United States Drug Patent 5,605,674: Claim Scope, Expiration, and Patent Landscape

U.S. Patent No. 5,605,674 covers a chlorofluorocarbon-free metered-dose inhaler formulation using 1,1,1,2-tetrafluoroethane, commonly called HFA-134a or norflurane, to deliver a therapeutically effective medicament to the lungs. The claim is broad at the formulation level but limited by the requirement for an aerosol container, a metering valve, HFA-134a-containing propellant, and pulmonary inhalation delivery.

The patent issued February 25, 1997. Based on the patent’s pre-1995 filing regime, its 17-year patent term from issuance ended February 25, 2014, absent a term adjustment or other record-specific modification. It is therefore expired and does not present a current blocking patent right in the United States. The patent is relevant historically because it addressed the transition from CFC propellants to hydrofluoroalkanes in pressurized metered-dose inhalers.

What does U.S. Patent 5,605,674 cover?

The issued independent claim covers:

An aerosol formulation;
Contained in an aerosol container;
The container equipped with a metering valve;
Containing a therapeutically effective amount of a medicament;
Using a propellant substantially free of chlorofluorocarbons;
With the propellant comprising 1,1,1,2-tetrafluoroethane; and
A formulation suitable for delivery to the lung by inhalation.

The claim is directed to a complete inhaler presentation rather than only to a chemical composition. A composition of HFA-134a and a drug, standing alone, would not necessarily satisfy the claim because the claim also requires the aerosol container, metering valve, and pulmonary inhalation suitability.

Claim limitation analysis

Claim limitation	Scope and practical effect
"An aerosol formulation"	Covers a formulation intended for aerosol delivery. The term does not specify a particular drug, concentration, particle size, or excipient.
"Contained in an aerosol container"	Requires the formulation to be packaged in a container. Bulk formulation or an unfilled composition is outside this limitation.
"Equipped with a metering valve"	Limits the claim to a pressurized metered-dose inhaler or comparable metering aerosol package. Dry-powder inhalers and conventional nebulizers are generally outside the literal claim.
"A therapeutically effective amount of a medicament"	Broad functional limitation. No specific active ingredient or dose is required.
"Propellant substantially free of chlorofluorocarbons"	Targets CFC replacement. The phrase lacks a numerical CFC threshold in the claim and would require interpretation based on the specification, prosecution history, and technical context.
"Comprising 1,1,1,2-tetrafluoroethane"	HFA-134a must be present, but "comprising" generally permits additional propellants or components unless another limitation excludes them.
"Suitable for delivery to the lung by inhalation"	Requires pulmonary suitability. A formulation intended solely for topical, nasal, or other delivery would face a material claim-scope issue.

How broad is the HFA-134a formulation claim?

The claim is broad with respect to the medicament and excipients, but narrower with respect to the delivery system.

The claim does not identify:

A particular active pharmaceutical ingredient;
A specific drug class;
An ethanol concentration;
A surfactant;
A suspension or solution formulation;
A canister material;
A valve geometry;
A dose per actuation;
A particle-size distribution;
A nominal fill weight;
A particular manufacturing process; or
A specific therapeutic indication.

The use of "comprising" allows additional formulation components. A formulation could therefore include ethanol, a surfactant, a stabilizer, a co-solvent, or another propellant, provided HFA-134a is present and the remaining claim requirements are met.

The claim does not require HFA-134a to be the only propellant. A mixed HFA system could fall within the literal scope if it includes HFA-134a and remains substantially free of CFCs. The scope would still depend on how "propellant" is construed and whether the formulation is suitable for pulmonary delivery.

What formulations are protected by U.S. Patent 5,605,674?

The patent potentially covers both solution and suspension pressurized metered-dose inhalers using HFA-134a.

Solution formulations

Solution systems commonly dissolve the active ingredient in HFA-134a with a polar co-solvent such as ethanol. The claim does not require ethanol, but an ethanol-containing HFA-134a solution would generally fit the claim structure if it is packaged in a metering-valve inhaler for lung delivery.

