# United States Drug Patent 8,592,397: Claim Scope, Validity Risks, Exclusivity and Patent Landscape for Tenofovir Disoproxil Fumarate/Emtricitabine

US 8,592,397 is a formulation patent directed to chemically stable fixed-dose oral dosage forms containing 300 mg tenofovir disoproxil fumarate (TDF) and 200 mg emtricitabine (FTC), the active-ingredient combination marketed in Truvada. Its commercial value depends on whether a competing product uses the claimed excipient categories, meets the specified stability results, and falls within any enforceable patent term or regulatory listing.

The patent does not claim TDF or FTC as chemical entities. It does not claim the general concept of combining the two antiretrovirals. Its principal subject matter is a stable tablet formulation and, in narrower claims, treatment of HIV using that formulation.

The strongest practical exposure is for a generic or authorized-generic product that reproduces the claimed TDF/FTC strengths, uses pregelatinized starch or microcrystalline cellulose with croscarmellose sodium and magnesium stearate, and is packaged with silica-gel desiccant. The principal validity risks are obviousness, anticipation by earlier TDF/FTC combination formulations, functional-claim interpretation, and the breadth of the excipient Markush groups.

What does US Patent 8,592,397 claim?

The independent claims cover two principal formulation categories.

Claim	Core subject matter	Key limitation
1	Fixed-dose TDF/FTC dosage form	300 mg TDF, 200 mg FTC; specified binder, disintegrant and lubricant; less than 10% degradation after six months at 40°C/75% RH with silica-gel desiccant
19	Similar fixed-dose formulation	Adds pregelatinized starch and maize starch to the expressly listed excipient alternatives
20	Fixed-dose TDF/FTC formulation	Less than 1% TDF degradation over 24 hours
24	Similar fixed-dose TDF/FTC formulation	Less than 1% TDF degradation over 24 hours; includes pregelatinized starch and maize starch

The patent also contains dependent claims directed to:

Oral administration.
Less than 5% degradation after six months.
Less than 1%, 0.1%, or 0.01% TDF degradation over 24 hours.
Specific excipient combinations and quantities.
Less than 1% impurities related to TDF and FTC.
Treatment of HIV infection.
Pregelatinized starch as the starch component.

The claims are composition claims unless they expressly recite treatment. Claims 15-17 are method-of-treatment claims that depend on the formulation claims.

What formulation components are protected by US 8,592,397?

Claim 1 uses functional categories rather than a single formula. A covered product must contain:

Component	Claimed alternatives
Active ingredients	300 mg TDF and 200 mg FTC
Binder	Povidone, gelatin, hydroxypropyl methylcellulose, cellulose, microcrystalline cellulose, starch or acacia
Disintegrant	Sodium starch glycolate, crospovidone, cross-linked sodium carboxymethylcellulose or alginic acid
Lubricant	Magnesium stearate, stearic acid or talc
Stability condition	Less than 10% degradation of TDF or FTC after six months at 40°C/75% RH with silica-gel desiccant

Claims 19 and 24 expand or modify some listed excipient categories by expressly adding pregelatinized starch and maize starch.

A product does not necessarily avoid infringement merely because it uses a different trade name or grade of excipient. The key issue is whether the material falls within the relevant chemical or functional category. For example:

Microcrystalline cellulose is expressly listed as a binder in claims 1, 19, 20 and 24.
Pregelatinized starch is expressly included in several dependent and independent claims.
Croscarmellose sodium corresponds to cross-linked sodium carboxymethylcellulose and is directly relevant to the disintegrant limitation.
Colloidal silicon dioxide is included in claims 10 and 11, although the independent claim language supplied for claim 1 does not require it.
Lactose is present in the narrow formulations but is not itself the principal distinguishing limitation in claim 1.

Which specific formulations are covered?

Claims 7-13 narrow the broad Markush claims to particular excipient systems.

Claim	Formulation described in the claim
7	TDF, FTC, pregelatinized starch, croscarmellose sodium, lactose monohydrate, microcrystalline cellulose and magnesium stearate
8	50 mg pregelatinized starch, 60 mg croscarmellose sodium, 80 mg lactose monohydrate, 300 mg microcrystalline cellulose and 10 mg magnesium stearate
9	50 mg pregelatinized starch, 60 mg croscarmellose sodium, lactose monohydrate, 200 mg microcrystalline cellulose and 10 mg magnesium stearate
10	Claim 7-type formulation with colloidal silicon dioxide
11	50 mg pregelatinized starch, 60 mg croscarmellose sodium, 175 mg lactose monohydrate, 200 mg microcrystalline cellulose, 10 mg magnesium stearate and 5 mg colloidal silicon dioxide
12	Hydroxypropyl methylcellulose, lactose, pregelatinized starch and magnesium stearate
13	112 mg hydroxypropyl methylcellulose, lactose, pregelatinized starch and 7 mg magnesium stearate

Claims 8, 9 and 11 contain a total tablet mass that can be calculated from the stated quantities:

Claim 8: 1,500 mg before any unquantified material or processing variation.
Claim 9: 1,400 mg before the unspecified lactose quantity.
Claim 11: 1,502 mg before any additional processing or coating material.

