US Patent 7,138,524: Fexofenadine Hydrochloride Form I Patent Scope and Landscape

US Patent 7,138,524 protected a specific crystalline form of fexofenadine hydrochloride: Form I anhydrous fexofenadine hydrochloride. The claim did not cover fexofenadine hydrochloride generally, every polymorph, the active pharmaceutical ingredient in solution, or all pharmaceutical uses. The patent issued on November 21, 2006, and its standard United States patent term ended in December 2023, subject to any recorded patent-term adjustment or disclaimer. The claimed form is now outside its ordinary enforceable patent term.

The claim covered a solid-state form of the antihistamine fexofenadine hydrochloride, the active ingredient historically marketed as Allegra by Hoechst Marion Roussel, Aventis, and later Sanofi. Because fexofenadine is a small molecule, biosimilar provisions do not apply. Generic competition proceeded through abbreviated new drug applications, not the biosimilar pathway.

What compound does US Patent 7,138,524 protect?

Claim 1 identifies:

Form I anhydrous 4-[4-[4-(hydroxydiphenylmethyl)-1-piperidinyl]-1-hydroxybutyl]-α,α-dimethylbenzeneacetic acid hydrochloride.

This chemical name describes fexofenadine hydrochloride. The operative patent limitation is not merely the chemical identity. It is the requirement that the compound exist as:

Fexofenadine hydrochloride;
An anhydrous solid;
The specific crystalline polymorph designated Form I.

The patent therefore is a polymorph patent. Its legal value depends on whether an accused product contains Form I, rather than another form of fexofenadine hydrochloride.

What is fexofenadine hydrochloride?

Fexofenadine hydrochloride is the active metabolite of terfenadine and is marketed as a second-generation H1 antihistamine. It is used for allergic rhinitis and chronic idiopathic urticaria. The compound is generally administered orally in tablets, orally disintegrating tablets, capsules, and oral suspensions.

The original active-ingredient and therapeutic-use patents were separate from the Form I patent. Those earlier rights expired before US Patent 7,138,524 became commercially important.

What is the precise scope of claim 1?

Claim 1 is narrow in chemical and solid-state scope. A product would need to satisfy both the compound limitation and the Form I anhydrous limitation.

Claim element	Scope
Active molecule	Fexofenadine
Salt form	Hydrochloride
Physical state	Solid crystalline material
Hydration state	Anhydrous
Polymorph	Form I
Covered product	Form I anhydrous fexofenadine hydrochloride
Express coverage of other polymorphs	No
Express coverage of amorphous material	No
Express coverage of solutions	No
Express coverage of a manufacturing process	No, based on the quoted claim
Express coverage of a method of treatment	No, based on the quoted claim

The claim is likely infringed by a drug product that contains Form I anhydrous fexofenadine hydrochloride as the active ingredient, even if the product also contains conventional excipients. The presence of a tablet coating, binder, disintegrant, or other inactive ingredient would not ordinarily remove the Form I material from the product.

The claim does not automatically cover:

Fexofenadine free base;
Fexofenadine hydrochloride Form II or another polymorph;
A hydrate or solvate;
Amorphous fexofenadine hydrochloride;
A liquid formulation in which the crystalline form is no longer present;
A chemically different salt;
A process that produces a different solid-state form.

The central infringement issue would be whether Form I exists in the drug substance or finished dosage form at the relevant point in the supply chain.

How would Form I infringement be established?

Solid-state infringement would normally require analytical evidence. The principal techniques would include:

Powder X-ray diffraction;
Differential scanning calorimetry;
Thermogravimetric analysis;
Infrared or Raman spectroscopy;
Karl Fischer water analysis;
Solid-state nuclear magnetic resonance;
Microscopy and particle characterization.

Powder X-ray diffraction would likely be the primary method for distinguishing Form I from other crystalline or amorphous forms. Thermal behavior and water-content data would help establish the anhydrous limitation.

The analysis must address two separate questions:

Does the sample contain crystalline Form I?
Is the claimed material anhydrous rather than a hydrate or solvate?

