United States Patent 8,101,582: Claim Scope, Tobradex ST Coverage, and Generic Entry Risk

US Patent 8,101,582 is a formulation-driven method-of-treatment patent covering topical ophthalmic compositions that combine tobramycin, dexamethasone, deacetylated xanthan gum, and selected ionizable species. Its commercial target is the viscous ophthalmic suspension associated with Tobradex ST. The claims do not cover tobramycin or dexamethasone generally. They require a narrow combination of active-ingredient concentrations, polymer concentration, pH, viscosity, and ionic-control characteristics. [1]

The patent’s principal commercial claim is claim 16, particularly when read with dependent claims 18 through 22. That claim set maps closely to a composition containing 0.3% tobramycin, 0.05% dexamethasone, deacetylated xanthan gum, sodium chloride or sodium sulfate, a pH of 5 to 6, and a specified viscosity profile.

The patent is a small-molecule formulation patent, not a biologic patent. Biosimilar law is therefore not relevant. Generic risk turns on formulation design, labeling, ANDA certification, and whether a proposed product induces use within the claimed inflammatory indications.

What does US Patent 8,101,582 protect?

The patent protects methods of treating an inflamed eye where infection is present or a risk of infection exists, using a specific aqueous ophthalmic composition. The claims require all of the following core elements:

Claim element	Required limitation
Therapeutic use	Treatment of an eye affected by an ophthalmic inflammatory condition
Infection context	Infection or risk of infection exists
Aminoglycoside	Tobramycin at 0.1% to 0.5% w/v
Corticosteroid	Dexamethasone at 0.03% to 0.1% w/v
Polymer	Deacetylated xanthan gum at 0.3% to 0.9%
Vehicle	Aqueous, ophthalmically acceptable vehicle
Ionic control	One or more ionizable species in an amount sufficient to limit ionic interactions between tobramycin and deacetylated xanthan gum
Rheology	In vitro viscosity of 10 to 700 cps, or in narrower claims 10 to 300 cps
Test conditions	6 sec^-1 shear rate and 25°C
pH	5 to 6
Administration	Topical application or provision to the affected eye in the relevant claim sets

The patent therefore operates as a combination claim. A product normally must satisfy the full combination to create a direct infringement case based on the claimed method. A formulation that contains tobramycin and dexamethasone but uses a different polymer, lacks the required ionic species, has a pH outside 5 to 6, or falls outside the specified viscosity range may avoid literal infringement, subject to equivalents and induced-infringement theories.

Which claims are independent in US 8,101,582?

Claims 1, 11, and 16 are the principal independent claims.

Claim 1: broadest viscosity formulation method

Claim 1 covers treating an inflamed eye with the required formulation where viscosity is 10 to 700 cps. It does not expressly require the narrower 10 to 300 cps range or the express topical-application wording found in claim 11 and claim 16.

Its limitations include:

tobramycin at 0.1% to 0.5% w/v;
dexamethasone at 0.03% to 0.1% w/v;
deacetylated xanthan gum at 0.3% to 0.9%;
ionizable species sufficient to limit tobramycin-polymer ionic interactions;
viscosity of 10 to 700 cps at 6 sec^-1 and 25°C;
pH of 5 to 6; and
treatment of ophthalmic inflammation where infection or infection risk exists.

Claim 11: narrower viscosity and express topical-use requirements

Claim 11 narrows the viscosity to 10 to 300 cps and states that providing the composition includes topically applying a therapeutically effective amount to the affected eye.

This claim is commercially important because it is directed to the expected use of a topical ophthalmic suspension rather than merely describing provision of the composition.

Claim 16: direct topical-application claim

Claim 16 also requires topical application but returns to the broader 10 to 700 cps viscosity range. The dependent claims then narrow the formulation and indication:

claim 18: sodium chloride, sodium sulfate, or both;
claim 19: 0.3% tobramycin;
claim 20: 0.05% dexamethasone;
claim 21: in vitro/in vivo viscosity ratio of 0.01 to 0.65; and
claim 22: inflammation resulting from trauma or ocular surgery.

Claims 19 and 20 are particularly significant because the 0.3%/0.05% combination corresponds to the standard commercial strength associated with Tobradex ST.

How do the dependent claims narrow the patent scope?

The dependent claims narrow the broad formulation concept along four dimensions: electrolyte identity, viscosity, active-ingredient concentration, and clinical indication.

