US Patent 5,326,758: Temazepam Formulation Claims, Patent Scope, Expiration, and Generic Risk

US Patent 5,326,758 covers a narrow method of treating transient insomnia with orally administered crystalline temazepam that meets specified dose, surface-area, and particle-size requirements. The patent does not broadly cover temazepam, all temazepam formulations, or all insomnia treatments. Its practical scope is limited to administering a formulation within defined physical and dosage parameters.

The patent’s baseline 17-year term for a pre-June 8, 1995 application would have placed expiration on or about July 5, 2011, based on the July 5, 1994 issue date. The patent therefore does not create current U.S. generic-entry blocking risk. The principal commercial issue was historical protection for low-dose 7.5 mg temazepam, particularly the formulation later associated with low-dose Restoril and generic temazepam capsules.

What does US Patent 5,326,758 protect?

The patent protects a treatment method requiring all of the following elements:

A human patient.
Treatment of transient insomnia.
Oral administration.
Crystalline temazepam.
A defined temazepam dose.
A specific surface area of 0.65 to 1.1 m²/g.
At least 95% of the temazepam particles having a size below 65 microns.
A formulation consisting essentially of the specified temazepam material.

The patent is therefore a formulation-dependent method-of-use patent. It combines a therapeutic indication with drug-product specifications.

Claim	Dose limitation	Surface area	Particle-size limitation	Legal scope
1	5 to 10 mg	0.65 to 1.1 m²/g	95% below 65 microns	Broadest claim
2	6 to 8 mg	0.65 to 1.1 m²/g	95% below 65 microns	Narrower dose range
3	Exactly 7.5 mg	0.65 to 1.1 m²/g	95% below 65 microns	Narrow species claim

Claims 2 and 3 are presented as separate method claims rather than conventional dependent claims. Claim 3 is the narrowest and most commercially targeted claim because it focuses on the 7.5 mg dose.

How do the three claims differ?

Claim 1 covers administration of 5 through 10 mg. It captures 5, 6, 7.5, 8, 9, and 10 mg doses if the other physical and therapeutic limitations are met.

Claim 2 narrows the dose to 6 through 8 mg. It captures the 7.5 mg dose but excludes 5 mg, 5.5 mg, 8.5 mg, 9 mg, and 10 mg doses.

Claim 3 covers only 7.5 mg. It is narrower in dose but may have greater commercial relevance because 7.5 mg temazepam was developed as a lower-dose insomnia product.

The physical limitations remain identical in every claim. A formulation outside the surface-area range or particle-size limitation would not literally satisfy the claims, even if it contained 7.5 mg of crystalline temazepam and carried an insomnia indication.

What is the meaning of “consisting essentially of” in this patent?

“Consisting essentially of” creates an intermediate claim boundary. It permits excipients and other formulation components that do not materially change the claimed characteristics, while excluding components that materially alter the relevant formulation properties.

The relevant properties are likely the dissolution, absorption, particle-size distribution, surface area, or therapeutic behavior of the crystalline temazepam. The phrase is narrower than “comprising” but broader than “consisting of.”

A capsule containing crystalline temazepam, lactose, starch, magnesium stearate, or similar conventional excipients could potentially fall within the formulation language. An added active ingredient, coating system, particle-engineering agent, or release-modifying component could create a more substantial non-infringement argument if it materially changes the claimed characteristics.

The claim does not expressly define:

The analytical method for measuring surface area.
The analytical method for measuring particle size.
Whether particle size refers to volume, mass, or number distribution.
The identity or concentration of permitted excipients.
A dissolution specification.
A bioequivalence specification.
A particular capsule shell, tablet, suspension, or packaging configuration.

Those omissions could have generated claim-construction disputes during the patent’s enforceable life.

What formulations are protected by US 5,326,758?

The patent potentially covers an oral formulation containing crystalline temazepam with:

A dose between 5 and 10 mg for claim 1;
A dose between 6 and 8 mg for claim 2; or
A 7.5 mg dose for claim 3;
A surface area between 0.65 and 1.1 m²/g; and
A particle-size distribution in which 95% of particles are below 65 microns.

The claims are not limited to capsules by their text. Tablets, powders, sachets, or other oral dosage forms could fall within the literal language if they satisfy the formulation and administration limitations. Commercial temazepam products have principally been oral capsules, making capsules the most relevant product form.

The claims also do not require a specific brand, manufacturer, excipient, manufacturing process, dissolution profile, or pharmacokinetic profile. The formulation must meet the stated physical parameters, regardless of who manufactures it.

Is this a compound patent or a formulation patent?

US 5,326,758 is a formulation and method-of-use patent, not a basic temazepam compound patent.

The patent does not claim:

Temazepam as a chemical compound;
All pharmaceutical uses of temazepam;
All oral temazepam products;
The benzodiazepine class;
A general method of treating insomnia with temazepam;
A manufacturing process for synthesizing temazepam.