The claims do not require every excipient to be present in a particular physical form unless the claim says so. A formulation that substitutes a different binder, disintegrant and lubricant could avoid literal infringement if the substitute does not fall within the relevant claim language. That strategy would still require review for the doctrine of equivalents and for other patents in the formulation family.

How broad are the independent claims?

Claims 1, 19, 20 and 24 are broad because they combine:

Fixed active-ingredient amounts.
Open-ended excipient categories.
A stability performance requirement.

The breadth is limited in several ways.

First, the active quantities are specific: 300 mg TDF and 200 mg FTC. A tablet with materially different strengths should not literally meet this limitation, although dosage equivalence and product labeling could create separate regulatory and infringement issues.

Second, each formulation must contain an excipient from the required binder, disintegrant and lubricant groups. A formulation containing only a filler, glidant and coating agent would not meet the claim unless those materials also fall within the stated categories.

Third, the stability requirement is part of the claim. A formulation with the same nominal ingredients but without the claimed degradation performance may fall outside the literal scope, subject to how the claim is construed and how stability is measured.

Fourth, claims 20-26 are vulnerable to overlap and redundancy. Claims 20 and 24 both use a less-than-1% TDF degradation limitation over 24 hours, while claims 21, 22, 25 and 26 impose progressively tighter thresholds. These claims could create evidentiary disputes over assay precision, sampling intervals, degradation products and the relevant baseline.

What does the stability limitation require?

The six-month stability limitation requires testing under accelerated conditions of 40°C and 75% relative humidity, with silica-gel desiccant or desiccant packaging. Claim 1 requires less than 10% degradation of TDF or FTC. Claim 6 narrows the result to less than 5%.

Claims 3-5 and 20-26 impose short-term TDF degradation thresholds:

Claim limitation	Required result
Claims 3 and 20	Less than 1% TDF degradation over 24 hours
Claims 4 and 21	Less than 0.1% TDF degradation over 24 hours
Claims 5 and 22	Less than 0.01% TDF degradation over 24 hours

These limitations raise several infringement and validity questions:

Whether “degradation” means loss of parent drug, formation of specified impurities, or total related substances.
Whether the test must be performed on an uncoated tablet, coated tablet, packaged product or finished commercial package.
Whether “over a 24-hour period” refers to a single 24-hour interval or a specified accelerated-stability protocol.
Whether the claim requires both TDF and FTC to satisfy the threshold or permits one of them to satisfy it.
Whether the silica-gel packaging condition is a required structural limitation or merely a testing condition.

A generic applicant would normally need comparative stability data and analytical methods to determine whether its product meets these limitations. A patent owner would likely seek batch records, formulation composition, packaging specifications and accelerated-stability data in discovery.

How do claims 7-13 affect infringement risk?

The narrow formulation claims create a higher-risk zone for products that reproduce the known Truvada-type tablet architecture.

A product containing the following combination is particularly exposed:

300 mg TDF.
200 mg FTC.
Pregelatinized starch.
Croscarmellose sodium.
Lactose monohydrate.
Microcrystalline cellulose.
Magnesium stearate.
Optional colloidal silicon dioxide.

Claims 8, 9 and 11 are quantity-specific. A product can avoid those claims if it uses materially different amounts, but it may still fall within claim 1, claim 7 or claim 10. Quantity changes therefore do not automatically provide a complete design-around.

A formulation using hydroxypropyl methylcellulose, lactose, pregelatinized starch and magnesium stearate is separately relevant to claims 12 and 13. The 112 mg hydroxypropyl methylcellulose and 7 mg magnesium stearate limitations in claim 13 provide a narrower literal-infringement target.

Is US 8,592,397 a compound patent or a formulation patent?

It is a formulation patent. The patent does not claim:

TDF as a molecule.
FTC as a molecule.
The combination of TDF and FTC without formulation limitations.
Tenofovir alafenamide.
A long-acting injectable product.
A biologic or biosimilar.
A manufacturing process for synthesizing TDF or FTC.

