US Patent 10,335,390: Secnidazole Microgranule Claims, Patent Scope, Expiration and Competitive Landscape

US Patent No. 10,335,390 protects methods of treating bacterial vaginosis with an oral secnidazole microgranule formulation. The patent is directed to Solosec-type therapy: a 2-gram, single-dose product in which secnidazole is the sole active drug, the microgranules have a 400-to-841-micrometer particle size, and treatment produces specified pharmacokinetic or clinical outcomes.

The patent is method-of-treatment protection, not a broad composition patent. A competing product must satisfy the claimed formulation, particle-size, active-ingredient and treatment limitations to fall within the principal claims.

What does US Patent 10,335,390 cover?

US 10,335,390 covers treating bacterial vaginosis by administering secnidazole in a defined microgranule formulation. The central limitations are:

Claim element	Scope
Disease	Bacterial vaginosis
Active ingredient	Secnidazole
Formulation	Microgranules
Particle size	400 to 841 micrometers
Active-drug requirement	Secnidazole is the sole drug in the microgranule formulation
Pharmacokinetic alternative	Cmax of about 34.5-58.3 µg/mL or about 17.4-26.5 µg/mL
Pharmacokinetic alternative	Tmax of about 3-4 hours or about 2-6 hours
Administration	Primarily oral; food-mixed administration is separately claimed
Dose	A dependent claim specifies 2 grams
Dosing schedule	Single dose
Patient population	Women, pregnant women, recurrent BV patients and patients meeting specified diagnostic criteria
Outcome	Symptom resolution or alleviation, clinical response and Nugent-score improvement
Contraception	Co-administration with ethinyl estradiol and/or norethindrone without affecting contraceptive efficacy

The patent issued July 2, 2019, from an application claiming priority to an April 2013 filing. The nominal patent term therefore runs into April 2033, subject to any applicable patent-term adjustment. (U.S. Patent No. 10,335,390, 2019.)

How many independent claims does US 10,335,390 have?

The patent has three principal independent method claims: claims 1, 17 and 18.

Claim 1: Cmax-based treatment method

Claim 1 requires all of the following:

Treating bacterial vaginosis in a subject in need of treatment.
Administering a therapeutically effective amount of secnidazole.
Using a microgranule formulation.
Having microgranules with a particle size of 400-841 micrometers.
Having secnidazole as the sole drug in the microgranule formulation.
Producing one of two defined Cmax ranges.

The Cmax limitation is unusual because it contains two alternative exposure ranges:

About 34.5-58.3 µg/mL; or
About 17.4-26.5 µg/mL.

A product or treatment protocol that satisfies only the dose and formulation limitations but produces a Cmax outside both ranges may not meet claim 1. Infringement analysis would depend on whether the claimed Cmax is interpreted as an inherent property of the accused product and whether the “about” language captures the measured exposure.

Claim 17: Narrow Tmax range

Claim 17 requires a Tmax of about 3-4 hours. It otherwise repeats the core microgranule and sole-drug limitations.

This is narrower than claim 18 and may be easier to challenge if clinical pharmacokinetic data show that the product’s Tmax falls outside the range.

Claim 18: Broader Tmax range

Claim 18 requires a Tmax of about 2-6 hours. It is broader than claim 17 on the pharmacokinetic limitation but remains limited by the 400-841-micrometer particle-size range and the requirement that secnidazole be the sole drug in the formulation.

Claims 17 and 18 are alternative routes to infringement. A product could fall outside the Cmax ranges in claim 1 but still potentially satisfy claim 18 if its Tmax is within the claimed range.

What formulation is protected by US 10,335,390?

The patent protects a microgranule formulation rather than every secnidazole dosage form.

Claim 3 identifies formulation components that may be present:

Sugar spheres
Povidone
Polyethylene glycol
Ethyl acrylate/methyl methacrylate copolymer
Talc

These components correspond to a multiparticulate oral formulation in which secnidazole is deposited or incorporated on microgranules. The claim does not require every listed excipient. It requires at least one selected compound from the group.

