United States Patent 10,537,538: Claim Scope, Exclusivity, and Patent Landscape for Liquid T4 Thyroid Preparations
U.S. Patent No. 10,537,538 protects a packaged, ready-to-use liquid thyroid preparation containing T4 in an alcohol-free 85% glycerol-in-water vehicle, supplied in a one-component LDPE single-dose container enclosed in a multilayer sachet. The dependent claims add conversion limits for T4-to-T3 degradation, defined stability conditions, a T4-to-glycerol concentration ratio, and a 5-to-250 microgram dose range.
The patent is directed primarily to formulation and packaging control. It does not broadly cover every liquid levothyroxine product. Its practical strength depends on whether a competing product uses the claimed glycerol concentration, LDPE container, sachet architecture, dose range, and stability profile.
What does U.S. Patent 10,537,538 cover?
The independent claim requires all of the following elements:
| Claim element |
Required limitation |
| Dosage form |
Ready-to-use pharmaceutical preparation |
| Active ingredient |
T4 thyroid hormone |
| Vehicle |
Alcohol-free solution containing 85% glycerol in water |
| Optional active |
T3 may be present at less than 2.5% |
| Packaging |
Single-dose container |
| Container material |
One-component LDPE plastic container |
| External package |
Sealed sachet |
| Sachet materials |
Laminated films using selected combinations of listed polymers, aluminum, paper, and barrier materials |
| Storage function |
The product must remain within specified T4-to-T3 conversion limits in dependent claims |
| Dose range |
5 to 250 micrograms of T4 under claim 8 |
The claim is cumulative. A product that omits one mandatory limitation may avoid literal infringement of claim 1, although the doctrine of equivalents could remain relevant in litigation.
The claim does not expressly require a particular thyroid-hormone salt, manufacturing process, brand, indication, delivery device, or administration route. The technical language points to a liquid levothyroxine product, but infringement analysis would turn on the legally operative meaning of “T4 thyroid hormone” and the product’s formulation and packaging records.
How broad is claim 1 of U.S. Patent 10,537,538?
Claim 1 has meaningful formulation specificity and substantial packaging specificity. The principal narrowing limitations are the 85% glycerol vehicle and the LDPE container inside a sealed multilayer sachet.
Formulation scope
The phrase “consisting essentially of” is important. It generally permits components that do not materially alter the basic and novel characteristics of the claimed preparation, while potentially excluding excipients that materially affect stability or function. The claim therefore does not necessarily require a formulation containing only T4, glycerol, and water.
The claimed vehicle is not any glycerol solution. It is an alcohol-free solution of 85% glycerol in water. A formulation containing 80% or 90% glycerol would not literally satisfy the stated 85% limitation unless the patent’s specification or claim-construction record gives the term a broader range.
Claim 1 also permits T3 at less than 2.5%. The optional T3 language creates two covered formulation categories:
- A preparation containing T4 without T3.
- A preparation containing T4 and less than 2.5% T3.
A product containing 2.5% or more T3 would fall outside that express limitation, subject to claim-construction and equivalents issues.
Packaging scope
The packaging limitations are central. The container must be:
- single-dose;
- one-component;
- made of LDPE; and
- placed in a sealed sachet made from laminated films.
A multidose bottle, glass ampule, prefilled syringe, unit-dose container made from a different plastic, or an LDPE container without the required sachet would present a stronger noninfringement position.
The sachet limitation is broad in material selection because the claim lists numerous possible materials, including polyethylene, aluminum, polyethylene terephthalate, ionomer resins, paper, ethylene vinyl alcohol, copolymer resins, propylene, and fluorinated-chlorinated resins. The claim does not appear to require every listed material. It covers a laminate using a plurality of different materials selected from that group.
What do claims 2 through 6 protect?
Claims 2 through 6 add performance limitations based on T4 conversion to T3 during storage. These claims are narrower than claim 1 but potentially more valuable in a product dispute because they connect the composition and package to measurable stability results.
| Claim |
Storage condition |
Maximum T4-to-T3 conversion |
| 2 |
12 months, 25°C ±2°C, 60% ±5% RH |
Less than 2.5% |
| 3 |
12 months, 25°C ±2°C, 60% ±5% RH |
Less than 1.5% |
| 4 |
12 months, 30°C ±2°C, 65% ±5% RH |
Less than or equal to 2.4% |
| 5 |
6 months, 25°C ±2°C, 60% ±5% RH |
Less than 1.2% |
| 6 |
6 months, 30°C ±2°C, 65% ±5% RH |
Less than 2.0% |
These are product claims with functional or performance language. A patentee would likely need analytical evidence showing that the accused product, in the claimed package, satisfies the specified storage result.