Suspension formulations

Suspension systems disperse micronized drug particles in liquefied HFA-134a. Surfactants or other formulation aids may be included. The claim does not distinguish between a dissolved active and a suspended active.

Mixed-propellant systems

Because the claim uses "comprising," a formulation containing HFA-134a and another non-CFC propellant may fall within the claim, subject to the complete claim language and prosecution history.

Formulations outside the principal scope

The claim is less likely to reach:

Dry-powder inhalers;
Nebulizer solutions that do not use a metering aerosol valve;
CFC-containing formulations that do not meet the "substantially free" requirement;
Formulations using only HFA-227 without HFA-134a;
Nonpulmonary aerosol products;
Bulk propellant or drug mixtures not contained in the claimed inhaler package.

When did U.S. Patent 5,605,674 lose exclusivity?

The patent expired February 25, 2014, based on its February 25, 1997 issuance date and the 17-year term applicable to the relevant pre-June 8, 1995 filing framework under 35 U.S.C. § 154(c). An expired patent cannot support an injunction, damages claim, or Paragraph IV delay for future U.S. generic approval.

Event	Date or status
U.S. patent issued	February 25, 1997
Statutory term under applicable regime	17 years from issuance
Expected expiration	February 25, 2014
Current status	Expired
Current enforceability against new products	None
Current 30-month ANDA stay potential	None based on this patent

A patent-term adjustment or terminal disclaimer could affect the precise expiration date. The commercial conclusion remains unchanged: the patent is no longer an enforceable U.S. exclusion right.

What is the Orange Book status of U.S. Patent 5,605,674?

The patent is not a current source of Orange Book protection because it has expired. Orange Book listing depends on submission by an NDA holder and FDA acceptance of the patent as relevant to the approved drug product. The patent number alone does not establish that it was ever listed against a particular inhaled medicine.

The patent is also formulation-platform oriented rather than directed to a named active ingredient. Such patents may be submitted for listing when they claim an approved drug product or its use, but listing practice and FDA treatment depend on the NDA, the approved labeling, the patent claims, and the applicable FDA rules. The expired status means it cannot currently create a regulatory stay for an ANDA applicant.

Paragraph IV implications

A Paragraph IV certification is relevant only when an ANDA applicant addresses an unexpired listed patent. Because U.S. Patent 5,605,674 expired in 2014:

It cannot support a new Paragraph IV challenge with a 30-month stay;
It cannot delay approval of a current ANDA;
It cannot create a patent-based first-filer advantage;
It cannot block a generic HFA-134a inhaler.

Historical ANDA filings may have addressed the patent while it was in force, but the patent’s current status eliminates its forward-looking regulatory leverage.

Does the patent cover specific inhaled drugs?

The claim is not limited to a named drug. It could theoretically read on a broad range of HFA-134a pressurized inhalers, including products containing bronchodilators, corticosteroids, anticholinergics, or combination therapies.

Potentially relevant product categories include:

Product category	Examples of active-ingredient types	Relevance to the claim
Short-acting beta agonists	Albuterol or salbutamol	Potentially relevant if delivered by HFA-134a metered-dose inhaler
Inhaled corticosteroids	Fluticasone, beclomethasone, ciclesonide	Potentially relevant where the product uses a metering valve and pulmonary aerosol delivery
Long-acting beta agonists	Formoterol or salmeterol	Product-specific formulation and regulatory patents may be more important
Combination inhalers	Corticosteroid plus bronchodilator	Separate active-specific, device, and formulation rights may apply
Anticholinergic inhalers	Ipratropium or related agents	Claim does not exclude the class, but product formulation details control

The patent does not establish that any particular commercial product infringed. Infringement would require a product-by-product comparison against every claim limitation, including the container, metering valve, HFA-134a propellant, CFC status, and lung-delivery suitability.

