US Patent 5,776,433: Flunisolide HFA Aerosol Formulation Scope, Expiration, and Patent Landscape

US Patent 5,776,433 protects solution aerosol formulations of flunisolide using hydrofluorocarbon propellants, ethanol, and specified optional excipients. Its core coverage is directed to HFA-134a, HFA-227ea, or mixtures of those propellants containing approximately 0.1% to 0.9% flunisolide and 3% to 30% ethanol. The patent also covers selected metered-dose inhalers, canister coatings, and an inhaled method for treating bronchial asthma.

The patent has expired under the ordinary 20-year US patent term calculated from its nonprovisional filing date. It therefore presents no current US blocking right against generic or branded flunisolide inhalation products. Its historical commercial relevance was primarily the HFA reformulation marketed as Aerospan.

What does US Patent 5,776,433 cover?

The patent covers a pharmaceutical aerosol in which flunisolide is dissolved in a hydrofluorocarbon propellant system with ethanol as the principal cosolvent. The central composition claim is claim 1.

Claim element	Scope
Active ingredient	Flunisolide
Flunisolide concentration	About 0.1% to about 0.9% by weight
Propellant	HFA-134a, HFA-227ea, or a mixture
Ethanol	About 3% to about 30% by weight
Physical form	Solution aerosol
CFC status	Claim 5 requires the formulation to be free of chlorofluorocarbon propellants
Therapeutic use	Inhaled treatment of bronchial asthma
Device	Metered-dose inhaler containing the claimed formulation

The chemical identities are:

HFA-134a: 1,1,1,2-tetrafluoroethane
HFA-227ea: 1,1,1,2,3,3,3-heptafluoropropane

The claim is directed to a solution rather than a conventional suspension. That distinction matters because a formulation in which flunisolide remains suspended rather than dissolved may avoid the express “solution” limitation, subject to the complete claim construction and infringement facts.

How should claim 1 be interpreted?

Claim 1 is the broadest formulation claim. It requires all of the following:

Flunisolide in solution.
A concentration of approximately 0.1% to 0.9% by weight.
A propellant selected from HFA-134a, HFA-227ea, or their mixture.
Ethanol at approximately 3% to 30% by weight.
A formulation meeting the “consisting essentially of” transition.

“Consisting essentially of” is narrower than “comprising” but broader than “consisting of.” It permits additional ingredients that do not materially alter the basic and novel characteristics of the claimed formulation. In this patent, the apparent basic characteristics are a dissolved flunisolide-HFA-ethanol aerosol system. An added excipient that materially changes solubility, aerosol performance, stability, or delivery could create a claim-construction issue.

The numerical terms “about 0.1%,” “about 0.9%,” and “about 3% to about 30%” introduce a degree of tolerance around the stated endpoints. The permissible range is fact-dependent and would ordinarily depend on specification support, analytical precision, prosecution history, and the extent to which a competing formulation preserves the claimed formulation characteristics.

What formulations are protected by claims 2 through 14?

Claims 2 through 14 narrow claim 1 by selecting propellants, excipients, and concentration ranges.

Claim	Additional limitation
2	HFA-134a as the propellant
3	HFA-227ea as the propellant
4	Mixture of HFA-134a and HFA-227ea
5	No chlorofluorocarbon propellant
6	Water at about 0.005% to 1% by weight
7	Sorbitan trioleate at about 0.001% to 0.1%
8	Cetylpyridinium chloride at about 0.001% to 0.2%
9	Flavoring agent
10	About 0.3% menthol
11	About 0.2% to 0.5% flunisolide, 10% to 20% ethanol, and HFA-227ea
12	Claim 11 plus about 0.001% to 0.005% sorbitan trioleate
13	About 0.2% to 0.5% flunisolide, 10% to 20% ethanol, and HFA-134a
14	Claim 13 plus about 0.001% to 0.005% sorbitan trioleate

Claims 11 and 13 are commercially important fallback compositions because they identify narrower concentration windows and a single HFA propellant. Claims 12 and 14 add very low levels of sorbitan trioleate.

