United States Patent 5,413,999: Claim Scope, Indinavir Coverage, Patent Expiration, and Generic Entry Risk

U.S. Patent No. 5,413,999 is a Merck patent covering HIV-1 protease inhibitors, including the indinavir chemical series used in Crixivan. Its claims include broad Markush compounds, narrower indinavir-related structures, pharmaceutical compositions, and methods for treating AIDS, treating HIV infection, and inhibiting HIV protease. The patent issued on May 9, 1995, and its primary U.S. patent term expired in September 2012. It no longer blocks generic or other commercial development in the United States.[1-4]

The supplied claim text contains image placeholders for the chemical structures. The analysis below therefore focuses on the textual limitations, the claim hierarchy, and the known relationship between U.S. Patent 5,413,999 and indinavir.

What drug and technology does U.S. Patent 5,413,999 cover?

U.S. Patent 5,413,999 covers hydroxyethylamine-containing peptidomimetic compounds designed to inhibit retroviral proteases, particularly HIV protease. The patent is associated with indinavir, an HIV protease inhibitor marketed by Merck as Crixivan.

Indinavir sulfate received FDA approval on March 13, 1996, for treatment of HIV infection in combination with other antiretroviral agents. The product is an orally administered small-molecule capsule and oral solution formulation.[2]

Item	Data
U.S. patent	5,413,999
Technology	HIV protease inhibition
Principal commercial compound	Indinavir
Brand	Crixivan
Originator	Merck & Co.
Patent type	Small-molecule composition, formulation, and method-of-use claims
Issue date	May 9, 1995
FDA approval of Crixivan	March 13, 1996
Primary patent expiration	September 2012
Regulatory pathway for generics	ANDA, not biosimilar pathway

Indinavir is not a biologic. The relevant competitive pathway is an abbreviated new drug application under Section 505(j) of the Federal Food, Drug, and Cosmetic Act, not a biosimilar application under the Public Health Service Act.

How are the claims of U.S. Patent 5,413,999 structured?

The claim set has four principal layers:

Broad chemical genus claims.
Narrower compound subgenus and species claims.
Pharmaceutical composition claims.
Therapeutic and enzymatic-use claims.

Claim 1: broad Markush compound claim

Claim 1 covers compounds defined by a complex formula containing variable groups V, Q, R1, R3, R5, and R12. The claim permits substantial variation in the substituents attached to the protease-inhibitor core.

The principal structural options include:

V being absent or a defined carbonyl-related or cyclic moiety.
Q being absent, oxygen, nitrogen-containing, or a substituted heterocycle.
R1 being an alkyl, aryl, heterocyclic, or carbocyclic substituent.
R1 substituents including halogen, alkoxy, aryl, cycloalkyl, amino, sulfonamide, carbamate, ester, and polyether groups.
R3 being benzyl or substituted benzyl.
R5 containing aminoalkyl, aminoether, heterocyclic, benzofuryl, indolyl, azacyclic, azabicyclic, or benzopiperidinyl groups.
R12 being a defined side chain or a pharmaceutically acceptable salt.

This is a classical medicinal-chemistry Markush claim. Its commercial value is not limited to one marketed molecule. It seeks to cover a family of HIV protease inhibitors sharing the claimed hydroxy-containing peptidomimetic architecture and specified side-chain options.

The breadth is constrained by the required formula, stereochemistry represented in the omitted figures, functional-group definitions, and the specific relationship between the substituents. A molecule does not infringe merely because it is an HIV protease inhibitor or because it contains a hydroxyethylamine motif.

Claims 2 through 5: progressively narrower compound claims

Claims 2 to 5 narrow the scope of claim 1.

Claim 2 removes V and restricts the compound to a formula with V absent. It retains broad alternatives for R1 and substituted benzyl groups for R3.

Claim 3 narrows the R1 alternatives by removing several substituent categories and retaining selected aryl, cycloalkyl, heterocyclic, and carbamate-related groups.

Claim 4 identifies specific heterocycles, including:

Piperidinyl
Pyridyl
Thienyl
Pyrrolyl
Thiazolyl
Imidazolyl
Furyl
Benzimidazolyl
Pyrazinyl
Isoxazolyl
Pyridazinyl
Quinolinyl

Claim 5 narrows R1 to a C1-4 alkyl group substituted with pyridyl or aryl. This claim is materially closer to the indinavir-related species than the broader genus claims.

Claims 2 through 5 are dependent claims. Their enforceability depends on satisfying both the inherited limitations from the parent claim and the added restrictions in the dependent claim.

Claim 6: defined compound alternatives

Claim 6 covers a compound formula in which R1 is selected from a finite group of depicted substituents. Because the chemical images are not reproduced in the supplied text, the exact alternatives cannot be identified from the text alone.

