United States Patent 4,247,547 (Tretinoin Gel): Scope, Claim Map, and US Patent Landscape

US Drug Patent 4,247,547 claims a specific topical tretinoin gel system defined by (i) a narrow tretinoin concentration window, (ii) an alcohol/propylene glycol solvent system, (iii) an antioxidant chosen from enumerated stabilizers, and (iv) a hydroxypropyl cellulose (HPC) gelling agent that turns the solvent into a gel. The estate’s enforceable scope is anchored to those structural constraints and the “consisting essentially of” vehicle limitations, which can narrow infringement risk against formulations that change solvent class, switch to different gelling polymers, omit antioxidants, or use different tretinoin levels outside the recited ranges.

Key takeaways on claim scope (fast answer)

Independent claim 1 requires: tretinoin 0.01% to 0.025% w/w, vehicle that “consists essentially of” an organic solvent selected from ethanol, isopropanol, and propylene glycol (84% to 99% w/w), plus an antioxidant soluble in that solvent and an effective amount of HPC to gel.
Dependent claims narrow antioxidant identity (BHA, BHT, α-tocopherol, ascorbic acid, propyl gallate), antioxidant level (0.01% to 0.10% w/w), and HPC level (0.5% to 5% w/w).
Claim 10 adds an acne vulgaris use framing and tightens the formulation windows: tretinoin 0.01% to 0.025%, antioxidant 0.025% to 0.075%, and HPC 0.5% to 3.0% w/w, in a defined alcohol/propylene glycol solvent blend.
Optional additives are permitted in dependent claim 5–9 (dye, perfume oil, sunscreen, antimicrobial, topical corticosteroid), but they still sit inside the claim 1 “consisting essentially of” architecture.
In practice, the highest-risk design space for a generic or reformulation is where competitors keep (a) tretinoin in-bounds, (b) ethanol/isopropanol/propylene glycol vehicle, (c) the antioxidant class, and (d) HPC as the gelling agent.

What patents protect tretinoin topical acne gels stabilized with antioxidants and gelling hydroxypropyl cellulose?

Immediate answer: 4,247,547 protects a tretinoin gel with an HPC gel matrix in an alcohol/propylene glycol solvent and an antioxidant soluble in that solvent, with defined concentration ranges.

Claim 1: the structural “spine” of protection

Independent claim 1 locks four elements:

Drug load
- Tretinoin: 0.01% to 0.025% by weight
Solvent system
- 84% to 99% by weight of an organic solvent selected from ethanol, isopropanol, propylene glycol
- The solvent selection is categorical. Claim 1’s group does not include glycol ethers or other alcohols outside those enumerated.
Antioxidant function and solubility constraint
- “An effective amount to inhibit oxidation”
- “A pharmaceutically acceptable antioxidant soluble in said organic solvent”
- This ties the antioxidant to functional performance (oxidation inhibition) and formulation feasibility (soluble in the chosen solvent system).
Gelling agent
- “An effective amount to cause gelling of hydroxypropyl cellulose”

Key legal-scope effect: the claim uses “vehicle system consisting essentially of” the three recited components: (a) solvent, (b) antioxidant, (c) HPC gelling action. “Consisting essentially of” typically permits minor, non-material additions but blocks substantial substitutions that would materially change the basic and novel characteristics.

Claim 2: enumerated antioxidant identities

Claim 2 narrows the antioxidants to:

BHA (butylated hydroxyanisole)
BHT (butylated hydroxytoluene)
α-tocopherol
Ascorbic acid
Propyl gallate

This matters because a competitor using a different stabilizer (example: a different phenolic antioxidant not in the list, or a chelator-based stabilization approach) can potentially fall outside the literal scope depending on whether the antioxidant is argued to be outside the claimed “selected from” list.

Claim 3: quantitative narrowing

Antioxidant: 0.01% to 0.10% w/w
HPC: 0.5% to 5.0% w/w

This can produce clean design-around opportunities by moving antioxidant or polymer levels outside the cited windows, though “consisting essentially of” can still create non-literal infringement arguments if close.

Claim 4: solvent mixture permutations

Claim 4 allows mixtures:

ethanol + propylene glycol
isopropanol + propylene glycol
ethanol + isopropanol

Still within the enumerated solvent family.

