US Patent 8,921,387: Buprenorphine Injectable Depot Claims, Patent Scope, Expiration, and Competitive Landscape
US Patent 8,921,387 protects a specific injectable depot formulation containing buprenorphine free base, PLGA polymer, and N-methyl-2-pyrrolidone (NMP). Its principal commercial relevance is the composition platform used for long-acting buprenorphine treatment of opioid use disorder, including the Sublocade product category. The patent’s strongest protection is formulation-specific: a competing product must generally practice the claimed concentration ranges, polymer characteristics, solvent system, and, for claim 7, monthly parenteral treatment.
The patent does not broadly cover every injectable buprenorphine product, every PLGA depot, or every extended-release opioid-dependence treatment.
What does US Patent 8,921,387 cover?
US Patent 8,921,387 covers an injectable, flowable composition that forms a solid implant after administration and contact with water or bodily fluid. The independent formulation claim requires three principal components:
| Required element |
Claimed range or characteristic |
| Buprenorphine free base |
8 wt% to about 22 wt% |
| PLGA biodegradable thermoplastic polymer |
About 25 wt% to about 50 wt% |
| N-methyl-2-pyrrolidone |
About 30 wt% to about 70 wt% |
| Polymer molecular weight |
About 5,000 to about 40,000 Daltons |
| Dosage form |
Injectable and flowable |
| Transformation |
Solid implant formation upon contact with water or bodily fluid, under claim 2 |
Claim 1 is an open-ended “comprising” claim. That language permits additional ingredients, provided the accused composition still contains all required claim elements. It does not require the formulation to contain only buprenorphine, PLGA, and NMP.
The claims are directed to a solvent-exchange or phase-inversion depot system. NMP keeps the composition injectable before administration. After injection, water or bodily fluid enters the formulation and NMP diffuses outward. PLGA precipitates or solidifies, creating an in situ implant that releases buprenorphine over time.
How do the individual claims of US 8,921,387 operate?
Claim 1: Core formulation claim
Claim 1 is the central composition claim. An accused formulation would need to satisfy each of the following elements:
- Buprenorphine must be present as the free-base form.
- Buprenorphine must comprise 8 wt% to approximately 22 wt%.
- PLGA must comprise approximately 25 wt% to approximately 50 wt%.
- The PLGA molecular weight must be approximately 5,000 to approximately 40,000 Daltons.
- NMP must comprise approximately 30 wt% to approximately 70 wt%.
- The overall product must be injectable and flowable.
The claim does not expressly require a particular needle gauge, injection volume, release duration, particle size, sterilization method, or finished-product strength. Those features may be relevant to other patents, regulatory approval, or infringement analysis, but they are not express limitations of claim 1.
Claim 2: In situ implant formation
Claim 2 adds the requirement that the composition is transformed into a solid implant by contact with water or bodily fluid. This narrows the formulation claim to systems that undergo the specified post-injection solidification process.
A preformed solid implant, a conventional aqueous solution, a microsphere suspension, and a lipid-based depot would not automatically satisfy claim 2. The relevant question would be whether the product itself is a flowable composition that becomes a solid implant after administration.
Claim 3: 50/50 PLGA
Claim 3 requires a 50/50 poly(DL-lactide-co-glycolide) polymer. The “50/50” ratio ordinarily refers to the approximate molar or compositional balance between lactide and glycolide units.
This limitation narrows the claim against formulations using other lactide:glycolide ratios, such as 75:25 or 85:15, although the effect of approximation language and the doctrine of equivalents would depend on the facts.
Claim 4: Lower molecular-weight PLGA range
Claim 4 limits the polymer to an average molecular weight of approximately 9,000 to approximately 20,000 Daltons. This range is narrower than claim 1’s 5,000-to-40,000-Dalton range.
Molecular weight can influence injectability, implant formation, polymer erosion, and release kinetics. A competitor using PLGA below 9,000 or above 20,000 Daltons could avoid literal infringement of claim 4 while potentially remaining within claim 1.
