US Patent 5,294,615: Terazosin Hydrochloride Polymorph Scope, Expiration, Litigation and Generic Risk

US Patent 5,294,615 protects a defined crystalline polymorph of terazosin hydrochloride, together with pharmaceutical compositions containing that polymorph and certain soft gelatin dosage forms. The patent does not broadly protect terazosin, terazosin hydrochloride as a chemical entity, every terazosin formulation, or every use of terazosin.

The patent issued on March 15, 1994, and its statutory term expired on March 15, 2011. It therefore presents no current US patent barrier to generic terazosin development. Its historical value was concentrated in the solid-state form and soft gelatin capsule formulation used for Hytrin products. [1][2]

What drug and active ingredient does US Patent 5,294,615 cover?

The claimed compound is terazosin hydrochloride, chemically identified as 1-(4-amino-6,7-dimethoxy-2-quinazolinyl)-4-(2-tetrahydrofuroyl)piperazine monohydrochloride.

Terazosin is an alpha-1 adrenergic receptor antagonist. It has been marketed for:

Hypertension;
Benign prostatic hyperplasia, or BPH; and
Certain cardiovascular indications, including congestive heart failure in the historical patent claims.

The compound was marketed by Abbott Laboratories under the Hytrin brand. Current generic products are generally identified as terazosin hydrochloride capsules or tablets, depending on the manufacturer and approved dosage form.

What are the claims of US Patent 5,294,615?

The claims divide into four technical groups.

Claim	Subject matter	Scope
1	Crystalline polymorph of terazosin hydrochloride	Product claim defined by 13 powder X-ray diffraction peaks
2	Pharmaceutical composition	Polymorph plus a pharmaceutically acceptable carrier
3	Unit dosage form	Soft elastic gelatin shell, polymorph, and non-aqueous liquid fill
4	Liquid carrier	Claim 3 composition in which the carrier includes polyethylene glycol
5	Dosage amount	Active drug amount between 1 mg and 20 mg
6	Method of treatment	Hypertension treatment using the claim 3 dosage form
7	Method of treatment	BPH treatment using the claim 3 dosage form
8	Method of treatment	Congestive heart failure treatment using the claim 3 dosage form

The independent product claim is claim 1. Claims 2 through 8 depend on the claimed polymorph and narrow the subject matter by adding formulation, dosage-form, dose, or treatment limitations.

What crystalline form does US Patent 5,294,615 protect?

Claim 1 protects a particular crystalline polymorph of terazosin hydrochloride characterized by the following powder X-ray diffraction peaks:

2-theta value	Permitted variance
5.5°	±0.2°
10.6°	±0.2°
11.1°	±0.2°
16.7°	±0.2°
19.4°	±0.2°
21.3°	±0.2°
22.0°	±0.2°
22.7°	±0.2°
23.1°	±0.2°
24.4°	±0.2°
24.9°	±0.2°
25.5°	±0.2°
27.8°	±0.2°

The claim is a solid-state identity claim. The central infringement question is whether the accused terazosin hydrochloride material exhibits the claimed diffraction pattern within the stated tolerances.

The claim does not appear to require a particular particle size, residual solvent level, water content, manufacturing process, dissolution profile, or crystal habit. Those attributes could still affect infringement, regulatory equivalence, or product performance, but they are not express limitations in the quoted claim.

How would infringement of the polymorph claim be evaluated?

A typical analysis would compare the accused material against claim 1 using:

Powder X-ray diffraction;
Sample preparation under controlled conditions;
Instrument calibration;
Peak position and relative intensity assessment;
Evaluation of polymorph mixtures; and
Testing of representative commercial lots.

The claim lists peak positions rather than a complete intensity profile. That language makes peak presence and position central, while leaving greater room for disputes over relative intensity, peak resolution, preferred orientation, impurities, and mixtures of polymorphs.

A polymorph mixture could create litigation risk if the claimed form is present and the claim is interpreted to cover material containing the claimed crystalline form. Whether a mixture infringes would depend on claim construction, the specification, and the evidence concerning the accused product.

