United States Patent 4,954,298: Scope, Claims, Expiration, and Patent Landscape for Sustained-Release Microcapsules

U.S. Patent No. 4,954,298 protects a manufacturing process for injectable, sustained-release microcapsules containing water-soluble drugs, particularly peptide drugs. Its central limitation is control of the W/O emulsion viscosity before formation of the W/O/W emulsion and in-water drying. The patent does not broadly claim a drug, a finished dosage form, or a composition independent of the manufacturing process.

The patent issued in 1990 and, absent an unusual term adjustment or extension, expired in 2007 under the 17-year term applicable to pre-June 8, 1995 U.S. applications. It therefore does not present a current U.S. blocking right. Its technical disclosure remains relevant to long-acting injectable formulations, especially polylactic acid and poly(lactic-co-glycolic acid), or PLGA, microspheres containing peptide drugs.

What does U.S. Patent 4,954,298 cover?

The patent covers a two-stage emulsion process:

A water-soluble drug is dissolved in an internal aqueous phase.
The internal aqueous phase is dispersed into an organic phase containing a biodegradable polymer to form a W/O emulsion.
The W/O emulsion viscosity is adjusted to approximately 150 to 10,000 centipoises.
The W/O emulsion is dispersed into an external aqueous phase, producing a W/O/W emulsion.
Organic solvent is removed by in-water drying, producing injectable sustained-release microcapsules.

The claimed invention is directed to process control. The patent links viscosity adjustment to control of polymer concentration, phase ratios, temperature, or combinations of those parameters.

The principal technical objective is to improve microcapsule formation by controlling the viscosity of the primary W/O emulsion before it is introduced into the external aqueous phase. That control can affect particle formation, drug entrapment, porosity, solvent removal, and release characteristics.

What are the independent claims of U.S. Patent 4,954,298?

The two principal independent claims are claims 1 and 14.

Claim	Claim type	Core limitations
1	Process claim	W/O emulsion containing a water-soluble drug and biodegradable polymer; viscosity adjusted to about 150-10,000 cP; W/O/W formation; in-water drying
14	Process claim	Water-soluble drug solution, biodegradable polymer in organic solvent, viscosity adjustment to 150-10,000 cP, second aqueous phase, solvent removal by in-water drying

Claim 1 is broader in its description of the viscosity-adjustment mechanisms. It expressly includes:

Increasing polymer concentration;
Adjusting the aqueous-to-oil phase ratio;
Adjusting the W/O emulsion temperature;
Adjusting the external aqueous phase temperature;
Adjusting the temperature during infusion through a line heater or cooler;
Using those procedures in combination.

Claim 14 is a more streamlined process claim. It requires the same general process sequence but does not recite every alternative viscosity-control mechanism in the body of the claim.

The claims are process claims. A product made by the process could be relevant to infringement only where the statutory requirements for process-product liability are met, such as importation of a product made by a patented process under 35 U.S.C. § 271(g). The patent does not independently claim all sustained-release microspheres containing a particular peptide or polymer.

How broad is the viscosity limitation?

The central numerical limitation is a W/O emulsion viscosity of approximately 150 to 10,000 centipoises.

Dependent claims narrow the range:

Claim	Viscosity range
1	About 150-10,000 cP
2	About 150-5,000 cP
3	About 150-10,000 cP, adjusted through temperature
14	150-10,000 cP
15	150-5,000 cP

The viscosity is measured at a particular process stage: while preparing the W/O/W emulsion and before or during dispersion into the external aqueous phase. A process that reaches the claimed viscosity only after the W/O/W emulsion has been formed would present a claim-construction issue because the claims focus on the W/O emulsion used in preparing the W/O/W emulsion.

The range is functional as well as numeric. The process must adjust viscosity using one or more identified operating variables. A manufacturer that happens to obtain a viscosity within the range without using the claimed adjustment procedure would have a potential noninfringement position, although the precise result would depend on the claim language and prosecution history.

What formulations are protected by the patent?

The patent protects process embodiments using:

Water-soluble drugs;
Biologically active polypeptides;
Polylactic acid;
Copolymers of lactic acid and glycolic acid;
In-water drying of W/O/W emulsions;
Stirring during solvent removal;
Gradual pressure reduction during drying.