Dependent claims	Narrowing feature	Commercial effect
2, 8, 12, 17	Inorganic electrolytes, organic buffers, or combinations	Broadens the permitted ionic-control category
3, 9	Specified salts and buffering systems	Creates a closed list of named ionic species
4, 10, 13, 18	Sodium chloride, sodium sulfate, or both	Closely targets likely commercial formulations
5, 11	Viscosity of 10 to 300 cps	Removes higher-viscosity embodiments
6, 14	Initial viscosity of 25 to 175 cps	Adds a starting-rheology limitation
7, 15, 21, 23-25	In vitro/in vivo viscosity ratio of 0.01 to 0.65	Adds a performance-based limitation
19	Tobramycin at 0.3%	Targets the commercial strength
20	Dexamethasone at 0.05%	Targets the commercial strength
22	Trauma or ocular surgery	Narrows the treatment indication

Claims 23 through 25 repeat the viscosity-ratio limitation in the context of the three independent claim branches. These claims may provide fallback positions if a broader claim is challenged on validity or scope.

What formulation is most directly covered?

The highest-risk formulation profile is:

Parameter	Commercially targeted profile
Tobramycin	0.3% w/v
Dexamethasone	0.05% w/v
Polymer	Deacetylated xanthan gum
Electrolyte	Sodium chloride, sodium sulfate, or both
Vehicle	Aqueous ophthalmic vehicle
pH	5 to 6
Viscosity	10 to 700 cps, with narrower claims at 10 to 300 cps
Initial viscosity	25 to 175 cps
Viscosity ratio	0.01 to 0.65
Use	Topical treatment of inflammatory eye conditions with infection or infection risk
Surgical indication	Trauma or ocular surgery under claim 22

A formulation that matches the 0.3% tobramycin and 0.05% dexamethasone strengths but substitutes a non-xanthan polymer is outside the literal polymer limitation. A formulation that uses xanthan gum but not deacetylated xanthan gum presents a separate claim-construction issue. The patent does not merely require xanthan gum; it requires the deacetylated form.

Why is deacetylated xanthan gum important?

The polymer limitation is central to the patent’s technical scope. Tobramycin is a polycationic aminoglycoside. Xanthan gum is an anionic polysaccharide. Ionic interactions between the active ingredient and polymer can change viscosity, dosing uniformity, suspension behavior, and ocular residence characteristics.

The claimed ionizable species reduce or limit those interactions. The patent therefore combines:

a deacetylated xanthan-gum vehicle;
an aminoglycoside antibiotic;
an ophthalmic corticosteroid; and
an electrolyte or buffer system that controls polymer-drug interaction.

The functional language requiring an amount "sufficient to limit ionic interactions" creates both scope and proof issues. In an infringement dispute, the patentee would likely need to establish that the selected salt or buffer performs the claimed interaction-limiting function. A generic manufacturer could contest whether the formulation meets that functional limitation, although laboratory data showing the formulation’s ionic environment and viscosity profile could support infringement.

What is the significance of the viscosity limitations?

The viscosity limitations are measured under defined conditions: 6 sec^-1 shear rate and 25°C. This matters because viscosity is not a single universal property. Results can vary with:

shear rate;
temperature;
instrument geometry;
measurement protocol;
polymer hydration time;
electrolyte concentration; and
formulation aging.

The claims contain three rheology layers:

Rheology limitation	Claims
10 to 700 cps	1 and 16
10 to 300 cps	5 and 11
Initial viscosity of 25 to 175 cps	6 and 14
In vitro/in vivo viscosity ratio of 0.01 to 0.65	7, 15, 21, 23, 24 and 25

The in vitro/in vivo ratio is unusually important. It attempts to capture a formulation that is sufficiently viscous in laboratory testing but behaves differently after administration to the eye. That limitation may create evidentiary complexity because the parties must agree on how the in vivo component is measured or calculated.

What is the patent’s strongest claim position?

The strongest practical claim position is the combination of:

claim 16;
claim 18’s sodium chloride or sodium sulfate limitation;
claim 19’s 0.3% tobramycin limitation;
claim 20’s 0.05% dexamethasone limitation; and
claim 22’s trauma or ocular-surgery indication.

This combination closely tracks the commercial product profile and narrows the factual disputes. A product that has the commercial active strengths, deacetylated xanthan gum, sodium chloride or sodium sulfate, pH 5 to 6, and the specified viscosity profile would face the most direct infringement exposure if its labeling includes postoperative or traumatic ocular inflammation.

The broadest enforceable position is not necessarily the strongest litigation position. Claims 1 and 16 cover a wider viscosity range, but broader claims are more exposed to prior-art combinations involving viscous ophthalmic vehicles, electrolyte-controlled polymers, and antibiotic-steroid formulations.

What prior-art and validity issues affect the patent?

The principal validity issues are likely to concern obviousness and claim construction rather than written-description issues.

Obviousness risk

The relevant prior-art categories include:

tobramycin/dexamethasone ophthalmic compositions;
xanthan-gum or modified-xanthan-gum ophthalmic vehicles;
electrolyte-controlled polymer systems;
viscous ocular suspensions;
formulations designed to increase ocular residence time; and
postoperative antibiotic-steroid ophthalmic products.