The particle-size limitation is central. A formulation composed primarily of particles below 400 micrometers or above 841 micrometers may avoid the literal particle-size requirement, depending on how the claim is construed and whether the relevant measurement is based on a mean, range, sieve fraction or substantial portion of the batch.

Why the sole-drug limitation matters

The claims require secnidazole to be the sole drug in the microgranule formulation. This limitation distinguishes the claimed product from a combination microgranule containing another active pharmaceutical ingredient.

The limitation does not necessarily prohibit administration of another drug separately. Claims 19 and 26-28 specifically address co-administration with hormonal contraceptives. A formulation containing secnidazole and a second active drug would present a different analysis from secnidazole microgranules administered at the same time as a separately formulated contraceptive.

Does the patent cover Solosec?

The claims are closely aligned with the approved Solosec product and its labeled use for bacterial vaginosis in adult women. Solosec is an oral secnidazole 2-gram granule product administered as a single dose, generally sprinkled onto soft food and consumed without chewing the granules. (FDA, 2023.)

The patent’s claim coverage overlaps with the product’s principal commercial attributes:

Solosec attribute	Relationship to US 10,335,390
Secnidazole active ingredient	Directly required
2-gram dose	Expressly covered by claim 16
Oral administration	Covered by claim 2
Single-dose regimen	Covered by claims 14 and 15
Food administration	Covered by claims 4 and 25
Female BV population	Covered by claim 5
Microgranule delivery	Required by independent claims
Pharmacokinetic exposure	Required by claims 1, 17 or 18
Contraceptive co-administration	Addressed by claims 19 and 26-28

The patent therefore has high product relevance for a generic applicant seeking to copy the approved Solosec formulation and labeled dosing method. It is less likely to block a materially different secnidazole formulation that does not use the claimed particle-size range or does not produce the claimed pharmacokinetic profile.

What are the dependent claim limitations?

The dependent claims create multiple fallback positions for the patent owner.

Patient and diagnosis limitations

Claims 5-13 narrow the method to:

Female subjects
Pregnant females
Women with three or more BV episodes in 12 months
Women with four or more BV episodes in 12 months
Confirmed or suspected BV
Patients presenting with thin, homogeneous discharge
Positive KOH Whiff test
Vaginal pH of at least 4.7
Clue cells exceeding 20% of epithelial cells
Nugent score of at least four

These limitations may reduce practical claim breadth but can create additional positions in litigation if a broad claim is challenged.

Single-dose and 2-gram limitations

Claims 14-16 cover:

Single-dose administration
A single dose as the only dose required to achieve the claimed outcome
A 2-gram dose

These claims map directly onto the commercial dosing model for Solosec. A generic product using the same 2-gram, single-dose regimen would face a substantial infringement risk if its formulation also meets the microgranule and pharmacokinetic limitations.

Clinical-response limitations

Claims 20-24 require determining a post-treatment outcome. A clinical responder may be defined by:

Reduced thin, homogeneous discharge
Negative KOH Whiff test
Clue cells below 20%
Nugent score below four
A combination of these findings

Claims 29 and 30 add timing limitations, covering symptom resolution within approximately seven days or symptom alleviation within approximately three days.

These claims create evidentiary issues. In a method patent case, the patent owner may need to show that the accused labeling, instructions or clinical-use protocol directs treatment in a manner satisfying the claimed outcome. The product does not necessarily infringe merely because some patients experience the claimed clinical result.

What is the Orange Book status of US 10,335,390?

The relevant Orange Book question is whether the patent is listed against Solosec and whether it is associated with an approved method of use. The FDA Orange Book identifies patents submitted by NDA sponsors for approved drug products and lists applicable use codes where method-of-use protection is asserted. (FDA, 2024.)

US 10,335,390 is part of the patent estate associated with secnidazole treatment and is relevant to abbreviated new drug application risk analysis. A definitive current Orange Book status requires review of the live FDA Orange Book entry, including the patent number, expiration date, use code and any delisting or certification history.

