U.S. Patent 6,132,420: Claim Scope, Expiration, Patent Strength, and Osmotic Drug-Delivery Landscape

U.S. Patent No. 6,132,420 protects an osmotic drug-delivery architecture that uses an incompressible liquid or gel to fill the space around an osmotic-agent tablet. The claimed filler reduces trapped gas and improves device start-up time. The patent is directed to delivery-device structure and assembly methods, not to a particular active pharmaceutical ingredient.

The claims divide into four groups:

A capsule-based osmotic device with a beneficial-agent chamber, osmotic-agent chamber, movable piston and incompressible filler.
A broader enclosure containing an osmotic tablet and filler.
A method for removing gas from the gap surrounding the osmotic tablet.
A device claim combining a partitioned enclosure, permeable osmotic chamber and incompressible filler.

The strongest commercial relevance is for oral or implantable osmotic pumps using a tablet-form osmotic engine, particularly systems using polyethylene glycol, including PEG 400, as the filler.

What does U.S. Patent 6,132,420 claim?

The core inventive concept is the combination of four physical elements:

Claim element	Required feature
Enclosure	Capsule or other enclosure containing the delivery system
Osmotic engine	Osmotic agent, generally in tablet or tabular form
Filler	Incompressible fluid, lubricating liquid or gel
Position of filler	Filler at least partially or substantially surrounding the osmotic agent

Independent claim 1 requires a capsule with two chambers. The first chamber contains the beneficial agent. The second chamber contains the osmotic agent and incompressible fluid additive. A movable separating member, such as a piston, separates the chambers. A fluid-permeable portion allows environmental fluid to enter the osmotic chamber.

Independent claim 11 is structurally broader in some respects. It requires an enclosure, an osmotic-agent tablet and an incompressible fluid filler at least partially surrounding the tablet. It does not expressly require a two-chamber capsule or a movable piston.

Independent claim 21 is a method claim. It covers improving start-up time by placing incompressible fluid in the gap between the tablet and the enclosure, thereby removing gas from that space.

Independent claim 22 combines the partitioned-chamber configuration with a permeable osmotic chamber and incompressible filler. Claim 23 narrows claim 22 by requiring a movable piston, osmotic tablet and delivery orifice.

How do claims 1 through 10 define the patented device?

Claims 1 through 10 create a progressively narrower capsule-based claim set.

Claim 1: principal capsule architecture

Claim 1 requires:

A capsule;
A first chamber containing a beneficial agent;
A second chamber containing an osmotic agent;
An opening for delivery of the beneficial agent;
A movable separating member between the chambers;
A fluid-permeable wall portion in the osmotic chamber; and
An incompressible fluid additive substantially surrounding the osmotic agent.

A device that lacks the two-chamber arrangement, the movable separator or the surrounding incompressible additive would have a substantial non-infringement position under the literal wording of claim 1.

The phrase "substantially surrounding" is important. It does not necessarily require complete encapsulation of the osmotic agent by the filler. A filler occupying the annular gap around most of a tablet could satisfy the limitation, depending on the factual record and claim construction.

Claims 2 and 5: tablet-form osmotic agents

Claims 2 and 5 require the osmotic agent to be in tabular or tablet form. These claims exclude systems in which the osmotic agent is only a loose powder, liquid, polymeric gel or fully dissolved formulation.

The claim set therefore places commercial emphasis on a preformed osmotic tablet positioned inside a larger chamber.

Claims 3 and 20: sliding piston

Claim 3 identifies the separating member as a slidable piston. Claim 20 applies the same narrowing feature to the architecture of claim 19.

A diaphragm, elastomeric membrane or fixed partition may fall outside these dependent claims, although such structures could still be relevant to the broader independent claims if they satisfy the relevant "movable separating member" or "partition" language.

Claim 4: permeable membrane

Claim 4 narrows the fluid-permeable portion to a membrane. The independent claim does not expressly require a membrane and could potentially encompass other permeable structures, such as a porous plug or permeable wall section.

