United States Patent 4,677,191: Scope, Claims, Expiration, and PLGA Patent Landscape

U.S. Patent 4,677,191 covers catalyst-free lactic acid-glycolic acid copolymers, commonly called PLGA, with a weight-average molecular weight of approximately 5,000 to 30,000 and dispersity of approximately 1.5 to 2. It also covers methods for producing those polymers by heat and reduced pressure without a catalyst. The patent issued on June 30, 1987, and its 17-year U.S. term expired on June 30, 2004. It has no current U.S. blocking effect, no live Orange Book exclusivity, and no present Paragraph IV threat.

The patent remains relevant as prior art for PLGA formulation, drug-delivery, microparticle, microsphere, implant, and depot technologies. Its commercial value today is historical and technical rather than exclusionary.

What does U.S. Patent 4,677,191 protect?

The patent has two principal claim groups:

Composition claims covering a defined catalyst-free lactic acid-glycolic acid copolymer.
Manufacturing claims covering catalyst-free polycondensation under heat and reduced pressure.

The independent claims are claims 1 and 6.

Claim	Claim type	Core limitation
1	Composition	Catalyst-free lactic acid/glycolic acid copolymer; weight-average molecular weight about 5,000-30,000; dispersity about 1.5-2
2	Composition dependent claim	Claim 1 polymer with 50-95 wt% lactic acid and 50-5 wt% glycolic acid
3	Composition dependent claim	Claim 1 polymer with 60-95 wt% lactic acid and 40-5 wt% glycolic acid
4	Composition dependent claim	Claim 1 polymer with 60-85 wt% lactic acid and 40-15 wt% glycolic acid
5	Composition dependent claim	Approximately 75±2 mol% lactic acid and 25±2 mol% glycolic acid
6	Process	Catalyst-free polycondensation of lactic acid, glycolic acid, or low-molecular-weight polymers under heat and reduced pressure
7	Process dependent claim	Low-molecular precursor formed without catalyst, water removed, followed by at least about 10 hours of polycondensation
8	Process dependent claim	Resulting polymer has weight-average molecular weight of about 5,000-30,000
9	Process dependent claim	50-95 wt% lactic acid and 50-5 wt% glycolic acid
10	Process dependent claim	60-95 wt% lactic acid and 40-5 wt% glycolic acid
11	Process dependent claim	60-85 wt% lactic acid and 40-15 wt% glycolic acid
12	Process dependent claim	Approximately 75±2 mol% lactic acid and 25±2 mol% glycolic acid

The claims do not cover every PLGA polymer. They require a particular combination of composition, molecular-weight distribution, and, for process claims, catalyst-free polycondensation conditions.

How should claim 1 be construed?

Claim 1 is a product-by-property claim directed to a copolymer rather than to a finished drug-delivery system.

Catalyst-free limitation

The phrase "free from catalyst" is a central limitation. A polymer manufactured with a conventional esterification or polycondensation catalyst would present a non-infringement argument if the catalyst remained part of the claimed manufacturing process or product definition. The practical legal analysis would depend on whether the accused product itself contains catalyst residues, whether the claim treats catalyst absence as a product limitation, and how the patent specification defines the term.

The claim does not necessarily exclude every processing aid, solvent, initiator, stabilizer, or purification material. It specifically focuses on the absence of a catalyst in producing the copolymer. A process using a catalyst and later removing it would raise a separate claim-construction issue because the product claim is framed as a copolymer "free from catalyst," while the process claims expressly require catalyst-free reaction conditions.

Molecular-weight limitation

The claimed weight-average molecular weight is approximately 5,000 to 30,000. This is narrower than many commercial PLGA grades used in controlled-release products, which may extend into higher molecular-weight ranges.

The molecular-weight limitation creates several analytical issues:

The measurement method can affect the reported value.
Gel permeation chromatography conditions, calibration standard, solvent, and sample preparation can change the result.
"About" creates a potential boundary range but does not eliminate the need for reliable analytical testing.
A polymer with a measured molecular weight materially above 30,000 or below 5,000 would have a stronger non-infringement position under claim 1.

Dispersity limitation

The claim requires a dispersity of about 1.5 to 2. At the time of the patent, this characteristic was often expressed through molecular-weight distribution terminology. Modern analysis generally uses dispersity, represented as Mw/Mn.

This limitation narrows the claim materially. A polymer can fall within the molecular-weight range but outside the claimed dispersity range. Conversely, a polymer with the correct dispersity can still avoid the claim if its molecular weight or composition is outside the claimed range.

A current freedom-to-operate analysis would need to test both Mw and dispersity using a validated analytical method and compare the results with the patent's examples and disclosure.

