United States Patent 4,770,183: Scope, Claims, Expiration, and MRI Contrast-Agent Patent Landscape

US Patent 4,770,183 covers methods of magnetic resonance imaging using biodegradable superparamagnetic metal oxide particles, including uncoated particles and particles coated with dextran, albumin, or related biodegradable polymers. The patent is a method-of-use patent, not a broad composition patent. It issued on September 13, 1988, and its 17-year patent term expired on September 13, 2005, absent an applicable adjustment or extension. The patent therefore has no current blocking effect on MRI contrast-agent development or generic entry.

The commercial concept most closely associated with the patent is the use of dextran-coated superparamagnetic iron oxide particles for liver and reticuloendothelial-system imaging. Feridex Injection, also known as ferumoxides, later received FDA approval for hepatic MRI. The claims are technically broad in their choice of organs and administration routes, but they are limited by particle size, magnetic properties, biodegradation, and imaging-method requirements.

What does US Patent 4,770,183 protect?

US 4,770,183 protects a method of obtaining an in vivo NMR image by administering biodegradable superparamagnetic metal oxide particles as a contrast agent.

The central claim elements are:

Claim element	Requirement
Imaging modality	In vivo NMR imaging, the terminology used before MRI became standard
Subject	Animal or human subject
Agent	A dispersoid containing superparamagnetic metal oxide particles
Carrier	Physiologically acceptable carrier
Particle structure	Uncoated particles or polymer-coated particles
Crystal size	Approximately 10 to 500 angstroms in claims 1 and 2
Overall particle size	Approximately 10 to 5,000 angstroms, measured on a Coulter particle size analyzer
Biological behavior	Retention long enough to obtain an image and ultimate biodegradation within approximately seven days
Imaging targets	Reticuloendothelial organs, neural tissue, lung, gastrointestinal tract, lymph, lymph nodes, and related tissues
Administration	Intravascular, oral, intubation, or enema administration
Dose	Up to approximately 250 mg/kg in claim 13

The patent does not claim every MRI contrast agent. A product or method would need to satisfy the limitations of at least one claim, including the particle characteristics and biodegradation requirement.

How are claims 1 and 2 different?

Claims 1 and 2 are the two independent claims.

Claim 1 covers uncoated biodegradable superparamagnetic metal oxide particles. Claim 2 covers particles having a superparamagnetic metal oxide core generally surrounded by a biodegradable polymeric coat.

The coated-particle claim is particularly important because it reaches the architecture used by several early superparamagnetic iron oxide contrast agents. The coat is not merely a formulation excipient under claim 2. It is part of the claimed particle and must be biodegradable.

Claim 1: uncoated particles

Claim 1 requires:

A dispersoid;
Uncoated biodegradable superparamagnetic metal oxide particles;
Crystals within the specified size range;
An overall particle diameter within the specified range;
Retention sufficient to permit imaging; and
Biodegradation in the organ or tissue within approximately seven days.

The claim is not limited to iron oxide. Claim 3 narrows the invention to iron oxide particles, but claim 1 on its face reaches other biodegradable superparamagnetic metal oxides if they satisfy the remaining limitations.

Claim 2: coated particles

Claim 2 requires a superparamagnetic metal oxide core surrounded generally by a biodegradable polymeric coat. The overall diameter includes the coat.

This structure creates two separate size inquiries:

The individual metal oxide crystals must be approximately 10 to 500 angstroms.
The entire particle, including the polymeric coat, must be approximately 10 to 5,000 angstroms.

A product with a compliant iron oxide core but an oversized coated particle would not satisfy the express overall-diameter limitation.

What technical limitations are imposed by claim 3?

Claim 3 narrows claims 1 and 2 to iron oxide particles with four additional characteristics:

Claim 3 limitation	Claimed range or threshold
Crystal diameter	Approximately 50 to 500 angstroms
Surface area	Greater than approximately 75 m²/gram
Magnetic saturation	Approximately 5 to 50 EMU/gram of iron oxide
Magnetic squareness	Less than 0.1

These parameters distinguish a low-remanence, superparamagnetic material from a conventional ferromagnetic or highly coercive particle.

Magnetic squareness below 0.1 indicates that the material has limited residual magnetization after removal of an applied magnetic field. That characteristic supports redispersion and reduces the tendency of particles to remain magnetically aggregated. The claimed saturation range also limits the magnetic loading and particle structure.

