Details for Patent: 5,681,849

United States Patent 5,681,849 (Terbinafine topical): What is claimed, what it covers, and how the US landscape sits

US Patent 5,681,849 claims a terbinafine-based topical formulation and a seborrhoic dermatitis treatment method, with tight constraints on excipients (no anionic surfactants), formulation classes (water/lower alkanol/nonionic surfactant; spray/gel/fluid gel; optional emulsion with specified oil phase), and quantitative ranges (water 50-85 wt%, alkanol 5-35 wt%, terbinafine 0.1-5 wt%, and active-to-surfactant and active-to-oil-phase ratios).

What are the independent claims and what do they cover?

Claim 1 (independent): topical pharmaceutical composition

• Active agent: terbinafine compound of Formula I in free base or acid addition salt form.
• Vehicle system:
  • Water
  • Lower alkanol
  • Water-soluble or water-miscible nonionic surfactant
• Hard negative limitation: no anionic surfactant is present
• No fatty material limitation appears in dependent claim 5 (but it is part of the protected narrowing layer).

This claim sets the core infringement test as follows: an accused topical must contain (i) terbinafine (free base or specified salt form of Formula I), (ii) a water/lower alkanol/nonionic surfactant system, and (iii) exclude anionic surfactants.

Claim 10 (independent): method for treatment

• Indication: “treatment of seborrhoic skin.”
• Act: administer a pharmaceutically effective amount of a composition per Claim 1 to a patient in need.

If a product practices Claim 1 in use, Claim 10 is the pathway for method liability tied to seborrhoic dermatitis.

How do dependent claims narrow the composition?

Water and alcohol ranges (Claim 2 to Claim 4)

• Claim 2: water content 50 to 85 wt%
• Claim 3: lower alkanol 5 to 35 wt%
• Claim 4: alkanol is ethanol

These ranges create a practical “design-around surface.” A competitor outside the claimed ranges (or using a different solvent system) may avoid literal scope, even if the formula still contains terbinafine and a nonionic surfactant system without anionic surfactants.

Fatty material exclusion (Claim 5)

• Claim 5: composition is substantially free of fatty material

This operates as another narrowing excipient control. “Substantially free” is typically litigated as a materiality concept tied to the formulation’s composition and functional role. It is still a claim-limiting requirement.

Dosage form constraints (Claim 6)

• Claim 6: composition is a spray, a gel or a fluid gel

If an accused product uses the same excipient system but is packaged/used as a cream/ointment/solution with different physical form requirements, the literal match to these form limitations becomes a gating issue. Infringement analysis usually hinges on the claim’s structural definition of the product.

Surfactant type (Claim 7)

• Claim 7: surfactant is a polyoxyethylene fatty alcohol ether

This narrows Claim 1’s “any water-soluble/water-miscible nonionic surfactant” to a specific nonionic class in that dependent layer.

Active-to-surfactant ratio (Claim 8 and Claim 11)

• Claim 8: active agent to surfactant ratio about 1:0.5 to about 1:15
• Claim 11: repeats the same ratio range in the context of Claim 7’s surfactant specificity

This matters because formulations can comply with water/alcohol and the “no anionic surfactant” rule yet drift out of the claimed ratio envelope.

Active loading range (Claim 9)

• Claim 9: terbinafine 0.1% to 5% by total composition weight (w/w)

This is a key numeric boundary. It also impacts typical marketed strengths (many products are in the 1% class, but the claim still gates any higher or lower strength).

Emulsion subclass protection (Claims 12 to 15)

Claim 12 (dependent, broader than some others in structure but specific in phase architecture):

• Claims a topical pharmaceutical composition in the form of an emulsion
• Emulsion architecture:
  • Oil phase: contains terbinafine of Formula I (free base or acid addition salt)
  • Aqueous phase: water + lower alkanol + water-soluble/water-miscible nonionic surfactant
• Hard negative limitation preserved: no anionic surfactant is present

This claim adds a phase-structure requirement. If a competitor uses a microemulsion, oleaginous dispersion, or different emulsion type, literal infringement may turn on whether it meets this “emulsion” definition and whether terbinafine is located in the “oil phase” as claimed.

Claim 13: specifies the oil phase

• Isopropyl myristate as the oil phase.

Claim 14: specifies active-to-oil-phase ratio

• active agent to oil phase about 1:5 to about 1:40.

Claim 15: repeats ratio and locks it to the same oil-phase system

• ratio between compound of Formula I and oil phase about 1:5 to about 1:40 on w/w basis.

Claim-by-claim “scope map” for infringement triage

What is the practical patent landscape around this formulation concept (US)?

