United States Patent 8,664,239: Tacrolimus Extended-Release Patent Scope, Claim Analysis, and Patent Landscape
U.S. Patent No. 8,664,239 protects a method of administering an extended-release tacrolimus formulation once daily in the evening to suppress kidney-transplant rejection. The patent is formulation- and performance-specific. Its central limitation is a dissolution profile requiring substantially zero-order release, minimum release thresholds at four and eight hours, and less than 62% release at 15 hours under a defined USP II test.
The claims do not cover every once-daily tacrolimus product. They target a product that combines:
- Tacrolimus as the active ingredient;
- Extended release;
- A defined in-vitro dissolution profile;
- Evening administration;
- Kidney-transplant rejection prevention;
- Oral, once-daily dosing;
- In several dependent claims, specified doses and hydrophilic vehicles, including poloxamer and polyethylene glycol/poloxamer combinations.
The patent is relevant to Envarsus XR-type tacrolimus products and to abbreviated new drug applications that seek approval for materially similar extended-release tacrolimus formulations.
What patent is U.S. Patent 8,664,239?
U.S. Patent 8,664,239 is directed to methods of using an extended-release tacrolimus composition for kidney-transplant immunosuppression. The claims are method claims rather than claims directed solely to a composition.
| Field |
Analysis |
| Patent number |
U.S. 8,664,239 |
| Technology |
Extended-release oral tacrolimus |
| Active ingredient |
Tacrolimus |
| Therapeutic use |
Suppression of kidney-transplant rejection |
| Dosage schedule |
Once daily in the evening |
| Core dosage form |
Oral extended-release pharmaceutical composition |
| Key release standard |
Substantially zero-order release |
| Key dissolution test |
USP II Paddle, 50 rpm, 900 mL aqueous medium, pH 4.5, 0.005% hydroxypropylcellulose |
| Core release thresholds |
At least 8% at 4 hours; at least 15% at 8 hours; less than 62% within 15 hours |
| Narrower formulation limitations |
Hydrophilic or water-miscible vehicle, including poloxamer and polyethylene glycol/poloxamer |
| Commercial relevance |
Envarsus XR-related tacrolimus extended-release patent estate |
The patent should be analyzed together with related tacrolimus extended-release patents listed for Envarsus XR and with the approved product labeling and Orange Book records. FDA, Approved Drug Products with Therapeutic Equivalence Evaluations; FDA, Envarsus XR Prescribing Information.
What does claim 1 of U.S. Patent 8,664,239 cover?
Claim 1 requires a combination of patient, disease, product, administration, and dissolution limitations. Each limitation must be satisfied for literal infringement.
Claim 1 limitation map
| Claim element |
Scope |
| Patient |
Kidney-transplant patient |
| Medical objective |
Suppression of kidney rejection |
| Route |
Oral |
| Frequency |
Once daily |
| Timing |
In the evening |
| Product |
Extended-release pharmaceutical composition |
| Active ingredient |
Tacrolimus |
| Release behavior |
Substantially zero-order |
| Four-hour release |
At least 8% released |
| Eight-hour release |
At least 15% released |
| Fifteen-hour release |
Less than 62% released |
| Test method |
USP II Paddle |
| Agitation |
50 rpm |
| Medium volume |
900 mL |
| Medium |
Aqueous, pH 4.5 |
| Additive |
0.005% hydroxypropylcellulose |
The claim is narrower than a general claim to extended-release tacrolimus. A product that is administered once daily in the morning, a product that releases tacrolimus too quickly or too slowly under the specified test, or a product used for liver-transplant rather than kidney-transplant patients may avoid literal infringement of claim 1, depending on the product label and facts of use.
Why the dissolution limitations matter
The dissolution criteria are substantive claim limitations, not merely product-development descriptions. A competing formulation must be evaluated under the stated test conditions. Release data generated using a different medium, pH, paddle speed, vessel volume, or sampling protocol may not establish whether the claim is met.
The claim imposes three cumulative performance requirements:
- Release of at least 8% by four hours;
- Release of at least 15% by eight hours;
- Release of less than 62% by 15 hours.
The wording creates a defined release window. It excludes formulations that release less than 8% by four hours, less than 15% by eight hours, or 62% or more by 15 hours.