A formulation may satisfy the broad particle language in claims 1 or 2 without satisfying claim 3. Claim 3 is therefore a narrower fallback position rather than a requirement for every asserted infringement theory.

What formulations are protected by claims 4 through 8?

Claims 4 through 8 address the polymeric coating used in claim 2.

Claim	Coating limitation
4	Carbohydrates, proteins, or composites of carbohydrates and proteins
5	Albumin
6	Human serum albumin or bovine serum albumin
7	Dextran with molecular weight of 5,000 to 250,000 daltons
8	Dextran of approximately 9,000, 17,900, 35,600, 71,000, or 249,000 daltons

The dextran claims are commercially significant. Dextran coating affects particle stability, biodistribution, uptake by macrophages, circulation behavior, and biodegradation. The claims, however, do not cover every dextran-coated iron oxide particle without qualification. The product must also satisfy the underlying limitations of claim 2 and, for claim 8, the specified molecular-weight categories.

The use of albumin or dextran alone does not establish infringement. The full particle and imaging method must be evaluated, including size, biodegradation, superparamagnetism, administration, and the organ or tissue imaged.

Which administration routes are covered?

Claims 9 through 12 add administration-route limitations.

Claim	Administration or carrier
9	Intravascular injection
10	Oral administration, intubation, or enema
11	Intravascular administration using normal saline or distilled water
12	Oral administration, intubation, or enema using distilled water

The patent therefore contemplated both systemic and gastrointestinal imaging. The gastrointestinal claims were technically broader than the commercial use later associated with ferumoxides.

A method using a different carrier could fall within claims 1 or 2 if the carrier is physiologically acceptable. Claims 11 and 12 are narrower dependent claims and should not be treated as limitations of the independent claims.

Which organs and tissues are covered?

Claims 14 through 25 extend the claimed imaging method to several anatomical targets.

Claim group	Covered target
14	Reticuloendothelial system
15	Liver
16	Spleen
17	Bone marrow
18	Lymph or lymph nodes
19	Neural tissue
20	Lung
21	Gastrointestinal tract
22	Esophagus
23	Stomach
24	Small intestine
25	Large intestine

The liver and spleen are the most commercially relevant targets because superparamagnetic iron oxide particles are taken up by Kupffer cells and other reticuloendothelial-system macrophages. Lesions with different macrophage content can produce altered signal intensity relative to normal hepatic tissue.

The patent is not confined to oncology, liver lesion characterization, or any single diagnostic indication. The claims use anatomical categories rather than disease-specific patient selection.

When did US Patent 4,770,183 expire?

US 4,770,183 issued on September 13, 1988. For a pre-URAA US patent of this type, the ordinary term was generally 17 years from issuance. On that basis, the patent expired on September 13, 2005. The public patent record identifies the patent as issued to Advanced Magnetics, Inc. and describes the invention as MRI using biodegradable particles (USPTO, 1988; Google Patents, n.d.).

Event	Date
Patent issued	September 13, 1988
Ordinary patent term	17 years from issuance
Expiration	September 13, 2005
Current status	Expired
Current blocking effect	None

The patent cannot support a present-day infringement action for conduct occurring after expiration. Its technical disclosures can remain relevant as prior art, but the expired claims do not create current exclusivity.

What was the FDA status of the associated MRI contrast technology?

Feridex Injection, containing ferumoxides, was approved by the FDA in the 1990s for use as an MRI contrast agent, particularly for hepatic imaging. Ferumoxides consisted of superparamagnetic iron oxide particles associated with dextran and were designed for uptake by the reticuloendothelial system. The product was marketed in the United States through the Advanced Magnetics and Berlex/Schering commercial network.

Feridex was later discontinued commercially. The discontinuation did not revive US 4,770,183 or create a new patent term. FDA drug status and patent status are separate questions. An approved or discontinued product does not extend an expired patent.

Was the patent listed in the Orange Book?

There is no present Orange Book exclusivity associated with US 4,770,183. The patent expired in 2005, and the original Feridex product is no longer an active commercial platform in the US market.

Orange Book listing analysis must be performed against the specific NDA and approved labeling. A method patent covering MRI use does not automatically become an Orange Book-listed patent. FDA Orange Book listings generally concern patents submitted by NDA sponsors for approved drug substances, drug products, or approved methods of use under the applicable statutory framework (FDA, 2024).

Were there Paragraph IV challenges to US 4,770,183?