Its value depended on the relationship between particle engineering, dose strength, and treatment of transient insomnia. That made the patent narrower than a compound patent but potentially useful against a low-dose product that matched the claimed physical specifications.

When did US Patent 5,326,758 expire?

The patent issued on July 5, 1994. For a U.S. application governed by the pre-URAA patent-term rule, the ordinary term was 17 years from issue. On that basis, the baseline expiration date was July 5, 2011, before any adjustment or extension.

Event	Date or status
Patent issued	July 5, 1994
Baseline pre-URAA term	17 years from issue
Baseline expiration	July 5, 2011
Current enforceability	Expired by ordinary term
Current generic blocking effect	None from this patent

The patent’s expiration eliminates prospective infringement liability for acts occurring after expiration. It does not eliminate potential historical claims for conduct occurring during the enforceable term.

Patent-term adjustment, patent-term extension, terminal disclaimers, or other prosecution-specific events could affect a precise legal calculation. The ordinary term, however, places the patent well outside the current enforceable exclusivity period.

What was the FDA and Orange Book relevance?

The patent was relevant to the U.S. regulatory market for temazepam, a benzodiazepine approved for short-term treatment of insomnia. FDA labeling identifies temazepam capsules in strengths including 7.5 mg, 15 mg, 22.5 mg, and 30 mg. The 7.5 mg strength is the dosage most closely aligned with claim 3 of US 5,326,758.[2]

The patent’s regulatory relevance came from the relationship between:

A low-dose temazepam strength;
A crystalline active ingredient;
Particle-size and surface-area specifications; and
The transient-insomnia treatment indication.

An Orange Book listing, if applicable during the patent’s commercial life, would have required an ANDA applicant to address the patent through one of the Hatch-Waxman certification pathways. A current Orange Book listing would not restore enforceability after expiration.

The patent should be separated from regulatory exclusivity. FDA marketing exclusivity and patent exclusivity are different rights. Any historical regulatory exclusivity for temazepam would have expired long before the present market, and US 5,326,758 does not create current FDA exclusivity.

Did the patent create Paragraph IV risk for generic temazepam?

During its enforceable period, an ANDA applicant seeking approval for a potentially relevant 7.5 mg temazepam product could have faced a Paragraph IV issue if the patent was listed for the reference product and the applicant contended that the patent was invalid, unenforceable, or not infringed.

The most plausible design-around positions would have included:

Using a dose outside the claimed ranges;
Using a non-crystalline form, if pharmaceutically and regulatorily acceptable;
Using particles that failed the 95%-below-65-micron limitation;
Using a surface area below 0.65 or above 1.1 m²/g;
Demonstrating that the product was not intended for transient insomnia;
Challenging the definiteness or enablement of the physical specifications;
Contesting the construction of “consisting essentially of.”

A generic applicant could also argue that the claims were not infringed because the ANDA product did not meet one or more formulation parameters. A product that matched 7.5 mg but used a different particle-size distribution would have had a stronger non-infringement position than a product reproducing the claimed crystalline material.

Because the patent expired in 2011, it no longer presents a live Paragraph IV barrier. A Paragraph IV certification against an expired patent has no practical ability to delay approval under the ordinary 30-month stay mechanism.

What is the biosimilar risk for temazepam?

There is no biosimilar pathway for temazepam. Temazepam is a chemically synthesized small molecule regulated through the ANDA framework, not a biologic regulated under the 351(k) biosimilar pathway.

Competitive entry risks therefore concern:

Generic temazepam capsules;
Strength-specific ANDA approvals;
Formulation differences;
Controlled-substance distribution requirements;
Manufacturing capacity;
Labeling and brand substitution.

Temazepam is a Schedule IV controlled substance in the United States. Controlled-substance status can increase commercial and compliance barriers, but it does not extend the patent term or create biologic-style exclusivity.

How strong was the patent estate for temazepam?

The estate represented by US 5,326,758 was narrow but technically specific.

Strengths

Claim 3 directly targeted the commercially recognizable 7.5 mg strength.
The claims required measurable physical properties.
The patent combined formulation limitations with a therapeutic indication.
A matching product could face both product-characterization and method-of-use arguments.

Weaknesses

The claims did not cover temazepam generally.
The dose ranges were easy to avoid through strength selection.
The particle-size and surface-area limits created potential non-infringement positions.
The patent did not claim a manufacturing process.
The patent term has expired.
The indication limitation could complicate induced-infringement theories depending on labeling and prescribing behavior.

The estate was therefore commercially meaningful during the protected period but did not create durable control over the temazepam market.

What patent litigation and settlement agreements affect this patent?

No current litigation or settlement involving US 5,326,758 can create ongoing market exclusivity because the patent has expired. Historical litigation, if any, would be relevant only to damages, claim construction, validity, or the timing of generic entry during the patent term.

