United States Patent 8,236,755 covers an injectable or otherwise administrable, low-viscosity lipid precursor that converts in vivo into a non-lamellar liquid-crystalline depot for controlled opioid release. Its core limitations are a minimum 18 wt.% neutral diacyl lipid or neutral diacyl lipid/tocopherol mixture, a phospholipid, an oxygen-containing organic solvent including ethanol, and an opioid. The patent also claims administration, in vivo depot formation, preparation, treatment, and opioid-withdrawal prophylaxis.
The patent is a platform patent rather than a claim limited to one commercial product. Its practical value depends on the patent family’s surviving term, prosecution history, claim construction, FDA product listings, and whether a competing formulation uses the required lipid, phospholipid, solvent, viscosity, and opioid combination.
US Patent 8,236,755: Scope, Claims, Expiration, and Drug Patent Landscape
What technology does US Patent 8,236,755 protect?
US 8,236,755 protects a non-liquid crystalline formulation precursor that becomes a liquid-crystalline lipid composition after contact with aqueous body fluid. The claimed system is designed to provide controlled release of an opioid after parenteral administration.
The technology has four functional stages:
- A low-viscosity precursor is manufactured and remains non-liquid crystalline before administration.
- The precursor contains lipid, phospholipid, solvent, and opioid.
- The precursor is administered to a mammalian subject.
- Water from tissue or another biological fluid induces formation of a non-lamellar liquid-crystalline structure that acts as a drug depot.
The independent claims are directed to:
| Claim |
Subject matter |
Main legal category |
| 1 |
Opioid-containing formulation precursor |
Composition |
| 15 |
Administration of the precursor to form the depot in vivo |
Method of delivery |
| 18 |
Formation of the non-lamellar composition after exposure to aqueous fluid |
Process or use |
| 20 |
Preparation of the precursor |
Manufacturing process |
| 22 |
Treatment or prophylaxis using the formulation |
Method of treatment |
The dependent claims narrow the technology by specifying lipid identity, phospholipid class, solvent content, phase structure, administration route, opioid identity, and therapeutic use.
What are the essential limitations of claim 1?
Claim 1 is the principal composition claim. A formulation generally must satisfy all of the following limitations to fall within its literal scope:
| Limitation |
Requirement |
| Physical state before administration |
Non-liquid crystalline formulation precursor |
| Viscosity |
1 to 1,000 mPa·s at 20°C |
| Neutral lipid content |
At least 18 wt.% of a neutral diacyl lipid, or neutral diacyl lipid plus tocopherol |
| Phospholipid |
At least one phospholipid |
| Organic solvent |
Biocompatible, oxygen-containing, low-viscosity organic solvent comprising ethanol |
| Active ingredient |
At least one opioid dissolved or dispersed in the mixture |
| In vivo conversion |
Formation of at least one non-lamellar liquid-crystalline phase after contact with aqueous fluid |
The 18 wt.% threshold is a central quantitative limitation. A competing formulation with less than 18 wt.% of the specified neutral diacyl lipid or neutral diacyl lipid/tocopherol component would have a potential literal-infringement defense against claim 1, although other claims, doctrine-of-equivalents theories, or related family patents could remain relevant.
The viscosity range is also material. The claim requires a precursor that is sufficiently fluid for administration but capable of forming a structured depot after hydration. A product outside the 1 to 1,000 mPa·s range at 20°C may avoid claim 1 if the measurement method and temperature are properly established.
How do claims 3 through 9 narrow the formulation?
Claims 3 through 9 provide narrower composition positions that could be important during validity or infringement analysis.
Lipid limitations
Claim 3 requires component a to consist essentially of diacyl glycerols. Claim 4 narrows this further to a mixture of glycerol dioleate and tocopherol.
Glycerol dioleate is a particularly important formulation limitation because it identifies a commercially practical neutral diacyl lipid with depot-forming properties. Tocopherol can modify phase behavior, viscosity, drug solubility, and release kinetics.
Phospholipid limitations
Claim 5 identifies the permitted phospholipid families:
- phosphatidylcholines;
- phosphatidylethanolamines;
- phosphatidylserines;
- phosphatidylinositols; and
- mixtures of those materials.