The expression “substantially zero order” may create claim-construction and scientific disputes. Zero-order release generally refers to release at an approximately constant rate over time. The patent’s numerical thresholds provide objective boundaries, but they may not fully resolve how “substantially” is measured or whether a release curve qualifies when the rate varies across intervals.
How do claims 2 through 12 narrow the patent scope?
The dependent claims add release limits, dosing duration, dose levels, food restrictions, patient status, and excipient limitations.
Claims 2 and 3: additional release and duration requirements
Claim 2 requires:
- No more than 20% release within four hours; and
- No more than 40% release within 10 hours.
This claim narrows claim 1 by adding upper release limits. A formulation can satisfy claim 1 but fail claim 2 if it releases more than 20% by four hours or more than 40% by 10 hours.
Claim 3 requires once-daily administration for at least seven days. A single dose or short-term administration would not meet this additional limitation.
Claims 4 through 6: dose limitations
| Claim |
Tacrolimus amount per administered composition |
| Claim 4 |
0.1 to 15 mg |
| Claim 5 |
0.5 to 5 mg |
| Claim 6 |
1 mg |
Claim 6 is the narrowest dose claim. It is commercially relevant because 1 mg extended-release tacrolimus capsules are a standard strength for Envarsus XR. A product using a 1 mg tacrolimus dose can fall within claim 6 if all claim 1 limitations are also satisfied.
The dose limitations concern the amount of tacrolimus in the administered composition. They do not, by themselves, define the patient’s total daily dose if multiple units are administered, unless the claim language and product facts establish that each administered composition contains the specified amount.
Claim 7: administration without simultaneous food intake
Claim 7 requires oral administration without simultaneous food intake. This limitation may be relevant because food affects tacrolimus absorption. Envarsus XR labeling instructs patients to take the product consistently with respect to meals, and the approved label identifies clinically meaningful food effects. FDA, Envarsus XR Prescribing Information.
A label that instructs administration in a fasting state or otherwise directs administration without food may increase induced-infringement exposure if the remaining claim limitations are met.
Claim 8: de novo kidney-transplant patients
Claim 8 narrows the patient population to de novo kidney-transplant patients. “De novo” generally refers to patients beginning immunosuppressive therapy in connection with a new transplant rather than patients converted from an existing tacrolimus regimen.
A product labeled only for conversion or maintenance therapy may have a noninfringement position under claim 8, although it could remain exposed under claim 1 or other patent claims.
Claims 9 through 12: vehicle limitations
Claim 9 requires tacrolimus to be present in a hydrophilic or water-miscible vehicle. Claim 10 lists numerous vehicle classes, including:
- Polyethylene glycol;
- Polyoxyethylene oxide;
- Poloxamer;
- Polyoxyethylene stearate;
- Polyvinylpyrrolidone;
- Polyvinyl alcohol;
- Hydroxypropyl methylcellulose;
- Hydroxypropyl cellulose;
- Methylcellulose;
- Sodium carboxymethylcellulose;
- Cyclodextrins;
- Xanthan gum;
- Mixtures of the listed materials.
Claim 11 narrows the vehicle to poloxamer. Claim 12 requires a mixture of polyethylene glycol and poloxamer.
These claims are important because they tie the method claims to formulation architecture. A competitor may avoid claims 11 and 12 by using a different vehicle system, but it could still fall within claim 1 or claim 9 if the product satisfies the release and administration limitations.
What formulations are protected by U.S. Patent 8,664,239?
The patent protects use of formulations that produce a delayed, controlled tacrolimus release profile. The claims do not require a particular capsule shell, tablet geometry, coating material, manufacturing process, or exact excipient concentration.
The strongest formulation nexus is found in claims 9 through 12:
| Formulation feature |
Relevant claim |
| Hydrophilic or water-miscible vehicle |
Claim 9 |
| Broad listed vehicle categories |
Claim 10 |
| Poloxamer |
Claim 11 |
| Polyethylene glycol plus poloxamer |
Claim 12 |
The patent therefore presents two separate infringement pathways:
- A performance-based pathway under claims 1 through 8, where the product’s release profile and labeled use are central; and
- A composition-linked pathway under claims 9 through 12, where the vehicle system must also fall within the claimed categories.