The supplied text states “from about 0.2 percent to about 0.5 by weight” in claims 11 and 13. That language appears incomplete as a transcription. The intended limitation is likely “0.2 percent to 0.5 percent by weight,” but the issued patent text should control any formal claim analysis.

Does the patent cover flunisolide suspension formulations?

The strongest literal scope is for a solution aerosol. The patent does not expressly claim every flunisolide aerosol, every inhaled flunisolide product, or every HFA formulation. A product using a suspension, a different propellant, no ethanol, or ethanol outside the claimed range would not satisfy every express limitation of claim 1.

Potential design-around variables include:

Using a suspension rather than a solution.
Using a propellant outside HFA-134a and HFA-227ea.
Omitting ethanol or using a concentration outside the claimed range.
Using a different corticosteroid.
Using a different delivery system that does not meet the metered-dose inhaler claims.

Those variables would require analysis under both literal infringement and the doctrine of equivalents. The patent’s “consisting essentially of” language could complicate a design-around based solely on adding a minor excipient.

What method-of-use protection does claim 15 provide?

Claim 15 covers a method of treating bronchial asthma by administering, via inhalation, an amount of a claim 1 formulation sufficient to treat the disease.

The method claim requires:

The claimed solution aerosol formulation.
Administration by inhalation.
Treatment of bronchial asthma.
An amount sufficient to treat the condition.

It does not expressly require a particular dose, dosing frequency, inhaler actuation volume, patient population, or treatment duration. The method claim is therefore dependent on the formulation limitations in claim 1. A product that does not contain the claimed formulation would not fall within claim 15 merely because it treats asthma by inhalation.

The claim is also narrower than a general claim to treating respiratory inflammation, allergic rhinitis, chronic obstructive pulmonary disease, or other corticosteroid-responsive conditions.

What metered-dose inhalers are protected by claims 16 through 19?

Claim 16 covers a metered-dose inhaler with:

An aerosol canister defining a formulation chamber; and
A claim 1 formulation contained in that chamber.

Claims 17 through 19 add container limitations:

Claim 17: the formulation chamber is coated with a resin inert to flunisolide.
Claim 18: the resin is an epoxy resin.
Claim 19: the aerosol canister is glass.

These claims are narrower than the composition claims because they require a particular product configuration. A metal canister without the specified coating may fall outside claims 17 and 18 but could still implicate claim 16 if it contains the claim 1 formulation.

The canister and coating claims address compatibility and stability concerns associated with flunisolide and HFA-based formulations. They do not independently protect an empty inhaler or a canister containing a noninfringing formulation.

What is the patent’s priority, expiration, and legal status?

Item	Information
US patent	5,776,433
Subject	Flunisolide aerosol formulations
Filing and priority	Mid-1990s HFA reformulation patent family
Issue date	July 7, 1998
Ordinary US term	20 years from the earliest effective nonprovisional filing date
Expected ordinary expiration	Approximately February 2016, based on the recorded filing history
Current status	Expired
Current blocking effect	None in the United States

The patent issued before the American Inventors Protection Act changed the publication and term framework for later applications. Its term was generally measured from the earliest effective US nonprovisional filing date, not from the issue date. Any patent-term adjustment or terminal disclaimer shown in the official USPTO record would control the exact expiration date. Public patent databases identify the patent as expired, and the term has ended under the ordinary statutory calculation (USPTO, n.d.; Google Patents, n.d.).

Because the patent is expired, the remaining issues are historical validity, claim construction, and freedom-to-operate history rather than prospective enforcement.

What was the FDA and Orange Book status of the flunisolide HFA product?

The principal product associated with this technology was Aerospan, a flunisolide inhalation aerosol approved by the FDA under NDA 021731. Aerospan used an HFA-based formulation and was developed as a replacement for older CFC-propelled flunisolide inhalers.

Regulatory item	Status
Product	Aerospan
Active ingredient	Flunisolide
Dosage form	Inhalation aerosol
FDA pathway	New drug application
NDA	021731
Regulatory relevance	HFA reformulation of flunisolide inhalation therapy
Patent relevance	US 5,776,433 covered the formulation architecture
Current patent barrier	None after expiration

The FDA’s Orange Book records listed patent information for approved drug products where applicable. Orange Book listing does not itself establish that every claim is valid or infringed. It creates a statutory framework for abbreviated new drug application certification and regulatory timing while the listed patent remains in force (FDA, n.d.-a).

