US Patent 10,596,155: Scope, Claims, Expiration, Orange Book Status, and Competitive Patent Landscape

US Patent 10,596,155 protects a narrowly defined, single-dose intravaginal metronidazole gel for bacterial vaginosis. The claims combine composition parameters, solvent-selection criteria, rheology, vaginal retention, and clinical outcomes. The commercial profile most closely corresponds to Nuvessa, a 1.3% metronidazole vaginal gel containing 65 mg of metronidazole in a single 5-gram dose.

The principal enforcement risk is not ordinary metronidazole use. It is a competing product that reproduces the claimed single-dose, high-viscosity, mucoadhesive formulation and achieves the specified Nugent-score outcome.

What does US Patent 10,596,155 cover?

The independent claims cover methods of treating bacterial vaginosis by administering a single intravaginal dose of a metronidazole gel. The composition must satisfy multiple quantitative limitations.

Claim element	Requirement
Indication	Bacterial vaginosis
Route	Intravaginal administration
Dosing	One administration over one day
Metronidazole amount	60 to 70 mg; dependent claim 10 narrows this to 65 mg
Water	About 30% to about 60% by weight
Mucoadhesive polymer	Required
Solvent system	About 30% to about 60% by weight
High-solubility solvent	Saturated metronidazole solubility of at least 50 mg/g at 25°C
Second solvent group	Saturated metronidazole solubility of at least 20 mg/g at 25°C
Clinical result	Nugent score below 4 within 20 to 31 days
Viscosity under claim 2	About 200,000 to 400,000 mPa·s
pH under claims 4 and 5	About 3.0 to 5.0; narrower claim at about pH 4.0

The patent is therefore a combination patent. A formulation must meet the compositional limitations, and the claimed method requires administration to a bacterial-vaginosis patient with the specified clinical result.

How many independent claims does US 10,596,155 have?

The supplied claim set has two independent method claims: claims 1 and 14.

Claim 1 is a broad independent method claim subject to the core composition and clinical-response limitations. Claim 14 incorporates the same core requirements but adds two important restrictions:

The high-solubility solvent represents about 1% to 5% of the solvent system.
The formulation has the specified 200,000 to 400,000 mPa·s viscosity.

Claim 14 is narrower than claim 1 but may be commercially significant because it tracks a practical formulation architecture rather than merely claiming a broad solvent combination.

What do claims 2 through 13 add?

The dependent claims create fallback positions:

Claim 2: high viscosity measured under a highly specific Bohlin CVO 100 protocol.
Claim 3: in vitro skin-distribution and receiver-fluid performance relative to a prior test composition.
Claims 4 and 5: acidic pH, with claim 5 centered at approximately pH 4.
Claims 6 through 8: solvent identity, including aromatic alcohols, alkylene diols, and polyoxyalkylenes.
Claim 9: hydroxyethylcellulose, carbomer, polycarbophil, or combinations.
Claim 10: exactly or approximately 65 mg metronidazole.
Claim 11: the patient is not Amsel positive within five days.
Claim 12: solvent system at approximately 40% to 45% of the formulation.
Claim 13: the high-solubility solvent is 1% to 5% of the solvent system, while the lower-threshold solvents represent 95% to 99%.

What formulation does the patent most closely describe?

The claim structure describes a single-dose vaginal gel containing approximately 65 mg of metronidazole, a high water fraction, a mucoadhesive polymer, and a ternary solvent system.

The solvent categories are important:

Solvent class	Claimed examples
High-solubility solvent	Benzyl alcohol, 2-methylbenzyl alcohol, phenoxyethanol
Lower-threshold solvent	Ethylene glycol, propylene glycol
Polyoxyalkylene	Polyethylene glycol or polypropylene glycol

Claim 8 requires a ternary system containing:

A lower aromatic alcohol;
A lower alkylene diol; and
A polyoxyalkylene.

Claim 13 then narrows the system so that the aromatic alcohol component represents only approximately 1% to 5% of the total solvent system. This limitation can be commercially important because a formulation may use a small amount of aromatic alcohol to increase metronidazole solubility while relying primarily on glycols or polyethers as the vehicle.