Claims 6 through 8: filler composition

The filler may be:

A lubricating liquid;
A gel; or
A composition containing PEG.

Claim 10 specifically requires sodium chloride as the osmotic agent and PEG as the fluid additive. PEG 400 is not required until claim 16, which depends on the separate enclosure claim set.

Claim 9: gap-filling and start-up time

Claim 9 expressly links the filler to a gap between the capsule’s inner surface and the osmotic agent. The filler must occupy that gap to improve start-up time.

This limitation provides a technically concrete infringement issue. Evidence would likely focus on:

Tablet dimensions;
Chamber dimensions;
The existence and size of the annular gap;
Filler volume;
Gas displacement;
Wetting or imbibition delay;
Delivery-rate data during the first phase of operation.

What do claims 11 through 20 protect?

Claims 11 through 20 cover a second claim family centered on an enclosure rather than specifically on a capsule.

Claim 11: broader enclosure claim

Claim 11 requires an enclosure containing:

At least one osmotic-agent tablet;
An incompressible fluid filler; and
A filler that at least partially surrounds the tablet.

It also requires that the tablet imbibe fluid and swell to cause delivery of the beneficial agent. The claim does not expressly require:

A capsule;
A piston;
A delivery orifice;
A first chamber;
A permeable membrane; or
PEG.

This makes claim 11 potentially the broadest structural claim in the patent, although the requirement for an osmotic-agent tablet and surrounding incompressible filler remains a meaningful limitation.

Claims 12 through 16: filler and osmotic-agent options

Claim 12 allows the fluid filler itself to be an osmotic agent. Claims 14 and 15 identify a lubricating liquid or gel. Claim 16 narrows the filler to PEG 400.

Claim 13 covers a fluid-swellable osmotic material that causes delivery at a controlled rate. This language reaches beyond conventional sodium chloride tablets and may encompass polymeric or otherwise swellable osmotic materials, subject to the other limitations of claim 11.

Claims 17 through 20: chamber, gap and piston limitations

Claim 17 requires the filler to occupy a gap between the enclosure and tablet. Claim 18 adds separate beneficial-agent and osmotic-agent chambers. Claim 19 requires a partition between those chambers. Claim 20 specifies a slidable piston.

These dependent claims create fallback positions if claim 11 is challenged for lack of novelty or inadequate breadth.

What does method claim 21 cover?

Claim 21 protects a method of improving osmotic-device start-up time by filling the gap around the osmotic tablet with an incompressible fluid.

The claim has five practical requirements:

Requirement	Scope implication
Existing osmotic delivery system	The method applies to a device, not merely a tablet
Enclosure	The tablet must be inside an enclosure
Osmotic-agent tablet	The claim is tablet-specific
Gap	There must be a space between tablet and enclosure
Incompressible fluid	The fluid must displace gas from the gap

Claim 21 is potentially significant in manufacturing disputes because it can be asserted against a process even where the final marketed product is difficult to inspect. Relevant evidence may include assembly instructions, filling steps, batch records, design drawings and quality-control protocols.

The claim does not expressly require PEG, sodium chloride, a piston, a membrane or a delivery orifice. A non-PEG liquid or gel could fall within the claim if it satisfies the incompressible-fluid and gap-filling limitations.

How does claim 22 differ from claims 1 and 11?

Claim 22 is an intermediate architecture between claims 1 and 11.

Feature	Claim 1	Claim 11	Claim 22
Capsule specifically required	Yes	No	No
Two chambers required	Yes	No	Yes
Partition required	Movable separating member	No	Yes
Osmotic tablet required	Not expressly in claim 1	Yes	Not expressly in claim 22
Permeable osmotic chamber	Yes	Not expressly	Yes
Incompressible filler	Yes	Yes	Yes
Beneficial-agent chamber	Yes	Not expressly	Yes
Delivery orifice	Opening required	No	Not until claim 23

Claim 22 may be broader than claim 1 because it does not require a capsule or expressly require a tablet. It is narrower than claim 11 because it requires partitioned chambers and a permeable portion of the enclosure.