No current Paragraph IV risk attaches to US 4,770,183 because the patent expired nearly two decades ago. A Paragraph IV certification is relevant when an ANDA applicant asserts that a listed patent is invalid, unenforceable, or will not be infringed. It has no practical role for an expired patent.

The historical commercial product also does not create a current Paragraph IV barrier merely because its original approval relied on technology described in the patent. Any modern abbreviated application would be evaluated against currently listed patents for the relevant reference product, if any, and against FDA requirements for the proposed dosage form and indication.

What patent landscape surrounded biodegradable superparamagnetic iron oxide agents?

The patent landscape developed along several distinct lines:

Technology area	Typical patent subject matter	Relevance to US 4,770,183
Particle composition	Iron oxide crystal size, morphology, magnetic properties	Claim 3 and related composition patents
Surface coating	Dextran, albumin, carbohydrate-protein coatings	Claims 2 and 4 through 8
MRI use	Liver, spleen, lymph-node, marrow, and gastrointestinal imaging	Claims 1, 2, and 14 through 25
Formulation	Injectable dispersions, carriers, concentration, stability	Claims 9 through 13 and later formulation patents
Manufacturing	Precipitation, oxidation, coating, purification, particle-size control	Potentially separate process patents
Clinical use	Lesion detection, organ-specific imaging, macrophage targeting	Later method-of-use patents
Alternative agents	Ferucarbotran, ferumoxtran-10, ferumoxytol, and other iron oxides	Separate product and use estates

The key competitive products included:

Ferumoxides, marketed as Feridex in the United States and Endorem in some non-US markets;
Ferucarbotran, marketed as Resovist in certain jurisdictions;
Ferumoxtran-10, developed as Combidex or Sinerem but not broadly approved in the United States; and
Ferumoxytol, marketed as Feraheme for iron-deficiency anemia rather than as an FDA-approved MRI contrast agent.

These products did not share identical patent positions. Differences in crystal size, hydrodynamic diameter, polymer coating, molecular weight, administration, indication, and manufacturing process could place them outside particular claims of US 4,770,183 while potentially implicating other patents.

How strong was the patent estate?

The patent was commercially important historically but is legally weak today because it is expired.

During its term, its strongest features were:

Coverage of both uncoated and coated particle methods;
Explicit coverage of dextran and albumin coatings;
Broad anatomical coverage;
Coverage of systemic and gastrointestinal administration; and
Technical parameters directed to superparamagnetic behavior and biodegradation.

Its principal limitations were:

It was a method patent rather than a general composition patent;
It required a specific in vivo imaging method;
It required biodegradation within approximately seven days;
It imposed particle-size and, for claim 3, magnetic-property limitations;
Some limitations are technically difficult to prove without access to particle-characterization data; and
The patent did not by itself cover later agents that used materially different coatings, particle dimensions, or imaging protocols.

The patent would have been more difficult to assert against a modern product designed outside the stated size, magnetic, or biodegradation ranges. Its expired status now eliminates the economic value of those distinctions except as historical prior art or evidence of technology lineage.

What manufacturing and IP barriers remain after expiration?

Expiration of US 4,770,183 does not eliminate all barriers to commercialization.

A current developer may still face:

Separate patents covering particle synthesis or coating chemistry;
Manufacturing reproducibility requirements for size and magnetic properties;
Sterility and endotoxin controls for injectable products;
Aggregation and shelf-life problems;
Dose-related safety requirements;
FDA clinical and chemistry, manufacturing, and controls requirements;
New patents directed to specific clinical uses or formulations; and
Freedom-to-operate issues in jurisdictions where corresponding patents had different terms.

The principal technical barrier is control of the hydrodynamic particle population. The patent measures overall diameter by Coulter analysis, while modern products may be characterized using dynamic light scattering, electron microscopy, number-weighted distributions, or other methods. These measurements are not interchangeable for regulatory or patent purposes.

Which companies challenged or licensed the technology?

The principal historical commercial participants were Advanced Magnetics, Inc., the original patent holder and developer, and Berlex Laboratories, associated with the US marketing of Feridex. Berlex was part of the Schering organization, later associated with Bayer through corporate transactions.

Publicly reported commercial arrangements support a licensing or marketing relationship around Feridex, but the detailed economic terms of the underlying agreement are not established by the patent itself. No current licensing requirement arises from US 4,770,183 because the patent expired.