The patent does not appear, from the supplied claims, to require a particular tacrolimus crystal form, particle size, capsule material, coating thickness, dissolution apparatus other than the specified test, or manufacturing sequence.
How does U.S. Patent 8,664,239 compare with composition and formulation patents?
U.S. 8,664,239 is a method-of-treatment patent. Its legal risk differs from a composition patent.
| Patent type |
Primary infringement focus |
Typical design-around |
| Method patent |
Label, patient population, dosing schedule, and actual use |
Alternative indication, timing, or dosing instruction |
| Composition patent |
Product structure and ingredients |
Different excipient system or dosage form |
| Dissolution-profile patent |
Measured release behavior |
Altered release kinetics |
| Manufacturing patent |
Production process |
Alternative manufacturing route |
| Method-of-use patent |
Claimed therapeutic use |
Different labeled use or treatment population |
A generic applicant may have difficulty avoiding a method claim if FDA approval requires a label that directs the claimed once-daily evening use. A product may have a stronger noninfringement position if its proposed label omits evening dosing, excludes de novo patients, or uses a materially different release profile.
What is the FDA and Orange Book status of the related tacrolimus product?
Envarsus XR is an FDA-approved extended-release tacrolimus product for prophylaxis of organ rejection in kidney-transplant patients, used with other immunosuppressants. FDA approved Envarsus XR on July 10, 2015, under NDA 206406. FDA, Envarsus XR Approval Letter.
The product is distinct from immediate-release tacrolimus capsules and from other extended-release tacrolimus products. The FDA label identifies Envarsus XR as an extended-release tablet administered once daily, with strengths including 0.75 mg, 1 mg, and 4 mg. FDA, Envarsus XR Prescribing Information.
The Orange Book is the principal FDA source for listed patents and regulatory exclusivities associated with approved small-molecule products. The Envarsus XR listing should be reviewed together with the relevant patent-use codes and current patent expiration information. FDA, Orange Book.
Because U.S. 8,664,239 issued in 2014 from an application claiming priority to an earlier tacrolimus formulation development program, its ordinary patent-term analysis points to expiration in the 2027 period, subject to any patent-term adjustment, terminal disclaimer, or other recorded term event. The effective blocking date must be confirmed against the USPTO patent record and current Orange Book listing.
When does tacrolimus extended-release exclusivity expire?
Tacrolimus itself is an old active pharmaceutical ingredient and does not receive new chemical entity exclusivity for an extended-release product. The principal barriers are formulation, method-of-use, and regulatory exclusivities.
| Exclusivity category |
Relevance |
| New chemical entity exclusivity |
Not available for tacrolimus |
| Five-year NCE exclusivity |
Not applicable to Envarsus XR |
| Three-year clinical-investigation exclusivity |
Potentially relevant to qualifying new clinical investigations |
| Pediatric exclusivity |
Depends on FDA grant and the relevant product record |
| Patent exclusivity |
Driven by listed tacrolimus formulation and method patents |
| Orphan exclusivity |
Not the principal Envarsus XR pathway |
The commercial protection period is therefore determined mainly by the listed patent estate and any applicable FDA regulatory exclusivity. A generic applicant can file an ANDA before patent expiration, but launch generally depends on patent resolution, a settlement, a successful Paragraph IV challenge, or expiration of the relevant patent barriers.
Which companies are challenging the Envarsus XR patent estate?
Generic competition to extended-release tacrolimus can proceed through ANDA filings containing Paragraph IV certifications against listed patents. The principal commercial risk comes from generic applicants seeking approval for a product bioequivalent to Envarsus XR or otherwise relying on the reference product’s safety and efficacy findings.
Public patent litigation involving Envarsus XR has included disputes between Veloxis-related entities and generic pharmaceutical companies over ANDA filings and listed tacrolimus patents. The specific patents, defendants, statutory stay dates, and case outcomes must be assessed from the relevant district-court dockets and FDA Orange Book updates because litigation status changes independently of the patent’s issued claims.
A complete Paragraph IV analysis requires separating:
- The patents listed for the reference product;
- The patents challenged by each ANDA applicant;
- The certification language used;
- Whether a 30-month stay was triggered;
- Whether the case ended in judgment, dismissal, settlement, or license;
- Whether the settlement permits an authorized generic or delayed launch.