Functionally, claim 6 appears to protect selected species within the broader claim 1 genus. Such claims are generally more useful in litigation than a broad Markush claim when the accused product is a specifically identified molecule.

Claim 7: a specific compound

Claim 7 covers a specific compound shown in the omitted chemical figure, together with pharmaceutically acceptable salts. This is likely the central species claim for the commercially relevant indinavir structure or a closely related indinavir compound.

A species claim typically has a narrower literal scope than a Markush claim but can provide stronger infringement and validity positions when the claimed structure is clearly disclosed, enabled, and supported by the patent specification.

Claims 8 through 10: pharmaceutical compositions

Claim 8 covers a pharmaceutical composition containing a compound according to claims 3, 4, 5, or 6 and a pharmaceutically acceptable carrier.

Claim 9 limits that composition to use in:

Treating AIDS
Treating HIV infection
Inhibiting HIV protease

Claim 10 covers a composition containing the specific compound shown in the claim figure and a pharmaceutically acceptable carrier.

These claims are not limited to capsules unless the patent’s omitted figures or specification impose additional dosage-form limitations. On the supplied text, the carrier may include conventional pharmaceutical excipients, including diluents, binders, disintegrants, lubricants, solvents, and stabilizers.

The claims therefore target drug-product compositions at a functional level rather than protecting only the Crixivan capsule design.

Claims 11 through 13: therapeutic method claims

Claims 11 through 13 cover administering a compound according to claims 5 or 7 to a mammal for:

Treating AIDS
Treating HIV infection
Inhibiting HIV protease

These claims are method-of-treatment claims. They require an act of administration and a specified therapeutic purpose. They do not necessarily cover manufacture, sale, or possession of the compound outside the claimed therapeutic context.

Because the claims use “mammal,” they are broader than claims limited to human treatment. FDA-approved use in humans would nevertheless be the principal commercial relevance.

What is the claim hierarchy of U.S. Patent 5,413,999?

Claim	Category	Relative scope	Commercial relevance
1	Broad compound genus	Broadest	Covers a large family of HIV protease inhibitors
2	Compound subgenus	Narrower	Removes V and limits the core
3	Further compound subgenus	Narrower	Reduces permitted R1 substituents
4	Heterocycle-focused subgenus	Narrower	Lists specific heterocyclic groups
5	Arylmethyl/pyridyl-related subgenus	Narrow	Closely approaches commercial species
6	Defined species group	Narrow	Selected compounds shown in the patent
7	Specific compound	Narrowest chemical claim	Likely directed to the principal commercial species
8	Pharmaceutical composition	Product-level	Compound plus carrier
9	Composition-use claim	Product/use	HIV, AIDS, or protease inhibition
10	Specific composition	Product-level	Specific compound plus carrier
11	Treatment method	Use claim	AIDS treatment
12	Treatment method	Use claim	HIV treatment
13	Enzyme-inhibition method	Use claim	HIV protease inhibition

What patents protect indinavir and Crixivan?

Crixivan’s historical U.S. patent estate included composition-of-matter and related pharmaceutical patents. U.S. Patent 5,413,999 is the principal patent identified with the indinavir chemical invention. Other Merck patents were associated with related compound, formulation, or process coverage.

Patent	General role in estate	Status relevance
U.S. 5,413,999	HIV protease inhibitor compounds, including indinavir-related species	Expired
U.S. 5,446,039	Related HIV protease inhibitor coverage	Expired
U.S. 5,585,397	Related compound or therapeutic protection	Expired
Other related Merck patents	Manufacturing, formulations, intermediates, or alternative protease inhibitors	Must be reviewed individually

The exact Orange Book status of a patent can change over time because FDA listings may be delisted, expire, or be removed after product discontinuation. The Orange Book should be read together with the FDA product approval history and the patent records maintained by the USPTO.[2-4]

When did U.S. Patent 5,413,999 lose exclusivity?

U.S. Patent 5,413,999 expired in September 2012. The patent was filed under the pre-1995 U.S. patent-term regime, but the Uruguay Round Agreements Act applied a 20-year term from the earliest effective nonprovisional filing date to patents in force after June 8, 1995.[1]

The key timeline is:

Date	Event
1992	Earliest relevant U.S. filing period for the invention
May 9, 1995	U.S. Patent 5,413,999 issued
March 13, 1996	FDA approved Crixivan
2001	Five-year NCE exclusivity period generally ended
September 2012	Primary patent term expired
After September 2012	No remaining exclusion based on Patent 5,413,999

The patent’s expiration is distinct from FDA regulatory exclusivity. New chemical entity exclusivity prevented FDA approval of an ANDA for five years after approval, subject to the statutory Paragraph IV exception. That period ended long before the patent expired.

What was the Orange Book status of Crixivan?