Its value is therefore narrower than the core compound patents historically associated with Viread and Emtriva. The patent is relevant to tablet composition, stability and potentially HIV-treatment use, but it does not independently block every TDF/FTC product.

What is the relationship to Truvada?

Truvada contains 200 mg emtricitabine and 300 mg tenofovir disoproxil fumarate in a once-daily tablet. The FDA approved Truvada for HIV treatment in 2004 and later approved it for pre-exposure prophylaxis in 2012 (U.S. Food and Drug Administration, 2004, 2012).

The claimed strengths therefore correspond to the commercial Truvada dosage. The inventive focus of US 8,592,397 is the stability of the fixed-dose formulation, not the clinical selection of the TDF/FTC combination.

The patent should be analyzed against at least four separate patent layers:

Patent layer	Commercial subject matter	Relevance to US 8,592,397
TDF compound and prodrug patents	Tenofovir disoproxil and related salts	Separate chemical-entity rights
FTC compound patents	Emtricitabine and related chemistry	Separate chemical-entity rights
TDF/FTC combination patents	Fixed-dose combination and therapeutic use	Potentially overlapping active-ingredient scope
Formulation patents	Excipients, stability, coating, packaging and impurity control	Directly relevant

A product can avoid this patent while remaining exposed to a different patent layer. Conversely, expiration or invalidity of the compound patents does not automatically eliminate formulation-patent exposure.

What is the Orange Book status of US 8,592,397?

The supplied claim text does not establish that US 8,592,397 is listed in the FDA Orange Book for Truvada. Orange Book listing must be confirmed from the FDA publication for the relevant NDA and product.

The Orange Book generally identifies patents that the NDA holder or patent owner submitted as covering the approved drug substance, drug product or method of use. A formulation patent is more likely to qualify for listing if it claims the approved dosage form or a method of using that dosage form. A patent that only claims manufacturing information or an unapproved formulation generally presents a different listing analysis (U.S. Food and Drug Administration, 2024).

For diligence purposes, the following distinctions matter:

An Orange Book listing can trigger a Paragraph IV notice and a potential 30-month stay.
A patent not listed in the Orange Book generally cannot support the same automatic Hatch-Waxman stay.
A listed patent can still be challenged for invalidity, noninfringement or improper listing.
A method-of-use listing may be addressed through a section viii statement if the generic labeling omits the patented use.
A formulation patent is more difficult to carve out if the approved product and generic product necessarily use the same dosage-form architecture.

When does US 8,592,397 lose exclusivity?

A precise expiration date cannot be calculated from the claims alone. The controlling date depends on the earliest effective nonprovisional or international filing date, any terminal disclaimer, patent-term adjustment and patent-term extension. The patent issued on November 26, 2013, but the issue date does not determine the expiration date.

The nominal term for a modern U.S. utility patent is generally 20 years from the applicable earliest nonprovisional filing date, subject to adjustments under 35 U.S.C. §§ 154 and 156. Patent-term calculations should therefore be taken from the USPTO Patent Center record and the official patent term data, not from the grant date (U.S. Patent and Trademark Office, 2024).

The commercial exclusivity analysis also requires separating:

Patent expiration.
FDA five-year or three-year regulatory exclusivity.
Pediatric exclusivity.
Orphan-drug exclusivity.
Any settlement-based launch date.
The actual date on which a generic may launch under its ANDA.

US 8,592,397 is a small-molecule formulation patent and should not be treated as a biologic exclusivity right.

Are Paragraph IV challenges likely?

A Paragraph IV challenge would likely focus on three theories.

Anticipation

The challenger would search for an earlier TDF/FTC fixed-dose tablet containing overlapping excipient classes and stability data. Prior art showing the exact 300 mg/200 mg combination, conventional tablet excipients and acceptable accelerated stability could be significant.

The strongest anticipation reference would need to disclose all limitations of the relevant claim, including the specified stability result where that result is treated as limiting. A reference disclosing the same composition but not the claimed performance may still support an obviousness challenge, but anticipation would be less direct.

Obviousness

Obviousness is the main litigation risk. TDF, FTC and the 300 mg/200 mg fixed-dose combination were known before the patent. The listed binders, disintegrants, lubricants, lactose, microcrystalline cellulose and silica-based desiccants are conventional pharmaceutical excipients.

A challenger would argue that:

The active ingredients and strengths were established.
Tablet excipient selection was routine.
Moisture protection and desiccant packaging were predictable responses to stability problems.
The stability results are expected properties of a conventional formulation.
The claimed alternatives are broad and cover routine formulation choices.

The patent owner would respond that the combination had an unexpected stability profile, that TDF/FTC presented compatibility or moisture-sensitivity problems, and that the specific excipient system produced an unexpected reduction in degradation or impurities.