A generic manufacturer could contest infringement by asserting that its API is another polymorph, a mixture in which Form I is not present, or an amorphous or hydrated form. The result would depend on claim construction, the patent's specification, expert testing, and the product's manufacturing and storage conditions.

When did US Patent 7,138,524 expire?

US Patent 7,138,524 was issued on November 21, 2006. Public patent records identify a December 2002 priority date and a US filing pathway associated with the fexofenadine hydrochloride polymorph application. Under the Uruguay Round Agreements Act, the relevant term for a post-1995 US application generally runs 20 years from the earliest effective nonprovisional filing date, not from the grant date.[1]

The ordinary patent-term analysis is:

Event	Date or period
Priority filing	December 2002
US patent grant	November 21, 2006
Standard 20-year term endpoint	December 2023
Current status	Expired by ordinary term, absent an unusual term adjustment

A patent-term adjustment could move the endpoint modestly. The controlling source for a precise day-level calculation is the USPTO patent record and the patent's face-page term data. The patent's commercial blocking value ended no later than the ordinary December 2023 term unless a specific adjustment or disclaimer changed that date.

What patents originally protected fexofenadine and Allegra?

The fexofenadine patent estate developed in layers. The key categories were the active compound, pharmaceutical compositions, therapeutic uses, formulations, and crystalline forms.

Patent category	Representative protection	Commercial significance
Active compound	Earlier fexofenadine patents	Protected the molecule and core pharmaceutical use
Pharmaceutical composition	Fexofenadine-containing dosage forms	Covered drug products and excipient combinations in defined claims
Therapeutic use	Treatment of allergic conditions	Covered administration for specified indications
Salt or solid form	Fexofenadine hydrochloride and polymorphs	Addressed manufacturing, stability, and product-quality issues
Form I polymorph	US 7,138,524	Covered the identified anhydrous crystalline form

US Patent 5,375,693 is commonly associated with the original fexofenadine compound and pharmaceutical-use estate. Its term ended well before the Form I patent. The earlier expiration opened the market to generic fexofenadine products, while later solid-form rights could still create a narrower barrier if a generic used the patented polymorph.[2]

The existence of an earlier expired compound patent did not invalidate a later polymorph patent. A new crystalline form can be patentable if it satisfies novelty, nonobviousness, utility, and disclosure requirements. The later patent, however, cannot restore exclusivity over the underlying molecule itself.

What was the FDA and Orange Book status?

Fexofenadine hydrochloride was approved by the FDA as Allegra. The product later transitioned from prescription to over-the-counter status. FDA records identify fexofenadine hydrochloride products in tablet, orally disintegrating, capsule, and suspension formats.[3]

The Orange Book analysis requires separating FDA regulatory exclusivity from patent rights:

Issue	Effect
New chemical entity exclusivity	Expired
Original drug patent exclusivity	Expired
Form I patent term	Ended in December 2023 under the ordinary term calculation
Generic approval route	ANDA
Biosimilar pathway	Not applicable
OTC status	Fexofenadine products are marketed over the counter
Current commercial barrier	Brand recognition, distribution, formulation, and manufacturing scale rather than the expired Form I patent

A patent appears in the Orange Book only if the NDA holder submits it and FDA accepts it as relevant to an approved drug product or method of use under FDA listing rules. A patent directed solely to a crystalline API form may be listed only if it meets the applicable listing requirements and relates to the approved drug product.[4]

The Orange Book should not be treated as a complete record of every patent that once affected Allegra. Patents may be omitted, delisted, expire, or cease to have practical relevance after an OTC conversion. The expiration of US 7,138,524 independently removes its current US enforcement value regardless of historical listing status.

Were there Paragraph IV challenges to the fexofenadine estate?