The patent’s validity defense would focus on whether a skilled formulation scientist would have combined the known active ingredients with deacetylated xanthan gum and an electrolyte to obtain the claimed viscosity and ocular-performance profile.

The patentee’s likely response would emphasize the interaction between tobramycin and the polymer, the selected electrolyte concentration, and the claimed viscosity behavior. The functional relationship between the components is more important than the individual ingredients viewed separately.

Indefiniteness and enablement issues

Potential disputes include:

the meaning of "sufficient to limit ionic interactions";
the test used to establish the in vitro/in vivo viscosity ratio;
the meaning of "initial viscosity";
the process used to determine whether xanthan gum is deacetylated;
the reproducibility of measurements at 6 sec^-1 and 25°C; and
whether the full 0.3% to 0.9% polymer range is enabled across all listed ionic species.

These issues do not automatically invalidate the claims. They identify the technical evidence likely to control a dispute.

What is the Orange Book status of US 8,101,582?

US 8,101,582 was associated with the ophthalmic tobramycin/dexamethasone product Tobradex ST and was listed as a formulation or method patent for the relevant NDA product. The patent is distinct from the earlier Tobradex product patents because it focuses on the xanthan-gum-based suspension technology rather than the basic antibiotic-steroid combination. [2][3]

The recorded patent-term endpoint commonly associated with US 8,101,582 is September 8, 2025, subject to the official patent-term calculation and any applicable regulatory adjustments. The patent’s practical blocking value therefore depended heavily on the timing of ANDA filings, Paragraph IV certifications, litigation, and settlement terms.

Item	US 8,101,582
Patent type	Small-molecule formulation and method-of-treatment patent
Primary product association	Tobradex ST
Active ingredients	Tobramycin and dexamethasone
Key excipient	Deacetylated xanthan gum
Key ionic species	Sodium chloride and sodium sulfate, among others
Core route	Topical ophthalmic administration
Common commercial strengths	0.3% tobramycin and 0.05% dexamethasone
Recorded term endpoint	September 8, 2025
Biosimilar pathway	Not applicable
Generic pathway	ANDA, with possible Paragraph IV certification

When does generic entry risk arise?

Generic entry risk arises when an ANDA applicant proposes a product and labeling that together satisfy the patent’s formulation and method limitations. The risk is highest where the proposed product:

uses deacetylated xanthan gum;
contains 0.3% tobramycin and 0.05% dexamethasone;
uses sodium chloride or sodium sulfate;
has a pH of 5 to 6;
falls within the claimed viscosity range; and
carries indications covering inflammatory eye conditions with infection or infection risk.

A product can reduce literal infringement risk by changing one or more claim-critical parameters, such as:

using a different viscosity-enhancing polymer;
using a non-covered polymer grade;
selecting a different electrolyte system;
adjusting pH outside the claimed range;
altering viscosity outside the measured claim range; or
using labeling that does not encourage the claimed treatment method.

The last option is difficult for a generic applicant if FDA requires labeling that substantially overlaps the reference product’s approved indications. A proposed label can avoid some method-of-use claims through a skinny label, but formulation limitations cannot be removed from the product itself.

Which companies are likely to challenge the patent?

The commercially relevant challengers are ANDA applicants seeking approval for generic tobramycin/dexamethasone ophthalmic suspension products. Public patent litigation records should be reviewed for each applicant because challenge timing, named defendants, district-court cases, and settlement terms can differ.

The likely challenger categories are:

generic ophthalmic manufacturers;
specialty pharmaceutical companies with sterile ophthalmic manufacturing capacity;
contract manufacturers filing through ANDA sponsors; and
companies developing alternate xanthan-based or non-xanthan formulations.

The key litigation question is not whether a company markets generic tobramycin/dexamethasone. It is whether its proposed formulation and label meet the specific deacetylated-xanthan, electrolyte, viscosity, and pH limitations.

How does US 8,101,582 compare with ordinary Tobradex patents?

Issue	Conventional Tobradex coverage	US 8,101,582 coverage
Core actives	Tobramycin and dexamethasone	Tobramycin and dexamethasone
Main innovation	Antibiotic-steroid ophthalmic combination	Xanthan-gum formulation and ionic control
Polymer requirement	Not necessarily	Deacetylated xanthan gum required
Electrolyte requirement	Not necessarily	Required in the independent claims
Viscosity limitation	May be absent or different	Central to the claims
pH limitation	May be absent or different	pH 5 to 6
Product target	Tobradex-type products generally	Tobradex ST-type suspension
Main generic design-around	Change active combination or dosage form	Change polymer, electrolyte, pH, or rheology

The patent does not create a monopoly over all generic tobramycin/dexamethasone ophthalmic products. It targets a particular delivery platform.

What manufacturing and intellectual-property barriers remain?

