Orange Book listing associated only with this patent.

The patent could have affected FDA approval timing before expiration through listed-patent certification procedures, including Paragraph IV challenges. Those procedures have no present blocking effect from this expired patent.

What was the Orange Book status of the patent?

US Patent 4,863,743 was historically associated with an extended-release potassium chloride product, particularly the K-Dur product family. The relevant regulatory framework was the Hatch-Waxman system for small-molecule drugs, not the biologics pathway.

The practical Orange Book consequences were:

an ANDA applicant could have needed to address the patent through a certification;
a Paragraph IV certification could have triggered patent litigation;
a timely infringement suit could have generated a 30-month FDA approval stay;
expiration removed the patent from the category of an enforceable patent obstacle.

Orange Book status must be assessed by NDA product, strength and historical listing date. A patent’s appearance in a historical Orange Book record does not establish that it remains enforceable today. FDA identifies current and historical listed patents through the Orange Book patent and exclusivity datasets.[1]

Which companies challenged the potassium chloride patent estate?

The principal historical generic-entry disputes involved Schering-Plough and generic manufacturers seeking approval for extended-release potassium chloride products. Publicly reported litigation and antitrust proceedings included disputes involving Upsher-Smith Laboratories and ESI Lederle.

The litigation became commercially significant because settlement agreements allegedly delayed generic entry while providing value to generic challengers. The Federal Trade Commission challenged the settlements in the Schering-Plough proceedings, and the later US Supreme Court decision in FTC v. Actavis cited the case in discussing reverse-payment settlements under antitrust law.[2][3]

The significance for Patent 4,863,743 was historical:

generic applicants had an incentive to challenge the patent before expiration;
the patent owner had an incentive to enforce the formulation claims;
settlements could affect the timing of generic competition;
after expiration, the patent no longer supported a forward-looking exclusionary strategy.

The existence of past litigation does not establish that the patent was valid, infringed or enforceable for every accused product. Those conclusions depend on the specific pleadings, claim construction, prior art and settlement terms.

What patent litigation affects US Patent 4,863,743 today?

No current litigation based solely on US Patent 4,863,743 should create a meaningful US launch risk because the patent expired in 2006. Any current dispute involving potassium chloride extended-release products would more likely concern:

later formulation patents;
manufacturing-process patents;
trademarks and trade dress;
regulatory exclusivity;
product liability;
antitrust conduct;
or patents covering a different delivery platform.

The expired patent may remain relevant in freedom-to-operate analysis as prior art and as a historical reference for claim scope. It cannot provide a current injunction against a new generic product.

What formulations are protected by the patent?

The strongest coverage is for a product that closely matches the following profile:

potassium chloride crystals around 30 to 50 mesh, particularly approximately 40 mesh;
individual crystal coating;
ethylcellulose at about 9% to 15% of coated-crystal weight;
ethylcellulose viscosity above 40 centipoise, particularly 85 to 110 centipoise;
hydroxypropylcellulose or polyethylene glycol at about 0.5% to 3%;
compression into a tablet;
magnesium stearate, microcrystalline cellulose and cross-linked polyvinylpyrrolidone within the dependent-claim ranges.

The patent is weaker against:

matrix tablets;
uncoated-crystal tablets;
capsules or liquid dosage forms;
formulations using a different coating polymer;
products using only polymers outside the claimed Markush group;
formulations outside the claimed concentration ranges;
crystal sizes outside the claimed mesh ranges;
and products with a non-tablet release mechanism.

Because the patent has expired, this distinction now matters primarily for historical litigation analysis, patent landscaping and technical comparison.

How does the patent compare with competing potassium chloride products?

Product architecture	Relationship to Patent 4,863,743
Individually coated potassium chloride crystals in a tablet	Closest technical match
Microencapsulated potassium chloride tablet	Potentially within scope, depending on coating composition and ranges
Wax-matrix potassium chloride tablet	Less likely to satisfy the individual coated-crystal limitation
Polymer-matrix tablet	Generally distinct from the claimed coated-crystal architecture
Liquid potassium chloride	Outside the tablet limitation
Powder or effervescent formulation	Outside the claimed tablet structure unless separately converted into a claimed tablet
Capsule containing coated crystals	Outside the tablet limitation of claim 1

K-Dur-type products were commercially important because they used extended-release potassium chloride technology in a solid oral dosage form. Klor-Con M, Micro-K and other potassium chloride products competed in the same therapeutic market, but commercial similarity does not establish patent infringement. The formulation composition and release mechanism must be compared claim element by claim element.

Does the patent create biosimilar risk?

No. Potassium chloride is a small-molecule inorganic active ingredient. Biosimilar provisions under the Public Health Service Act do not apply. The relevant competitive pathways are:

ANDA approval for a therapeutically equivalent generic;
505(b)(2) approval for certain differentiated formulations;
or an NDA for a new product.

The patent did not cover a biologic, protein, antibody or other biosimilar-sensitive product.

What manufacturing and intellectual-property barriers remain?

US Patent 4,863,743 did not claim a manufacturing method in the claims provided. It is a product and method-of-treatment patent. The principal technical barrier it historically created was the need to reproduce a controlled coating process on individual potassium chloride crystals while maintaining:

coating uniformity;
release performance;
tablet mechanical strength;
acceptable disintegration;
potassium chloride assay;
and stability.

