United States Patent 5,591,762: Telmisartan Claims, Scope, Expiration, and Patent Landscape

US Patent 5,591,762 is the principal composition-of-matter patent associated with telmisartan, marketed by Boehringer Ingelheim as Micardis. Its claims cover a broad class of substituted benzimidazole derivatives, narrower telmisartan-related compounds, pharmaceutical compositions, and antihypertensive treatment methods. The patent is expired, and it no longer creates a current US barrier to generic telmisartan entry. The principal commercial compound is claim 5, not the entire genus in claim 1.

What drug does US Patent 5,591,762 protect?

US 5,591,762 protects telmisartan and structurally related angiotensin II receptor blockers.

The compound in claim 5 is telmisartan:

4'-[[2-n-propyl-4-methyl-6-(1-methylbenzimidazol-2-yl)-benzimidazol-1-yl]methyl]-biphenyl-2-carboxylic acid.

Telmisartan is a nonpeptide angiotensin II receptor type 1, or AT1, antagonist. The FDA approved Micardis, containing telmisartan, on November 10, 1998 for hypertension. The compound is also used in cardiovascular risk-reduction indications and in combination products containing hydrochlorothiazide or amlodipine.[1]

The patent covers more than telmisartan. It also claims:

Telmisartan analogues containing different alkyl or cycloalkyl substituents.
Benzimidazole groups carrying methyl, fluorine, or trifluoromethyl substitution.
Carboxylic acid, ester, and tetrazole analogues.
Pharmaceutically acceptable salts.
Pharmaceutical compositions.
Methods for treating hypertension.

How are the claims of US 5,591,762 structured?

The claims form a descending scope hierarchy.

Claim	Subject matter	Relative scope
1	Broad formula I genus with defined R1, R2, R3, and R4 substituents	Broadest
2	Claim 1 compounds with R2 in the 6-position	Narrower
3	Claim 2 compounds with methyl R1 and defined benzimidazole, alkyl, carboxy, or tetrazole substitutions	Narrower
4	Six expressly identified compounds and salts	Specific Markush selection
5	Telmisartan and pharmaceutically acceptable salts	Product-specific
6	Telmisartan tetrazole analogue and salts	Product-specific
7	Pharmaceutical compositions containing claims 1-6 compounds	Composition claim
8	Hypertension treatment using claims 1-6 compounds	Method-of-use claim

A product that falls within claim 5 does not need to be assessed against the full genus in claim 1 for literal infringement. Claim 5 is independently enforceable as a product claim, subject to validity, infringement, and expiration issues.

What chemical structures are covered by claim 1?

Claim 1 covers a benzimidazole-based molecular framework with a substituted biphenyl group. Its key limitations are:

R1 must be located in the 4-position and must be C1-4 alkyl, C3-7 cycloalkyl, or trifluoromethyl.
R2 must be a benzimidazol-2-yl group, optionally N-substituted with C1-6 alkyl or C3-7 cycloalkyl.
The benzimidazole phenyl nucleus may contain fluorine, methyl, or trifluoromethyl substitution.
R3 must be C1-5 alkyl or cyclopropyl.
R4 must be a 1H-tetrazolyl group or an RaO-CO group.
Ra may be hydrogen or straight-chain or branched C1-4 alkyl.
Pharmaceutically acceptable salts are included.

The RaO-CO limitation captures the carboxylic acid form when Ra is hydrogen and ester forms when Ra is alkyl. Telmisartan falls within the carboxylic acid embodiment.

The broad claim is compositionally important because it reaches compounds that differ from telmisartan at several positions. A competitor does not necessarily avoid the patent by changing only one substituent if the modified compound remains within the listed Markush ranges.

Why is claim 5 commercially important?

Claim 5 identifies telmisartan by its complete chemical structure. It is the clearest product claim for the marketed active ingredient.

The commercial importance of claim 5 exceeds that of the broader genus because it provides:

A direct claim to the active pharmaceutical ingredient.
A simpler infringement analysis than claim 1.
A stronger basis for Orange Book listing than a method or composition claim.
Coverage independent of a specific dosage form.
Coverage of pharmaceutically acceptable salts.

A generic manufacturer making telmisartan itself would have been exposed to claim 5 during the patent term unless it established invalidity, noninfringement, or a legally effective entry date after expiration.

What does claim 6 protect?

Claim 6 covers the tetrazole analogue of telmisartan:

4'-[[2-n-propyl-4-methyl-6-(1-methylbenzimidazol-2-yl)-benzimidazol-1-yl]methyl]-2-(1H-tetrazol-5-yl)-biphenyl.

This compound replaces telmisartan’s biphenyl carboxylic acid with a tetrazole group. Tetrazoles are common carboxylic-acid bioisosteres in angiotensin receptor blockers, but the claim does not cover every tetrazole-containing ARB. It is limited to the specified benzimidazole-biphenyl structure and its salts.

Claim 6 would not, by itself, cover telmisartan because telmisartan has a carboxylic acid at the corresponding biphenyl position. Claim 5 performs that function.

What formulations are protected by US 5,591,762?

