United States Patent 5,462,740: Scope, Claims, Expiration, and Patent Landscape for Rectal Diazepam Compositions

U.S. Patent No. 5,462,740 covered viscous rectal compositions containing an antiepileptic drug, a pH buffer, a cellulose-ether thickener, and water or a water-miscible organic solvent. Its most commercially significant embodiment was a diazepam rectal gel corresponding to Diastat. The patent issued on October 31, 1995, and its 17-year patent term expired on October 31, 2012. It is no longer an enforceable exclusionary right in the United States.[1]

The patent remains relevant for historical analysis of Diastat, generic entry, formulation strategy, and the transition from rectal to intranasal rescue medicines. It does not create a current U.S. patent barrier to generic diazepam rectal gel products.

What invention does U.S. Patent 5,462,740 cover?

The patent covers a viscous, seizure-inhibiting pharmaceutical composition designed for rectal administration. Its technical objective is to combine:

An antiepileptic agent;
A buffer maintaining a pH of approximately 5.5 to 7.5;
A cellulose ether thickener;
Water or a water-miscible organic solvent;
Sufficient viscosity for rectal injection; and
Sufficient solvent capacity to keep the active drug from precipitating.

The commercial relevance lies in the formulation architecture. Diazepam has limited water solubility. A water-miscible organic solvent can improve solubilization, while the cellulose ether increases viscosity and allows administration through a rectal applicator.

The patent is a composition patent. It does not primarily claim the rectal applicator, a dosing syringe, a patient-use protocol, or a specific manufacturing process.

What are the independent claims in U.S. Patent 5,462,740?

Claims 1 and 8 are the principal independent claims.

Claim	Core subject matter	Key limitations
1	Broad viscous antiepileptic composition	0.1-2.5 wt.% antiepileptic; pH 5.5-7.5 buffer; 1-10 wt.% cellulose ether; 25-95 wt.% solvent; viscosity suitable for rectal injection
8	Narrow diazepam formulation	0.25-0.75 wt.% diazepam; pH 5.5-7.5 buffer; 1-10 wt.% cellulose ether; 25-75 wt.% nontoxic water-miscible organic solvent; balance water

Claim 8 is the commercially important claim because it specifically targets a diazepam rectal composition. It is narrower than claim 1 in active ingredient and solvent concentration but remains broad in the choice of cellulose ether, buffer, and organic solvent.

How broad is claim 1 of U.S. Patent 5,462,740?

Claim 1 is broad in the identity of the antiepileptic drug but narrow in formulation architecture.

A potentially infringing composition would generally need to satisfy all of the following limitations:

It is a composition that inhibits epileptic seizures.
It contains approximately 0.1-2.5 wt.% of an antiepileptic agent.
It contains a buffer system maintaining pH at approximately 5.5-7.5.
It contains approximately 1-10 wt.% cellulose ether.
The thickener imparts viscosity suitable for rectal injection.
It contains approximately 25-95 wt.% solvent.

The claim uses "comprising," an open-ended transition. Additional excipients, preservatives, flavoring agents, stabilizers, or other ingredients would not avoid the claim if all required elements were present.

The claim does not require diazepam. It can potentially cover formulations containing other antiepileptic agents, subject to the claim limitations and the scope of the specification.

What drugs are covered by the Markush group in claim 2?

Claim 2 narrows claim 1 to antiepileptic agents selected from six drug classes:

Barbiturates;
Benzodiazepines;
Dipropylacetic acid derivatives;
Hydantoins;
Oxazolidinediones; and
Succinimides.

Claim 3 narrows claim 2 further to diazepam. The claim structure means that a diazepam formulation must satisfy claim 1 and the additional limitations incorporated through claims 2 and 3.

The Markush language is significant because claim 2 is not limited to a single named drug. It reaches members of the listed classes, although any enforcement analysis would depend on whether the accused active ingredient falls within the relevant class and whether the complete formulation meets the remaining limitations.

What formulation characteristics are protected by claims 4 through 7?

Viscosity under claim 4

Claim 4 specifies an apparent viscosity of approximately 1,000 to 8,000 centipoise. This limitation gives the claim a measurable rheological boundary that is absent from claim 1.