What do claims 2 through 5 add?

Claims 2 through 5 narrow claim 1 by specifying lactic-acid and glycolic-acid ratios.

Claims 2, 3, and 4 are expressed in weight percent:

Claim 2: 50-95 wt% lactic acid.
Claim 3: 60-95 wt% lactic acid.
Claim 4: 60-85 wt% lactic acid.

Because glycolic acid makes up the balance, the ranges are reciprocal. Claim 4 is the narrowest broad-range composition claim among claims 2 through 4.

Claim 5 uses molar percentage rather than weight percentage:

Approximately 75±2 mol% lactic acid.
Approximately 25±2 mol% glycolic acid.

A 75:25 molar ratio does not translate identically to a 75:25 weight ratio because lactic acid and glycolic acid have different molecular weights. A party assessing claim 5 must therefore avoid substituting weight percent for mol percent without conversion.

Scope hierarchy

Composition range	Relative scope
50-95 wt% lactic acid	Broadest express composition range
60-95 wt% lactic acid	Narrower
60-85 wt% lactic acid	Narrower still
75±2 mol% lactic acid	Specific molar-ratio embodiment

The dependent claims preserve the independent claim's catalyst-free, molecular-weight, and dispersity limitations. A polymer within the lactic-acid range but containing catalyst residues, an out-of-range molecular weight, or an out-of-range dispersity would not necessarily satisfy the full claim.

What do claims 6 through 12 protect?

Claim 6 covers a manufacturing process, not merely the resulting polymer. It requires:

Lactic acid and glycolic acid, or low-molecular-weight polymers or copolymers of those materials;
A polycondensation reaction;
Heating;
Reduced pressure; and
Absence of a catalyst.

The process claim is potentially broader than claim 1 in one respect because claim 6 initially requires a molecular weight of not less than approximately 5,000 rather than expressly limiting the result to 5,000-30,000. Claim 8 narrows the process to the 5,000-30,000 range.

Claim 7 adds a two-stage process:

Formation of a low-molecular-weight polymer or copolymer while removing water without a catalyst.
A subsequent polycondensation reaction lasting approximately 10 hours or longer.

Claims 9 through 12 add the same composition ranges found in claims 2 through 5.

Process-risk analysis

A process is most likely to implicate claim 6 if it uses direct melt polycondensation of lactic acid and glycolic acid under vacuum or reduced pressure without a catalyst. The principal design-around routes historically included:

Use of an organometallic, acid, or other catalyst;
Ring-opening polymerization of lactide and glycolide rather than direct polycondensation;
Use of a different reaction sequence;
Production of a polymer outside the claimed molecular-weight or dispersity parameters;
Use of a composition outside the claimed lactic-acid/glycolic-acid ranges.

A process that begins with lactide and glycolide and uses ring-opening polymerization would require separate analysis. It would not automatically satisfy claim 6, which is directed to lactic acid, glycolic acid, or low-molecular polymers or copolymers undergoing polycondensation.

When did U.S. Patent 4,677,191 expire?

U.S. Patent 4,677,191 issued on June 30, 1987. Because it belongs to the pre-Uruguay Round patent-term period, its ordinary term was 17 years from grant. The patent therefore expired on June 30, 2004, absent an unusual adjustment or extension.

Event	Date
U.S. patent issuance	June 30, 1987
Ordinary 17-year expiration	June 30, 2004
Current status	Expired
Current enforceability	None in the United States

The patent is not eligible for a modern patent-term extension tied to an approved drug product. Patent-term extension under 35 U.S.C. § 156 applies to qualifying regulatory review periods and does not convert this expired polymer patent into a currently enforceable right without a documented extension.

What is the Orange Book status of U.S. Patent 4,677,191?

U.S. Patent 4,677,191 is not an Orange Book drug-product patent. It claims a polymer and a polymer-production process, not a specific approved drug product, dosage form, or method of use identified in an FDA-approved labeling record.

The FDA Orange Book generally lists patents submitted by an NDA holder for an approved drug product, including eligible drug-substance, drug-product, and method-of-use patents. A historical PLGA material patent does not become an Orange Book patent merely because PLGA is used in an approved injectable or implantable product (FDA, 2024).

Consequences include:

No current Orange Book patent listing should be assumed.
The patent does not create a live Paragraph IV filing target.
A generic or follow-on applicant would not ordinarily need to certify against this expired polymer patent.
Any current regulatory patent issue would arise from later patents covering a specific formulation, dosage form, manufacturing method, or method of use.

Were Paragraph IV challenges, litigation, or settlements associated with this patent?