What product is associated with US Patent 10,596,155?

The claim profile corresponds closely to Nuvessa, a single-dose 1.3% metronidazole vaginal gel. A 1.3% concentration in a 5-gram dose provides approximately 65 mg of metronidazole, matching claim 10.

The FDA-approved product is distinct from conventional metronidazole vaginal gel products that generally use a lower concentration and a multi-day dosing schedule. The Nuvessa label identifies a single 5-gram vaginal dose for bacterial vaginosis. [2]

Product	Active ingredient	Typical dose	Dosing profile
Nuvessa	Metronidazole 1.3%	Approximately 65 mg in 5 g	Single intravaginal dose
MetroGel-Vaginal	Metronidazole 0.75%	Approximately 37.5 mg in 5 g	Usually once daily for five days
Oral metronidazole	Metronidazole	Dose varies	Multi-dose oral regimen

The patent does not cover every metronidazole vaginal product. A conventional 0.75% gel administered over five days would generally fall outside the single-dose and 60-to-70 mg limitations, even if it used a carbomer or another mucoadhesive polymer.

When does US Patent 10,596,155 lose exclusivity?

The reported patent record identifies US 10,596,155 as issuing on March 24, 2020. Its ordinary patent term is associated with a February 3, 2035 expiration date, subject to any applicable patent-term adjustment, terminal disclaimer, or other USPTO term calculation. [1]

Event	Date
Earliest reported priority date	February 3, 2014
Patent issuance	March 24, 2020
Expected ordinary expiration	February 3, 2035
FDA product approval for Nuvessa	December 2017
Potential commercial generic-entry window	Before 2035 only if a challenge succeeds, a settlement permits entry, or the patent is not enforceable

The relevant freedom-to-operate date is not determined solely by the patent's nominal expiration. A generic applicant must assess the complete Orange Book listing, related continuation patents, terminal disclaimers, pediatric exclusivity, and any patent litigation settlement.

What is the Orange Book status of US 10,596,155?

For an approved drug product, the key regulatory question is whether US 10,596,155 is listed in the FDA Orange Book against the relevant Nuvessa drug application and whether an applicant must make a Paragraph IV certification.

The Orange Book identifies patents submitted by an NDA holder for an approved product. Listing does not establish validity or infringement. It does, however, create a potential statutory stay if an ANDA applicant files a Paragraph IV certification and the patent holder brings suit within the statutory period. [3]

For a single-dose metronidazole gel, the relevant regulatory patent analysis should distinguish:

Formulation patents;
Method-of-use patents;
Drug-delivery patents;
Manufacturing patents;
Patents listed against the Nuvessa NDA; and
Unlisted patents that may still support a conventional infringement action.

US 10,596,155 is particularly suited to method-of-use listing because its independent claims require treating bacterial vaginosis and achieving a defined Nugent-score result. The composition limitations may also support a product-based infringement theory if the approved formulation is covered by the listed claims.

A generic applicant seeking approval for the same 65-mg single-dose product would face the greatest risk from a Paragraph IV certification directed to this patent and any related patents covering the formulation.

What Paragraph IV challenges could target the patent?

A Paragraph IV challenger would likely focus on four issues.

Lack of written description or enablement

The claims cover broad solvent categories defined partly by metronidazole-solubility thresholds. A challenger could argue that the specification does not adequately support the full range of solvents, solvent ratios, polymers, water content, viscosity, and clinical outcomes.

The risk is highest for claims that combine broad numerical ranges with a mandatory clinical result. The patent must support the claimed genus across the full scope, not only the specific commercial formulation.

Obviousness

The relevant prior-art combinations could include:

Conventional metronidazole vaginal gels;
Single-dose vaginal anti-infective formulations;
Mucoadhesive polymers;
Aromatic alcohol and glycol solvent systems;
High-viscosity vaginal gels; and
Clinical protocols using Nugent scores to assess bacterial-vaginosis response.

The strongest obviousness argument would need to show that a skilled formulator would have selected the claimed solvent system, metronidazole amount, water range, viscosity, and single-dose regimen with a reasonable expectation of achieving the claimed clinical endpoint.