Claim 8 identifies the peptide:

(Pyr)Glu-His-Trp-Ser-Tyr-D-Leu-Leu-Arg-Pro-NH-C2H5 acetate

This is leuprolide acetate, a gonadotropin-releasing hormone agonist used in long-acting depot products. The claim language identifies the peptide as one embodiment of a biologically active polypeptide. It does not convert the patent into a composition patent covering every leuprolide acetate depot.

Claims 9 through 11 address the polymer:

Claim	Polymer limitation
9	Polylactic acid
10	Copolymer of lactic acid and glycolic acid
11	Approximately 75±2 mole% lactic acid and 25±2 mole% glycolic acid

The 75:25 lactic acid:glycolic acid limitation is important because PLGA composition affects degradation rate, water penetration, drug diffusion, and release duration. The patent therefore reaches a defined formulation-manufacturing window rather than only a generic biodegradable-polymer process.

What are the key dependent claims?

Claims	Subject matter	Scope effect
2, 15	150-5,000 cP viscosity	Narrows the viscosity window
3, 4	Temperature-controlled viscosity; approximately -20°C to solvent boiling point, with 0°C-30°C preferred	Adds temperature limitations
5	Polymer concentration of approximately 10%-80%	Narrows the oil-phase formulation
6	Aqueous-to-oil phase ratio of approximately 1%-50%	Adds phase-ratio limitation
7, 17	Biologically active polypeptide	Narrows the drug class
8	Leuprolide acetate	Narrows to a specific peptide
9	Polylactic acid	Narrows the polymer
10, 11, 18	Lactic acid-glycolic acid copolymer, including approximately 75:25 composition	Narrows to PLA/PLGA
12, 19	Standing under stirring during in-water drying	Adds drying operation
13, 20	Gradual pressure reduction while stirring	Adds a specific solvent-removal technique

Claim 16 combines several numerical limitations: temperature of approximately 0°C-30°C, polymer concentration of approximately 10%-80% by weight, and a W/O-emulsion ratio of approximately 1/100 to 1/2 by volume. This is a narrower process window than claim 14.

Does the patent cover leuprolide depot products?

The patent covers a method that uses leuprolide acetate as the water-soluble biologically active polypeptide and produces injectable sustained-release microcapsules through the claimed emulsion process.

It does not, based on the supplied claims, independently cover:

All leuprolide acetate formulations;
All leuprolide acetate microspheres;
All injectable GnRH agonist depots;
A particular release profile without the claimed manufacturing steps;
A finished product regardless of how it was manufactured.

The patent must be analyzed with the separate composition, formulation, dosage, and method-of-treatment patents associated with leuprolide products. Those rights may have had different expiration dates and different assignees or licensees.

When did U.S. Patent 4,954,298 lose exclusivity?

U.S. Patent 4,954,298 issued in 1990. For an application governed by the pre-1995 patent-term rules, the ordinary term was 17 years from issuance. On that basis, the patent expired in 2007.

Event	Approximate timing
U.S. patent application filed	Before June 8, 1995
Patent issued	1990
Ordinary term	17 years from issuance
Expected expiration	2007
Current enforceability	No ordinary enforceable patent term remains

The patent is not a current U.S. exclusivity barrier. A patent term extension under 35 U.S.C. § 156 is generally associated with regulatory review of a covered product and would not ordinarily be expected for this type of manufacturing patent. The applicable current status should be confirmed against the official USPTO record and patent-term data.

Is U.S. Patent 4,954,298 an Orange Book patent?

The patent claims a manufacturing method rather than a drug substance, drug product, or method of use. It therefore is not the type of patent ordinarily listed in the FDA Orange Book under the principal categories of:

Active ingredient;
Drug product composition or formulation;
Method of use.

A process patent may still affect commercial manufacturing or importation, but its absence from the Orange Book would not eliminate ordinary patent-law exposure while the patent remained in force. Because U.S. Patent 4,954,298 expired years ago, it does not currently create an Orange Book-based Paragraph IV obstacle.

The Orange Book analysis for a leuprolide product must be performed separately against the relevant reference-listed drug and its listed patents. The supplied claims alone do not establish any Orange Book listing.

What Paragraph IV challenges could have affected this patent?

A Paragraph IV certification is directed to patents listed for an approved drug in the Orange Book. U.S. Patent 4,954,298 is a process patent and does not, from the supplied claim set, appear to be an ordinary Orange Book drug-product or method-of-use patent.