No current Paragraph IV dispute, settlement agreement, or enforceable U.S. litigation position arises from U.S. Patent 4,677,191 because the patent expired in 2004.

Paragraph IV litigation is generally associated with an unexpired patent listed for an approved drug product and challenged by an ANDA applicant. This patent is a platform polymer patent and is not a conventional Orange Book-listed drug patent.

A historical litigation search should distinguish:

Litigation involving U.S. Patent 4,677,191 itself;
Litigation involving later PLGA patents;
Litigation involving specific products such as microspheres, injectable depots, implants, or peptide formulations;
Regulatory disputes involving Orange Book-listed patents unrelated to this patent.

The existence of PLGA litigation in the pharmaceutical sector does not establish that this patent was asserted in those cases.

What is the broader PLGA patent landscape?

The strongest later patent positions generally moved from basic PLGA composition to application-specific technology.

Formulation patents

Later patent estates commonly cover:

Injectable microspheres and microparticles;
Long-acting peptide or protein delivery;
Particle-size distributions;
Porosity and morphology;
Residual solvent controls;
Reconstitution properties;
Release-rate profiles;
Stabilizers and excipients;
Drug loading and encapsulation efficiency;
Specific depot formulations.

These patents can remain relevant even though U.S. Patent 4,677,191 has expired. A product may use public-domain PLGA but still infringe a later formulation patent.

Method-of-use patents

Method-of-use patents may cover the use of PLGA depots for:

Hormonal therapies;
Antipsychotic treatment;
Opioid dependence;
Oncology;
Ophthalmic delivery;
Vaccines;
Peptides and proteins.

The key distinction is that U.S. Patent 4,677,191 does not claim administration to a patient, a therapeutic indication, a dose, or a release profile.

Manufacturing and quality patents

Later manufacturing patents may create practical barriers through claims directed to:

Continuous or semi-continuous polymerization;
Specific lactide or glycolide starting materials;
End-group control;
Acid or ester end groups;
Residual monomer reduction;
Molecular-weight control;
Scale-up conditions;
Aseptic processing;
Particle formation and drying.

Manufacturing know-how can remain commercially important even where foundational composition claims have expired. Trade secrets, process capability, supplier qualification, and regulatory comparability can be more significant than the expired patent.

How strong is the patent estate today?

The patent estate of U.S. Patent 4,677,191 is legally weak as a current exclusionary asset because all claims are expired. Its technical disclosure was comparatively important because it identified a catalyst-free PLGA platform with defined molecular-weight distribution and composition parameters.

Factor	Assessment
Current U.S. enforceability	None
Foundational composition scope	Broad within defined parameters
Process scope	Moderate, but limited to catalyst-free polycondensation
Formulation coverage	None apparent from the stated claims
Method-of-use coverage	None
Orange Book relevance	None apparent
Paragraph IV relevance	None for the expired patent
Prior-art significance	High for later PLGA patent prosecution and validity analysis
Generic launch barrier	None from this patent
Manufacturing barrier	No patent barrier, but process and quality barriers may remain

The patent's strongest historical feature was the combination of catalyst-free production and tightly specified polymer properties. Its weakest feature for current enforcement is the absence of claims to a drug product or therapeutic application.

How does this patent compare with later PLGA patents?

Issue	U.S. Patent 4,677,191	Later PLGA patents
Core subject matter	PLGA composition and polycondensation	Drug formulations, delivery systems, manufacturing, or use
Catalyst limitation	Central	Often replaced by specific catalyst, solvent, or polymerization conditions
Molecular-weight limitation	Central	Often combined with end groups, degradation rate, or particle properties
Drug-specific claims	None apparent	Common
Dosage-form claims	None apparent	Common
FDA Orange Book potential	Low	Higher for approved drug products
Current term	Expired June 30, 2004	Depends on filing date and patent family
Commercial risk	No current blocking risk	Product-specific and potentially material

What generic entry risks exist for PLGA products?

A generic or follow-on applicant using PLGA faces no entry risk from U.S. Patent 4,677,191 itself. The relevant risks are later patents covering the finished product or its manufacturing process.

A practical patent review should separate:

The polymer supplier's composition patents.
The drug sponsor's formulation patents.
Manufacturing patents held by the sponsor or contract manufacturer.
Method-of-use patents listed for the reference product.
Device or delivery-system patents.
Regulatory exclusivity that is independent of patent rights.

For injectable microspheres and implants, formulation and process patents often present greater exposure than basic PLGA composition patents. Biosimilar risk is generally not the correct framework for a small-molecule or polymer-based depot product. Depending on the active ingredient and product classification, the relevant pathway may be an ANDA under section 505(j), a 505(b)(2) application, or a biologics pathway if the active product is a biologic. PLGA itself does not determine the FDA pathway.