Indefiniteness

Several limitations invite claim-construction disputes:

"About" 30% to 60%;
Solubility of at least 50 mg/g or 20 mg/g;
Viscosity of 200,000 to 400,000 mPa·s;
"At least about 25 to about 55 fold";
Measurement under a particular rheometer protocol; and
Nugent score below 4 within a 20-to-31-day window.

The viscosity limitation is relatively structured because the claim specifies equipment and test conditions. The solvent-solubility limitation may create greater dispute over test methodology, solvent purity, temperature control, and whether solubility is measured in the neat solvent or a solvent mixture.

Infringement-proof problems

The Nugent-score limitation is an outcome limitation. A patent owner may have difficulty proving infringement solely from a generic product label because individual patient outcomes vary. The formulation and dosing limitations are easier to establish through product testing and batch records.

A generic applicant could attempt a "skinny label" or carve-out strategy for a method claim, but this would be difficult if the approved product is labeled for the same bacterial-vaginosis indication and requires the same single-dose administration.

What patent litigation affects Nuvessa and metronidazole vaginal gel?

The supplied claim set does not identify a reported final court judgment invalidating US 10,596,155. The principal litigation risk would arise when an ANDA applicant seeks approval for a 65-mg single-dose metronidazole vaginal gel.

A typical dispute would proceed as follows:

Stage	Business consequence
ANDA filing with Paragraph IV certification	Patent holder receives notice and evaluates suit
Patent litigation filed within the statutory period	FDA approval may be stayed for up to 30 months, subject to statutory exceptions
Claim-construction and validity motions	Determines whether the narrow formulation claims survive
Settlement	May permit an agreed generic-entry date before patent expiry
Trial or appeal	Determines enforceability and launch risk
Generic launch at risk	Possible before final judgment, with damages exposure if infringement is later established

No settlement date, authorized-generic arrangement, or final judgment should be inferred from the existence of the patent alone.

How strong is the patent estate?

The patent has moderate-to-strong protection against a direct copy of the commercial single-dose formulation, but weaker protection against design-around products.

Strengths

The 65-mg amount aligns with the commercial single-dose product.
The claims combine formulation and clinical-use requirements.
The viscosity protocol is detailed and may reduce measurement ambiguity.
The ternary solvent system provides a specific technical signature.
The single-dose regimen differentiates the product from older five-day metronidazole gels.

Weaknesses

A competing product can avoid infringement by changing the dose, dosing schedule, solvent system, polymer, or viscosity.
Outcome limitations involving Nugent scores may be difficult to prove on a product-by-product basis.
Broad "about" ranges and solubility thresholds may invite validity challenges.
Conventional metronidazole products remain outside much of the claim scope.

The patent is strongest against a product that copies the Nuvessa formulation and seeks the same labeled single-dose indication. It is less effective against a different concentration, a multi-day regimen, an alternative vehicle, or a non-gel delivery system.

What generic launch scenarios exist?

Scenario 1: Direct single-dose copy

A generic applicant develops a 65-mg, 5-gram, high-viscosity gel with comparable solvent and polymer composition. This product faces the highest infringement risk and is the most likely to generate a Paragraph IV dispute.

Scenario 2: Reformulated single-dose gel

A competitor changes the aromatic alcohol, polymer, water fraction, or rheology while retaining a one-day regimen. The product may avoid literal infringement but could face a doctrine-of-equivalents argument depending on the technical substitution.

Scenario 3: Multi-day vaginal gel

A lower-concentration product administered for several days is less likely to infringe claims 1 or 14 because the claims require a single administration over one day. This is the commercial position occupied by conventional metronidazole vaginal gel.

Scenario 4: Non-gel delivery system

A vaginal tablet, suppository, foam, or ring would generally avoid the gel-specific limitations, although separate patents could apply to the delivery technology.

How does US 10,596,155 compare with conventional MetroGel-Vaginal patents?