The product’s commercial significance declined after patent expiration and changes in the inhaled corticosteroid market. Public FDA records also show that Aerospan is not an actively marketed product with a current, enforceable patent barrier comparable to a recently approved inhaled corticosteroid.

When did flunisolide HFA lose exclusivity?

US patent exclusivity ended around February 2016 under the ordinary patent-term calculation. Regulatory exclusivity, if any, was separate from patent protection and would have expired earlier than the patent.

The relevant exclusivity sequence was:

Event	Approximate timing
HFA formulation patent filing	Mid-1990s
US patent issued	July 7, 1998
Aerospan FDA approval	2006
Ordinary patent expiry	Approximately February 2016
Current status	No enforceable exclusivity from US 5,776,433

The patent did not receive a meaningful post-approval extension that would preserve current exclusivity. Patent expiration removed the principal formulation-based barrier associated with this patent.

Were there Paragraph IV challenges or generic litigation?

There is no established current Paragraph IV litigation threat associated with US 5,776,433 because the patent has expired. A Paragraph IV certification is designed to challenge a listed patent before its expiration. Once the listed patent is no longer enforceable, the commercial value of a new Paragraph IV challenge falls sharply.

Public FDA and court records do not establish a material, continuing Paragraph IV dispute directed specifically at this expired patent. The absence of a current dispute does not imply that no historical ANDA certification or patent correspondence ever existed. It means that US 5,776,433 is not a present litigation barrier for an abbreviated flunisolide inhalation product.

No biosimilar pathway applies. Flunisolide is a small-molecule corticosteroid, so competing products would proceed through an ANDA or other small-molecule pathway rather than the biologics license application and biosimilar framework.

How strong was the patent estate for the technology?

The estate was technically focused rather than broad. Its principal strengths were:

Coverage of dissolved flunisolide in HFA propellants.
Coverage of both HFA-134a and HFA-227ea.
Concentration ranges broad enough to encompass likely therapeutic formulations.
Dependent claims directed to excipients and specific concentration windows.
Device claims linking the formulation to a metered-dose inhaler.

Its limitations were equally clear:

No broad claim to all flunisolide inhalers.
No express coverage of every suspension formulation.
No coverage of propellants outside the listed HFA group.
No independent claim to flunisolide as an active ingredient.
Expiration after the product’s commercial launch.
Narrow device claims requiring specific canister or coating characteristics.

The strongest historical enforcement position would have been against a product that copied the claimed solution formulation, used HFA-134a or HFA-227ea, included ethanol within the claimed range, and marketed the formulation in a metered-dose inhaler.

How does US Patent 5,776,433 compare with competing patent strategies?

Patent strategy	Typical protection	Relative position
Composition patent	Flunisolide, HFA propellant, ethanol	Core protection in US 5,776,433
Formulation improvement	Water, surfactant, flavor, menthol	Covered by dependent claims 6-10
Narrow formulation	Specific flunisolide and ethanol ranges	Covered by claims 11-14
Method of use	Inhaled asthma treatment	Covered by claim 15
Device combination	Canister plus formulation	Covered by claims 16-19
Manufacturing patent	Filling, mixing, valve crimping, or processing	Not expressly covered by the supplied claims
Regulatory exclusivity	FDA approval-based exclusivity	Separate from the patent
Biosimilar protection	Biologic reference product	Not applicable

The patent is a classic CFC-to-HFA reformulation patent. Its value depended on controlling the replacement propellant system during the transition away from ozone-depleting CFCs. It did not create a broad platform monopoly over inhaled corticosteroids or all non-CFC inhalers.

What generic launch risks exist today?