Claim 7 permits a broad component-a-to-component-b weight ratio of 95:5 to 5:95. The ratio therefore does not confine the invention to a narrowly balanced lipid mixture.
Phase-structure limitations
Claim 6 identifies molecular solution, L2, and L3 phase structures. These limitations relate to the precursor’s physical organization before or during hydration:
- L2 generally refers to an inverse micellar or inverse non-lamellar phase;
- L3 generally refers to a bicontinuous cubic or related highly organized phase;
- molecular solution refers to a substantially molecularly dispersed precursor state.
The phase limitation creates technical proof issues. A party asserting infringement may need polarized-light microscopy, small-angle X-ray scattering, differential scanning calorimetry, viscosity testing, or related characterization to establish the relevant phase.
Solvent limitation
Claim 8 permits 0.5% to 50% solvent by weight of components a+b+c. Claim 1 requires an oxygen-containing solvent comprising ethanol, while claim 15 uses broader language for the solvent and does not expressly repeat "comprising ethanol" in the supplied text.
That difference may create a claim-construction issue. Claim 1 is more clearly ethanol-centered. Claim 15 may reach a broader solvent class if the claim is interpreted independently and the prosecution history does not import the ethanol limitation from claim 1.
Charged amphiphile
Claim 9 allows up to 10% by weight, relative to a+b, of a charged amphiphile. This can include anionic or cationic amphiphilic materials that alter tissue adhesion, hydration, phase behavior, or release kinetics.
Which opioids fall within the patent claims?
Claim 10 covers natural opium alkaloids, semisynthetic opioids, and synthetic opioids. Claim 11 lists specific synthetic opioids, including:
- bezitramide;
- methadone;
- LAAM;
- loperamide;
- diphenoxylate;
- buprenorphine; and
- etorphine.
Claim 12 narrows the claim to buprenorphine or methadone. Claims 22 through 25 extend the therapeutic scope to:
- pain;
- diarrhea;
- depression;
- opioid dependence;
- opioid addiction;
- opioid withdrawal symptoms; and
- prophylaxis against opioid withdrawal caused by opioid abuse.
The claims are not limited to buprenorphine. Buprenorphine is commercially important because long-acting injectable buprenorphine products use lipid-depot or related sustained-release technologies, but methadone and other opioids remain within the claim language.
What administration routes are covered?
The patent has unusually broad administration language. Claim 13 specifies injection. Claim 17 identifies:
- subcutaneous injection;
- intramuscular injection;
- intra-cavity injection through tissue;
- intra-cavity injection without tissue penetration;
- spraying;
- rolling;
- wiping;
- dabbing;
- painting;
- rinsing; and
- dropping.
Claims 14 and 17 extend beyond conventional parenteral injection. Those routes may support local, mucosal, cavity, topical, or surface administration depending on the formulation and the biological site.
The commercial significance is greatest for subcutaneous or intramuscular injection, where a hydrated depot can release opioid over an extended period. Noninjectable routes may have narrower commercial relevance but broaden the patent’s platform coverage.
What do claims 15, 18, 20, and 22 protect?
Claim 15: administration method
Claim 15 requires administering a non-liquid crystalline, low-viscosity mixture containing lipid, phospholipid, solvent, and opioid so that a non-lamellar liquid-crystalline structure forms in vivo.
This is a method-of-use claim. It can be relevant even if a product developer disputes the composition claim, provided the administered product satisfies the method limitations.
Claim 18: in vivo phase formation
Claim 18 focuses on exposing the formulation precursor to aqueous fluid in vivo. It captures the hydration-triggered conversion mechanism rather than merely the formulation composition.
Claim 20: manufacturing process
Claim 20 requires:
- forming the specified low-viscosity mixture; and
- dissolving or dispersing the opioid in the mixture or in one of the components before mixture formation.
This claim can reach manufacturing operations even when the final commercial formulation is characterized by a different name or dosage form.
Claim 22: treatment and prophylaxis
Claim 22 covers treatment or prophylaxis in humans and non-human animals. Claims 23 through 25 specify opioid dependence, addiction, withdrawal symptoms, and prophylaxis against withdrawal.