Claim 5: Carboxy-terminal PLGA
Claim 5 requires a polymer with a carboxy terminal group. End-group chemistry can affect polymer hydrophilicity, degradation, drug release, and interaction with the active ingredient.
A competitor using an ester-capped PLGA or another terminal-group configuration could avoid claim 5. That design would not necessarily avoid claim 1 if the formulation otherwise satisfies the broader limitations.
Claim 6: Buprenorphine-to-polymer ratio
Claim 6 requires a buprenorphine-to-polymer weight ratio between 0.01:1 and 2:1. This is a broad ratio range. It may capture many formulations that fall within the concentration limits in claim 1.
The ratio is calculated independently from the individual weight percentages. For example, a formulation containing 15 wt% buprenorphine and 35 wt% PLGA has a ratio of approximately 0.43:1.
Claim 7: Monthly opioid-dependence treatment
Claim 7 is a method claim requiring:
- treatment of a patient with opioid dependency;
- parenteral administration;
- a therapeutically effective amount;
- use of the composition of claim 1; and
- administration once per month.
The method claim is narrower than the formulation claim because infringement requires the treatment method and monthly dosing limitations. A product could potentially infringe claim 1 without infringing claim 7 if it is used for another indication, administered at another interval, or not used in the claimed patient population.
When does US Patent 8,921,387 expire?
US Patent 8,921,387 was issued on December 30, 2014. Its earliest priority date is generally identified as December 1, 2008, producing a nominal patent expiration date of December 1, 2028, subject to any applicable patent-term adjustment, terminal disclaimer, or regulatory extension recorded in the official patent file.[1]
| Event |
Date |
| Earliest priority date |
December 1, 2008 |
| Patent grant |
December 30, 2014 |
| Nominal 20-year expiration |
December 1, 2028 |
| Regulatory exclusivity for Sublocade |
Separate from patent term |
| Patent term extension |
Must be confirmed in the USPTO and FDA records |
Patent expiration does not eliminate FDA regulatory exclusivity before the end of the relevant period. Conversely, FDA exclusivity does not extend the patent unless a statutory patent-term extension or adjustment applies.
What is the Orange Book status of US 8,921,387?
The FDA Orange Book is the relevant source for determining whether a patent is listed against an approved small-molecule drug product.[2] For a long-acting buprenorphine injection, the listed patents can include formulation, method-of-use, manufacturing, or drug-delivery patents.
US 8,921,387 is commercially relevant to the Sublocade product because its claims correspond to a buprenorphine-in-PLGA/NMP in situ depot. The Orange Book analysis must distinguish between:
- patents listed against the reference listed drug;
- patents that remain unexpired;
- patents subject to a pediatric extension;
- patents challenged through a Paragraph IV certification; and
- patents that are not listed because they cover manufacturing or other non-listable subject matter.
An Orange Book listing does not establish ultimate validity or infringement. It triggers statutory notice and potential litigation consequences under the Hatch-Waxman Act.
What Paragraph IV risks apply to generic buprenorphine depot products?
A generic applicant seeking approval before patent expiration may submit a Paragraph IV certification asserting that a listed patent is invalid, unenforceable, or not infringed.[3] For a product implicating US 8,921,387, the applicant would likely focus on:
- whether its buprenorphine concentration falls outside 8 wt% to 22 wt%;
- whether its PLGA concentration falls outside 25 wt% to 50%;
- whether it uses a polymer outside the claimed molecular-weight range;
- whether it uses a solvent other than NMP;
- whether the product forms a solid implant in vivo;
- whether the active ingredient is buprenorphine free base; and
- whether claim 7 is infringed by the proposed labeling.
A generic formulation could challenge the patent through a Paragraph IV notice while also designing around one or more limitations. The most practical design-around paths are a different depot mechanism, a different solvent, a different polymer system, a different concentration profile, or a nonmonthly dosing regimen.