For a generic applicant, the principal regulatory question is whether the ANDA applicant must:

Make a Paragraph IV certification asserting that the patent is invalid, unenforceable or not infringed;
Submit a section viii statement and omit the patented method from labeling; or
Wait for patent expiration.

Because the claims are directed to the labeled single-dose treatment of BV, a section viii strategy may be difficult if the generic label necessarily describes the same microgranule formulation and dosing regimen.

When does US 10,335,390 lose exclusivity?

The nominal expiration date is in April 2033, based on the patent’s April 2013 priority and filing history. The legally operative date may change because of patent-term adjustment, terminal disclaimers or other USPTO term calculations.

The patent does not create regulatory exclusivity independent of the patent term. Secnidazole’s new-drug regulatory exclusivity began with FDA approval of Solosec in December 2017. The five-year new chemical entity exclusivity period would have ended in December 2022, subject to the specific FDA exclusivity determination. (FDA, 2017.)

The principal remaining barrier is therefore patent protection rather than NCE exclusivity.

What Paragraph IV challenges and litigation affect secnidazole?

A Paragraph IV challenge would likely focus on one or more of these issues:

Challenge theory	Potential target
Noninfringement	Particle size outside 400-841 micrometers
Noninfringement	Cmax or Tmax outside claimed ranges
Noninfringement	Secnidazole not the sole drug or different formulation architecture
Invalidity	Obviousness of the microgranule formulation and dosing method
Invalidity	Written-description or enablement support for the PK ranges
Invalidity	Indefiniteness of “about,” “therapeutically effective amount” or clinical-outcome limitations
Regulatory strategy	Omission of the patented method under section viii

The supplied claim record does not establish a specific filed Paragraph IV case, settlement agreement or final infringement judgment involving US 10,335,390. A complete litigation conclusion cannot be drawn from the claims alone.

How strong is the patent estate for secnidazole?

The estate is strongest against a generic that copies the commercial product in all material respects:

Same active ingredient
Same microgranule architecture
Same particle-size range
Same 2-gram dose
Same single-dose administration
Same food-mixing instructions
Same BV indication

The estate is weaker against a product that uses a different multiparticulate design, changes particle-size distribution, produces materially different PK exposure or seeks a label that omits the patented use.

Patent strength by claim category

Claim category	Commercial strength
Core microgranule formulation and particle size	High against a copied product
2-gram single-dose use	High when linked to the claimed formulation
Cmax ranges	Moderate; dependent on reproducible PK evidence
Tmax ranges	Moderate; broad claim 18 is more difficult to design around
Food administration	Moderate; likely relevant to the commercial label
Female and recurrent-BV populations	Moderate to low as standalone barriers
Pregnancy limitations	Narrow population coverage
Diagnostic criteria	Narrow and evidence-intensive
Contraceptive interaction claims	Potentially important for labeling and clinical-use instructions
Three- and seven-day outcomes	Narrow, outcome-dependent protection

Are biosimilars or generic competitors the main risk?

Biosimilar risk is not relevant because secnidazole is a small-molecule drug, not a biologic. The relevant competitors are generic secnidazole products and alternative BV therapies, including metronidazole and clindamycin.

A generic applicant would likely evaluate both formulation design-around and litigation. A noninfringing product could avoid the patent by using:

A different particle-size distribution;
A non-microgranule dosage form;
A formulation with a different release profile;
A different dosing regimen;
A label that omits the patented method, if commercially viable.

The commercial value of a design-around depends on whether it preserves the principal advantages of Solosec: single-dose oral administration, food-mixing convenience and patient adherence.

What licensing or ownership transactions affect the patent?

Lupin acquired Symbiomix Therapeutics, the developer of Solosec, in 2017. The transaction transferred the commercial program and associated intellectual-property interests to Lupin. (Lupin Limited, 2017.)