Claims 5–9: permitted additives

Dependent claims add optional formulation components:

dye (claim 5)
perfume oil (claim 6)
sunscreen (claim 7)
antimicrobial (claim 8)
topical corticosteroid (claim 9)

These do not expand the invention beyond the core tretinoin/solvent/antioxidant/HPC architecture because they are dependent on claim 1’s “consisting essentially of” vehicle restriction.

Claim 10: acne vulgaris formulation with tightened ranges

Claim 10 recasts the formulation “for topical treatment of acne vulgaris consisting essentially of”:

Tretinoin: 0.01% to 0.025%
Organic solvent: 84% to 99% of ethanol, isopropanol, propylene glycol, and mixtures
Antioxidant: 0.025% to 0.075%
HPC: 0.5% to 3.0%

Scope difference vs claim 1: claim 10 is narrower on antioxidant and HPC ranges and adds a treatment framing. If a product matches claim 1 but not claim 10’s tighter windows, it may still fall under claim 1 depending on which claim is asserted.

How broad are US 4,247,547 claims compared with typical tretinoin gel formulations?

Immediate answer: The claim set is moderately broad on solvent flexibility within a three-solvent group, and narrow on the specific antioxidant identity/level and the need for HPC gelling in that vehicle.

Breadth drivers (scope is larger)

Solvent flexibility within the enumerated group (ethanol, isopropanol, propylene glycol; and mixtures).
Antioxidant is functionally defined as “oxidation inhibition” and “soluble” plus enumerated candidates.
Optional secondary ingredients are permitted in dependent claims.

Breadth restrictors (scope is smaller)

Tretinoin is tightly constrained to 0.01%–0.025% w/w.
HPC is required as the gel-forming polymer in the claimed vehicle.
“Consisting essentially of” limits the ability to introduce additional major vehicle components that would affect gel properties, solvent system identity, or stabilization architecture.

What design-arounds could avoid literal scope of claim 1 and claim 10?

Immediate answer: Changes that typically reduce literal infringement risk include shifting (i) tretinoin concentration outside the ranges, (ii) solvent away from the three enumerated solvents, (iii) replacing HPC as the gelling polymer, or (iv) selecting an antioxidant outside the enumerated list or outside the claimed concentration windows.

High-signal variables to move

Tretinoin level
- Moving below 0.01% or above 0.025% can exit claims 1 and 10.
Solvent family
- Using solvents not in the ethanol/isopropanol/propylene glycol group can defeat the claim 1 “selected from” element.
Gelling polymer
- Replacing HPC with different gel formers (or using HPC only as a minor excipient) can reduce literal coverage.
Antioxidant identity
- Selecting a stabilizer not listed in claim 2 (or arguing the solubility/inhibition function is not met within the “pharmaceutically acceptable antioxidant soluble in said organic solvent” requirement).
Quantitative windows
- Adjust antioxidant and HPC levels to be outside the specified bands of claims 3 and 10.

“Consisting essentially of” practical implication

Even if an element is changed, the formulation may still be argued to have the same “basic and novel” characteristics if additives materially change only insignificantly. Conversely, a substantial reformulation that replaces gel formers or solvent class tends to strengthen non-infringement positions.

How many claims cover antioxidants, solvent systems, and gelling agents in US 4,247,547?

Immediate answer: The patent’s claim scope concentrates on the core combination in claim 1, with quantitative and identity tightening in claims 2–4 and further narrowing in claim 10.

Claim coverage matrix (what each claim contributes)

Claim	Tretinoin %	Solvent family (ethanol/isopropanol/propylene glycol)	Antioxidant identity	Antioxidant %	HPC %	Additives
1	0.01–0.025	84–99 (chosen from listed)	Functional “antioxidant” (soluble in solvent)	Not fixed	“effective amount” for gel	Vehicle “consisting essentially of”
2	Same as 1	Same as 1	BHA, BHT, α-tocopherol, ascorbic acid, propyl gallate	Not fixed	Not fixed	None
3	Same as 1	Same as 1	Same as 2	0.01–0.10	0.5–5.0	None
4	Same as 1	Mixtures among listed solvents	Same as 1	Not fixed	Not fixed	None
5	Same as 1	Same as 1	Same as 1	Not fixed	Not fixed	Dye
6	Same as 1	Same as 1	Same as 1	Not fixed	Not fixed	Perfume oil
7	Same as 1	Same as 1	Same as 1	Not fixed	Not fixed	Sunscreen
8	Same as 1	Same as 1	Same as 1	Not fixed	Not fixed	Antimicrobial
9	Same as 1	Same as 1	Same as 1	Not fixed	Not fixed	Topical corticosteroid
10	0.01–0.025	84–99 (listed)	Enumerated antioxidant list	0.025–0.075	0.5–3.0	None (within “consisting essentially of”)

What Orange Book status exists for tretinoin gels tied to 4,247,547?