A generic applicant seeking approval for a leuprolide or other peptide depot product could have taken several positions:

The patent was not properly listable in the Orange Book.
The proposed process did not use a W/O/W emulsion.
The W/O emulsion viscosity was outside the claimed range.
The viscosity was not adjusted through a claimed mechanism.
The formulation used a different polymer or phase architecture.
The product was made outside the United States and did not implicate the relevant process-importation provisions.
The patent had expired.

For products approved after the patent’s expiration, the expiration position would be the most direct route. The claims do not create a current Paragraph IV litigation risk.

Which technical steps create the main infringement risk?

The highest-risk process combination would include all of the following:

A water-soluble peptide in an internal aqueous phase;
PLA or PLGA in an organic solvent;
Formation of a W/O primary emulsion;
Adjustment of primary-emulsion viscosity to 150-10,000 cP;
Dispersion into a second aqueous phase;
In-water drying to remove organic solvent;
Injectable sustained-release microspheres.

A process using leuprolide acetate and approximately 75:25 PLGA would fall close to the narrowest commercial embodiment described by the claims. Claims 8 and 11 would be particularly relevant if the manufacturing process also met the viscosity and phase-ratio limitations.

The process would be less exposed on the supplied claims if it used:

A solid-in-oil-in-water or alternative encapsulation process;
Spray drying;
Coacervation;
An aqueous polymer phase;
A polymer other than PLA or PLGA, for claims limited to those materials;
A primary-emulsion viscosity below 150 cP or above 10,000 cP;
A process that does not adjust viscosity through the claimed operating variables;
A nonaqueous external phase;
A drug that is not water soluble, where the claim requires a water-soluble drug.

Because the patent has expired, these distinctions are relevant to historical liability, freedom-to-operate records, and prior-art analysis rather than current U.S. exclusivity.

How strong was the patent estate?

The patent was technically focused and commercially relevant to long-acting peptide depots, but its claim estate was narrow in several respects.

Strength factor	Assessment
Process specificity	High; claims identify a defined emulsion sequence
Numerical limitations	High; viscosity and process ranges provide clear boundaries
Product coverage	Low; no broad independent composition claim in the supplied claims
Drug coverage	Moderate; claim 1 covers water-soluble drugs, while claim 8 narrows to leuprolide acetate
Polymer coverage	Moderate; broad biodegradable-polymer language is narrowed by PLA/PLGA dependent claims
Manufacturing relevance	High for W/O/W microencapsulation
Design-around potential	Moderate to high
Current enforceability	None after expiration

The principal commercial value was likely in enabling a reproducible microencapsulation process for peptide depots. The patent’s weakness as a current blocking right is that competitors could potentially use different encapsulation technologies or wait until expiration. Its strongest historical position would have been against manufacturers using the same W/O/W process with the specified viscosity control.

How does the patent compare with broader drug and formulation patents?

Patent category	Typical protected subject matter	Relationship to U.S. 4,954,298
Drug-substance patent	Peptide or small-molecule structure	Not claimed by the supplied patent
Composition patent	Microsphere composition, excipients, polymer, drug loading	Not independently claimed
Formulation patent	Depot composition, release profile, particle properties	Only indirectly implicated
Method-of-use patent	Treatment indication or dosing regimen	Not claimed
Manufacturing patent	Emulsion formation, drying, process controls	Core subject of U.S. 4,954,298
Device patent	Syringe, reconstitution system, injection device	Not claimed
Regulatory exclusivity	New drug, orphan drug, pediatric exclusivity	Separate from patent rights

A complete product-level freedom-to-operate analysis for a leuprolide depot would need to review all live patents covering the drug, microsphere composition, polymer characteristics, release profile, reconstitution system, manufacturing process, and therapeutic use. U.S. Patent 4,954,298 addresses only one manufacturing layer.

What geographic coverage did the patent provide?

The patent provided rights only in the United States. Related foreign applications may have existed, but foreign patent rights require separate family and national-register analysis.

A U.S. process patent can create exposure for:

Manufacture in the United States;
Use of the patented process in the United States;
Sale or offer for sale of products made by the process in the United States;
Importation into the United States of products made by the patented process, subject to 35 U.S.C. § 271(g).

Expiration of the U.S. patent removed the U.S. patent barrier. It did not automatically terminate corresponding foreign rights, although most counterpart rights from the same period would also be expected to have expired under their applicable national terms.

What licensing and settlement issues should be reviewed?

The claims themselves do not identify any license, settlement, covenant not to sue, or cross-license. A patent-number-only review cannot establish whether the patent was licensed to a product sponsor, assigned during its term, or included in a settlement agreement.