Claim 23 adds the key commercial features of a piston, tablet and delivery orifice.

What is the patent’s central technical contribution?

The patent addresses delayed activation of an osmotic pump caused by gas trapped between the osmotic tablet and the surrounding enclosure.

In a conventional system, environmental fluid must enter the osmotic chamber and contact the osmotic agent. If air remains in the annular space, the fluid may initially wet only part of the tablet or may require additional time to displace the air. The resulting delay can affect:

Time to first delivery;
Initial delivery-rate accuracy;
Dose uniformity;
Reproducibility across units;
Performance after storage or temperature cycling.

The claimed incompressible filler occupies the gap and reduces the volume of gas that must be displaced. The filler also may lubricate movement of the tablet, piston or surrounding components.

The patent therefore protects a device-level performance solution rather than a new osmotic-active composition.

How strong is the patent estate for U.S. Patent 6,132,420?

The patent’s strength is concentrated in a narrow but technically specific combination.

Strengths

Multiple independent claims cover different structural configurations.
Claim 11 does not require the capsule-and-piston arrangement of claim 1.
Claim 21 reaches the manufacturing or assembly method.
The claims cover liquids, gels and PEG-containing fillers.
The claims address both product configuration and start-up performance.
Dependent claims provide fallback positions for tablet, piston, membrane, PEG 400 and sodium chloride embodiments.

Limitations

The claims require an incompressible filler to surround or at least partially surround the osmotic agent.
Several important claims require a tablet or tabular osmotic agent.
Claim 1 requires a two-chamber capsule and movable separator.
The claim language is tied to a particular physical mechanism and may not reach osmotic pumps using a dry annular space, a liquid reservoir elsewhere in the system or a non-tablet osmotic engine.
"Substantially surrounding," "at least partially surrounding" and "incompressible" could create claim-construction disputes.

The patent is stronger against products that visibly use PEG 400 or another liquid filler in the annular gap around a sodium chloride osmotic tablet. It is weaker against systems that use a different start-up mechanism or place fluid outside the osmotic-agent chamber.

When did U.S. Patent 6,132,420 lose exclusivity?

U.S. Patent No. 6,132,420 was issued on October 17, 2000. Its enforceable term depended on the effective nonprovisional filing date, any priority claims, patent-term adjustment and any terminal disclaimer. Under 35 U.S.C. § 154, the ordinary term for a post-June 8, 1995 utility patent is generally 20 years from the earliest effective U.S. nonprovisional filing date, subject to statutory adjustments.

The patent is no longer a current blocking patent. Its ordinary patent term would have expired years ago, absent an unusual term adjustment or other statutory extension. The device claims also do not appear to qualify for Hatch-Waxman patent-term extension because they are not directed to a drug active ingredient or a drug product approval.

As a result, the patent is primarily relevant for:

Historical freedom-to-operate analysis;
Validity and patent-family mapping;
Prior-art chronology;
Interpretation of later osmotic-device patents;
Technical diligence involving legacy products.

What is the Orange Book status of U.S. Patent 6,132,420?

The patent is not, by itself, an Orange Book drug patent. The claims cover a delivery device and manufacturing method. They do not claim:

A named active ingredient;
A specific approved drug product;
A drug formulation identified by active pharmaceutical ingredient;
A method of treating a disease; or
A regulatory use of a drug.

A patent of this type would generally not create an Orange Book-listed patent barrier unless separately associated with an approved drug product and listed under the applicable FDA patent-listing rules. The patent number alone should not be treated as creating a Paragraph IV or generic-launch obstacle.

Does the patent create biosimilar risk?