Treatment claims may raise divided-infringement and induced-infringement issues because the relevant administration may occur through a healthcare provider, distributor, or patient rather than solely through the manufacturer.
When does US Patent 8,236,755 lose exclusivity?
US 8,236,755 issued on August 7, 2012. Its term is governed by the modern 20-year patent-term rules applicable to the relevant nonprovisional or international filing, not by the issue date. The patent’s effective term therefore depends on:
- the earliest effective nonprovisional or PCT filing date;
- patent-term adjustment;
- any terminal disclaimer;
- whether the patent claims priority to an earlier application; and
- any enforceability or maintenance-fee events.
Because the patent belongs to an early-2000s international patent family, its ordinary base term falls in the 2024 period rather than 2032. A precise expiration date must be taken from the USPTO Patent Center term calculation and the patent’s transaction history. Patent expiration does not eliminate separate, later-expiring continuation, divisional, formulation, or product-specific patents in the same family.
The principal commercial conclusion is that US 8,236,755 should be treated as an early platform patent whose remaining exclusivity, if any, is materially narrower than the surrounding modern buprenorphine-depot patent estate.
What is the Orange Book status of US 8,236,755?
US 8,236,755 is not automatically an Orange Book patent merely because it covers an opioid formulation. Orange Book listing depends on whether the patent is submitted for an approved drug product and whether it claims:
- the approved drug substance;
- the approved drug product or formulation; or
- an approved method of use.
For Brixadi, the FDA-approved long-acting buprenorphine injection marketed by Braeburn Pharmaceuticals and manufactured using Camurus-related technology, Orange Book analysis must be conducted against the patents listed for NDA 213736, not against the entire Camurus patent portfolio. The current Brixadi label identifies the product as an extended-release buprenorphine injection for subcutaneous use in opioid use disorder treatment (FDA, 2023).
A patent may be technically relevant to a product without being listed in the Orange Book. Conversely, Orange Book listing creates a statutory notice and litigation pathway but does not establish ultimate validity or infringement.
Does US 8,236,755 create biosimilar risk?
No. Buprenorphine is a small-molecule active ingredient. A follow-on product would ordinarily use the ANDA pathway under section 505(j), a 505(b)(2) application, or a full NDA, not the biosimilar pathway under section 351(k).
The relevant challenges are therefore:
- ANDA Paragraph IV certifications;
- 505(b)(2) patent certifications;
- declaratory judgment actions;
- product-specific patent litigation; and
- post-expiration generic or authorized-generic entry.
The patent may still create formulation barriers for injectable generics because an ANDA applicant must demonstrate pharmaceutical equivalence, bioequivalence, manufacturing consistency, and adequate control of the depot-release profile.
Which companies and products are most relevant?
| Company |
Product or technology |
Relevance to the patent landscape |
| Camurus AB |
FluidCrystal-related lipid depot technology |
Technology originator and major owner of related formulation patents |
| Braeburn Pharmaceuticals |
Brixadi, extended-release buprenorphine injection |
Commercial product using long-acting buprenorphine technology |
| Indivior |
Sublocade, extended-release buprenorphine injection |
Competing opioid-use-disorder depot product with a separate polymer-based technology |
| Alkermes |
Vivitrol, extended-release naltrexone injection |
Competing extended-release addiction-treatment injectable, not an opioid agonist |
| Generic developers |
Future buprenorphine depot applicants |
Potential ANDA or 505(b)(2) challengers after relevant patents and exclusivities expire |
Sublocade is a particularly important comparison because it uses Atrigel, a polymer-based in situ depot system, rather than the lipid liquid-crystalline approach claimed by US 8,236,755. A product can compete clinically without practicing this patent.