A formulation with viscosity in this range is more likely to satisfy claim 4, assuming the other claim 1 elements are present. A formulation outside the range may still implicate claim 1 if it remains suitable for rectal injection.

The term "apparent viscosity" creates technical questions concerning test method, temperature, shear rate, spindle, and instrument configuration. Those parameters can affect whether a formulation falls within a claimed viscosity range. A meaningful infringement analysis would therefore compare testing conditions, not only a single reported viscosity number.

Cellulose ether under claims 5 and 6

Claim 5 identifies four cellulose ethers:

Methyl cellulose;
Carboxymethylcellulose;
Hydroxypropylcellulose; and
Hydroxypropylmethylcellulose.

Claim 6 narrows claim 5 to hydroxypropylmethylcellulose, commonly abbreviated HPMC.

These claims create a formulation-specific barrier against a product using one of the named cellulose ethers. A product using a non-cellulosic thickener, such as a carbomer or another polymeric viscosity modifier, would not literally satisfy claims 5 or 6. It could still require analysis under the broader claim 1 if the material qualifies as a cellulose ether, and under equivalents principles depending on the facts.

Solvent under claim 7

Claim 7 permits water alone or water combined with a water-miscible organic solvent. The solvent must be present in an amount effective to inhibit precipitation of the antiepileptic agent.

This limitation links solvent selection to a performance result. Suitable solvents for diazepam formulations may include pharmaceutically acceptable water-miscible organic solvents, such as propylene glycol or ethanol, depending on the formulation and regulatory specifications.

A formulation using a non-water-miscible solvent, or one in which the solvent does not perform the claimed precipitation-inhibition function, presents a stronger non-infringement position. The analysis would still depend on claim construction and experimental evidence.

How does claim 8 differ from claim 1?

Claim 8 is a diazepam-specific independent claim with tighter concentration limits.

Limitation	Claim 1	Claim 8
Antiepileptic agent	0.1-2.5 wt.%	Diazepam at 0.25-0.75 wt.%
Buffer pH	5.5-7.5	5.5-7.5
Cellulose ether	1-10 wt.%	1-10 wt.%
Solvent	25-95 wt.%	25-75 wt.% nontoxic water-miscible organic solvent
Water	Not expressly required	Balance of composition
Rectal administration	Required through claim language	Required through inherited formulation context
1,000-8,000 cps viscosity	Not required	Not required unless separately incorporated by claim construction

Claim 8 does not expressly require the specific 1,000-8,000 cps range in claim 4. It also does not limit the cellulose ether to HPMC. A diazepam product using another cellulose ether could therefore fall within claim 8 if the remaining limitations were satisfied.

What patent protected Diastat and when did it expire?

U.S. Patent 5,462,740 was assigned originally to Athena Neurosciences, Inc., the company associated with the development of diazepam rectal gel.[1] The patent issued October 31, 1995.

Because the application falls within the pre-Uruguay Round patent-term regime, the relevant term was generally 17 years from issuance rather than 20 years from the earliest effective nonprovisional filing date. On that basis, the patent expired October 31, 2012.[1]

Event	Date
Patent issued	October 31, 1995
FDA approval of Diastat rectal gel	1997
Patent expiration	October 31, 2012
Current enforceability	Expired

FDA approved Diastat rectal gel under NDA 020648 in 1997. The product was indicated for the acute treatment of intermittent, stereotypic episodes of frequent seizure activity in patients with epilepsy who were maintained on stable regimens of antiepileptic drugs.[2]

What was the Orange Book status of U.S. Patent 5,462,740?

U.S. Patent 5,462,740 was listed in the FDA Orange Book in connection with diazepam rectal gel, including the Diastat product line.[3] The listing gave the innovator a basis to assert the patent against an abbreviated new drug application before expiration.

The Orange Book listing did not extend the patent term. Once the patent expired in 2012, it ceased to function as a prospective barrier to ANDA approval or commercial generic entry.

The Orange Book analysis should distinguish:

Patent listing status;
Patent expiration;
FDA regulatory exclusivity;
Patent litigation;
Current enforceability.