The commercial risk is higher if the generic must use the same in situ PLGA/NMP platform to achieve bioequivalence or comparable release. The regulatory burden for a complex injectable depot can make a technically available design-around less commercially attractive.
What regulatory exclusivity applies to Sublocade?
Sublocade was approved by the FDA in November 2017 for the treatment of moderate-to-severe opioid use disorder in patients who have initiated treatment with a transmucosal buprenorphine-containing product.[4] It is a once-monthly extended-release buprenorphine injection.
Sublocade is a drug-device or complex injectable product from a regulatory perspective because approval depends on more than the active ingredient. The FDA must evaluate:
- depot formation;
- release kinetics;
- injection performance;
- syringe and needle compatibility;
- local and systemic safety;
- dose proportionality;
- manufacturing controls; and
- product quality over shelf life.
The product is not a biologic. A competing applicant would ordinarily pursue an ANDA only if it can meet the statutory requirements for sameness and bioequivalence. Depending on FDA product-specific guidance and the complexity of the dosage form, a 505(b)(2) application may be more practical than a conventional ANDA.
How does the patent compare with competing buprenorphine products?
| Product |
Company |
Delivery system |
Typical dosing |
Relationship to US 8,921,387 |
| Sublocade |
Indivior |
PLGA/NMP in situ depot |
Monthly |
Closely aligned with claimed platform |
| Brixadi |
Braeburn Pharmaceuticals |
Extended-release injectable depot |
Weekly or monthly, depending on product |
Different commercial depot platform; separate patent estate |
| Probuphine |
Titan Pharmaceuticals/Braeburn-related commercial history |
Six-month subdermal implant |
Approximately six months |
Preformed implant, not the claimed injectable flowable composition |
| Generic transmucosal buprenorphine |
Multiple manufacturers |
Sublingual or buccal dosage forms |
Daily or frequent dosing |
Generally outside the composition claims |
Brixadi presents the principal branded injectable competitor. Its delivery technology and patent estate are distinct from a PLGA/NMP in situ implant. A different delivery platform can reduce direct infringement risk under US 8,921,387, although other patents may cover the competing formulation, manufacturing process, device, or treatment method.
What formulation and manufacturing barriers remain after patent expiration?
Patent expiration would remove the term-based exclusion right for the claimed invention, but it would not eliminate technical barriers. A competitor must still establish:
- reproducible polymer molecular weight;
- consistent lactide:glycolide composition;
- controlled NMP content;
- reliable syringeability;
- consistent implant formation;
- predictable buprenorphine release;
- acceptable injection-site tolerability;
- sterility assurance;
- container-closure integrity; and
- commercial-scale batch uniformity.
The critical manufacturing variables are closely connected. Small changes in polymer molecular weight, terminal chemistry, residual solvent, drug loading, or water exposure can alter depot formation and release kinetics.
These factors create potential trade-secret and know-how barriers even when patent protection has expired. A competitor may also face separate process patents, device patents, formulation patents, and regulatory exclusivity.
How strong is the patent estate around the claimed technology?
US 8,921,387 is strongest against a product that duplicates the full architecture: buprenorphine free base in the specified concentration range, 50/50 or related PLGA, NMP, and an injectable in situ solid-forming depot.
Its practical strength has four characteristics:
- Narrow technical focus. The patent is not a broad buprenorphine monopoly.
- Multiple dependent limitations. Claims 2 through 6 provide fallback positions around implant formation, polymer ratio, molecular weight, terminal group, and drug-to-polymer ratio.
- Method-of-use coverage. Claim 7 links the formulation to monthly opioid-dependence treatment.
- Design-around potential. A competitor can target solvent, polymer, concentration, dosing interval, or delivery mechanism.
Validity risks would typically center on anticipation or obviousness based on earlier PLGA depot systems, buprenorphine formulations, NMP-based in situ implants, and prior opioid-dependence treatments. The combination of concentration ranges and polymer characteristics may provide patentability support, but the strength of that position depends on the prosecution history and the prior-art record.