Immediate answer: Not enough information is provided to reliably map this patent number to a specific FDA-listed drug product in the Orange Book.

When does US 4,247,547 lose exclusivity, and how does that affect generic entry risk?

Immediate answer: Not enough information is provided to determine expiration and exclusivity milestones for this specific patent number.

Which companies could be practicing the formulation space of claim 1 (ethanol/isopropanol/propylene glycol tretinoin gels with HPC)?

Immediate answer: Not enough information is provided to identify practicing companies tied specifically to 4,247,547’s formulation constraints.

What patent litigation or settlements affect the enforceability of US 4,247,547?

Immediate answer: Not enough information is provided to identify litigation history, parties, or settlement terms tied to 4,247,547.

How strong is the patent estate for this tretinoin gel formulation concept?

Immediate answer: Claim strength is tied to narrow formulation elements (solvent family, antioxidant solubility/identity, HPC gel former, and numeric ranges). That structure can improve enforceability against close copies while increasing the likelihood of partial or complete non-infringement against products that deviate in polymer, solvent class, stabilizer choice, or composition windows.

Strength indicators from the claim language

The independent claim is specific about solvent composition and gel former type.
Dependent claims enumerate antioxidant candidates and quantitate bands, strengthening obviousness-type differentiation among alternatives.
“Consisting essentially of” constrains substitutes while leaving room for minor excipients.

Vulnerability indicators from the claim language

Numeric ranges invite “range design-around.”
Enumerated solvent and antioxidant lists limit literal capture of non-listed alternatives.
If prior art discloses ethanol/isopropanol/propylene glycol tretinoin gels stabilized with antioxidants and gelled with HPC, the claim set’s novelty may be contested on obviousness grounds (not assessed here because no prior art set is provided).

What formulations are protected by 4,247,547 beyond the generic gel core?

Immediate answer: Claims 5–9 expand coverage to versions that include:

dyes
perfume oils
sunscreens
antimicrobials
topical corticosteroids

These are “extra ingredients” contingent on meeting claim 1’s core tretinoin/vehicle/HPC/antioxidant architecture.

Key Takeaways

US 4,247,547 claims a tretinoin gel that is defined by a 0.01%–0.025% tretinoin concentration, an 84%–99% solvent selected from ethanol/isopropanol/propylene glycol, an antioxidant soluble in the solvent to inhibit oxidation, and hydroxypropyl cellulose to gel the vehicle.
Claim 2 limits antioxidant identity to BHA, BHT, α-tocopherol, ascorbic acid, or propyl gallate.
Claim 3 narrows antioxidant and HPC amounts (0.01%–0.10% antioxidant; 0.5%–5.0% HPC).
Claim 10 adds an acne vulgaris context and tightens antioxidant (0.025%–0.075%) and HPC (0.5%–3.0%).
Main non-infringement routes are moving outside the numeric windows, changing solvent family, replacing HPC, or using antioxidant/stabilization systems outside the enumerated identities and functional/solubility constraints.

FAQs

Does adding a corticosteroid to a tretinoin HPC gel fall under 4,247,547?
If the formulation still meets claim 1’s core tretinoin/solvent/antioxidant/HPC “consisting essentially of” vehicle, claim 9 can capture products with a topical corticosteroid.
Can a tretinoin gel be non-infringing if tretinoin is 0.03%?
Literal claim 1 and claim 10 require tretinoin 0.01%–0.025%; outside that range, literal coverage is avoided.
What happens if the antioxidant is a phenolic not listed in claim 2?
Literal scope for claim 2 is limited to the enumerated antioxidants; claim 1 still requires “an antioxidant,” but the enumerated set matters for downstream dependent claim coverage.
Would replacing hydroxypropyl cellulose with a different gelling polymer avoid infringement?
Claim 1 requires gelation of hydroxypropyl cellulose in the claimed vehicle; replacing the gel former can break the claim element.
Does changing from ethanol to another solvent automatically avoid claim 1?
Claim 1 limits the solvent to those selected from ethanol, isopropanol, propylene glycol; switching outside that set can avoid the “selected from” element.

References

US Patent 4,247,547.

Details for Patent: 4,247,547

Summary for Patent: 4,247,547