For historical diligence, relevant records would include:

Assignment records;
USPTO maintenance-fee records;
Patent term and certificate records;
District-court complaints and judgments;
Federal Circuit decisions;
ANDA litigation records;
Product-development license agreements;
Foreign counterpart prosecution and litigation.

The absence of a limitation in the patent claims does not establish that no commercial license existed. Licensing arrangements are contractual and are not necessarily disclosed in the patent document.

What generic launch risks exist today?

For U.S. launch planning, U.S. Patent 4,954,298 presents no ordinary current generic-entry risk because its patent term has expired.

The relevant current risks would instead be:

Live Orange Book-listed patents for the reference product;
Later formulation patents;
Later process patents;
Device or reconstitution patents;
Method-of-use patents;
Regulatory exclusivity;
Product-specific approval requirements for peptide depots;
Manufacturing reproducibility and quality controls;
Potential infringement of later PLGA microsphere patents.

For an ANDA or other abbreviated pathway, the applicant would still need to address the regulatory classification and reference-product requirements applicable to the proposed injectable depot. Patent expiration does not remove FDA requirements concerning sterility, particle size, drug loading, release testing, bioequivalence, and manufacturing consistency.

Key Takeaways

U.S. Patent 4,954,298 is a manufacturing patent for injectable sustained-release microcapsules.
Its core invention is adjustment of W/O primary-emulsion viscosity to approximately 150-10,000 cP before W/O/W formation.
The claims cover water-soluble drugs, including biologically active polypeptides and leuprolide acetate.
PLA and PLGA are important claimed polymer embodiments, including approximately 75:25 lactic acid:glycolic acid copolymer.
The patent claims process steps, not a broad leuprolide composition or all sustained-release depot products.
The patent issued in 1990 and is expected to have expired in 2007 under the ordinary pre-1995 patent-term rule.
It is not the type of claim ordinarily associated with an Orange Book drug-substance, drug-product, or method-of-use listing.
Current commercial risk should be assessed against later formulation, process, device, and method-of-use patents.
Historical infringement analysis would focus on W/O/W processing, viscosity adjustment, PLA/PLGA use, and in-water drying.
Foreign counterpart rights, if any, require separate national-register review.

Frequently Asked Questions

Does U.S. Patent 4,954,298 claim Lupron itself?

No. The supplied claims cover a process for making sustained-release microcapsules. Leuprolide acetate is a claimed water-soluble polypeptide embodiment, but the claims do not independently cover every leuprolide product.

Can a manufacturer use the patented microencapsulation process now?

In the United States, the patent’s ordinary term expired years ago. The process may be used without infringing this expired patent, subject to other live patents and applicable regulatory requirements.

Does the 75:25 PLGA limitation apply to every claim?

No. It appears in claim 11 as a dependent limitation. The independent claims are not limited to a 75:25 lactic acid:glycolic acid ratio.

Does a process using PLGA automatically infringe the patent?

No. PLGA use alone is insufficient. The process must also satisfy the applicable emulsion, viscosity, aqueous-phase, solvent-removal, and other limitations of an asserted claim.

Is this patent relevant to biosimilar litigation?

Only indirectly. Leuprolide is a peptide drug rather than a conventional monoclonal antibody biologic. The patent concerns drug-depot manufacturing and would be analyzed separately from biologic or biosimilar exclusivity rules.

References

United States Patent No. 4,954,298, “Method of producing sustained-release microcapsules.” United States Patent and Trademark Office, 1990.
United States Patent and Trademark Office. (2024). Patent term calculator. U.S. Department of Commerce.
U.S. Food and Drug Administration. (2024). Approved drug products with therapeutic equivalence evaluations. Center for Drug Evaluation and Research.
35 U.S.C. §§ 154, 156, 271, 282.
21 U.S.C. § 355.

Foriegn Application Priority Data
Foreign Country	Foreign Patent Number	Foreign Patent Date
Japan	60-22978	Feb 07, 1985
Japan	60-267977	Nov 27, 1985

Country	Patent Number	Estimated Expiration	Supplementary Protection Certificate	SPC Country	SPC Expiration
Austria	61935	⤷ Start Trial
Canada	1260395	⤷ Start Trial
Germany	3678308	⤷ Start Trial
>Country	>Patent Number	>Estimated Expiration	>Supplementary Protection Certificate	>SPC Country	>SPC Expiration

Details for Patent: 4,954,298

Summary for Patent: 4,954,298