Claim 7 covers pharmaceutical compositions containing a therapeutically effective amount of a compound within claims 1 through 6.

The claim is not limited to a particular:

Tablet;
Capsule;
Oral solution;
Excipient;
Release profile;
Dose strength;
Manufacturing process; or
Fixed-dose combination.

A composition claim tied to the patent compounds can therefore reach an oral dosage form containing telmisartan, but the claim does not independently establish protection for every formulation technology. A formulation containing telmisartan could also be subject to separate formulation patents if it includes a protected excipient system, dissolution profile, particle form, or combination.

US 5,591,762 should therefore be treated as a core compound patent, not as a complete formulation portfolio.

Does the patent protect telmisartan combination products?

Claim 7 could cover a composition containing telmisartan, but it does not expressly claim hydrochlorothiazide, amlodipine, or a particular fixed-dose combination ratio.

Micardis HCT combines telmisartan with hydrochlorothiazide. Twynsta combines telmisartan with amlodipine. Combination-product protection generally depends on separate claims directed to:

The combination of active ingredients;
Specific dosage ratios;
Formulation characteristics;
Treatment of a defined patient population; or
Manufacturing and packaging configurations.

The existence of US 5,591,762 does not establish that all combination products remain protected after expiration of the compound patent.

What method-of-use protection does claim 8 provide?

Claim 8 covers treating hypertension by administering an antihypertensive amount of a compound within claims 1 through 6 to a mammalian host suffering from hypertension.

The method claim has three central limitations:

The administered compound must fall within claims 1 through 6.
The amount must be antihypertensively effective.
The patient must suffer from hypertension.

The claim does not specify a dose, dosing frequency, route, treatment duration, or particular patient subgroup. During the patent term, a direct method-of-use claim could create risk for a generic product promoted for hypertension. After expiration, claim 8 no longer blocks that use in the United States.

When did US Patent 5,591,762 lose exclusivity?

The Orange Book historical record identifies November 11, 2012 as the listed expiration date for the core telmisartan patent.[2] The patent is expired and does not provide current US exclusivity.

Event	Date
Patent grant	January 7, 1997
Micardis FDA approval	November 10, 1998
Listed core patent expiration	November 11, 2012
Current status	Expired
Current US compound-patent barrier	None from US 5,591,762

The patent’s expiration eliminated the principal composition-of-matter barrier for generic telmisartan. Any later patent would need to protect a separate statutory subject matter, such as a formulation, polymorph, combination, dosage regimen, or manufacturing process. Such a patent could not restore exclusivity for the already expired telmisartan compound claim itself.

What was the FDA exclusivity status of Micardis?

Micardis received five-year new chemical entity exclusivity under the Hatch-Waxman framework. That exclusivity period ran from the 1998 approval date and ended before the core patent expired.

The FDA approval and exclusivity periods were therefore distinct:

Regulatory exclusivity delayed certain ANDA submissions.
Patent exclusivity delayed commercial entry based on the enforceable patent rights.
The patent expiration date controlled the end of the principal US compound barrier.

FDA exclusivity is not renewable merely because the product remains commercially successful or continues to receive additional indications.[1,2]

Were there Paragraph IV challenges to telmisartan?

Generic telmisartan applicants could challenge listed patents through an ANDA Paragraph IV certification, stating that the patent was invalid, unenforceable, or would not be infringed. The relevant commercial consequence was potential ANDA litigation under the Hatch-Waxman statute.

The central Paragraph IV risk would have involved:

Claim 5 for telmisartan;
Claim 7 for compositions containing telmisartan; and
Claim 8 for hypertension treatment.

A Paragraph IV certification against a listed patent could trigger a 30-month FDA approval stay if the patent holder filed a timely infringement action. That stay would not exceed the patent’s enforceable term.

Because US 5,591,762 has expired, a new Paragraph IV strategy against this patent has no current commercial value. Generic applicants now rely on post-expiration certification and ordinary ANDA approval pathways rather than defeating a live claim 5 injunction.

Which companies challenged or entered the telmisartan market?

The US telmisartan market has included multiple generic manufacturers, including companies such as Mylan, Teva, Lupin, Torrent, Aurobindo, Glenmark, Zydus, and Dr. Reddy’s Laboratories. Market participation and FDA approval do not, by themselves, establish that each company filed a Paragraph IV certification against US 5,591,762.

After expiration, generic entry depended more heavily on:

ANDA approval;
Drug-substance sourcing;
Bioequivalence;
Manufacturing capacity;
Pricing;
Distribution contracts; and
Combination-product strategy.

The expired core patent does not prevent competition among approved generic manufacturers.

What is the patent landscape for telmisartan today?

The relevant landscape has four layers.

Core compound protection

US 5,591,762 is the foundational telmisartan-related patent. Its principal claim 5 is expired.

Formulation and solid-state protection

Separate patents may address:

Telmisartan particle size;
Amorphous or crystalline forms;
Tablet dissolution;
Solubilization;
Excipient systems;
Stability;
Granulation;
Manufacturing processes; and
Fixed-dose combinations.

These rights must be assessed independently from US 5,591,762. A formulation patent cannot be assumed to cover the active ingredient in every dosage form.