A competing product could face testing disputes involving:
- the analytical method used to measure T3;
- whether conversion is calculated against initial T4, remaining T4, or total thyroid hormone;
- batch-to-batch variation;
- the precise temperature and humidity exposure;
- container orientation and storage history;
- sampling time;
- assay precision and detection limits.
Claims 2 through 6 also create invalidity exposure if the stability thresholds were inherent in prior-art products or were not adequately enabled across the claim scope. Their commercial value is greater where the thresholds distinguish the claimed product from earlier liquid T4 formulations.
What does claim 7 protect?
Claim 7 requires a T4-to-glycerol weight ratio of approximately 4 to 400 parts per million.
This limitation is technically important because it defines the active concentration relative to the principal vehicle rather than merely stating a T4 dose. At 85% glycerol, the ratio corresponds to a broad concentration window. The use of “about” introduces interpretive flexibility but also creates potential disputes over the acceptable boundaries.
Claim 7 can capture products with different unit doses if the T4-to-glycerol ratio remains within the claimed range. A competitor could seek design-around opportunities by changing:
- glycerol concentration;
- total fill volume;
- T4 concentration;
- use of a different polyol;
- inclusion of water or another vehicle component outside the claim’s formulation architecture.
What does claim 8 protect?
Claim 8 limits the single-dose unit to 5 to 250 micrograms of T4. This range encompasses common levothyroxine strengths, including many pediatric and adult doses.
The claim is commercially relevant because standard thyroid-replacement products commonly use dose strengths within this window. Products above 250 micrograms per unit would fall outside claim 8 but could remain within claim 1 or other claims.
The dose limitation does not require a particular dosing schedule or indication. It is a unit-dose limitation tied to the packaged preparation.
What patents protect liquid T4 products?
U.S. Patent 10,537,538 should be assessed as one part of a broader patent family and product estate. The relevant protection categories are:
| Protection category |
Relevance to T4 liquid products |
| Core formulation patents |
Protect glycerol-based or aqueous T4 compositions |
| Stability patents |
Protect low degradation or low T4-to-T3 conversion |
| Packaging patents |
Protect LDPE unit-dose containers and barrier sachets |
| Manufacturing patents |
Protect filling, sealing, mixing, or sterilization processes |
| Method-of-use patents |
Protect administration to defined patient populations or under specific conditions |
| Labeling and regulatory exclusivity |
Protect approved uses independently of patent scope |
| Trademark rights |
Protect product branding but do not block generic formulation entry |
Patent No. 10,537,538 is strongest against a product that reproduces the complete combination of formulation, unit-dose LDPE package, multilayer sachet, and claimed stability behavior. It is weaker against a liquid product using a bottle, glass container, syringe, different polyol, different glycerol concentration, or a materially different barrier package.
When does U.S. Patent 10,537,538 lose exclusivity?
The patent issued on February 18, 2020. Its exact expiration date depends on the earliest effective nonprovisional or international filing date, terminal disclaimers, and any patent-term adjustment. A 20-year term is calculated from the relevant earliest U.S. or PCT filing date under 35 U.S.C. §154. Patent-term adjustment may extend the nominal date, while a terminal disclaimer may shorten it.
The patent should therefore be analyzed using the USPTO Patent Center term record rather than the issue date alone. Regulatory exclusivity for a related levothyroxine product is separate from the patent term and may expire earlier. FDA approval does not establish that all relevant patents are enforceable, and Orange Book listing does not guarantee validity.
What is the Orange Book status of U.S. Patent 10,537,538?
A patent is Orange Book-relevant only if it claims the approved drug, an approved method of using the drug, or an approved drug product formulation under FDA listing rules. Packaging claims may be listed where they claim the approved drug product or its formulation and packaging configuration.
For a liquid levothyroxine product, the Orange Book analysis should distinguish:
- patents listed against the approved NDA;
- patents covering the active ingredient or formulation;
- patents covering an approved method of use;
- patents listed only for a delivery system or package;
- patents omitted, delisted, expired, or subject to a regulatory dispute.