How broad is claim 2 for pharmaceutical compositions?

Claim 2 covers a pharmaceutical composition containing:

A therapeutically effective amount of the claim 1 polymorph; and
A pharmaceutically acceptable carrier.

This is materially broader than claims 3 through 5 because it does not require:

A soft elastic gelatin shell;
A non-aqueous liquid carrier;
Polyethylene glycol;
A 1 mg to 20 mg dose; or
A particular therapeutic indication.

A tablet, capsule, powder, suspension, or other dosage form could fall within claim 2 if it contains the claimed polymorph and a pharmaceutically acceptable carrier. The claim does not, however, cover a formulation containing only a different terazosin polymorph, amorphous terazosin hydrochloride, terazosin free base, or another salt unless the accused material also satisfies the claim 1 polymorph limitation.

What formulations are protected by claims 3, 4 and 5?

Soft gelatin capsule protection under claim 3

Claim 3 is narrower than claim 2. It requires a unit dosage form with:

An outer soft elastic gelatin shell;
An inner composition filling the shell;
The claimed terazosin hydrochloride polymorph as the active drug; and
A pharmaceutically acceptable non-aqueous liquid carrier.

The claim therefore targets a liquid-filled soft gelatin capsule rather than a conventional compressed tablet or hard-shell capsule.

Polyethylene glycol protection under claim 4

Claim 4 narrows claim 3 by requiring that the non-aqueous carrier comprise poly(ethylene glycol), commonly referred to as PEG.

This limitation could cover PEG-based liquid fills, including formulations in which PEG is combined with other pharmaceutically acceptable excipients. The claim does not specify a PEG molecular weight, concentration, grade, or ratio in the quoted language.

Dosage range under claim 5

Claim 5 requires the active drug component to be present in an amount between 1 mg and 20 mg. The claim is dependent on claim 3, so the soft gelatin capsule and non-aqueous liquid-fill limitations remain applicable.

A product containing 1 mg, 2 mg, 5 mg, 10 mg, or 20 mg of the active component could fall within the numerical range, subject to claim construction concerning endpoint inclusion. A product outside that range would not literally satisfy claim 5, but it could still implicate claims 2, 3, or 4.

What methods of treatment are protected by claims 6, 7 and 8?

Claims 6 through 8 are narrow method claims because each depends on the dosage form in claim 3.

Claim	Indication	Required dosage form
6	Hypertension	Claim 3 soft gelatin dosage form
7	Benign prostatic hyperplasia	Claim 3 soft gelatin dosage form
8	Congestive heart failure	Claim 3 soft gelatin dosage form

These claims do not broadly cover treating the listed diseases with any terazosin product. They require administering the claimed soft gelatin formulation containing the specified crystalline polymorph and non-aqueous liquid carrier.

A generic manufacturer selling a conventional terazosin tablet would face a weaker literal infringement theory under these method claims because the tablet would not satisfy the claim 3 dosage-form limitation. A liquid-filled soft gelatin capsule using the claimed polymorph would present a closer risk profile.

When did US Patent 5,294,615 expire?

US Patent 5,294,615 expired on March 15, 2011, based on its March 15, 1994 issue date and the pre-1995 patent-term framework applicable to the patent. [1][3]

Event	Date
Patent issued	March 15, 1994
Statutory expiration	March 15, 2011
Current status	Expired
Current enforceability	No enforceable patent term remains

No current patent-term extension or pediatric extension is associated with the patent in the cited public records. Any historical patent-term adjustment would have been included in the expiration calculation, but the patent is no longer in force.

What was the Orange Book status of US Patent 5,294,615?

The patent was associated with the Hytrin terazosin product and was relevant to the regulatory exclusivity framework for terazosin hydrochloride. The FDA Orange Book distinguishes between patents claiming the active ingredient, formulation, method of use, and other listed subject matter. [2]

Because US Patent 5,294,615 has expired, it has no current Orange Book blocking effect. A current abbreviated new drug application, or ANDA, applicant does not need to provide a Paragraph IV certification against an expired patent. The relevant historical certification issue would have arisen while the patent remained listed and enforceable.

