Details for Patent: 6,287,539
Summary for Patent: 6,287,539
| Title: | Methods of imaging using osmotically stabilized microbubble preparations | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Abstract: | A microbubble preparation formed of a plurality of microbubbles comprising a first gas and a second gas surrounded by a membrane such as a surfactant, wherein the first gas and the second gas are present in a molar ratio of from about 1:100 to about 1000:1, and wherein the first gas has a vapor pressure of at least about (760-x) mm Hg at 37° C., where x is the vapor pressure of the second gas at 37° C., and wherein the vapor pressure of each of the first and second gases is greater than about 75 mm Hg at 37° C.; also disclosed are methods for preparing microbubble compositions, including compositions that rapidly shrink from a first average diameter to a second average diameter less than about 75% of the first average diameter and are stabilized at the second average diameter; methods and kits for preparing microbubbles; and methods for using such microbubbles as contrast agents. | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Inventor(s): | Ernest G. Schutt, Charles David Anderson, David P. Evitts | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Assignee: | PHOTOGEN TECHNOLOGIES Inc , TARGESON Inc | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Application Number: | US08/841,846 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Patent Claim Types: see list of patent claims | Use; Dosage form; | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Patent landscape, scope, and claims: | United States Drug Patent 6,287,539: Claim Scope, Expiration, Patent Landscape, and Infringement RiskU.S. Patent No. 6,287,539 covers imaging methods using osmotically stabilized microbubbles containing a relatively soluble modifier gas and a relatively insoluble gas osmotic agent. The patent focuses on ultrasound and magnetic-resonance imaging, particularly vascular, myocardial, and perfusion imaging. Its core patent term has expired, leaving no current U.S. exclusionary right based on the issued claims. The technology remains relevant as prior art and as a technical ancestor of modern ultrasound contrast-agent platforms. What does U.S. Patent 6,287,539 protect?The patent protects methods of imaging that use microbubbles with a two-gas architecture:
The central stabilization theory is that the insoluble gas dilutes the soluble gas. Once introduced into physiological liquid, dissolved gases can diffuse into the bubble and generate osmotic pressure sufficient to offset Laplace pressure, slowing bubble dissolution. The patent describes this as osmotic stabilization rather than relying solely on a slowly diffusible perfluorocarbon gas or a rigid shell. (U.S. Patent No. 6,287,539, 2001). The patent does not claim a particular commercial drug product by brand name. It claims methods involving defined microbubble compositions and imaging uses. How many independent claims are in U.S. Patent 6,287,539?The supplied claim set has four principal independent claim groups:
The remaining claims are dependent claims directed to gas identity, membrane composition, delivery route, imaging target, preparation method, bubble size, and gas ratios. Claim 1: broadest issued method conceptClaim 1 requires:
The listed gas osmotic agents include perfluoropentane, perfluorohexane, perfluorocyclohexane, perfluoroheptane, perfluorocycloheptane, perfluoromethylcyclohexane, perfluorodimethylcyclopentane, perfluorotrimethylcyclobutane, and perfluorotriethylamine. Claim 1 is composition-specific through the required gas combination, but it is not limited to a particular surfactant, protein, lipid, particle size, anatomical site, or administration route. Claim 53: vapor-phase osmotic agentClaim 53 covers a similar imaging method in which the gas osmotic agent is the vapor of a compound that is liquid at 37°C and 760 Torr. Claim 54 narrows the class to higher-boiling perfluorinated compounds such as perfluorohexane and perfluoroheptane. This claim group is narrower than claim 1 in its physical-property requirement but potentially broader in the manner in which the osmotic agent is described. The claim does not require the membrane to be lipid, protein, or surfactant-based. Claim 70: preparation and activation methodClaim 70 is directed to a containerized preparation in which precursor components are converted into microbubbles by applying energy. The claim requires:
Dependent claims 77 through 87 focus on emulsified liquid perfluoropentane, pressure reduction, boiling, and a syringe container. This is the most relevant claim group for a point-of-care or reconstituted injectable contrast-agent format. Claim 92: proteinaceous microbubble membraneClaim 92 requires a proteinaceous membrane and a relatively soluble modifier gas combined with a relatively insoluble osmotic gas. Claim 102 specifies albumin. This group is technically relevant to albumin-shelled ultrasound contrast agents. It requires the osmotic two-gas mechanism, however, rather than merely an albumin shell and a perfluorocarbon gas. What gases and formulations are protected?Modifier gasesClaims 2, 3, 55, 56, 75, 97, and related claims cover fluorocarbon modifier gases, including:
Claims 4, 5, 57, 58, 73, 74, 95, and 96 cover nonfluorocarbon gases, including:
The claim architecture generally treats the modifier gas as the more water-soluble component and the gas osmotic agent as the more water-insoluble component. Gas osmotic agentsThe principal osmotic agents are fluorocarbons with low water solubility. The most commercially relevant claimed examples are:
Claim 6 adds a water-solubility limitation of not more than approximately 0.5 mM at 25°C and one atmosphere. Membrane materialsThe claims cover three principal membrane categories:
Claim 37 and related claims specifically identify mixtures of phospholipids and polyoxyethylene-polyoxypropylene copolymers. Claims 38 and 48 add hydroxyethyl starch. These formulation limitations can create a narrower infringement pathway where a product uses the claimed gas pair and ratio but does not fall within the broadest membrane description. What imaging uses are covered?Claims 49 through 52, 67 through 69, and 88 through 91 cover:
The patent therefore reaches the principal clinical use case for injectable ultrasound contrast agents: intravascular enhancement and myocardial perfusion assessment. The claims also cover imaging of an object or body cavity and are not limited to human diagnostic use. The method language can encompass veterinary, research, and nonhuman applications if all claim elements are present. What is the scope of the gas-ratio limitations?The core ratio is stated as the molar ratio of modifier gas to gas osmotic agent. Claim 1 recites approximately 1:100 to 1,000:1. This is an unusually broad numerical range spanning five orders of magnitude. The later claims attempt to create narrower ratio bands:
The ratio is a central limitation. A product using the same gas species but outside the claimed ratio would have a potential non-infringement position, subject to claim construction and the doctrine of equivalents. The record supplied contains apparent drafting or transcription defects. For example, claims 124 through 126 depend on themselves or on improperly numbered claims, and several claims contain typographical errors such as "1.000:1," "fluorocabon," and "sad emulsified." Those defects should be evaluated against the certified patent document, prosecution history, certificates of correction, and any reexamination record. They can affect enforceability, claim construction, or validity analysis, particularly for the later-added ratio and particle-size claims. What patent expiration date applies to U.S. Patent 6,287,539?The patent issued on September 11, 2001. Its effective U.S. patent term was governed by the 20-year term measured from the earliest effective nonprovisional filing date under 35 U.S.C. §154. Based on the patent’s priority and filing history, the ordinary term ended in 2017, subject to any patent-term adjustment, terminal disclaimer, or other prosecution-specific modification shown in the USPTO file. (United States Patent and Trademark Office, n.d.-a; U.S. Patent No. 6,287,539, 2001). Accordingly:
The patent is therefore relevant to freedom-to-operate analysis as expired prior art, not as a presently enforceable U.S. blocking patent. Any exact expiration calculation should use the USPTO Patent Center record, including patent-term adjustment and terminal-disclaimer data. (United States Patent and Trademark Office, n.d.-b). What is the Orange Book status of U.S. Patent 6,287,539?U.S. Patent 6,287,539 is not an Orange Book-listed drug patent that currently blocks an abbreviated new drug application. The patent claims imaging methods and microbubble technology rather than a currently marketed active ingredient, formulation, or method of use listed for a small-molecule reference product. An Orange Book listing would not revive an expired patent. A generic applicant cannot face a current patent term from this patent, and no Paragraph IV certification against an expired patent would create a meaningful launch barrier. The relevant FDA framework is the Approved Drug Products with Therapeutic Equivalence Evaluations, commonly called the Orange Book. (U.S. Food and Drug Administration, 2024). Which commercial contrast agents are technically adjacent?The closest commercial products use ultrasound-active gas microspheres but do not necessarily practice the claimed two-gas osmotic mechanism.
