Scope and claims of US Patent 4,943,565 (aspirin/acetaminophen/caffeine tablets with hydroxypropyl cellulose dissolution enhancer)

US 4,943,565 claims a narrow but high-value formulation space for combination tablets containing aspirin, acetaminophen, and caffeine, where dissolution time is reduced by adding a specific dissolution-enhancing polymer: nonionic hydroxypropyl cellulose ether with a defined hydroxypropyl substitution range (10% to 16% by weight of the polymer). Claim breadth is driven by (i) rigid composition windows for actives and caffeine, (ii) mandatory polymer selection and substitution range, and (iii) a functional dissolution limitation tied to a “predetermined period of time.”

What is US Patent 4,943,565 claiming and what is the core invention?

Core claim concept (independent claim 1 framing):
A tablet that contains by weight:

about 22–75% aspirin
about 22–75% acetaminophen
about 4–19% caffeine
and that dissolves within a “predetermined period of time,” improved by incorporating:
a dissolution-enhancing amount of nonionic hydroxypropyl cellulose ether polymer
having hydroxypropyl content of 10% to 16% by weight of the polymer
so that the polymer-containing tablet dissolves in less than the predetermined period.

Practical meaning: the patent protects not a general “aspirin/acetaminophen/caffeine” tablet, but a specific dissolution-improving polymer system defined by polymer nonionic identity plus hydroxypropyl substitution percent.

How the claims define the protected formulation universe

The claims split into two independent claim structures (1 and 9), with the remainder setting numeric sub-ranges:

Claim 1: polymer “in a dissolution enhancing amount” (functional, not purely numeric), with hydroxypropyl content 10–16% of polymer.
Claim 9: polymer amount is explicitly 0.5–5% by weight of the total tablet, with hydroxypropyl content 10–16% of the polymer.

Functional limitation: “predetermined period of time”

The phrase “said tablet dissolving in a predetermined period of time” appears in both independent claims. That language is central for infringement and validity analysis because it anchors the comparison point. In practice, it typically means the baseline tablet dissolves within a defined time window; the claimed improvement achieves a faster dissolution time.

Key consequence: an accused product can be argued to avoid infringement if it:

uses a polymer outside the hydroxypropyl content band (10–16%), or
does not use a nonionic hydroxypropyl cellulose ether in the required amount, or
does not achieve dissolution “in less than” the predetermined benchmark used in the patent’s formulation context.

What are the independent claim 1 and claim 9 boundaries on tablet composition?

Independent Claim 1 (composition + functional improvement):

Tablet composition windows (by weight):
- 22–75% aspirin
- 22–75% acetaminophen
- 4–19% caffeine
Dissolution condition:
- tablet dissolves in a predetermined period of time
Polymer limitation:
- incorporate a dissolution enhancing amount of hydroxypropyl cellulose ether nonionic polymer
- hydroxypropyl content 10–16% by weight of the polymer
Outcome:
- polymer-containing tablet dissolves in less than predetermined period.

Independent Claim 9 (adds explicit polymer loading):

Repeats the same actives and caffeine windows.
Repeats the dissolution condition and functional outcome.
Replaces the “dissolution enhancing amount” language with a defined loading:
- 0.5–5% by weight of the total tablet of the polymer
Repeats polymer substitution range:
- hydroxypropyl content 10–16% by weight of polymer.

Claim overlap and how it affects coverage

Claim 9 is a more concrete subset of Claim 1 because it narrows polymer amount to 0.5–5% and still requires the same substitution (10–16%).
Claim 1 can be broader in polymer amount depending on how “dissolution enhancing amount” is interpreted, but Claim 9 provides a strong numeric anchor for infringement and claim construction.

What specific polymer is required: nonionic hydroxypropyl cellulose ether with 10%–16% hydroxypropyl substitution?

Both independent claims require:

hydroxypropyl cellulose ether
explicitly nonionic
with hydroxypropyl content of 10% to 16% by weight of the polymer.

Why hydroxypropyl content controls risk

The “hydroxypropyl content” is a substitution/functional parameter tied to the identity of the polymer grade. In infringement terms, an accused formulation that uses hydroxypropyl cellulose outside 10–16% (for example, lower substitution or higher substitution) can avoid a key element even if dissolution is still improved.