These are separate legal and regulatory concepts. A product may remain listed in the Orange Book after a patent has expired, but an expired patent cannot block launch.

Were there Paragraph IV challenges to this patent?

A Paragraph IV certification would have been the standard ANDA mechanism for challenging an unexpired patent listed for diazepam rectal gel. The applicant would assert that the patent was invalid, unenforceable, or would not be infringed by the proposed generic product.

The practical window for a Paragraph IV dispute was limited because the patent expired in 2012. Generic development and regulatory filing could proceed through other certification pathways after expiration. A post-expiration ANDA applicant would not need to litigate the patent to obtain a commercial launch right based on the expired patent.

The patent’s age also reduced the commercial value of a Paragraph IV challenge. Any 30-month stay associated with a timely patent litigation strategy would have had to fit within the remaining patent term. The key commercial question was therefore timing, not only validity.

What patent litigation affected Diastat?

The patent created a potential litigation basis against generic diazepam rectal gel during its term. After October 31, 2012, the patent could no longer support an injunction against future sales based on continuing infringement.

Any historical litigation would require separation between:

Pre-expiration infringement claims;
Post-expiration sales;
ANDA litigation;
Patent-listing disputes; and
Regulatory exclusivity disputes.

The available patent record establishes the patent’s expiration but does not support treating U.S. Patent 5,462,740 as an active litigation barrier today.[1][3]

What generic entry risks existed for Diastat?

Before expiration, the principal generic risk was a formulation that reproduced the claim architecture:

Diazepam in the 0.25-0.75 wt.% range;
A pH buffer at 5.5-7.5;
Cellulose ether at 1-10 wt.%;
A water-miscible organic solvent at 25-75 wt.%;
Water as the balance; and
Rectal delivery in a viscous dosage form.

Potential design-around strategies included:

Using a non-cellulose thickener;
Using a different solvent system;
Moving outside the claimed concentration ranges;
Altering pH outside the claimed range;
Developing a non-rectal rescue product;
Using intranasal or buccal delivery; or
Creating a substantially different dosage form.

The formulation design-around options were commercially important because the patent did not cover diazepam as a molecule. It covered a defined delivery composition.

How does the patent compare with later seizure-rescue products?

The market moved toward non-rectal rescue products with simpler administration and different patent estates.

Product	Active ingredient	Route	FDA product	Relationship to U.S. 5,462,740
Diastat	Diazepam	Rectal gel	NDA 020648	Direct historical commercial embodiment
Nayzilam	Midazolam	Intranasal spray	NDA 211321	Different active ingredient and delivery system
Valtoco	Diazepam	Intranasal spray	NDA 211635	Same active ingredient, different route and formulation

Nayzilam was approved by FDA in 2019, and Valtoco was approved in 2020.[4][5] Neither product is a rectal cellulose-ether composition within the apparent core of U.S. Patent 5,462,740.

The comparison is commercially significant. Valtoco uses diazepam but avoids the rectal formulation limitations. Nayzilam avoids both the diazepam-specific limitation and the rectal delivery architecture. Their patent estates are expected to focus on nasal delivery devices, formulations, dosing, administration, and method-of-use claims rather than the expired rectal-gel composition.

Does biosimilar risk apply to U.S. Patent 5,462,740?

No. Diazepam is a small-molecule drug, not a biologic subject to the biosimilar pathway under the Public Health Service Act.

The relevant competitive pathways are:

ANDA approval for a generic drug;
505(b)(2) approval for a reformulated or repositioned diazepam product;
Full NDA development for a novel rescue formulation; and
State and federal substitution rules applicable to generic products.

The patent does not create biosimilar risk. Its commercial exposure is generic and reformulation competition.

How strong is the patent estate for this formulation?

The patent was commercially useful while active, but its present exclusionary strength is zero because it has expired.

Historically, its strongest features were:

A broad claim 1 covering multiple antiepileptic classes;
A specific diazepam claim in claim 3;
A diazepam composition claim independently stated in claim 8;
Functional solvent language addressing precipitation;
A defined cellulose-ether concentration range; and
A rectal viscosity requirement.