What are the geographic and commercial implications?

The patent's U.S. rights expired, but corresponding foreign family members had separate terms and may have expired on different dates. A global freedom-to-operate review cannot rely on the U.S. expiration date alone. European, Japanese, Canadian, and other national rights must be checked independently through their national registers and family records.

There is no direct revenue exposure from this expired patent. Its indirect commercial value lies in:

Prior-art support for invalidity challenges to later broad PLGA claims;
Freedom to use the disclosed catalyst-free polymer technology in the United States;
Benchmarking of polymer molecular weight and dispersity;
Historical assessment of PLGA supplier and formulation technology;
Identifying the technical starting point for later controlled-release patents.

Key Takeaways

U.S. Patent 4,677,191 claims catalyst-free lactic acid-glycolic acid copolymers and their catalyst-free production.
The principal product limitations are approximately 5,000-30,000 weight-average molecular weight and approximately 1.5-2 dispersity.
The composition claims narrow the lactic-acid content from 50-95 wt% to specific ranges, including approximately 75±2 mol%.
The process claims require heat, reduced pressure, polycondensation, and absence of a catalyst.
The patent expired on June 30, 2004.
It has no current U.S. blocking effect, no current Orange Book significance, and no present Paragraph IV risk.
Later PLGA formulation, manufacturing, drug-delivery, and method-of-use patents remain the relevant commercial risks.
Catalyst-based or ring-opening polymerization processes may provide design-around positions, subject to separate claim analysis.
The patent remains important as prior art and as a historical foundational PLGA patent.

FAQs About U.S. Patent 4,677,191 and PLGA

Can a company use PLGA covered by U.S. Patent 4,677,191 today?

Yes. The U.S. patent expired in 2004. Current use of PLGA must still be reviewed against later, unexpired patents covering specific drug formulations, particles, manufacturing methods, or therapeutic uses.

Does the patent cover PLGA microspheres?

The stated claims do not expressly require microspheres, microparticles, implants, injectables, or any other dosage form. A microsphere could contain a polymer within the claimed parameters, but the expired status removes current U.S. infringement risk from this patent.

Does claim 5 cover a 75:25 PLGA polymer by weight?

Not necessarily. Claim 5 is expressed in molar percentages. A 75:25 molar ratio must be distinguished from a 75:25 weight ratio because the monomer molecular weights differ.

Does ring-opening polymerization infringe claim 6?

Not automatically. Claim 6 is directed to polycondensation of lactic acid, glycolic acid, or low-molecular polymers or copolymers under heat and reduced pressure without a catalyst. Ring-opening polymerization of lactide and glycolide requires a separate element-by-element analysis.

Can this patent support a Paragraph IV certification?

Because the patent expired in 2004 and is not a current drug-product patent, it does not ordinarily create a present Paragraph IV certification issue. Any certification requirement would arise from a separate unexpired patent listed for the relevant reference drug.

Is the patent relevant to biosimilar development?

Only indirectly. The patent concerns a polymer delivery material, not a biologic active ingredient. Biosimilar developers may review it as technical prior art, but biosimilar exclusivity and patent analysis generally focus on the biologic product, formulation, device, and manufacturing estate.

References

U.S. Patent No. 4,677,191. (1987). Lactic acid-glycolic acid copolymer. United States Patent and Trademark Office.
United States Patent and Trademark Office. (2024). Patent term calculator and patent term guidance. https://www.uspto.gov/patents/laws/patent-term-calculator
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-data-files
U.S. Food and Drug Administration. (2024). Frequently asked questions on patents and exclusivity. https://www.fda.gov/drugs/development-resources/patent-and-exclusivity-information
U.S. Code, 35 U.S.C. §§ 154, 156, 271, and 282. (2024). Patent term, patent-term extension, infringement, and validity provisions.

Foriegn Application Priority Data
Foreign Country	Foreign Patent Number	Foreign Patent Date
Japan	59-140356	Jul 06, 1984

Country	Patent Number	Estimated Expiration	Supplementary Protection Certificate	SPC Country	SPC Expiration
Austria	39935	⤷ Start Trial
Austria	39936	⤷ Start Trial
Bulgaria	61520	⤷ Start Trial
Canada	1236641	⤷ Start Trial
Canada	1256638	⤷ Start Trial
Germany	3567470	⤷ Start Trial
>Country	>Patent Number	>Estimated Expiration	>Supplementary Protection Certificate	>SPC Country	>SPC Expiration

Details for Patent: 4,677,191

Summary for Patent: 4,677,191