Combination-product protection

Micardis HCT and Twynsta involve separate combination claims and regulatory products. The expiration of the core telmisartan patent does not automatically determine the status of every combination patent.

Foreign rights

US 5,591,762 has territorial effect only in the United States. European, Japanese, Canadian, and other national rights derive from separate national or regional patent grants. Expiration dates, claim amendments, supplementary protection certificates, and litigation outcomes can differ by country.

How strong was the patent estate?

The patent was strong during its enforceable term because it combined:

A direct claim to telmisartan;
A broad genus claim;
Narrower species claims;
Salt coverage;
Composition coverage; and
Hypertension method coverage.

The strongest commercial claim was claim 5. Claims 1 through 3 supplied fallback scope around the marketed molecule and related analogues. Claim 7 expanded the claim set into pharmaceutical products, while claim 8 addressed therapeutic use.

The estate is weak as a current US exclusivity asset because the core patent has expired. Its remaining value is historical, defensive, and analytical rather than exclusionary.

What generic launch risks remain after expiration?

Generic telmisartan launch risk is no longer centered on direct infringement of US 5,591,762. The remaining risks are operational and product-specific:

Risk	Relevance after core patent expiration
Claim 5 infringement	No current risk from the expired patent
Formulation patent	May affect a particular dosage form
Combination patent	Relevant to telmisartan-hydrochlorothiazide or telmisartan-amlodipine products
Method-of-use patent	Relevant only if unexpired and tied to labeling or promotion
Manufacturing patent	May require a process change
FDA approval	Required independently of patent status
Trade dress or trademark	Separate from patent rights
Supply chain	Can affect launch timing and price
International patent rights	May remain relevant outside the United States

Key Takeaways

US 5,591,762 is a foundational telmisartan patent.
Claim 5 directly covers telmisartan and its pharmaceutically acceptable salts.
Claim 1 covers a broader genus of substituted benzimidazole-biphenyl compounds.
Claim 6 covers a tetrazole analogue rather than telmisartan itself.
Claims 7 and 8 address pharmaceutical compositions and hypertension treatment.
The Orange Book-listed expiration date for the core patent was November 11, 2012.
The patent is expired and does not currently block US generic telmisartan.
Current risk must be evaluated through separate formulation, combination, manufacturing, and method-of-use patents.
The patent is a small-molecule estate, so biosimilar analysis does not apply. FDA ANDA requirements, rather than the biosimilar BLA pathway, govern generic telmisartan.

FAQs

Is telmisartan specifically named in US Patent 5,591,762?

Yes. Claim 5 recites telmisartan by its chemical structure, together with pharmaceutically acceptable salts.

Does US 5,591,762 cover losartan or valsartan?

No. The claims are directed to a benzimidazole-biphenyl chemical class and do not cover the distinct structures of losartan or valsartan.

Can an expired patent still block a telmisartan ANDA?

No. An expired patent cannot provide a current injunction against making or selling telmisartan in the United States. The ANDA must still satisfy FDA quality, pharmaceutical-equivalence, and bioequivalence requirements.

Does the patent cover telmisartan hydrochloride?

The patent covers pharmaceutically acceptable salts of the claimed compounds. The specific legal treatment of a particular telmisartan salt depends on whether it falls within the claim construction and pharmaceutical-acceptability requirements.

Is a telmisartan formulation automatically unpatented because US 5,591,762 expired?

No. Expiration of the core compound patent does not eliminate separate patents covering formulations, combinations, solid forms, manufacturing methods, or dosage regimens.

References

U.S. Food and Drug Administration. (1998). Micardis (telmisartan) prescribing information. FDA.
U.S. Food and Drug Administration. (2024). Approved drug products with therapeutic equivalence evaluations: Orange Book. FDA.
United States Patent and Trademark Office. (1997). U.S. Patent No. 5,591,762: Benzimidazole derivatives, processes for their preparation, their use and pharmaceutical compositions containing them. U.S. Department of Commerce.
United States Code. (2024). 35 U.S.C. §§ 154, 271, 282, and 286. Office of the Law Revision Counsel.

Foriegn Application Priority Data
Foreign Country	Foreign Patent Number	Foreign Patent Date
Germany	41 03 492.9	Feb 06, 1991
Germany	41 17 121.7	May 25, 1991
Germany	41 37 812.1	Nov 16, 1991
Germany	42 01 554.5	Jan 22, 1992

Country	Patent Number	Estimated Expiration	Supplementary Protection Certificate	SPC Country	SPC Expiration
European Patent Office	0502314	⤷ Start Trial	3/2011	Austria	⤷ Start Trial
European Patent Office	0502314	⤷ Start Trial	CA 2002 00023	Denmark	⤷ Start Trial
European Patent Office	0502314	⤷ Start Trial	SPC/GB02/037	United Kingdom	⤷ Start Trial
European Patent Office	0502314	⤷ Start Trial	C300478	Netherlands	⤷ Start Trial
>Country	>Patent Number	>Estimated Expiration	>Supplementary Protection Certificate	>SPC Country	>SPC Expiration

Details for Patent: 5,591,762

Summary for Patent: 5,591,762