How does this patent compare with later inhaler patent estates?

U.S. Patent 5,605,674 addressed the basic HFA-134a metered-dose inhaler platform. Later patent estates generally moved toward narrower and more commercially differentiated subject matter.

Patent category	Typical subject matter	Strategic importance
Propellant platform patents	HFA-134a, HFA-227, and mixtures	Important during the CFC transition; generally expired for early-generation patents
Drug-specific formulation patents	Particle engineering, suspension stability, ethanol level, concentration	Historically stronger against product-specific generic substitutions
Device patents	Metering valve, actuator, dose counter, canister, plume geometry	May create separate device-related barriers
Method-of-use patents	Treatment of asthma, COPD, or other respiratory conditions	Relevant only if the generic label and conduct fall within the claimed method
Manufacturing patents	Filling, mixing, suspension processing, and container preparation	May affect manufacturing routes but not necessarily the final product
Regulatory exclusivity	New chemical entity, pediatric, orphan, or three-year exclusivity	Separate from patent rights and usually time-limited

The '674 patent is therefore best viewed as an early platform patent. It does not capture the full patent estate associated with a modern inhaled product.

What patent litigation affects U.S. Patent 5,605,674?

No current litigation can be based on the expired patent as an enforceable U.S. right. The patent may have appeared in historical infringement disputes, ANDA litigation, licensing negotiations, or product-clearance analyses during its term. Those historical matters do not revive the patent.

For a current generic inhaler, the relevant litigation risk would instead arise from:

Unexpired drug-specific formulation patents;
Device and actuator patents;
Method-of-use patents listed in the Orange Book;
Manufacturing patents;
Continuations or divisionals with later expiration dates;
Patent rights covering alternative propellants or excipient systems;
Trade-secret or know-how disputes involving filling and suspension processes.

An expired platform patent may still appear in technical background or freedom-to-operate records, but it does not independently support a current launch injunction.

What manufacturing and intellectual-property barriers remain?

The expired patent removes one barrier but does not eliminate technical or commercial hurdles.

Formulation development

An HFA-134a inhaler must achieve adequate suspension or solution stability, consistent delivered dose, valve reproducibility, plume performance, and respirable particle delivery. These technical requirements can be difficult even when the core propellant technology is public.

Container and valve compatibility

The canister, valve elastomers, actuator, and formulation must be compatible. Extractables, leachables, corrosion, gasket swelling, and dose uniformity can create regulatory problems independent of patent protection.

In vitro and clinical equivalence

For an ANDA, FDA may require a combination of pharmaceutical equivalence, aerodynamic performance, spray-pattern data, dose uniformity, and comparative clinical or pharmacodynamic evidence. The exact evidentiary package depends on the product and FDA guidance.

Manufacturing know-how

Filling pressure, temperature control, mixing sequence, bulk-hold conditions, and valve crimping can affect product performance. These process controls may be protected by later patents or retained as trade secrets.

What generic launch risks exist after expiration?

The '674 patent creates no current launch risk. A generic HFA-134a metered-dose inhaler could practice the expired claim without liability under that patent.

Current risk analysis should focus on the product-specific estate:

Active-ingredient patents, if any remain;
Formulation patents covering concentration, excipients, or particle properties;
Device patents covering the actuator or metering valve;
Method-of-use patents listed for the reference product;
Pediatric or regulatory exclusivity;
Continuation patents with later expiration dates;
Manufacturing patents covering the proposed process.

For small-molecule inhalers, the applicable FDA pathway is generally an ANDA rather than a biosimilar application. Biosimilar risk is therefore not material to this patent. The principal competitive issue is generic or authorized-generic entry against inhaled products, not biosimilar substitution.

What is the geographic coverage?

U.S. Patent 5,605,674 provides rights only in the United States. Foreign patent family members, if any, had separate prosecution histories, claim scopes, and expiration dates. The expiration of the U.S. patent does not determine the status of corresponding rights in Europe, Japan, Canada, or other jurisdictions.