What litigation and settlement issues affect this patent?
Patent litigation involving a generic injectable buprenorphine product would likely proceed under the Hatch-Waxman framework if the patent is listed in the Orange Book. The principal legal issues would be:
- infringement under the proposed ANDA product and labeling;
- validity under anticipation and obviousness;
- written description and enablement;
- claim construction for “about,” “flowable,” and “transformed in situ”;
- interpretation of average polymer molecular weight;
- whether the proposed product contains buprenorphine free base;
- whether the product’s labeling induces infringement of claim 7; and
- the effect of any settlement on generic launch timing.
A settlement could permit an authorized generic, a licensed launch date, or a delayed generic entry date. A patent listing alone does not establish that litigation has occurred or that a settlement exists. Publicly verifiable conclusions require the relevant FDA listing, ANDA notice, court docket, and settlement filing.
What licensing deals are associated with US 8,921,387?
The patent claims identify the invention and patent ownership history, not the full commercial licensing chain. The commercial relationship among the patent owner, product sponsor, development partner, and manufacturing organizations must be evaluated through assignment records, SEC filings, transaction announcements, and FDA product records.
The patent itself does not grant a public license to third parties. Any license, covenant not to sue, field-of-use restriction, or royalty obligation would arise from a separate agreement.
Key Takeaways
- US 8,921,387 covers an injectable buprenorphine free-base depot using PLGA and NMP.
- Claim 1 requires specific weight-percent ranges and a PLGA molecular-weight range.
- Claims 2 through 6 narrow protection around implant formation, 50/50 PLGA, molecular weight, terminal chemistry, and drug-to-polymer ratio.
- Claim 7 covers monthly parenteral treatment of opioid dependency using the claim 1 composition.
- The nominal expiration date is December 1, 2028, subject to official patent-term records.
- Sublocade is the principal commercial product associated with the claimed platform.
- Brixadi and Probuphine use different delivery approaches and are not automatically covered by these claims.
- The most credible design-around strategies involve changing the solvent, polymer, concentration ranges, depot mechanism, or dosing schedule.
- Generic risk depends on Orange Book listing, Paragraph IV certifications, ANDA product design, and the outcome of any Hatch-Waxman litigation.
FAQs About US Patent 8,921,387
Does US Patent 8,921,387 cover all buprenorphine injections?
No. It targets a defined PLGA/NMP injectable composition containing buprenorphine free base within specified concentration ranges.
Can a competitor avoid the patent by using buprenorphine hydrochloride?
Potentially. The claims expressly recite buprenorphine free base. A different salt or chemical form could avoid literal infringement, although other patents and regulatory requirements would remain relevant.
Does using a different PLGA ratio avoid infringement?
It may avoid claim 3, which specifies 50/50 PLGA. It would not necessarily avoid claim 1 if the polymer otherwise satisfies claim 1’s limitations.
Is Brixadi a biosimilar to Sublocade?
No. Both are buprenorphine extended-release injections, but they are small-molecule drug products using different depot technologies. Brixadi is not a biosimilar under the Public Health Service Act.
Can a generic launch before December 2028?
A generic could launch earlier through a successful patent challenge, a license or settlement, an authorized generic arrangement, or a product design that does not infringe enforceable listed patents. Patent expiration alone does not determine market entry if other valid patents or regulatory protections remain.
References
- United States Patent and Trademark Office. (2014). US Patent No. 8,921,387, injectable compositions comprising buprenorphine.
- U.S. Food and Drug Administration. (n.d.). Approved drug products with therapeutic equivalence evaluations: Orange Book.
- U.S. Food and Drug Administration. (n.d.). ANDA submissions: Patent certifications and 30-month stays under the Hatch-Waxman Act.
- U.S. Food and Drug Administration. (2017). Sublocade prescribing information.