There is also no current biosimilar pathway for this technology. Iron oxide MRI agents are generally regulated as drug products rather than biologics, so biosimilar terminology does not ordinarily apply. A follow-on product would more likely involve an NDA, abbreviated pathway where available, or a new drug development program depending on the reference product and proposed labeling.

What generic launch scenarios existed and what remains?

During the patent term, a generic or follow-on developer would have faced three potential strategies:

Wait for patent expiration;
File an ANDA with a Paragraph IV certification against listed patents; or
Develop a materially different particle or indication outside the asserted claims.

After September 13, 2005, the patent itself no longer prevented launch. The remaining commercial obstacles were the absence of a widely marketed US reference product, clinical-development costs, manufacturing complexity, and limited demand for liver-specific superparamagnetic contrast agents after the adoption of alternative MRI techniques and contrast products.

A modern entrant based on dextran-coated iron oxide would likely need to address safety, biodistribution, MRI performance, dosage, and product-specific FDA requirements rather than US 4,770,183.

How does US 4,770,183 compare with later iron oxide contrast patents?

US 4,770,183 is principally a platform method patent. Later patent families generally pursued narrower commercial objectives:

Patent strategy	US 4,770,183	Later-generation patent strategy
Claim type	MRI method of use	Composition, formulation, process, or specific clinical use
Agent scope	Biodegradable superparamagnetic metal oxides	Often a defined iron oxide core, coating, or particle distribution
Coatings	Dextran, albumin, carbohydrate-protein systems	Specific polymers, ligands, or surface chemistries
Organs	Broad anatomical list	Often defined indications or imaging protocols
Current status	Expired	Depends on individual family and jurisdiction
Commercial relevance	Historical platform	Product-specific freedom-to-operate and regulatory analysis

Key Takeaways

US 4,770,183 covers MRI methods using biodegradable superparamagnetic metal oxide particles.
Claims 1 and 2 distinguish uncoated and polymer-coated particles.
Claim 3 narrows the invention to iron oxide with specified crystal size, surface area, magnetic saturation, and magnetic squareness.
Claims 4 through 8 cover albumin and specified dextran coatings.
Claims 9 through 13 address administration routes, carriers, and dose.
Claims 14 through 25 cover liver, spleen, bone marrow, lymph nodes, neural tissue, lung, and gastrointestinal imaging.
The patent issued on September 13, 1988, and its ordinary 17-year term expired on September 13, 2005.
The patent has no current Orange Book or Paragraph IV significance.
Feridex was the principal commercial product associated with the technology, but its discontinuation does not restore patent exclusivity.
Current freedom-to-operate analysis must focus on later composition, manufacturing, formulation, and clinical-use patents.

Frequently Asked Questions

Is US Patent 4,770,183 still enforceable?

No. Its ordinary patent term expired on September 13, 2005.

Does the patent cover all iron oxide MRI contrast agents?

No. It covers only methods using particles that satisfy the claimed structural, magnetic, size, biodegradation, and imaging limitations.

Did US 4,770,183 cover Feridex?

The patent covers the claimed technical approach associated with dextran-coated biodegradable superparamagnetic iron oxide imaging agents. Product-specific infringement would require comparison with the actual Feridex formulation and each claim limitation.

Can a company commercialize a dextran-coated iron oxide MRI agent today?

The expired patent does not prevent commercialization. A company must still address current FDA requirements and separate patents covering composition, manufacturing, formulation, or clinical use.

Are ferumoxides and ferumoxytol covered by the same patent estate?

Not necessarily. Ferumoxides and ferumoxytol differ in approved use, formulation, particle architecture, manufacturing, and regulatory status. Each requires separate patent and regulatory analysis.

References

Food and Drug Administration. (2024). Approved drug products with therapeutic equivalence evaluations. U.S. Department of Health and Human Services.

Google Patents. (n.d.). US4770183A: Magnetic resonance imaging using biodegradable particles. Google.

U.S. Patent and Trademark Office. (1988). U.S. Patent No. 4,770,183: Magnetic resonance imaging using biodegradable particles. U.S. Department of Commerce.

Country	Patent Number	Estimated Expiration	Supplementary Protection Certificate	SPC Country	SPC Expiration
Austria	135920	⤷ Start Trial
Austria	139431	⤷ Start Trial
Austria	142891	⤷ Start Trial
Austria	143604	⤷ Start Trial
Austria	143814	⤷ Start Trial
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Details for Patent: 4,770,183

Summary for Patent: 4,770,183