The formulation may be difficult to design around without sacrificing product performance. A manufacturer seeking an alternative must manage:

polymer hydration and batch consistency;
sterility and preservative compatibility;
suspension uniformity;
syringe or dropper delivery;
settling and redispersion behavior;
ophthalmic tolerability;
viscosity under the specified test conditions;
interaction between aminoglycoside and polymer;
pH stability; and
equivalence requirements under the ANDA pathway.

A noninfringing formulation may still require substantial development work to demonstrate pharmaceutical equivalence and bioequivalence or comparable local ocular performance. That development burden is a commercial barrier even after patent expiration.

What is the geographic scope of the patent?

US 8,101,582 has territorial effect in the United States. It does not directly block manufacture, sale, or use outside the United States. Foreign protection would depend on related national or regional family members, their prosecution histories, and their individual expiration dates.

The same formulation concept may have been pursued in Canada, Europe, Australia, or other markets, but foreign claims may differ materially. Patent-family analysis should distinguish:

national grants;
pending applications;
abandoned applications;
continuations and divisionals;
terminal disclaimers;
supplementary protection certificates; and
local regulatory exclusivity.

Key Takeaways

US 8,101,582 is a formulation-specific method patent associated with Tobradex ST-type ophthalmic suspension technology.
The core combination is tobramycin, dexamethasone, deacetylated xanthan gum, an ionizable species, pH 5 to 6, and a defined viscosity profile.
Claims 19 and 20 narrow the commercial embodiment to 0.3% tobramycin and 0.05% dexamethasone.
Sodium chloride and sodium sulfate are the most important expressly claimed ionic species.
Claims 1, 11, and 16 are the principal independent claims.
Claims 7, 15, 21, and 23 through 25 add an in vitro/in vivo viscosity-ratio limitation.
The highest infringement risk applies to products matching the Tobradex ST formulation and labeling for postoperative or traumatic ocular inflammation.
The principal design-around routes are substitution of the polymer, electrolyte, pH, viscosity profile, or product labeling.
The patent is relevant to ANDA litigation and Paragraph IV analysis, not biosimilar litigation.
The recorded patent-term endpoint is September 8, 2025.

FAQs About US Patent 8,101,582

Does US 8,101,582 cover generic tobramycin/dexamethasone eye drops?

No. It covers only products and methods meeting the claimed polymer, electrolyte, pH, viscosity, and treatment limitations. A generic product using a different formulation may fall outside the claims.

Is Tobradex ST protected by a composition claim in US 8,101,582?

The supplied claims are method claims. They protect treatment methods using the specified composition rather than claiming the composition in purely product-by-composition form.

Can a generic use xanthan gum without infringing?

Potentially, but the claim requires deacetylated xanthan gum. The manufacturer would need to establish that its polymer and formulation do not meet the claimed limitation, including under any doctrine-of-equivalents analysis.

Does a different electrolyte avoid US 8,101,582?

It may avoid narrower claims requiring sodium chloride or sodium sulfate. It may not avoid broader claims that cover inorganic electrolytes, organic buffering agents, or combinations, depending on the formulation and the interpretation of the ionic-interaction limitation.

Is a biosimilar application relevant to Tobradex ST?

No. Tobramycin/dexamethasone ophthalmic suspension is a small-molecule drug product. The relevant FDA pathway is an ANDA, not a biosimilar application under the Public Health Service Act.

References

United States Patent No. 8,101,582. (2012). Ophthalmic compositions containing xanthan gum. United States Patent and Trademark Office.
U.S. Food and Drug Administration. (2025). Approved drug products with therapeutic equivalence evaluations. FDA, Center for Drug Evaluation and Research.
U.S. Food and Drug Administration. (n.d.). Tobradex ST ophthalmic suspension prescribing information. Alcon Laboratories, Inc.

Applicant	Tradename	Generic Name	Dosage	NDA	Approval Date	TE	Type	RLD	RS	Patent No.	Patent Expiration	Product	Substance	Delist Req.	Patented / Exclusive Use	Submissiondate
Harrow Eye	TOBRADEX ST	dexamethasone; tobramycin	SUSPENSION/DROPS;OPHTHALMIC	050818-001	Feb 13, 2009		RX	Yes	Yes	8,101,582	⤷ Start Trial	Y			USE OF A COMBINATION OF TOBRAMYCIN AND DEXAMETHASONE TO TREAT OCULAR INFLAMMATION WHERE AN INFECTION OR RISK OF INFECTION EXISTS	⤷ Start Trial
>Applicant	>Tradename	>Generic Name	>Dosage	>NDA	>Approval Date	>TE	>Type	>RLD	>RS	>Patent No.	>Patent Expiration	>Product	>Substance	>Delist Req.	>Patented / Exclusive Use	>Submissiondate

Details for Patent: 8,101,582

Which drugs does patent 8,101,582 protect, and when does it expire?

Summary for Patent: 8,101,582