Nonionic limitation

Even if a cellulose ether dissolves faster, if it is ionic (or chemically characterized as ionic in relevant specs), it can fall outside the claimed “nonionic polymer” element.

How do dependent claims narrow polymer loading, hydroxypropyl percent, and actives/caffeine amounts?

Dependent claims 2, 5 (polymer loading range)

Claim 2: hydroxypropyl cellulose incorporated at 0.5–5% by weight of total tablet.
Claim 5: repeats 0.5–5% by weight.

These mirror Claim 9’s numeric polymer loading and strengthen enforceability for that specific band.

Dependent claims 3 (tight polymer range)

Claim 3: hydroxypropyl cellulose present at 0.8–2.0% by weight of total tablet.

This creates a narrower protected sub-range inside the broader 0.5–5% band.

Dependent claims 4 and 10 (tight hydroxypropyl substitution range)

Claim 4: hydroxypropyl content 10–13% (subset of 10–16%).
Claim 10: repeats the 10–13% range.

These dependent claims cover lower end substitution within the main 10–16% interval.

Dependent claim 6 (tightactives and caffeine weight windows)

Claim 6 sets an additional numeric specification:

aspirin: 30–45% by weight
acetaminophen: 30–45% by weight
caffeine: 9–11% by weight

This dependent claim is a practical target for formulation manufacturers because it narrows the actives distribution substantially relative to the broad 22–75% / 4–19% ranges.

Dependent claims 7 and 8 (mg-based dosage embodiments)

Claim 7:
- aspirin: 150–500 mg
- acetaminophen: 150–500 mg
- caffeine: 30–130 mg
- hydroxypropyl cellulose: 5–35 mg
Claim 8:
- aspirin: 200–300 mg
- acetaminophen: 200–300 mg
- caffeine: 60–70 mg
- hydroxypropyl cellulose: 5–10 mg

These are the most operational constraints: they anchor the claim to common tablet strengths and help translate polymer loading into real formulation work.

Numeric claim structure map

Claim	Actives (by weight)	Caffeine (by weight)	Polymer (total wt %)	Hydroxypropyl content (polymer wt %)	Other anchors
1	22–75% aspirin; 22–75% acetaminophen	4–19%	“dissolution enhancing amount”	10–16%	functional dissolution improvement
9	same	same	0.5–5%	10–16%	functional dissolution improvement
2 / 5	same	same	0.5–5%	10–16% (implied by claim 1/9)	depends on claim 1/9
3	same	same	0.8–2.0%	10–16%	tighter polymer wt%
4 / 10	same	same	0.5–5% (via claim linkage)	10–13%	tighter substitution range
6	30–45% aspirin	9–11%	(depends on claim 1)	10–16%	acetaminophen 30–45%
7	150–500 mg	30–130 mg	5–35 mg	10–16%	dosage-level embodiment
8	200–300 mg	60–70 mg	5–10 mg	10–16%	dosage-level embodiment

What is the infringement “design-around” space implied by these claims?

High-impact levers:

Hydroxypropyl content outside 10–16% of the polymer.
Use of a different polymer type (not hydroxypropyl cellulose ether; or not nonionic).
Polymer loading outside the required range (0.5–5% explicitly in claim 9 and dependent claims; or 0.8–2% in claim 3; or 5–10 mg in claim 8).
Not achieving the dissolution “less than predetermined period” outcome for the relevant baseline comparison used by the patent.

Specific “risk zones”

Formulas with 0.5–5% nonionic hydroxypropyl cellulose ether polymer and 10–16% hydroxypropyl substitution are within the strongest numeric scope.
Products aiming for a dissolution benefit typically cluster in this zone, which increases the likelihood of meeting the functional limitation unless dissolution is benchmarked in a way that avoids the claim’s “predetermined period” comparison.

How broad is the protection for actives and caffeine?

Actives and caffeine ranges are wide in independent claims:

aspirin: 22–75%
acetaminophen: 22–75%
caffeine: 4–19%

That breadth means the patent can cover multiple strengths and ratios as long as the tablet composition falls within those weight windows and the polymer/in-substitution/dissolution requirements are met.

Dependent claim 6 narrows this to a more specific commercial ratio (aspirin and acetaminophen each 30–45%; caffeine 9–11%), which likely maps to a known marketed composition.