The “center of gravity” is excipient architecture, not terbinafine chemistry

US 5,681,849 locks in:

• Terbinafine identity (Formula I; free base or acid addition salt)
• Nonionic surfactant-only system with explicit exclusion of anionic surfactants
• Water and lower alkanol as core vehicle components
• Optional emulsion phase architecture (including isopropyl myristate as a specific oil phase in the narrower layer)

In practice, that means competitive freedom depends less on the drug entity and more on whether competitors can:

1. keep terbinafine within the claimed loading range,
2. place the formulation within the claimed water/alcohol ranges,
3. avoid any anionic surfactant, and
4. match the product form and ratio constraints (for the narrower dependent layers).

The negative limitation “no anionic surfactant” is the high-value boundary

This is the strongest “hard” limitation across Claim 1 and preserved in Claim 12:

• an accused product that uses any anionic surfactant (even if present as a minor component) can fall outside literal scope if “anionic surfactant” is interpreted to include the compound(s) used.

This is also where typical formulation updates occur because modern topical products frequently include sulfosuccinates, anionic emulsifiers, or anionic polymers. Any such inclusion is a direct scope risk.

Range and ratio constraints create “numerical design-around”

The claim includes multiple numeric boundaries:

• water: 50-85 wt%
• alkanol: 5-35 wt%
• drug loading: 0.1-5 wt%
• active:sufactant: ~1:0.5 to ~1:15
• active:oil phase: ~1:5 to ~1:40

In freedom-to-operate work, this set acts as a matrix:

• If a competitor chooses a different solvent loading strategy (outside 5-35 wt% alkanol, for example), or increases/decreases water outside 50-85 wt%, or formulates terbinafine outside 0.1-5 wt%, it can exit literal scope even while keeping the same core drug and “nonionic only” concept.

Emulsion claims are narrower than Claim 1 but can still be commercially relevant

Many topical liquid or gel products are emulsions or contain emulsified oils. Claims 12-15 carve out a specific subset:

• terbinafine in the oil phase (not solely in the aqueous phase),
• specific presence of water + lower alkanol + nonionic surfactant in the aqueous phase,
• no anionic surfactant,
• and in narrower dependent claims, oil phase isopropyl myristate and specific active-to-oil ratios.

So the risk to a competitor is highest if their product is a terbinafine-in-oil/aqueous nonionic lower-alkanol system using isopropyl myristate and aligns with the ratio ranges.

What does the method claim add to the landscape?

Claim 10 does not broaden the formulation; it broadens the enforcement pathway:

• It ties infringement to use for seborrhoic skin with a composition meeting Claim 1.

For commercial products, this can matter when:

• the formulation is already sold for one indication, but labeling or “intended use” supports seborrhoic dermatitis,
• or when combination products include a terbinafine composition matching Claim 1 and are marketed for seborrheic conditions.

Key takeaways

• Claim 1 is the main scope driver: terbinafine (Formula I) in free base or acid salt form with water + lower alkanol + water-miscible nonionic surfactant and an express “no anionic surfactant” requirement.
• Dependent claims layer in product form and formulation ranges: water 50-85 wt%, alkanol 5-35 wt% (ethanol in one layer), terbinafine 0.1-5 wt%, plus “substantially free of fatty material,” and dosage form as spray/gel/fluid gel.
• Ratio and surfactant identity narrow further: polyoxyethylene fatty alcohol ether and active:sufactant ratio ~1:0.5 to ~1:15.
• Emulsion protection is narrower but specific: oil phase with terbinafine, aqueous phase with water + lower alkanol + nonionic surfactant, no anionic surfactant; optional isopropyl myristate and active-to-oil ratio ~1:5 to ~1:40.
• Method claim 10 ties use to seborrhoic skin: administering a Claim 1-matching composition for that indication.

FAQs

1) What excipient constraint most directly limits claim coverage?

The formulation must contain “no anionic surfactant.” This applies to both Claim 1 and the emulsion Claim 12 layer.

2) What are the core quantitative ranges that affect literal infringement?

Water 50-85 wt%, lower alkanol 5-35 wt%, and terbinafine 0.1-5 wt%.

3) Does the patent require a specific nonionic surfactant in Claim 1?

No. Claim 1 allows any water-soluble or water-miscible nonionic surfactant. A specific surfactant identity (polyoxyethylene fatty alcohol ether) appears in dependent Claim 7.

4) Is the emulsion claim broader or narrower than Claim 1?

Narrower. Claim 12 requires an emulsion with terbinafine in the oil phase, plus the same lower-alkanol/water/nonionic and no-anionic requirements.

5) What does the method claim add?

It adds enforcement based on administration for seborrhoic skin using a composition that meets Claim 1.

References

[1] US Patent 5,681,849. Topical pharmaceutical composition comprising terbinafine and nonionic surfactants; claims 1-15 and method claim 10.