The patent’s formulation and crystalline-form claims were more relevant to capsule products resembling the patented dosage form than to every terazosin product. A generic applicant could have addressed the patent through a Paragraph IV certification, a statement that the patent was not infringed or was invalid, or a certification based on non-listing or expiration, depending on the regulatory record at the time.

Were there Paragraph IV challenges and generic litigation?

Terazosin became subject to generic competition after the expiration of the relevant pioneer exclusivity and patent barriers. The ordinary Hatch-Waxman framework permitted ANDA applicants to challenge listed patents through Paragraph IV certifications. [4]

The commercial result is clear: generic terazosin products entered the US market, and US Patent 5,294,615 is now expired. The patent should therefore be treated as historical prior art and an expired rights asset rather than an active litigation barrier.

A Paragraph IV challenge against this patent would have focused on several potential issues:

Whether the accused product used the claimed polymorph;
Whether the diffraction peaks were inherent in prior-art terazosin hydrochloride;
Whether the claimed polymorph was obvious over known terazosin salts and crystallization techniques;
Whether the claim adequately defined the polymorph;
Whether the soft gelatin formulation was novel and non-obvious;
Whether the method claims were infringed by the proposed label; and
Whether the claims were enabled across their full scope.

No present-day launch restriction flows from those historical issues because the patent term has ended.

How strong was the patent estate for terazosin?

The patent estate represented by US Patent 5,294,615 was technically focused rather than molecule-wide.

Dimension	Assessment
Active ingredient coverage	Limited; does not claim terazosin generically
Salt coverage	Limited to the claimed hydrochloride polymorph
Solid-state coverage	Strong if the accused material matches the listed XRPD pattern
Formulation coverage	Moderate to strong for soft gelatin liquid-filled capsules
Tablet coverage	Limited under claims 3-5; potentially relevant under claim 2
Method-of-use coverage	Narrow because claims 6-8 depend on claim 3
Manufacturing-process coverage	None apparent from the quoted claims
Geographic coverage	United States only
Current enforceability	None because the patent expired in 2011

The strongest historical position was against a soft gelatin capsule containing the same crystalline form in a PEG-containing liquid fill. The weakest position was against a tablet containing a different polymorph or against a product using terazosin free base or a different salt.

What manufacturing and intellectual-property barriers did the patent create?

The patent could have required a generic developer to characterize its terazosin hydrochloride solid form before filing or launch. The key technical work would include:

Crystallization-process development;
Polymorph screening;
XRPD comparison;
Thermal analysis;
Solid-state stability testing;
Control of polymorph conversion during granulation, encapsulation, and storage;
Evaluation of excipient compatibility; and
Selection of a dosage form that avoided the soft gelatin and PEG limitations.

A manufacturer could potentially design around the claims by using:

A non-claimed polymorph;
An amorphous form;
Terazosin free base;
Another salt;
A tablet rather than a soft gelatin capsule;
An aqueous or solid carrier rather than the claimed non-aqueous liquid fill; or
A formulation outside the 1 mg to 20 mg range for claim 5.

Those strategies would not necessarily avoid other patents, regulatory obligations, or product-quality requirements. They would, however, address the principal limitations of US Patent 5,294,615.

How does US Patent 5,294,615 compare with current generic terazosin risk?

Current generic risk is primarily regulatory and commercial, not patent-based.

Risk category	Current position
Patent blocking risk	Low; patent expired
Paragraph IV exposure	None against this expired patent
Biosimilar risk	Not applicable; terazosin is a small-molecule drug
Solid-state development risk	Still relevant for quality and equivalence, but not because this patent is enforceable
Formulation design risk	Depends on current patents and product-specific regulatory records
Manufacturing risk	Depends on process capability and polymorph control
Price competition	High because multiple generic suppliers can compete
Brand revenue protection	No continuing protection from this patent

Terazosin is not a biologic, so biosimilar litigation and biologics patent dance procedures do not apply. The relevant pathway is the ANDA process for small-molecule generics. [4][5]

Were there licensing deals associated with the patent?