What generic entry risks exist for this patent?
The highest-risk generic scenario is a product with:
- Once-daily oral tacrolimus dosing;
- An evening or night-time label instruction;
- Kidney-transplant rejection prophylaxis;
- A release profile meeting the claim 1 thresholds;
- A hydrophilic or water-miscible vehicle;
- Poloxamer or polyethylene glycol/poloxamer excipients;
- 1 mg or other claimed dose strengths.
A generic company may pursue several defenses or design-around strategies:
Alternative dosing language
If the proposed label directs morning dosing rather than evening dosing, it may avoid the express timing limitation. The strength of that strategy depends on actual use, physician instructions, product labeling, and whether the patent owner asserts induced infringement based on foreseeable off-label evening use.
Altered dissolution profile
A formulation that fails one or more numerical release thresholds may avoid literal infringement. The product must still meet FDA performance and bioequivalence requirements, so changing the release profile may create regulatory rather than purely legal constraints.
Alternative excipient system
A formulation that does not use a claimed hydrophilic or water-miscible vehicle, poloxamer, or polyethylene glycol/poloxamer mixture may avoid claims 9 through 12. This strategy does not necessarily avoid claim 1.
Different patient population
A label directed only to conversion or maintenance patients may reduce exposure to claim 8, but not necessarily to claim 1.
Noninfringing use code or skinny label
For a method-of-use patent, an ANDA applicant may attempt to omit the patented use from its labeling. This approach is more effective when the patented method is separable from the unpatented indications and dosing instructions. It is less effective when the patented method is embedded in the core reference-product label.
How strong is the patent estate around Envarsus XR?
The estate is stronger when evaluated as a portfolio rather than through U.S. 8,664,239 alone. A generic applicant may avoid one patent through a release-profile or vehicle modification but remain exposed to other patents covering:
- Tacrolimus extended-release composition technology;
- Controlled-release formulations;
- Dosing methods;
- Pharmacokinetic performance;
- Tablet or dosage-form architecture;
- Manufacturing methods;
- Specific therapeutic use.
U.S. 8,664,239 is strongest against a product that closely reproduces the claimed release profile and labeled evening-use regimen. It is weaker against a product that uses materially different release kinetics, a non-listed vehicle system, or a label that omits evening administration and de novo kidney-transplant use.
The key litigation vulnerabilities are likely to involve:
- Construction of “substantially zero order”;
- Reproducibility of the specified dissolution test;
- Whether the accused product meets each release threshold;
- Whether a generic label induces evening administration;
- Whether “without simultaneous food intake” is required for the accused use;
- Whether the claimed method is practiced by physicians or patients;
- Whether a hydrophilic vehicle is present in the legally relevant formulation.
What manufacturing and intellectual-property barriers apply?
The manufacturing barrier is not limited to the active ingredient. Extended-release tacrolimus requires control over drug loading, dissolution behavior, content uniformity, release reproducibility, and exposure variability.
Tacrolimus has a narrow therapeutic index. FDA requires careful demonstration of bioequivalence and product quality for generic and follow-on products. A formulation that changes release kinetics may alter peak and trough exposure even if total exposure is similar. FDA’s narrow therapeutic index guidance makes formulation and bioequivalence strategy commercially important. FDA, Bioequivalence Recommendations for Tacrolimus.
The relevant IP barriers can include:
- Polymer or surfactant selection;
- Drug dispersion or solubilization;
- Controlled-release matrix design;
- Tablet compression and coating;
- Dissolution-test reproducibility;
- Stability and moisture control;
- Manufacturing-process parameters;
- Product-specific clinical or pharmacokinetic data.
These barriers can make a technically noninfringing product more expensive or slower to develop, even where the patent claims can be avoided.
What revenue exposure does the patent create?
Envarsus XR competes in a high-value chronic immunosuppression market. Revenue exposure is concentrated in the long-term kidney-transplant population because patients generally require continuing immunosuppressive therapy.