If Patent No. 10,537,538 is listed for the relevant NDA, an ANDA applicant may need to submit a Paragraph IV certification or a section viii statement, depending on the listed claim and proposed labeling. If the patent is not listed, it may still be asserted under ordinary patent litigation, but it would not automatically trigger the Orange Book Paragraph IV framework.
What Paragraph IV challenges could affect this patent?
A generic applicant could challenge the patent on several grounds:
- Noninfringement. The proposed product could use a bottle, syringe, glass container, non-LDPE plastic, a different sachet, or a formulation other than 85% glycerol in water.
- Invalidity for anticipation. Earlier liquid T4 formulations or unit-dose packages could disclose the claimed combination.
- Obviousness. A challenger could combine known glycerol-based thyroid formulations with known LDPE unit-dose packaging and barrier sachets.
- Indefiniteness. The terms “about,” “one-component,” “consisting essentially of,” and conversion percentages may be challenged depending on the specification and prosecution history.
- Written description or enablement. The challenger could argue that the broad listed sachet materials and formulation scope are not supported across their full range.
- Lack of infringement of stability claims. The product may not satisfy the claimed storage conditions or may use a different assay interpretation.
A Paragraph IV dispute would likely require confidential product information, including formulation composition, container resin, sachet structure, fill volume, and stability data. Public FDA materials alone generally do not establish infringement.
Does biosimilar risk apply to Patent 10,537,538?
Biosimilar risk does not materially apply. T4 thyroid hormone is a chemically defined small molecule, not a biologic regulated through the biosimilar pathway under the Public Health Service Act.
The relevant competitive pathway is an ANDA for a generic levothyroxine product, a 505(b)(2) application for a differentiated formulation, or, in limited circumstances, a new NDA for a novel presentation. The main regulatory and patent risks involve pharmaceutical equivalence, bioequivalence, dose uniformity, stability, container closure performance, and labeling.
Which companies could challenge the estate?
Potential challengers would include manufacturers developing:
- generic levothyroxine oral solutions;
- unit-dose liquid thyroid products;
- pediatric liquid T4 formulations;
- low-volume prefilled liquid products;
- 505(b)(2) products using alternative excipients or packaging.
The principal competitive products in the U.S. thyroid market include tablet levothyroxine products from companies such as AbbVie, Viatris, Lannett, and other generic manufacturers, as well as liquid or capsule products associated with IBSA and other sponsors. Tablet manufacturers do not necessarily threaten Patent No. 10,537,538 because the claims are directed to a specific liquid preparation and package.
What litigation or settlement agreements affect this patent?
The supplied claims do not establish a litigation or settlement history. Patent litigation status must be determined from PACER, district-court dockets, PTAB records, FDA Paragraph IV notices, and the relevant NDA patent listing. A patent number alone does not show whether a generic challenge has been filed, whether a case settled, or whether a license exists.
No licensing right can be inferred from assignment data. Ownership, exclusive licensing, commercialization rights, and litigation authority are separate questions. The relevant commercial parties may include the patent owner, an NDA sponsor, a U.S. commercialization partner, and a contract manufacturer.
How strong is the patent estate for a liquid T4 product?
The patent has moderate blocking strength against an exact or near-exact copy of the claimed presentation. Its strength is lower against formulation and packaging alternatives.
| Risk factor |
Assessment |
| Exact 85% glycerol vehicle |
High risk if reproduced |
| Alcohol-free formulation |
High relevance to literal scope |
| One-component LDPE container |
High risk if reproduced |
| Multilayer sachet |
High risk if reproduced |
| 5-to-250 microgram dose |
Relevant to common strengths |
| T4-to-T3 stability thresholds |
Strong factual barrier if validated |
| Alternative bottle or syringe |
Potentially strong design-around |
| Alternative polyol or glycerol level |
Potentially strong design-around |
| Tablet or capsule product |
Generally outside claim scope |
| Biosimilar pathway |
Not applicable |
| Method-of-use protection |
Not present in the supplied claims |
The patent’s commercial value is concentrated in the integrated product-and-package combination. A competitor that changes only the outer sachet may still face infringement risk if the sachet remains within the listed material architecture. A competitor that changes the container material and formulation may have a substantially stronger position.