For a current US entrant, US 5,776,433 presents no direct patent-exclusion risk because it has expired. The principal remaining risks would be regulatory and technical:

Demonstrating pharmaceutical equivalence to the reference product.
Establishing bioequivalence for an orally inhaled product.
Matching delivered dose, aerodynamic particle size, spray pattern, valve performance, and actuation characteristics.
Demonstrating container-closure compatibility and formulation stability.
Addressing any later patents, regulatory exclusivity, or product-specific FDA requirements not contained in US 5,776,433.

A generic or follow-on product could still choose to design around the old claims for technical or commercial reasons. It does not need to do so to avoid infringement of an expired US patent.

What licensing and ownership issues are relevant?

The patent was associated with the HFA flunisolide formulation technology developed for commercial inhalation products. The commercial chain included the patent owner or technology developer, the NDA sponsor, and later commercial rights holders. FDA approval records identify the relevant product sponsor, but FDA materials do not establish the complete private licensing chain.

No current license under US 5,776,433 is commercially necessary because the patent term has ended. Historical license agreements could still matter for royalty audits, indemnification, ownership representations, or disputes concerning related foreign patents, know-how, trademarks, or regulatory data. Those private arrangements cannot be inferred from the issued patent claims alone.

Key Takeaways

US Patent 5,776,433 covers flunisolide solution aerosols using HFA-134a, HFA-227ea, or both, with 3% to 30% ethanol.
Claims 11 through 14 target narrower commercial formulations using approximately 0.2% to 0.5% flunisolide and 10% to 20% ethanol.
Claims 15 through 19 extend protection to inhaled asthma treatment and selected metered-dose inhaler configurations.
The patent does not broadly cover every flunisolide inhaler or every HFA formulation.
The patent expired around February 2016 under the ordinary US patent-term calculation.
No current Paragraph IV or biosimilar threat is created by this patent.
Aerospan was the principal FDA-approved product associated with the HFA flunisolide technology.
Current market barriers are more likely to involve FDA requirements, device performance, formulation development, and later intellectual property than US 5,776,433.

FAQs

Is US Patent 5,776,433 still enforceable?

No. The patent’s ordinary US term ended approximately in 2016, subject to the exact USPTO term calculation.

Does US Patent 5,776,433 cover HFA-134a and HFA-227ea equally?

Yes. Claim 1 covers either propellant or a mixture, while claims 2 through 4 separately identify those alternatives.

Can a generic use a flunisolide HFA suspension after this patent expires?

Yes, the expired patent does not block the product. A suspension may also avoid the express “solution” limitation, although separate patents and FDA requirements would remain relevant.

Was Aerospan protected by a biologic exclusivity period?

No. Flunisolide is a small molecule, and Aerospan was regulated through the small-molecule drug framework rather than the biosimilar pathway.

Does the patent protect the inhaler canister by itself?

No. Claims 16 through 19 require the canister to contain the specified flunisolide formulation. The claims do not independently cover an empty canister or a canister containing an unrelated formulation.

References

Food and Drug Administration. (n.d.-a). Approved drug products with therapeutic equivalence evaluations: Orange Book. U.S. Department of Health and Human Services. https://www.fda.gov/drugs/drug-approvals-and-databases
Food and Drug Administration. (n.d.-b). Drugs@FDA: FDA-approved drugs. U.S. Department of Health and Human Services. https://www.accessdata.fda.gov/scripts/cder/daf/
Google Patents. (n.d.). US5776433A: Flunisolide aerosol formulations. https://patents.google.com/patent/US5776433A
United States Patent and Trademark Office. (n.d.). Patent Center. U.S. Department of Commerce. https://patentcenter.uspto.gov/
United States Patent and Trademark Office. (n.d.). Patent term adjustment and patent term information. U.S. Department of Commerce. https://www.uspto.gov/patents/laws/patent-term-adjustment-pta-calculator

Country	Patent Number	Estimated Expiration	Supplementary Protection Certificate	SPC Country	SPC Expiration
Australia	1098695	⤷ Start Trial
Australia	680967	⤷ Start Trial
Canada	2178473	⤷ Start Trial
Germany	69424181	⤷ Start Trial
>Country	>Patent Number	>Estimated Expiration	>Supplementary Protection Certificate	>SPC Country	>SPC Expiration

Details for Patent: 5,776,433

Summary for Patent: 5,776,433