A global freedom-to-operate review must separately examine:

National-phase HFA-134a formulation patents;
Foreign continuations and divisionals;
Supplementary protection certificates;
Patent-term extensions;
Local regulatory exclusivity;
National claim construction;
Country-specific inhaler device rights.

The U.S. expiration date cannot be imported into other jurisdictions.

How strong was the patent estate?

The patent’s issued claim was commercially broad because it was not limited to one active ingredient, dose, or indication. Its principal weaknesses were structural:

It required an aerosol container and metering valve;
It required HFA-134a;
It required pulmonary suitability;
It did not cover all inhalation technologies;
It did not independently protect a specific branded drug;
Its expiration ended enforceability in 2014.

During its term, the claim could have been important against a competing HFA-134a pressurized inhaler that used the same delivery architecture. After expiration, its legal strength is zero, although its technical disclosure remains relevant prior art against later attempts to claim the same basic platform.

Key Takeaways

U.S. Patent 5,605,674 covers a CFC-free, HFA-134a metered-dose inhaler formulation for pulmonary delivery.
The claim is broad as to medicament and excipients.
The claim is limited to an aerosol container equipped with a metering valve.
HFA-134a must be present, but the claim does not require it to be the sole propellant.
The claim does not cover dry-powder inhalers or ordinary nebulizer products.
The patent issued February 25, 1997 and expired February 25, 2014 under the applicable 17-year term framework.
It cannot support current infringement litigation, a Paragraph IV stay, or an ANDA approval delay.
It is not a biosimilar patent issue because the relevant products are generally small-molecule inhalers.
Current launch risk depends on later drug-specific formulation, device, manufacturing, method-of-use, and regulatory rights.
Foreign patent status must be assessed separately from the expired U.S. right.

Frequently Asked Questions

Could a generic HFA-134a inhaler launch without licensing U.S. Patent 5,605,674?

Yes. The patent expired in 2014, so it no longer requires a license for U.S. manufacture, sale, or use.

Does the patent cover HFA-227-only inhalers?

No. The claim requires a propellant comprising HFA-134a. An inhaler using only HFA-227 would not satisfy that express limitation.

Does the patent cover a dry-powder inhaler containing the same medicament?

Generally no. The claim requires an aerosol container equipped with a metering valve and a propellant containing HFA-134a. A dry-powder inhaler does not use that claimed aerosol architecture.

Can the expired patent be used as prior art against a later inhaler patent?

Yes. Its disclosure and filing history may be prior art under the applicable patent statutes. Expiration removes enforcement rights but does not remove the patent from the prior-art record.

Does expiration of the patent eliminate all patent barriers for an HFA-134a inhaler?

No. Later patents may cover the active ingredient, formulation, device, manufacturing process, method of treatment, or commercial product configuration.

References

U.S. Patent No. 5,605,674. (1997). Aerosol formulation. United States Patent and Trademark Office.
United States Code, 35 U.S.C. § 154. (2023). Contents and term of patents; provisional rights.
United States Food and Drug Administration. (2024). Approved drug products with therapeutic equivalence evaluations. U.S. Department of Health and Human Services.
United States Food and Drug Administration. (2013). Regulatory requirements for approval of metered-dose inhalers and dry-powder inhalers. U.S. Department of Health and Human Services.
United States Environmental Protection Agency. (2024). Protection of stratospheric ozone: Class II substances and the transition from chlorofluorocarbons. U.S. Environmental Protection Agency.

Country	Patent Number	Estimated Expiration	Supplementary Protection Certificate	SPC Country	SPC Expiration
Australia	4595689	⤷ Start Trial
Australia	631155	⤷ Start Trial
Canada	2004598	⤷ Start Trial
>Country	>Patent Number	>Estimated Expiration	>Supplementary Protection Certificate	>SPC Country	>SPC Expiration

Details for Patent: 5,605,674

Summary for Patent: 5,605,674