Its weaknesses included:

Dependence on multiple formulation limitations;
Lack of molecule-level protection for diazepam;
Potential design-around options using different thickeners or routes;
Ambiguity associated with "about," "suitable for administration," and "effective to inhibit precipitation"; and
Expiration in 2012.

What manufacturing and IP barriers remain?

No patent barrier from U.S. Patent 5,462,740 remains. Commercial barriers can still arise from:

Product-specific FDA requirements;
Demonstration of bioequivalence or equivalent therapeutic performance;
Device and applicator compatibility;
Container-closure performance;
Stability of diazepam in the solvent system;
Control of viscosity and dose delivery;
Extractables and leachables;
Manufacturing-process validation; and
Market access, supply reliability, and reimbursement.

These are regulatory and operational barriers, not continuing rights under the expired patent.

Key Takeaways

U.S. Patent 5,462,740 covered viscous rectal antiepileptic compositions.
Claim 1 required an antiepileptic, pH buffer, cellulose ether, solvent, and rectal-injection viscosity.
Claims 3 and 8 were particularly relevant to diazepam rectal gel.
HPMC, methyl cellulose, hydroxypropylcellulose, and carboxymethylcellulose were expressly identified.
Claim 4 added a 1,000-8,000 cps apparent-viscosity range.
The patent issued October 31, 1995, and expired October 31, 2012.
Diastat was FDA-approved under NDA 020648 in 1997.
The patent is no longer an enforceable U.S. barrier to generic diazepam rectal gel.
Biosimilar analysis is inapplicable because diazepam is a small molecule.
Later rescue products such as Nayzilam and Valtoco use different delivery systems and separate patent estates.

FAQs About U.S. Patent 5,462,740

Can a generic diazepam rectal gel launch without licensing U.S. Patent 5,462,740?

Yes. The patent expired on October 31, 2012. A current generic applicant does not need a license to practice the expired patent in the United States.

Did U.S. Patent 5,462,740 cover all diazepam products?

No. It covered a defined viscous rectal composition. It did not cover diazepam as a compound, tablets, injectable diazepam, or all intranasal diazepam products.

Would a carbomer-thickened diazepam gel infringe claim 6?

Not literally, because claim 6 is limited to hydroxypropylmethylcellulose. The broader claims would require separate analysis, particularly whether the thickener is a cellulose ether and whether all other limitations are met.

Does claim 8 require viscosity of 1,000-8,000 cps?

Not expressly. That range appears in claim 4. Claim 8 independently requires the claim 1 formulation elements but does not expressly incorporate claim 4's viscosity range.

Can the expired patent affect current FDA approval of a generic product?

No. FDA may evaluate formulation, bioequivalence, safety, labeling, manufacturing, and device performance, but an expired patent cannot block approval or commercial launch.

Is Valtoco covered by U.S. Patent 5,462,740?

No. Valtoco is an intranasal diazepam product. The expired patent is directed to a viscous rectal composition containing a cellulose ether and specified solvent system.

References

United States Patent and Trademark Office. (1995). U.S. Patent No. 5,462,740, Rectal compositions for treating seizures.
U.S. Food and Drug Administration. (2023). Diastat rectal gel prescribing information, NDA 020648.
U.S. Food and Drug Administration. (2024). Approved drug products with therapeutic equivalence evaluations: Orange Book.
U.S. Food and Drug Administration. (2019). Nayzilam approval announcement and prescribing information, NDA 211321.
U.S. Food and Drug Administration. (2020). Valtoco approval announcement and prescribing information, NDA 211635.

Country	Patent Number	Estimated Expiration	Supplementary Protection Certificate	SPC Country	SPC Expiration
Australia	7686394	⤷ Start Trial
Canada	2171627	⤷ Start Trial
World Intellectual Property Organization (WIPO)	9507672	⤷ Start Trial
>Country	>Patent Number	>Estimated Expiration	>Supplementary Protection Certificate	>SPC Country	>SPC Expiration

Details for Patent: 5,462,740

Summary for Patent: 5,462,740