No meaningful biosimilar issue arises from these claims. Biosimilar litigation concerns biologic products under the Public Health Service Act. U.S. Patent 6,132,420 claims an osmotic delivery device and assembly method, not a biologic molecule or biologic manufacturing process.

The relevant competitive risk is conventional generic or device-component competition, not biosimilar substitution.

Which products could potentially infringe?

A product is most exposed if it has all or nearly all of the following characteristics:

A beneficial-agent reservoir;
A separate osmotic chamber;
A sodium chloride or comparable osmotic tablet;
A semipermeable or otherwise fluid-permeable chamber wall;
A piston or movable partition;
PEG 400, gel or lubricating liquid in the tablet-to-wall gap;
A delivery orifice;
Start-up performance attributable to gas displacement.

Potentially lower-risk designs include:

Osmotic systems with no filler around the tablet;
Systems using a swellable polymer without a discrete tablet;
Push-pull systems in which the osmotic engine does not occupy the claimed chamber configuration;
Devices using a rigid mechanical actuator;
Devices in which fluid is delivered through a separate reservoir rather than filling the tablet gap;
Formulations in which the osmotic agent is dissolved or dispersed rather than formed as a tablet.

Literal infringement requires satisfaction of every limitation of an asserted claim. A product that uses PEG 400 but lacks a surrounding osmotic tablet, for example, would not automatically infringe.

What prior-art and competitive technologies are relevant?

The relevant patent landscape includes several adjacent technology categories.

Elementary osmotic pumps

These systems use a semipermeable membrane around an osmotic agent and a delivery orifice. They are the closest technical field because the claimed device depends on environmental-fluid imbibition and osmotic swelling.

Push-pull osmotic systems

Push-pull systems use a drug layer and an osmotic push layer separated by a movable boundary. They may overlap with claims 1 and 22 when the push layer is a tablet surrounded by incompressible filler, but conventional push-pull architecture alone does not satisfy the filler limitations.

Osmotic capsules

Capsule-based systems with a piston and separate drug and osmotic chambers are directly relevant to claims 1 through 10 and claim 23.

Implantable osmotic pumps

Implantable pumps may use osmotic pressure to move a piston or diaphragm. They become relevant only if their chamber, osmotic agent and filler arrangement satisfies the claimed limitations.

Liquid-filled start-up systems

Liquid or gel-filled annular spaces are the closest competitive design category. These systems present the principal overlap risk because they address the same gas-displacement problem identified in claim 21.

What litigation, licensing and settlement issues affect the patent?

The supplied claims establish no active litigation, settlement or licensing obligation. Because the patent is expired, a new product launch would ordinarily not face an injunction based solely on U.S. Patent 6,132,420.

Historical ownership and licensing may still matter in a chain-of-title review. The analysis should distinguish:

Ownership of the issued patent;
Assignment of related continuation patents;
Licenses covering the underlying osmotic-platform technology;
Settlement agreements involving later, unexpired patents; and
Patent families claiming the same device but with different priority dates.

A historical license to the broader osmotic platform would not necessarily prove that U.S. Patent 6,132,420 itself remained enforceable. Conversely, expiration of this patent would not eliminate risk from later continuation or improvement patents.

How many patents cover the same osmotic-device concept?

The claims supplied support identification of one patent covering the specific filler-around-tablet concept. They do not establish the complete patent family or the number of related U.S. or foreign patents.

For freedom-to-operate purposes, the relevant search should cover:

Continuations and divisionals;
Foreign counterparts;
Later patents claiming PEG-filled osmotic chambers;
Patents directed to start-up-time reduction;
Patents claiming tablet lubrication or gas displacement;
Patents covering specific approved products using the architecture;
Later patents with overlapping claims but different expiration dates.

The issued claims should not be treated as an exhaustive statement of the historical patent estate.

What generic launch risks exist?

The patent itself presents no current U.S. generic-launch barrier because its term has expired. A product can still encounter separate risk from:

Later patents on a particular osmotic pump design;
Formulation patents covering the drug reservoir;
Method-of-use patents;
Device-component patents;
Manufacturing-process patents;
Trade secrets involving assembly and filling;
Regulatory requirements for delivery-rate equivalence.