The commercial impact of U.S. 8,664,239 depends on:
- The number of listed patents remaining in force;
- Whether a generic can obtain approval before patent expiry;
- Whether a Paragraph IV challenge succeeds;
- Whether a settlement permits an earlier launch;
- The degree of substitution between Envarsus XR, immediate-release tacrolimus, and other extended-release products;
- Payer and transplant-center switching practices;
- The availability of authorized generic supply.
A first-filer generic that obtains a favorable judgment or settlement could materially affect price and market share. A later entrant would face greater erosion risk because multiple generic suppliers could compete simultaneously after the principal patent barriers expire.
What is the likely generic launch scenario?
The principal scenarios are:
| Scenario |
Commercial result |
| Patent upheld and no settlement launch |
Generic entry delayed until patent expiry |
| Generic wins Paragraph IV litigation |
Launch may occur before expiry, subject to judgment and regulatory status |
| Settlement with licensed entry |
Entry occurs on the agreed date, potentially with restrictions |
| Noninfringing formulation |
Approval may proceed if FDA requirements are met |
| Patent expiry without successful challenge |
Multiple ANDA launches become more likely |
| Authorized generic launch |
Price erosion may begin before independent generic entry |
The most important diligence item is not merely whether U.S. 8,664,239 remains unexpired. It is whether the remaining patent portfolio contains claims that a commercially viable generic cannot avoid without changing the FDA-approved product profile.
Key Takeaways
- U.S. 8,664,239 is a method patent covering evening, once-daily oral administration of extended-release tacrolimus to suppress kidney rejection.
- Claim 1 requires a specific dissolution profile under a defined USP II test.
- Claims 2 through 12 add tighter release limits, dosing duration, dose amounts, food restrictions, de novo status, and excipient limitations.
- Poloxamer and polyethylene glycol/poloxamer vehicles are expressly targeted by claims 11 and 12.
- The patent does not cover every extended-release tacrolimus product.
- The principal generic vulnerabilities are the evening-dosing requirement, the dissolution thresholds, the meaning of “substantially zero order,” and the relationship between product labeling and induced infringement.
- Tacrolimus is not entitled to new chemical entity exclusivity. Patent and product-specific regulatory protections drive the commercial exclusivity analysis.
- The patent’s ordinary term points to the 2027 period, subject to USPTO-recorded adjustments and the current Orange Book record.
- Patent risk must be assessed across the full Envarsus XR estate, not through U.S. 8,664,239 alone.
- Biosimilar risk is not applicable because tacrolimus is a small-molecule drug. The relevant competitors are ANDA-based generic products.
FAQs About U.S. Patent 8,664,239
Does U.S. Patent 8,664,239 cover immediate-release tacrolimus?
No. The claims require an extended-release pharmaceutical composition and a defined controlled-release profile.
Does taking tacrolimus once daily automatically infringe the patent?
No. Once-daily administration is only one limitation. The product must also satisfy the claimed release profile, kidney-transplant use, evening administration, and other applicable limitations.
Can a generic avoid the patent by using a morning dosing label?
Potentially. Morning dosing could avoid the express evening-administration limitation, but the outcome depends on the full label, actual use, inducement allegations, and other patents in the estate.
Are Envarsus XR and Advagraf the same product?
No. Both are modified-release tacrolimus products, but they are distinct products with different formulations, regulatory histories, and market authorizations. Envarsus XR is the U.S. extended-release tacrolimus product associated with the patent estate discussed here.
Does a formulation using poloxamer necessarily infringe claims 11 and 12?
No. Poloxamer is only one limitation. The product must also satisfy the incorporated limitations of claim 9 and claim 1, including the claimed medical use, dosing schedule, release profile, and administration conditions.
References
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U.S. Patent and Trademark Office. (2014). U.S. Patent No. 8,664,239, Tacrolimus extended-release pharmaceutical composition and methods of use.
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U.S. Food and Drug Administration. (2015). Envarsus XR approval letter, NDA 206406.
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U.S. Food and Drug Administration. (2024). Envarsus XR prescribing information.
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U.S. Food and Drug Administration. (2024). Approved drug products with therapeutic equivalence evaluations, Orange Book.
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U.S. Food and Drug Administration. (2020). Product-specific guidance for tacrolimus.
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U.S. Food and Drug Administration. (2013). Bioequivalence recommendations for tacrolimus.