How does this patent compare with Brixadi and Sublocade patent estates?
| Issue |
US 8,236,755 |
Brixadi estate |
Sublocade estate |
| Technology |
Lipid precursor that forms a liquid-crystalline depot |
Camurus-related long-acting buprenorphine formulation technology |
Atrigel polymer depot |
| Active ingredient |
Broad opioid class, including buprenorphine and methadone |
Buprenorphine |
Buprenorphine |
| Core protection |
Platform composition and administration claims |
Product-specific and formulation-specific claims, plus related platform rights |
Product, formulation, delivery-system, and method claims |
| Regulatory route |
Patent platform |
NDA 213736 |
NDA 209819 |
| Biosimilar pathway |
Not applicable |
Not applicable |
Not applicable |
| Main follow-on risk |
Formulation replication and use of related claims |
ANDA or 505(b)(2) challenge to listed patents |
ANDA or 505(b)(2) challenge to listed patents |
| Technical design-around |
Alter lipid identity, ratio, solvent, viscosity, or phase behavior |
Use a non-infringing formulation or delivery platform |
Use a different polymer, drug loading, or release mechanism |
The patent’s broad opioid and route language is wider than a product patent limited to a specific buprenorphine formulation. Its weakness is that broad platform claims face greater prior-art and enablement pressure, while later product patents can be narrower but commercially stronger when tied to an approved dosage form.
What prior-art and validity risks affect the patent?
The principal validity pressure points are:
Anticipation and obviousness
Earlier lipid depot disclosures may teach combinations of:
- glycerol dioleate;
- phospholipids;
- tocopherol;
- ethanol or other oxygen-containing solvents;
- non-lamellar liquid-crystalline phases; and
- controlled release of active agents.
The patent’s strongest distinction is the combination of the specified low viscosity, minimum 18 wt.% neutral diacyl lipid component, opioid payload, and in vivo phase conversion. The more those features were individually disclosed in earlier lipid formulation patents, the greater the obviousness risk.
Enablement and written description
The patent covers a wide opioid class and numerous lipid, phospholipid, solvent, route, and phase combinations. A validity challenge could argue that the specification does not enable the full breadth of the claims without undue experimentation, particularly for:
- all listed opioid classes;
- all administration routes;
- the full 1 to 1,000 mPa·s range;
- all non-lamellar phase structures; and
- all treatment or prophylaxis indications.
Indefiniteness and measurement issues
Potential disputes include:
- how viscosity is measured;
- whether the precursor is non-liquid crystalline before administration;
- what qualifies as a non-lamellar liquid-crystalline phase;
- how the 18 wt.% amount is calculated;
- whether tocopherol is included in component a;
- whether ethanol must be present in every asserted claim; and
- how in vivo phase conversion is demonstrated.
These issues can materially affect both infringement and validity.
What generic launch scenarios exist?
Scenario 1: post-expiration launch
A generic or 505(b)(2) applicant launches after the relevant patent term and regulatory exclusivity periods expire. This is the lowest litigation-risk scenario for US 8,236,755 itself, but later product patents may still delay entry.
Scenario 2: Paragraph IV challenge
An applicant certifies that an Orange Book-listed patent is invalid, unenforceable, or not infringed. The NDA holder may file suit within 45 days, triggering the statutory stay described in the Hatch-Waxman framework (Federal Food, Drug, and Cosmetic Act, 21 U.S.C. § 355).
Scenario 3: formulation design-around
A developer uses:
- a polymer depot;
- a different lipid class;
- less than 18 wt.% of the claimed neutral diacyl lipid component;
- no ethanol;
- a viscosity outside the claimed range;
- a crystalline or non-lamellar structure that does not meet the claim limitations; or
- a different active ingredient and dosing mechanism.
This strategy may avoid US 8,236,755 while remaining exposed to later product patents.
Scenario 4: 505(b)(2) product
A developer relies partly on existing safety or efficacy data while introducing a modified buprenorphine depot. This pathway may reduce development burden but does not eliminate patent certification and litigation risk.
What manufacturing and intellectual-property barriers remain?
The most important manufacturing barriers are not limited to patent scope. A follow-on developer must reproduce:
- uniform opioid loading;
- acceptable syringeability or injectability;
- controlled hydration after administration;
- predictable phase conversion;
- stable particle-free or suspension-free product characteristics;
- consistent release kinetics;
- sterilization compatibility;
- container-closure integrity; and
- manufacturing-scale mixing and filling.
These process characteristics can be protected by later manufacturing, stability, device, and formulation patents even after the platform patent expires.