Generic applicants seeking prescription approval for fexofenadine could use Paragraph IV certifications against listed patents. A Paragraph IV certification states that a listed patent is invalid, unenforceable, or will not be infringed by the proposed ANDA product.[5]

The principal commercial entry barriers for generic fexofenadine were the earlier compound and use patents, not only US 7,138,524. Generic applicants could pursue several strategies:

Certify that listed patents had expired.
File Paragraph IV certifications against unexpired patents.
Use a section viii statement to omit a patented method of use where permitted.
Formulate the product without the claimed solid form.
Wait for patent expiration and launch under the ordinary ANDA route.

A Paragraph IV certification against a polymorph patent would have created litigation risk if the applicant's API supplier used Form I. The ANDA applicant could instead challenge the patent's validity, argue noninfringement, or design around the claimed form.

The statutory 30-month stay under the Hatch-Waxman Act would apply only if the patent and certification satisfied the statutory conditions and the NDA holder or patent owner sued within the prescribed period. The stay would not extend the patent term.[5]

What patent litigation affected fexofenadine?

Fexofenadine generated generic-drug litigation involving the broader Allegra patent estate and the timing of generic entry. The litigation environment included disputes over compound patents, formulations, and the scope of abbreviated new drug applications.

A patent-by-patent litigation conclusion requires matching each case to the asserted patent, product, court, and settlement terms. Publicly available litigation involving fexofenadine does not convert every Allegra-related dispute into a direct adjudication of US 7,138,524. The relevant distinction is:

Litigation over the original fexofenadine compound patent concerned molecule-level or use-level exclusivity.
Litigation over a Form I patent would concern crystalline-form identity, testing, claim construction, validity, and design-around.
Litigation over FDA approval could concern Orange Book listing, certification, or regulatory exclusivity rather than technical infringement.

No current US litigation can preserve an expired patent's prospective exclusionary term. A damages claim for pre-expiration conduct could remain legally distinct from current launch blocking, but the patent's ordinary term has ended.

How strong was the Form I patent estate?

The patent was commercially meaningful but technically narrow.

Strengths

It targeted a defined crystalline form used in pharmaceutical manufacturing.
Solid-form claims can be difficult to avoid if the manufacturing process naturally produces the claimed form.
The claim could reach the API inside a finished tablet.
Analytical testing can provide direct evidence of the polymorph.

Weaknesses

The claim did not cover fexofenadine hydrochloride generically.
A competing polymorph, hydrate, amorphous form, or alternative salt could avoid the literal claim.
Form I identity must be proved through analytical evidence.
The patent did not independently protect the active molecule after the earlier compound patents expired.
The patent term ended in 2023.

The practical strength depended on whether Form I was the commercially preferred or thermodynamically stable form. If Form I was the easiest form to manufacture and formulate, design-around could be difficult even though the claim language was narrow. If alternative forms had equivalent stability, dissolution, bioavailability, and manufacturability, the design-around risk was higher.

What generic entry risks existed?

Before expiration, generic applicants faced four principal risks:

Risk	Description
Direct infringement	The proposed API contained Form I anhydrous fexofenadine hydrochloride
Induced or contributory infringement	The product or supply chain encouraged use of the patented form
ANDA litigation	A Paragraph IV certification triggered suit and possible delay
Regulatory-product mismatch	The ANDA specification identified a form different from the material actually manufactured

After expiration, the Form I patent no longer provides a prospective launch injunction based solely on its unexpired term. Remaining risks would arise from other unexpired patents, regulatory requirements, trade secrets, contractual restrictions, or manufacturing disputes, not from the ordinary exclusionary term of US 7,138,524.

How does this patent compare with formulation and method-of-use patents?

US 7,138,524 is narrower than a formulation patent in one respect and broader in another.

A formulation patent generally requires a defined combination of active ingredient and excipients, dosage range, release profile, or delivery system. It may be avoided by changing the formulation while retaining the same API form.

A method-of-use patent requires administration of the drug for a specified disease, patient population, dose, or treatment schedule. It may be avoided through a noninfringing label or a section viii carve-out.