The patent record identifies the patent owner and inventorship but does not itself establish a continuing license, royalty arrangement, or settlement agreement. Patent ownership, product marketing rights, and regulatory sponsorship can be held by different entities, but a patent document alone does not prove the terms of any commercial agreement.

Because the patent expired in 2011, any historic license relating specifically to this patent has no remaining exclusionary effect against a new US generic entrant.

What is the commercial exposure from the expired patent?

The patent has no current standalone revenue-protection value. Its historical commercial importance came from the Hytrin soft gelatin presentation and the ability to delay or complicate competing products that used the same polymorph and formulation architecture.

Current revenue exposure is instead driven by:

Generic substitution;
Number of approved ANDA holders;
Retail and mail-order purchasing;
Reimbursement policy;
Dosage-form preferences;
Manufacturer shortages or discontinuations; and
Brand-prescribing persistence.

Public sources do not establish a current revenue stream attributable specifically to the expired patent. Any valuation model that assigns ongoing exclusivity value to US Patent 5,294,615 would be incorrect.

Key Takeaways

US Patent 5,294,615 covers a defined crystalline polymorph of terazosin hydrochloride.
Claim 1 is the core patent claim and uses 13 XRPD peak positions to identify the polymorph.
Claim 2 covers compositions containing that polymorph and a pharmaceutically acceptable carrier.
Claims 3 through 5 focus on soft gelatin, non-aqueous liquid-filled capsules, PEG-containing carriers, and 1 mg to 20 mg doses.
Claims 6 through 8 cover treatment of hypertension, BPH, and congestive heart failure only with the claim 3 dosage form.
The patent issued March 15, 1994, and expired March 15, 2011.
It has no current Orange Book blocking effect and creates no present Paragraph IV barrier.
Biosimilar analysis does not apply because terazosin is a small molecule.
Historical infringement risk was highest for soft gelatin capsules using the claimed polymorph and liquid-fill formulation.
Current generic entry risk is commercial and regulatory rather than patent-based.

FAQs

Does US Patent 5,294,615 cover all terazosin hydrochloride products?

No. It covers a specific crystalline polymorph identified by the listed XRPD peaks. It does not expressly cover every polymorph, amorphous terazosin hydrochloride, or every terazosin hydrochloride formulation.

Can a terazosin tablet infringe US Patent 5,294,615?

A tablet could potentially implicate claim 2 if it contains the claimed polymorph. Claims 3 through 5 are directed to a soft elastic gelatin dosage form and would generally not read literally on a conventional tablet.

Is terazosin subject to biosimilar competition?

No. Terazosin is a small-molecule drug regulated through the generic drug framework, principally the ANDA pathway, rather than the biosimilar pathway.

Could a different terazosin salt avoid this patent?

A different salt would generally avoid the express limitation requiring terazosin hydrochloride monohydrochloride, subject to the scope of other patents and any claim-construction issues.

Does the patent still affect US generic approval?

No. The patent expired in 2011. It no longer requires a Paragraph IV challenge and does not independently prevent FDA approval or commercial launch of a compliant generic terazosin product.

References

United States Patent and Trademark Office. (1994). U.S. Patent No. 5,294,615, crystalline form of terazosin hydrochloride and pharmaceutical compositions containing same.
U.S. Food and Drug Administration. (2024). Approved drug products with therapeutic equivalence evaluations: Orange Book.
United States Patent and Trademark Office. (2024). Patent term calculator and patent term guidance.
U.S. Food and Drug Administration. (2024). Abbreviated new drug application submissions: Patent certifications and exclusivity.
U.S. Food and Drug Administration. (2024). Terazosin hydrochloride drug products and labeling information.

Country	Patent Number	Estimated Expiration	Supplementary Protection Certificate	SPC Country	SPC Expiration
Austria	130853	⤷ Start Trial
Austria	182592	⤷ Start Trial
Canada	2107382	⤷ Start Trial
>Country	>Patent Number	>Estimated Expiration	>Supplementary Protection Certificate	>SPC Country	>SPC Expiration

Details for Patent: 5,294,615

Summary for Patent: 5,294,615