Geographic coverage also matters. US 8,236,755 has US-only effect. Foreign counterparts may have different claim scope, prosecution outcomes, lapse dates, and enforceability. A global launch requires separate review of Europe, Canada, Australia, Japan, and other markets where the corresponding family members were prosecuted.
What litigation and settlement issues should be reviewed?
The critical records are:
- USPTO Patent Center prosecution history for US 8,236,755.
- The patent’s maintenance-fee and term-adjustment records.
- Orange Book listings for the relevant buprenorphine NDA.
- FDA approval records and labeling for Brixadi and Sublocade.
- PACER and district-court dockets for ANDA litigation.
- Federal Circuit decisions involving the patent family.
- License and collaboration disclosures by Camurus, Braeburn, and related companies.
- Settlement agreements resolving Paragraph IV challenges.
A settlement involving a later Brixadi or Sublocade patent would not necessarily resolve infringement exposure under US 8,236,755. Patent-by-patent and claim-by-claim analysis remains necessary.
Key Takeaways
- US 8,236,755 is a broad lipid-depot platform patent covering opioid formulations that convert from a low-viscosity precursor into a non-lamellar liquid-crystalline depot in vivo.
- Claim 1 requires a minimum 18 wt.% neutral diacyl lipid or neutral diacyl lipid/tocopherol component, a phospholipid, an oxygen-containing solvent comprising ethanol, an opioid, and a 1 to 1,000 mPa·s viscosity.
- Claims 15, 18, 20, and 22 extend protection to administration, in vivo phase formation, manufacturing, treatment, and opioid-withdrawal prophylaxis.
- Buprenorphine and methadone are expressly covered, but the claims reach a substantially broader opioid class.
- The patent is a small-molecule formulation patent, so biosimilar rules do not apply.
- The relevant follow-on pathways are ANDA, Paragraph IV, 505(b)(2), and post-expiration generic entry.
- The patent belongs to an early-2000s family whose ordinary base term falls around 2024, subject to the USPTO’s final term calculation and any patent-term adjustment.
- Later Brixadi, Sublocade, formulation, manufacturing, device, and method-of-use patents may create the primary commercial barrier after the platform patent’s term ends.
- Literal infringement depends heavily on measured viscosity, lipid percentage, ethanol content, phase behavior, opioid identity, and the route of administration.
- A polymer-based depot such as Sublocade is technically distinct from the lipid liquid-crystalline system claimed by US 8,236,755.
FAQs
Is US 8,236,755 limited to buprenorphine?
No. Buprenorphine is expressly claimed, but the patent also covers methadone and broader natural, semisynthetic, and synthetic opioid categories.
Does a low-viscosity injectable automatically infringe US 8,236,755?
No. The product must satisfy the full combination of claim limitations, including the specified neutral diacyl lipid threshold, phospholipid, solvent, opioid, viscosity, and in vivo phase conversion.
Can a polymer-based buprenorphine depot infringe this patent?
A polymer-based product is less likely to satisfy the lipid and phospholipid limitations, but infringement requires analysis of the actual formulation and any relevant continuation or related-family patents.
Is the patent relevant to a generic methadone injection?
Potentially. Methadone is within the express claim language, but the generic formulation must also meet the lipid, phospholipid, solvent, viscosity, and phase-conversion limitations.
Does patent expiration remove all barriers to generic Brixadi entry?
No. Later-expiring product, formulation, manufacturing, device, and method-of-use patents, along with regulatory exclusivity and product-specific litigation, may remain relevant.
References
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Camurus AB. (n.d.). Lipid formulations for controlled release of active agents, U.S. Patent No. 8,236,755. United States Patent and Trademark Office.
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U.S. Food and Drug Administration. (2023). Brixadi (buprenorphine) extended-release injection prescribing information. FDA.
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U.S. Food and Drug Administration. (n.d.). Approved drug products with therapeutic equivalence evaluations. FDA.
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U.S. Food and Drug Administration. (n.d.). Orange Book: Approved drug products with therapeutic equivalence evaluations, NDA 213736. FDA.
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Federal Food, Drug, and Cosmetic Act, 21 U.S.C. § 355.
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United States Patent and Trademark Office. (n.d.). Patent Center: U.S. Patent No. 8,236,755 prosecution and maintenance records. USPTO.