The patent document itself does not establish a licensing deal, settlement agreement, covenant not to sue, or exclusive commercialization arrangement. A patent assignment also would not by itself prove a commercial license. Any analysis of licensing economics must distinguish recorded ownership from private contractual rights.

How does US 5,326,758 compare with competing temazepam patent strategies?

Patent strategy	Typical scope	Relevance to temazepam
Compound patent	Chemical molecule	Broadest, but normally expired first for older drugs
Formulation patent	Dosage form or physical properties	Narrower, potentially useful for low-dose products
Method-of-use patent	Treatment indication	Depends on labeling and actual use
Manufacturing patent	Synthesis or purification	Can create supply-chain barriers
Polymorph or solid-state patent	Crystal form or morphology	May affect active-ingredient sourcing
Device or delivery patent	Administration system	Limited relevance for conventional capsules

US 5,326,758 sits at the intersection of formulation and method-of-use protection. It does not provide a broad solid-state claim to all crystalline temazepam, nor does it claim a specific polymorph by crystal structure or diffraction pattern.

What generic launch scenarios existed?

During the patent term, three principal scenarios existed:

A generic matched the claimed formulation and waited for patent expiry.
A generic launched after a successful Paragraph IV challenge or settlement date.
A generic designed around the dose, surface area, particle-size distribution, or indication language.

After July 2011, the third scenario became commercially unnecessary for this patent. Generic manufacturers could focus on FDA requirements, bioequivalence, controlled-substance compliance, supply, and pricing.

What is the geographic coverage of US 5,326,758?

The patent covers the United States only. It does not create rights in Canada, Europe, Japan, or other markets. Foreign counterparts would require separate analysis of:

National filing and grant status;
Local claim scope;
Patent-term rules;
Supplementary protection certificates;
Opposition or revocation proceedings;
Local generic-entry rules.

A U.S. expiration has no automatic legal effect on foreign rights.

Key Takeaways

US 5,326,758 claims a narrow oral temazepam treatment method for transient insomnia.
The central technical limitations are crystalline temazepam, 0.65 to 1.1 m²/g surface area, and 95% of particles below 65 microns.
Claim 3 specifically targets a 7.5 mg dose.
The patent is not a broad temazepam compound patent.
The ordinary pre-URAA expiration date was July 5, 2011.
The patent creates no current U.S. generic or biosimilar-entry barrier.
Temazepam is a small molecule, so generic competition proceeds through the ANDA pathway rather than biosimilar approval.
The principal historical design-around routes involved dose, crystal form, surface area, particle-size distribution, and labeling.
No license or settlement can be inferred from the patent document alone.
Current commercial risk is driven by generic pricing, controlled-substance compliance, FDA approval status, and manufacturing capacity rather than this expired patent.

FAQs

Does a 7.5 mg temazepam capsule automatically infringe US 5,326,758?

No. It must also contain crystalline temazepam within the claimed surface-area range and particle-size distribution, and the method must involve oral treatment of transient insomnia.

Does the patent cover 15 mg or 30 mg temazepam?

No. The asserted claims cover 5 to 10 mg, 6 to 8 mg, or exactly 7.5 mg. A 15 mg or 30 mg dose falls outside the stated dose limitations.

Can a generic avoid the patent by using a different excipient?

Possibly, but excipient substitution alone may not avoid infringement. The key question is whether the resulting formulation still meets the claimed crystalline temazepam, surface-area, particle-size, dose, and treatment limitations.

Is temazepam subject to biosimilar competition?

No. Temazepam is a chemically synthesized small molecule. Competition occurs through generic ANDA products, not 351(k) biosimilars.

Does patent expiration remove FDA approval requirements for generic temazepam?

No. Expiration removes the patent barrier but does not eliminate FDA requirements for ANDA approval, bioequivalence, manufacturing quality, labeling, or controlled-substance compliance.

References

U.S. Patent No. 5,326,758. (1994). Temazepam formulation. United States Patent and Trademark Office. https://patents.google.com/patent/US5326758A/en
U.S. Food and Drug Administration. (2019). Restoril (temazepam) capsules prescribing information. https://www.accessdata.fda.gov/drugsatfda_docs/label/
U.S. Food and Drug Administration. (2024). Approved drug products with therapeutic equivalence evaluations. Orange Book. https://www.fda.gov/drugs/drug-approvals-and-databases/orange-book-over-counter
U.S. Code, 35 U.S.C. § 154. Patent term.
U.S. Code, 21 U.S.C. § 355. Abbreviated new drug applications and patent certifications.

Country	Patent Number	Estimated Expiration	Supplementary Protection Certificate	SPC Country	SPC Expiration
Belgium	1000318	⤷ Start Trial
Canada	1302886	⤷ Start Trial
Switzerland	673947	⤷ Start Trial
>Country	>Patent Number	>Estimated Expiration	>Supplementary Protection Certificate	>SPC Country	>SPC Expiration

Details for Patent: 5,326,758

Summary for Patent: 5,326,758