The Form I patent instead follows the API's solid-state identity. It can affect multiple dosage forms because tablets, capsules, and suspensions may all use the same API before incorporation into the final product. Its limitation is that it does not automatically reach alternative forms or products in which the claimed crystalline material is absent.

What is the current commercial significance?

The current commercial significance of US 7,138,524 is historical rather than exclusionary. Fexofenadine hydrochloride is a mature generic and OTC antihistamine. The principal competitive factors are:

API cost;
FDA-compliant manufacturing;
product quality and impurity control;
tablet and suspension manufacturing;
retail distribution;
private-label and store-brand contracts;
packaging and consumer recognition.

A generic manufacturer does not face a current US Form I patent barrier from the ordinary term of US 7,138,524. The patent remains relevant for prior-period infringement analysis, historical generic-entry strategy, and understanding the solid-form estate that supported Allegra commercialization.

Key Takeaways

US Patent 7,138,524 claimed Form I anhydrous fexofenadine hydrochloride.
It was a narrow polymorph patent, not a patent on fexofenadine generally.
The claim required the specific Form I crystalline form and the anhydrous state.
It did not expressly cover other polymorphs, hydrates, amorphous material, methods of treatment, or manufacturing processes.
Powder X-ray diffraction and complementary solid-state testing would be central to infringement analysis.
The ordinary US patent term ended in December 2023.
Fexofenadine is a small molecule, so biosimilar rules do not apply.
Generic competition proceeded through the ANDA framework and Paragraph IV or expiration certifications.
Current generic entry is not blocked by the expired Form I patent.
Remaining commercial barriers are primarily manufacturing, regulatory, supply-chain, and market-access barriers.

FAQs About US Patent 7,138,524 and Fexofenadine

Does US Patent 7,138,524 cover all fexofenadine hydrochloride?

No. The quoted claim is limited to Form I anhydrous fexofenadine hydrochloride. Other polymorphs, hydrates, solvates, and amorphous forms are outside the literal scope unless another claim or infringement theory applies.

Can a generic manufacturer use fexofenadine hydrochloride after the patent expired?

Yes. The expiration of the Form I patent removes that patent as a current US launch barrier. The generic product must still satisfy FDA requirements and avoid any separate unexpired patent rights.

Is fexofenadine a biologic requiring a biosimilar application?

No. Fexofenadine hydrochloride is a synthetic small-molecule drug. Generic manufacturers use the ANDA pathway, not the abbreviated biologics license application pathway.

Would a hydrate of fexofenadine hydrochloride infringe claim 1?

Not literally if the claim requires an anhydrous form and the product is a hydrate. The answer could depend on the full patent claims, prosecution history, claim construction, and any doctrine-of-equivalents analysis.

Does the patent cover Allegra's therapeutic use for allergies?

Not based on the quoted claim. Claim 1 is directed to a crystalline chemical form. Therapeutic-use protection would require separate method-of-treatment claims or another patent.

References

United States Patent and Trademark Office. (2024). Patent term adjustment and patent term calculation guidance. https://www.uspto.gov
United States Patent and Trademark Office. (2006). US Patent No. 7,138,524, Form I anhydrous fexofenadine hydrochloride.
U.S. Food and Drug Administration. (2024). Drugs@FDA: FDA-approved drugs and fexofenadine hydrochloride product information. https://www.accessdata.fda.gov
U.S. Food and Drug Administration. (2024). Approved drug products with therapeutic equivalence evaluations: Orange Book. https://www.fda.gov
Federal Food, Drug, and Cosmetic Act, 21 U.S.C. § 355(j); 21 C.F.R. § 314.94.

Country	Patent Number	Estimated Expiration	Supplementary Protection Certificate	SPC Country	SPC Expiration
Austria	220667	⤷ Start Trial
Australia	2426595	⤷ Start Trial
Australia	693892	⤷ Start Trial
>Country	>Patent Number	>Estimated Expiration	>Supplementary Protection Certificate	>SPC Country	>SPC Expiration

Details for Patent: 7,138,524

Summary for Patent: 7,138,524