What formulation patents are likely adjacent (and how this patent fits the landscape)?

Without the full publication and prosecution record, only the claim text can be analyzed. Still, the structure indicates the estate is focused on:

fixed-dose analgesic combination tablets (aspirin + acetaminophen + caffeine)
dissolution-enhancing cellulose ether grades defined by hydroxypropyl substitution.

Likely adjacent technology themes

In this class of patents, closely related claim sets typically include:

other grades of hydroxypropyl cellulose (outside 10–16% substitution)
alternative dissolution enhancers (other nonionic polymers or disintegrants)
manufacturing methods that produce faster dissolution (granulation, compression parameters, particle size)
coatings or matrix systems affecting dissolution.

This patent’s defining feature is the combination of:

actives ratio windows
substitution-specific hydroxypropyl cellulose ether
functional dissolution improvement.

What does the claim language imply about testing and evidentiary burdens?

Dissolution comparison is outcome-driven. The infringement analysis will hinge on dissolution testing relative to the patent’s “predetermined period of time” baseline.

Polymer identity is spec-driven. Hydroxypropyl cellulose ether must be nonionic, with hydroxypropyl content 10–16% by weight of polymer. That implies that polymer COAs and characterization (to the extent needed) become central to claim element satisfaction.

Dosage embodiments matter for commercial alignment. Claims 7 and 8 tie polymer mass and actives mg ranges to specific strength bands, which can be leveraged in product mapping across SKUs.

Key Takeaways

US 4,943,565 protects aspirin/acetaminophen/caffeine tablets that dissolve faster by adding nonionic hydroxypropyl cellulose ether with 10–16% hydroxypropyl content (by weight of polymer).
Strongest numeric coverage is in 0.5–5% polymer by total tablet weight (Claim 9 and dependent claims), with additional tighter bands at 0.8–2.0% (Claim 3).
Substitution is critical: 10–16% is the gate; dependent claims target 10–13%.
Commercial product risk concentrates in formulations that also fit the actives/caffeine ratios, especially 30–45% aspirin, 30–45% acetaminophen, 9–11% caffeine (Claim 6), and the strength embodiments in mg terms (Claims 7 and 8).
Design-arounds should evaluate polymer substitution specs, polymer loading, and whether dissolution results avoid the claimed “less than predetermined period” outcome.

FAQs

1) Does US 4,943,565 cover any aspirin/acetaminophen/caffeine tablet that uses hydroxypropyl cellulose?
No. The claims require nonionic hydroxypropyl cellulose ether with hydroxypropyl content 10–16% of the polymer, plus dissolution improvement relative to the patent’s predetermined period.

2) Can a formulation outside 0.5–5% hydroxypropyl cellulose escape coverage?
Claim 9 and dependent claims 2/5 explicitly require 0.5–5% polymer by total tablet weight. Claim 1 uses “dissolution enhancing amount,” but Claim 9 provides a clear numeric safe zone target for design-around where applicable.

3) How do claims 7 and 8 matter for real-world strengths?
They constrain not only polymer percentage but also mg ranges for aspirin, acetaminophen, caffeine, and polymer, aligning patent scope with specific tablet strengths and commercial SKUs.

4) What is the main element likely to be contested in infringement: dissolution or polymer specs?
Both. Polymer spec (nonionic identity and hydroxypropyl content 10–16%) is element-level. Dissolution is an outcome-level functional requirement tied to a predetermined benchmark.

5) Are the aspirin/acetaminophen/caffeine ranges broad enough to cover many ratios?
Yes for independent claims (22–75% aspirin; 22–75% acetaminophen; 4–19% caffeine). Dependent claim 6 narrows the ratio to a tighter center of gravity (30–45% / 30–45% / 9–11%).

Country	Patent Number	Estimated Expiration	Supplementary Protection Certificate	SPC Country	SPC Expiration
Canada	1288349	⤷ Start Trial
Japan	2604599	⤷ Start Trial
Japan	S6383025	⤷ Start Trial
>Country	>Patent Number	>Estimated Expiration	>Supplementary Protection Certificate	>SPC Country	>SPC Expiration

Details for Patent: 4,943,565

Summary for Patent: 4,943,565