What generic launch scenarios exist?
Scenario 1: Exact unit-dose liquid copy
A generic reproducing the 85% glycerol formulation, LDPE container, sachet, dose range, and stability profile faces the highest infringement risk. A Paragraph IV certification and district-court litigation would be likely if the patent is Orange Book listed and unexpired.
Scenario 2: Same active ingredient, bottle presentation
A multidose bottle or a different container system may avoid the packaging limitations. The product would still require separate analysis against other formulation or stability patents.
Scenario 3: Alternative vehicle
A formulation using a different glycerol concentration, another polyol, or a materially different aqueous system could avoid literal infringement of claim 1. It would require independent regulatory and bioequivalence support.
Scenario 4: Tablet or capsule launch
A conventional solid oral levothyroxine product would generally fall outside the supplied claims. Its competitive effect would be commercial rather than directly infringing.
What geographic coverage does the patent provide?
U.S. Patent 10,537,538 provides enforceable rights in the United States and its territories covered by U.S. patent law. Parallel protection requires separate national or regional patents. The existence of corresponding applications in Europe or other jurisdictions does not establish that equivalent claims issued, remain in force, or cover the same package.
For global freedom-to-operate work, the relevant comparison is by country:
| Jurisdiction |
Key question |
| United States |
Is the patent unexpired, enforceable, and Orange Book relevant? |
| Europe |
Did equivalent claims issue, and in which EPC states are they validated? |
| Canada |
Is a corresponding patent active and listed against an approved product? |
| Japan |
Were equivalent formulation or package claims granted? |
| Australia |
Are corresponding claims pending or enforceable? |
| Emerging markets |
Are national-phase rights active and commercially relevant? |
Key Takeaways
- Patent No. 10,537,538 claims a specific ready-to-use T4 liquid product and package.
- The core combination is T4 in alcohol-free 85% glycerol-in-water, a one-component LDPE unit-dose container, and a sealed multilayer sachet.
- Claims 2 through 6 add measurable T4-to-T3 conversion limits under defined stability conditions.
- Claim 7 covers a T4-to-glycerol ratio of about 4 to 400 ppm.
- Claim 8 covers unit doses from 5 to 250 micrograms.
- The patent does not broadly block all liquid levothyroxine products.
- The strongest design-around routes involve changing the container, package, vehicle, or glycerol concentration.
- Biosimilar procedures do not apply because T4 is a small-molecule active ingredient.
- Paragraph IV exposure depends on Orange Book listing and the patent’s unexpired status.
- Exact expiration, ownership, listing, litigation, and settlement conclusions require the live USPTO, FDA, and court records.
FAQs
Is a liquid levothyroxine bottle covered by U.S. Patent 10,537,538?
Not necessarily. The supplied claims require a single-dose one-component LDPE container placed inside a sealed multilayer sachet. A bottle may fall outside those limitations, although other patents could apply.
Does the patent cover levothyroxine sodium?
The claims use the term T4 thyroid hormone and do not expressly state “levothyroxine sodium.” Whether a particular salt satisfies the claim depends on claim construction, the specification, prosecution history, and the product’s chemical form.
Can a generic use the same 85% glycerol formulation in a glass ampule?
That change may avoid the express LDPE-container limitation. The generic would still need to assess the sachet, single-dose, stability, ratio, and any other patent claims in the relevant estate.
Are T4-to-T3 conversion limits regulatory requirements?
They may be product-quality or stability specifications, but the claims make them patent limitations. FDA approval requirements and patent claim requirements are separate legal standards.
Does an expired patent eliminate all market-entry risk?
No. Market entry may remain subject to other formulation, packaging, manufacturing, method-of-use, trademark, regulatory exclusivity, or contractual restrictions.
References
- United States Patent and Trademark Office. (2020). U.S. Patent No. 10,537,538.
- United States Code. (2023). 35 U.S.C. § 154: Contents and term of patents; provisional rights.
- United States Food and Drug Administration. (2023). Approved drug products with therapeutic equivalence evaluations.
- United States Food and Drug Administration. (2024). Orange Book: Approved drug products with therapeutic equivalence evaluations.
- United States Food and Drug Administration. (2024). Abbreviated new drug application submissions and patent certification requirements.
- United States Code. (2023). 21 U.S.C. § 355: New drugs.