The acquisition is more significant for ownership and commercialization than for a separate out-licensing arrangement. Patent ownership, assignment history and any field-specific rights should be confirmed through the USPTO assignment database and the current FDA sponsor records.

Key Takeaways

US 10,335,390 is a method-of-treatment patent focused on secnidazole microgranules for bacterial vaginosis.
The core limitations are a 400-841-micrometer particle size, secnidazole as the sole drug, and specified Cmax or Tmax exposure.
Claims 14-16 closely track a 2-gram, single-dose, orally administered product mixed with food.
The patent also covers defined female populations, recurrent BV, diagnostic criteria, clinical outcomes and contraceptive co-administration.
Nominal patent expiration is in April 2033, subject to the USPTO-calculated patent term.
NCE exclusivity from the 2017 FDA approval would have expired in December 2022.
The main competitive threat is a generic formulation that either challenges validity or designs around particle size, pharmacokinetics or the claimed administration method.
Biosimilar competition is not applicable.
The strongest infringement case would involve a copy of the Solosec formulation, label and single-dose treatment protocol.

FAQs

Does US 10,335,390 cover all secnidazole products?

No. It is limited to secnidazole administered in a microgranule formulation with a 400-841-micrometer particle size and additional pharmacokinetic or treatment limitations.

Can a generic avoid the patent by using a different secnidazole dose?

Possibly, but dose alone is not determinative. The generic would also need to assess particle size, formulation structure, PK exposure, labeling and the claimed BV treatment method.

Does mixing secnidazole with food create infringement risk?

It can. Claims 4 and 25 expressly cover mixing or combining the microgranule formulation with a food substance.

Does co-administration with birth-control pills fall within the patent?

Claims 19 and 26-28 address co-administration with ethinyl estradiol, norethindrone or both, including administration on the same or a different day and preservation of contraceptive efficacy.

Is the patent relevant to a metronidazole generic?

Generally no. The claims require secnidazole. A metronidazole product does not satisfy the active-ingredient limitation, although it may compete commercially with Solosec.

References

Food and Drug Administration. (2017). FDA approves Solosec (secnidazole) for bacterial vaginosis. U.S. Department of Health and Human Services.

Food and Drug Administration. (2023). Solosec prescribing information. U.S. Department of Health and Human Services.

Food and Drug Administration. (2024). Approved drug products with therapeutic equivalence evaluations: Orange Book. U.S. Department of Health and Human Services.

Lupin Limited. (2017). Lupin acquires Symbiomix Therapeutics for Solosec. Corporate transaction announcement.

U.S. Patent No. 10,335,390. (2019). Methods of treating bacterial vaginosis. United States Patent and Trademark Office.

Applicant	Tradename	Generic Name	Dosage	NDA	Approval Date	TE	Type	RLD	RS	Patent No.	Patent Expiration	Product	Substance	Delist Req.	Patented / Exclusive Use	Submissiondate
Evofem Inc	SOLOSEC	secnidazole	GRANULE;ORAL	209363-001	Sep 15, 2017		RX	Yes	Yes	⤷ Start Trial	⤷ Start Trial	Y			TREATMENT OF BACTERIAL VAGINOSIS IN ADULT WOMEN	⤷ Start Trial
Evofem Inc	SOLOSEC	secnidazole	GRANULE;ORAL	209363-001	Sep 15, 2017		RX	Yes	Yes	⤷ Start Trial	⤷ Start Trial	Y			TREATMENT OF BACTERIAL VAGINOSIS IN FEMALE PATIENTS 12 YEARS OF AGE AND OLDER	⤷ 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	2015311674	⤷ Start Trial
Australia	2018203882	⤷ Start Trial
Australia	2018217262	⤷ Start Trial
Canada	2959414	⤷ Start Trial
>Country	>Patent Number	>Estimated Expiration	>Supplementary Protection Certificate	>SPC Country	>SPC Expiration

Details for Patent: 10,335,390

Which drugs does patent 10,335,390 protect, and when does it expire?

Summary for Patent: 10,335,390