The expired patent remains useful as prior art against later attempts to claim the same use of an incompressible filler to remove gas around an osmotic tablet.

Key Takeaways

U.S. Patent 6,132,420 protects an osmotic delivery device using an incompressible liquid or gel around an osmotic-agent tablet.
Its technical purpose is to reduce trapped gas and improve start-up time.
Claims 1, 11, 21 and 22 are the principal independent claims.
Claim 11 is the broadest structural claim because it does not expressly require a capsule, piston or two chambers.
Claim 21 covers the manufacturing method of filling the tablet-to-enclosure gap with incompressible fluid.
PEG, PEG 400, gel and lubricating-liquid embodiments are expressly covered in dependent claims.
The patent is a device patent, not an active-ingredient, Orange Book or biosimilar patent.
The patent’s ordinary U.S. term has expired, so it does not create a current standalone generic-entry block.
Later patents, continuation rights and product-specific patents must be reviewed separately.
The highest historical infringement exposure involved osmotic systems using a sodium chloride tablet, PEG filler, semipermeable chamber and piston.

FAQs About U.S. Patent 6,132,420

Does U.S. Patent 6,132,420 claim PEG 400 specifically?

Yes. Claim 16 expressly identifies PEG 400 as the fluid filler. Claim 8 broadly covers a filler that includes PEG, while claim 10 combines PEG with sodium chloride as the osmotic agent.

Is a sodium chloride osmotic tablet required for every claim?

No. Sodium chloride and PEG are required together only by claim 10. The independent claims use broader terms such as "osmotic agent" and "osmotic-agent tablet."

Does the patent cover a dry gap around the osmotic tablet?

Generally, no. The independent claims require an incompressible fluid additive or filler that surrounds or at least partially surrounds the osmotic agent. Claim 21 specifically requires incompressible fluid in the gap.

Can a polymeric osmotic gel fall within the patent?

Potentially. Claim 13 refers to a fluid-swellable material that causes controlled delivery, and claims 7 and 15 expressly include gels. The product would still need to satisfy the remaining structural limitations.

Is a movable piston required for all claims?

No. A piston is required by dependent claims 3, 20 and 23. Claims 11 and 21 do not expressly require a piston, and claim 22 requires a partition but does not require a piston until claim 23.

Can the patent be used to block a generic drug launch today?

Not by itself. The patent’s U.S. term has expired, and its claims are not directed to a specific active ingredient or Orange Book-listed drug product. Later unexpired patents may create separate risks.

Does the patent cover the drug formulation inside the first chamber?

No. The claims require a beneficial agent in certain device configurations, but they do not claim a specific active ingredient or a formulation composition.

What is the main design-around strategy?

The clearest design-around options are eliminating the incompressible filler around the osmotic tablet, using a non-tablet osmotic engine, changing the chamber architecture, or using a different start-up mechanism that does not fill the tablet-to-wall gap.

References

U.S. Patent No. 6,132,420, claims 1-23 (2000).
35 U.S.C. § 154. Patent term.
U.S. Food and Drug Administration. (2023). Approved drug products with therapeutic equivalence evaluations (Orange Book).
U.S. Food and Drug Administration. (2024). Approved drug product patent listing requirements, 21 C.F.R. § 314.53.
U.S. Food and Drug Administration. (2024). Biosimilar and interchangeable biosimilar products.

Country	Patent Number	Estimated Expiration	Supplementary Protection Certificate	SPC Country	SPC Expiration
Argentina	006079	⤷ Start Trial
Argentina	010595	⤷ Start Trial
Austria	235224	⤷ Start Trial
>Country	>Patent Number	>Estimated Expiration	>Supplementary Protection Certificate	>SPC Country	>SPC Expiration

Summary for Patent: 6,132,420