Written description and enablement

The Markush groups cover numerous binders, disintegrants and lubricants. A challenger could argue that the disclosure does not support the full breadth of every claimed permutation, particularly where the patent relies on a limited number of examples.

Enablement risk increases if the claims cover a large number of formulations while requiring a stringent result, such as less than 0.01% degradation, without providing a reliable method for selecting successful formulations across the full scope.

What is the infringement risk for generic manufacturers?

The risk varies by formulation architecture.

Generic design	Relative risk under the supplied claims	Reason
Exact TDF/FTC strengths with pregelatinized starch, croscarmellose sodium, lactose, MCC and magnesium stearate	High	Tracks claims 7-11 and likely claim 1
Same actives and strengths with silica-gel desiccant	High	Directly implicates the stability and packaging limitations
Same actives with hydroxypropyl methylcellulose, lactose, starch and magnesium stearate	Medium to high	Potential claims 12-13 exposure
Different disintegrant outside the listed categories	Lower for literal infringement	May avoid a required claim element
Different lubricant outside magnesium stearate, stearic acid and talc	Lower for literal infringement	Required lubricant limitation may be absent
Different TDF or FTC strength	Lower under these claims	Does not meet the fixed-strength limitation
TDF/FTC product with no claimed stability result	Fact-dependent	Functional limitations and testing methodology become central
TAF/FTC product	Generally outside these claims	Tenofovir alafenamide is not TDF

The most effective design-around strategy is not necessarily changing one excipient. A robust design-around would alter several required elements, such as the binder, disintegrant, lubricant and packaging system, while maintaining dissolution, content uniformity and impurity specifications.

Does the patent create biosimilar risk?

No material biosimilar risk exists. TDF and FTC are small-molecule active ingredients, and Truvada is approved through the small-molecule drug pathway. The relevant competitive products are ANDA generics, not 351(k) biosimilars.

The regulatory pathway is therefore based on pharmaceutical equivalence, bioequivalence, labeling, manufacturing controls and patent certifications under section 505(j) of the Federal Food, Drug, and Cosmetic Act. A generic applicant normally evaluates listed patents through Paragraph I, II, III or IV certifications and may use a section viii statement for certain method-of-use patents (U.S. Congress, 2023).

What patent litigation and settlements affect generic entry?

The supplied information does not identify a litigation docket, Paragraph IV notice, settlement agreement or court judgment specific to US 8,592,397. The patent number alone does not establish whether the patent has been asserted, invalidated, disclaimed, licensed or settled.

The relevant litigation questions are:

Whether the patent was listed against the Truvada NDA.
Whether an ANDA applicant certified Paragraph IV.
Whether the NDA holder filed an infringement action within 45 days.
Whether a 30-month stay was imposed.
Whether a court entered a final judgment.
Whether a settlement provided an agreed launch date or license.
Whether the patent was later disclaimed or held unenforceable.

A settlement can materially change launch timing even when the patent appears facially weak. A court decision on a related TDF/FTC formulation patent may also affect claim construction, obviousness or prosecution-history arguments without directly invalidating US 8,592,397.

How strong is the patent estate?

The patent is stronger as a targeted formulation right than as a broad barrier to all TDF/FTC products.

Factor	Assessment
Active-ingredient differentiation	Weak; TDF and FTC and their dose combination were known
Excipient specificity	Moderate; claims identify conventional but defined categories
Stability limitation	Potentially meaningful if supported by reproducible comparative data
Narrow formulation claims	Stronger than broad Markush claims against exact copies
Obviousness exposure	Significant
Anticipation exposure	Depends on earlier TDF/FTC formulation disclosures
Enforcement evidence	Likely dependent on ANDA composition and stability records
Biosimilar relevance	None
Regulatory leverage	Material only if properly Orange Book listed
Design-around potential	Moderate to high

The best enforceable value likely resides in claims 7-13 and the narrower claims requiring particular excipient quantities or combinations. Claims 1, 19, 20 and 24 are broader but face greater validity and construction challenges.

What manufacturing and packaging barriers does the patent create?

The patent can affect more than the tablet blend. It may reach the commercial product as packaged, depending on claim construction and the role of the desiccant limitation.

A competing manufacturer should review:

Wet versus dry granulation.
Order of excipient addition.
Moisture content of TDF and FTC.
Compression force and tablet porosity.
Use of pregelatinized starch.
Croscarmellose sodium grade and concentration.
Magnesium stearate mixing time.
Blister versus bottle packaging.
Silica-gel desiccant quantity.
Accelerated-stability protocol.
TDF-related impurity profile.
FTC-related degradation products.
Batch-to-batch stability variation.