FDA labeling describes Definity, Optison, and Lumason as ultrasound contrast agents with different gases and shell technologies. The presence of a lipid or albumin shell alone does not establish infringement of the patent. The gas identity, gas ratio, physical state, and preparation method are critical. (Bracco Diagnostics Inc., 2022; GE Healthcare, 2022; Lantheus Medical Imaging, 2023). How strong was the patent estate?The patent had meaningful historical breadth because it combined:
Its principal weaknesses were structural:
The strongest historical claims were likely claims 1, 53, 70, and 92 because they established separate independent routes to the same technical concept. The strongest product-specific positions were claims 70 and 92 where a manufacturer used a containerized albumin or surfactant formulation with a defined two-gas mixture. What generic entry risks exist today?The direct generic-entry risk from U.S. Patent 6,287,539 is zero because the patent term has ended. There is no current Paragraph IV risk tied to this patent. Commercial entry into ultrasound contrast agents can still face other barriers:
For a competing product, the principal current risk is therefore regulatory and manufacturing execution, not this expired patent. What patent landscape surrounds osmotically stabilized microbubbles?The broader landscape includes five patent clusters: Early ultrasound contrast-agent patentsThese cover gas-filled microspheres, albumin shells, lipid shells, surfactants, and ultrasound image enhancement. They form the technical prior-art base against which the osmotic-stabilization claims were examined. Perfluorocarbon gas patentsThese focus on low-solubility gases such as perfluoropropane, perfluorobutane, and perfluorohexane. Many later commercial products rely on these gases without using the particular soluble-gas dilution mechanism claimed in U.S. 6,287,539. Lipid-shell and phospholipid patentsThese cover shell composition, PEGylation, particle-size control, lyophilized storage, reconstitution, and acoustic response. They are particularly relevant to Definity, Lumason, and related products. Albumin-shell patentsThese cover albumin microspheres and protein cross-linking or heat-denaturation methods. They are particularly relevant to Optison-type technology. Manufacturing and reconstitution patentsThese cover vial or syringe formats, liquid perfluorocarbon emulsions, vacuum-triggered bubble formation, freeze-drying, agitation, and controlled gas loading. Claims 70 through 87 sit in this category. What licensing or litigation history affects the patent?The supplied materials do not establish a current license, assignment, settlement, or active litigation proceeding specifically involving U.S. Patent 6,287,539. Because the patent is expired, any historical license or settlement would have limited present blocking effect unless it included separate surviving rights, confidential obligations, or unrelated patents. No current Paragraph IV litigation is attributable to this expired patent. Current litigation exposure for ultrasound contrast agents would more likely arise from later patents directed to approved products, lipid-shell formulations, manufacturing processes, or imaging methods. Key Takeaways
FAQs About U.S. Patent 6,287,539Does U.S. Patent 6,287,539 cover Definity?Not automatically. Definity uses perflutren in a lipid-shell microsphere. Infringement would require the claimed modifier-gas and gas-osmotic-agent combination, ratio, and other method limitations. The commercial label alone does not establish those elements. Does the patent cover Optison?Optison is an albumin-shelled perflutren product, making it technically closer to claim 92’s proteinaceous-membrane category. The patent would still require the claimed two-gas composition and ratio. The patent is expired in any event. Can a company file a Paragraph IV certification against this patent?A Paragraph IV certification is not a practical current challenge to an expired patent. U.S. Patent 6,287,539 no longer provides a patent-term barrier to generic or follow-on entry. Are the claims limited to human medical imaging?No. The claims refer to an object, body part, or body cavity. Some dependent claims identify vascular, myocardial, perfusion, and intravenous uses, but the independent claims are not limited exclusively to human patients. Does the patent claim the microbubble composition itself?No. The principal claims are method claims. They require use of the microbubble preparation for imaging. The patent does not present a standalone composition claim in the supplied claim set. ReferencesBracco Diagnostics Inc. (2022). Lumason (sulfur hexafluoride lipid-type A microspheres) prescribing information. U.S. Food and Drug Administration. GE Healthcare. (2022). Optison (perflutren protein-type A microspheres) prescribing information. U.S. Food and Drug Administration. Lantheus Medical Imaging. (2023). Definity (perflutren lipid microsphere) prescribing information. U.S. Food and Drug Administration. United States Patent and Trademark Office. (n.d.-a). Patent term adjustment. https://www.uspto.gov/patents/laws/patent-term-adjustment United States Patent and Trademark Office. (n.d.-b). Patent Center. https://patentcenter.uspto.gov/ U.S. Food and Drug Administration. (2024). Approved drug products with therapeutic equivalence evaluations. https://www.fda.gov/drugs/drug-approvals-and-databases/orange-book U.S. Patent No. 6,287,539. (2001). Osmotically stabilized microbubbles. United States Patent and Trademark Office. More… ↓ |
Drugs Protected by US Patent 6,287,539
| Applicant | Tradename | Generic Name | Dosage | NDA | Approval Date | TE | Type | RLD | RS | Patent No. | Patent Expiration | Product | Substance | Delist Req. | Patented / Exclusive Use | Submissiondate |
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| >Applicant | >Tradename | >Generic Name | >Dosage | >NDA | >Approval Date | >TE | >Type | >RLD | >RS | >Patent No. | >Patent Expiration | >Product | >Substance | >Delist Req. | >Patented / Exclusive Use | >Submissiondate |
International Family Members for US Patent 6,287,539
| Country | Patent Number | Estimated Expiration | Supplementary Protection Certificate | SPC Country | SPC Expiration |
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| Austria | 281183 | ⤷ Start Trial | |||
| Australia | 4922196 | ⤷ Start Trial | |||
| Australia | 5199701 | ⤷ Start Trial | |||
| Australia | 694135 | ⤷ Start Trial | |||
| Australia | 731099 | ⤷ Start Trial | |||
| Australia | 731671 | ⤷ Start Trial | |||
| Australia | 7478294 | ⤷ Start Trial | |||
| >Country | >Patent Number | >Estimated Expiration | >Supplementary Protection Certificate | >SPC Country | >SPC Expiration |