Those technical requirements can remain difficult even after patent expiration. They are not, however, patent barriers created by this patent. A current manufacturer must separately evaluate later patents, process know-how, FDA specifications, bioequivalence requirements and manufacturing controls.

What is the patent strength of US Patent 4,863,743?

Factor	Assessment
Claim breadth	Moderate to narrow
Technical specificity	High
Product coverage	Focused on coated-crystal tablets
Design-around potential	Significant
Method-claim breadth	Narrow
Manufacturing coverage	Limited based on claims provided
Current enforceability	None because expired
Historical commercial relevance	High for extended-release potassium chloride
Biosimilar relevance	None
Current Paragraph IV risk	None from this patent

The patent’s historical strength came from the combination of formulation variables rather than from broad coverage of potassium chloride. Its likely vulnerability points included the use of prior sustained-release coating technologies, known pharmaceutical excipients and obviousness arguments based on combining ethylcellulose with hydrophilic polymers.

Its current legal strength is zero as an exclusionary right because the patent term has ended.

What generic launch scenarios existed before patent expiration?

Before expiration, generic launch outcomes could have followed four principal paths:

A Paragraph IV applicant could challenge validity, enforceability or infringement and launch after litigation success.
The applicant could obtain a settlement with a negotiated entry date.
The applicant could design around the coated-crystal claims and pursue approval for a non-infringing formulation.
The applicant could wait for patent expiration and launch an equivalent product.

After September 2006, the fourth path became available without a challenge to the patent’s validity. Current generic competition therefore depends on FDA requirements and any later intellectual-property rights, not on Patent 4,863,743.

Key Takeaways

US Patent 4,863,743 covers extended-release potassium chloride tablets using individually coated crystals.
Claim 1 requires ethylcellulose, hydroxypropylcellulose or polyethylene glycol, specified concentration ranges and ethylcellulose viscosity above 40 centipoise.
Claims 2 through 9 add excipient, particle-size and polymer-viscosity limitations.
Claims 10 and 11 cover administration of the claimed tablet, including disintegration in water or aqueous food.
Claim 12 contains apparent dependency and range inconsistencies that require review of the issued patent and prosecution history.
The patent issued September 5, 1989, and its ordinary term would have expired September 5, 2006.
It is not a current US barrier to generic potassium chloride entry.
The patent had historical relevance to K-Dur-related generic litigation and Hatch-Waxman Paragraph IV disputes.
It has no biosimilar relevance.
Current freedom-to-operate analysis must focus on later patents, manufacturing processes, regulatory requirements and product-specific formulation rights.

FAQs

Can a generic potassium chloride tablet infringe US Patent 4,863,743 today?

No enforceable infringement claim can arise solely from this expired patent. A product could technically practice the former claim scope, but the expired patent cannot support a current injunction or damages claim for post-expiration conduct.

Did US Patent 4,863,743 cover Klor-Con M?

It may have been relevant to products using individually coated potassium chloride crystals, but product-specific coverage requires comparison of the commercial formulation with every asserted claim limitation. Brand identity alone does not establish infringement.

Is a potassium chloride matrix tablet covered by this patent?

Generally, a matrix tablet would not satisfy the “plurality of coated potassium chloride crystals” limitation unless the potassium chloride is also present as individually coated crystals. A matrix system may implicate different patents.

Can a 505(b)(2) applicant avoid the patent by using a liquid potassium chloride product?

The tablet limitation would generally exclude a liquid dosage form from literal infringement of claim 1. The applicant would still need to assess other patents, FDA requirements and any applicable exclusivity.

What is the principal design-around strategy for this patent?

The clearest historical design-around options were changing the release mechanism, using a matrix system, selecting a different coating-polymer system, altering the dosage form, or moving outside the claimed composition ranges.

References

U.S. Food and Drug Administration. (2024). Approved drug products with therapeutic equivalence evaluations: Orange Book. https://www.fda.gov/drugs/drug-approvals-and-databases/approved-drug-products-therapeutic-equivalence-evaluations-orange-book
Federal Trade Commission. (2003). In the matter of Schering-Plough Corporation, Upsher-Smith Laboratories, Inc., and American Home Products Corporation. FTC Docket No. 9297.
Federal Trade Commission v. Actavis, Inc., 570 U.S. 136 (2013).
Schering-Plough Corp. v. Federal Trade Commission, 402 F.3d 1056 (11th Cir. 2005).
U.S. Patent No. 4,863,743. (1989). Potassium chloride pharmaceutical dosage unit. United States Patent and Trademark Office.

Country	Patent Number	Estimated Expiration	Supplementary Protection Certificate	SPC Country	SPC Expiration
Austria	52918	⤷ Start Trial
Australia	5514086	⤷ Start Trial
Australia	583903	⤷ Start Trial
Canada	1270765	⤷ Start Trial
>Country	>Patent Number	>Estimated Expiration	>Supplementary Protection Certificate	>SPC Country	>SPC Expiration

Details for Patent: 4,863,743

Summary for Patent: 4,863,743