Issue	US 10,596,155 / Nuvessa profile	Conventional metronidazole vaginal gel
Dose	Approximately 65 mg	Generally approximately 37.5 mg per 5 g
Concentration	Approximately 1.3%	Approximately 0.75%
Administration	Single dose	Commonly five days
Polymer	Mucoadhesive polymer required	May use carbomer or another gel former
Solvent system	Defined multi-class solvent system	Different formulation architecture
Viscosity	200,000 to 400,000 mPa·s under specified method in dependent claims	Not necessarily within the claimed range
Clinical endpoint	Nugent score below 4 within 20 to 31 days	Not necessarily claimed in this combination
Primary competitive risk	Copy of single-dose formulation	Generic competition to older multi-day products

Key Takeaways

US 10,596,155 is a combination patent covering a single-dose intravaginal metronidazole gel for bacterial vaginosis.
The core claim requires 60 to 70 mg of metronidazole, 30% to 60% water, a mucoadhesive polymer, and a defined solvent system.
Claim 10's 65-mg limitation closely matches the commercial Nuvessa dose.
Dependent claims add high viscosity, pH, solvent identity, solvent ratios, and in vitro distribution requirements.
The reported ordinary expiration date is February 3, 2035, subject to the official USPTO term calculation and any applicable adjustments or disclaimers.
A Paragraph IV challenge would likely focus on obviousness, written description, enablement, indefiniteness, and the validity of the clinical-outcome limitation.
The patent does not broadly block all metronidazole vaginal products. Multi-day, lower-dose, or differently formulated products have meaningful design-around opportunities.
The greatest commercial exposure is a generic 65-mg, single-dose, high-viscosity gel seeking approval for the same bacterial-vaginosis indication.

FAQs About US Patent 10,596,155

Does US Patent 10,596,155 cover oral metronidazole?

No. The claims require intravaginal administration of a metronidazole gel for bacterial vaginosis.

Does the patent cover a five-day metronidazole vaginal-gel regimen?

Generally no. The independent claims require a single dose administered once for a total of one day.

Is 65 mg of metronidazole required?

Claim 1 permits 60 to 70 mg. Dependent claim 10 narrows the formulation to 65 mg.

Can a generic avoid the patent by changing the solvent system?

Potentially. A formulation outside the claimed solvent classes, solubility thresholds, and weight ranges may avoid literal infringement, subject to the doctrine of equivalents.

Does a Nugent score below 4 alone prove infringement?

No. The claimed clinical outcome is one element of a combination claim. Infringement would require proof that the accused method meets the dosing, formulation, solvent, and clinical-result limitations.

References

United States Patent and Trademark Office. (2020). US Patent No. 10,596,155: Methods of treating bacterial vaginosis using metronidazole.
U.S. Food and Drug Administration. (2017). Nuvessa (metronidazole) vaginal gel, 1.3%: Prescribing information.
U.S. Food and Drug Administration. (2024). Approved drug products with therapeutic equivalence evaluations: Orange Book.
U.S. Food and Drug Administration. (2024). Abbreviated new drug application approvals and patent certifications.

Applicant	Tradename	Generic Name	Dosage	NDA	Approval Date	TE	Type	RLD	RS	Patent No.	Patent Expiration	Product	Substance	Delist Req.	Patented / Exclusive Use	Submissiondate
Alembic Therap	NUVESSA	metronidazole	GEL;VAGINAL	205223-001	Mar 24, 2014		RX	Yes	Yes	10,596,155	⤷ Start Trial	Y				⤷ Start Trial
>Applicant	>Tradename	>Generic Name	>Dosage	>NDA	>Approval Date	>TE	>Type	>RLD	>RS	>Patent No.	>Patent Expiration	>Product	>Substance	>Delist Req.	>Patented / Exclusive Use	>Submissiondate

Country	Patent Number	Estimated Expiration	Supplementary Protection Certificate	SPC Country	SPC Expiration
Australia	2012275292	⤷ Start Trial
Australia	2016200825	⤷ Start Trial
Brazil	112013033759	⤷ Start Trial
>Country	>Patent Number	>Estimated Expiration	>Supplementary Protection Certificate	>SPC Country	>SPC Expiration

Details for Patent: 10,596,155

Which drugs does patent 10,596,155 protect, and when does it expire?

Summary for Patent: 10,596,155