A process change that avoids the claim may still produce a tablet with different dissolution or stability characteristics. The commercial design-around must therefore be evaluated against both patent scope and FDA product-quality requirements.

How does US 8,592,397 compare with competing patent categories?

Patent category	What it protects	Relative overlap
TDF compound patents	Tenofovir prodrug chemistry	Low direct overlap
FTC compound patents	Emtricitabine chemistry	Low direct overlap
TDF/FTC combination patents	Combination product or HIV treatment	Moderate to high, depending on claim language
US 8,592,397	Stable TDF/FTC dosage form with defined excipients and degradation results	Direct formulation overlap
TAF/FTC patents	Tenofovir alafenamide/emtricitabine products	Low; different tenofovir prodrug
Packaging patents	Moisture-control systems and containers	Potentially overlapping at the packaging level
Process patents	Granulation, blending, compression or coating	Potentially separate manufacturing exposure

The most important competitive distinction is between a generic that copies the commercial tablet architecture and one that develops a genuinely different formulation. The former faces direct claim-mapping risk. The latter may avoid this patent while still requiring a complete review of the broader TDF/FTC patent family.

Key Takeaways

US 8,592,397 is a TDF/FTC formulation patent, not a compound patent.
The claims center on 300 mg TDF plus 200 mg FTC in a chemically stable dosage form.
The broad claims require specified binder, disintegrant and lubricant categories.
The stability limitations are central to both infringement and validity analysis.
Claims 7-13 create the greatest risk for a generic that replicates the commercial excipient system.
The patent has substantial obviousness exposure because the active ingredients, strengths and many excipients were conventional.
A generic may reduce literal-infringement risk by changing multiple required formulation elements, not merely one excipient.
Biosimilar analysis is not relevant; the competitive pathway is ANDA-based generic entry.
Orange Book status, patent-term data, litigation history and settlements cannot be established from the claim text alone.
The patent’s commercial strength depends heavily on its effective expiration date, listing status and the exact ANDA formulation.

FAQs

Does US 8,592,397 cover Truvada by name?

No. The claims cover a dosage form containing the same active ingredients and strengths as Truvada, subject to excipient and stability limitations. They do not claim the Truvada trademark.

Can a generic avoid the patent by removing silica gel?

Possibly, but not necessarily. Silica-gel desiccant is expressly relevant to the six-month stability limitation in the supplied claims. A product using different packaging may avoid a claim requiring silica-gel packaging, but other claims may not require that specific package.

Does changing microcrystalline cellulose avoid infringement?

Not automatically. Microcrystalline cellulose is one of several alternative binders in the claims. Removing it could avoid a particular formulation claim only if the product also lacks another claimed binder and satisfies all other design-around conditions.

Does the patent cover TDF/FTC tablets for HIV prevention?

The composition claims are not limited to HIV treatment. The treatment claims recite treatment of HIV infection, but the formulation claims may apply based on the product’s composition and stability regardless of whether it is marketed for treatment or pre-exposure prophylaxis.

Is tenofovir alafenamide covered by this patent?

The supplied claims require tenofovir disoproxil fumarate. Tenofovir alafenamide is a different prodrug and should not meet the TDF limitation literally.

References

U.S. Food and Drug Administration. (2004). Truvada: New drug application approval letter and prescribing information. FDA.
U.S. Food and Drug Administration. (2012). FDA approves first drug for reducing the risk of sexually acquired HIV infection. FDA.
U.S. Food and Drug Administration. (2024). Approved drug products with therapeutic equivalence evaluations, Orange Book. FDA.
U.S. Patent and Trademark Office. (2024). Patent term adjustment and patent term information. USPTO.
U.S. Congress. (2023). Federal Food, Drug, and Cosmetic Act, 21 U.S.C. § 355.
U.S. Patent No. 8,592,397. (2013). Pharmaceutical dosage forms comprising tenofovir disoproxil fumarate and emtricitabine. United States Patent and Trademark Office.

Country	Patent Number	Estimated Expiration	Supplementary Protection Certificate	SPC Country	SPC Expiration
African Regional IP Organization (ARIPO)	2089	⤷ Start Trial
Argentina	040805	⤷ Start Trial
Argentina	043332	⤷ Start Trial
Argentina	101679	⤷ Start Trial
Austria	398455	⤷ Start Trial
Australia	2004206821	⤷ Start Trial
>Country	>Patent Number	>Estimated Expiration	>Supplementary Protection Certificate	>SPC Country	>SPC Expiration

Details for Patent: 8,592,397

Summary for Patent: 8,592,397