Crixivan was listed by FDA as a prescription antiretroviral drug containing indinavir sulfate. Its patent listings were relevant to ANDA applicants during the period when the patents remained unexpired.

Orange Book-listed patent issues included:

Identification of patents asserted to cover the drug substance or drug product.
Submission of patent expiration information by the NDA holder.
Potential Paragraph IV certifications by ANDA applicants.
Potential patent litigation under 21 U.S.C. § 355(j)(5)(B)(iii).

With the expiration of the relevant patents, U.S. Patent 5,413,999 no longer creates a current Orange Book patent barrier. Any present-day market-entry analysis must focus on current regulatory listing status, product discontinuation status, manufacturing economics, and any unrelated patents covering a particular generic formulation or manufacturing process.[2]

Were there Paragraph IV challenges to indinavir?

A Paragraph IV certification would have been the principal route for an ANDA applicant seeking approval before expiration of a listed Crixivan patent. The applicant would have certified that the patent was invalid, unenforceable, or would not be infringed.

Publicly material Paragraph IV litigation associated with indinavir is limited compared with the litigation histories of major small-molecule products such as omeprazole, atorvastatin, or sildenafil. U.S. Patent 5,413,999 is now expired, so a new Paragraph IV challenge to that patent would have no practical commercial purpose.

The historical risk analysis was different:

Period	Paragraph IV significance
Before 2001	NCE exclusivity and listed patents created significant barriers
2001-2012	ANDA applicants could challenge patents, but litigation could trigger a 30-month stay
After September 2012	Patent 5,413,999 no longer supports a blocking infringement action
Current period	Competition depends on approval, supply, formulation, and market demand

No biosimilar challenge is relevant because indinavir is a chemically synthesized small molecule.

What generic entry risks exist for indinavir?

The legal patent risk from U.S. Patent 5,413,999 is expired. The principal current risks are commercial and regulatory.

Generic approval risk

An indinavir ANDA applicant would need to establish pharmaceutical equivalence and bioequivalence to the relevant reference product. The applicant would also need to address:

Active ingredient identity as indinavir sulfate.
Dosage form and strength.
Dissolution and release characteristics.
Impurity profile.
Stability.
Labeling and discontinued-product issues.
Reference listed drug availability and suitability.

Formulation risk

The patent claims cover compositions containing the active compound and a pharmaceutically acceptable carrier. Those claims have expired. A later applicant could still face unrelated patents if it uses a protected:

Capsule composition
Oral solution vehicle
Solid-state form
Salt or hydrate
Manufacturing process
Packaging or stability system

Those risks must be assessed patent by patent. They cannot be inferred solely from U.S. Patent 5,413,999.

Commercial risk

Indinavir is an older protease inhibitor with substantial pill burden, dietary restrictions, adverse-effect concerns, and competition from newer antiretroviral regimens. Even with no blocking patent, a generic entrant would face limited demand and unfavorable manufacturing economics.

How strong was the patent estate for indinavir?

Historically, the estate was strong because it combined broad genus claims with narrower compound and method claims.

Strength factor	Assessment
Broad chemical coverage	Strong, subject to written-description and enablement challenges
Specific species coverage	Stronger than the genus claims for a matching molecule
Formulation coverage	Moderate, depending on the exact composition claim
Method-of-use coverage	Moderate, with infringement dependent on labeled or intended use
Remaining term	No current value because the principal patent expired
Biosimilar protection	Not applicable
Manufacturing barrier	Potentially relevant only under separate process patents
Current litigation value	None against a new entrant based solely on Patent 5,413,999

The broad Markush claim could have been challenged on written description, enablement, anticipation, obviousness, or indefiniteness grounds. The narrower species claims would generally have presented a more focused validity and infringement dispute.

Which companies compete with or replace indinavir?

Indinavir competes within the HIV protease inhibitor class and against newer antiretroviral classes.

Historical protease inhibitor competitors included:

Abbott’s ritonavir and lopinavir/ritonavir
Roche’s saquinavir
Bristol-Myers Squibb’s atazanavir
GlaxoSmithKline’s amprenavir and fosamprenavir
Janssen’s darunavir

Current HIV treatment has shifted toward integrase strand transfer inhibitor regimens, including dolutegravir- and bictegravir-based products. Those therapies generally offer lower pill burden and more favorable tolerability than indinavir-based treatment.

This competitive shift reduces the commercial value of an indinavir generic even though the patent barrier has ended.

What is the geographic coverage of U.S. Patent 5,413,999?

U.S. Patent 5,413,999 provides rights only in the United States. Parallel applications may have existed in other jurisdictions under related priority filings, but U.S. expiration does not determine foreign patent status.

For a global freedom-to-operate analysis, counsel would need to review:

European Patent Office family members
Canada
Japan
Australia
Brazil
China
India
Countries where Crixivan was marketed
National-phase applications and local patent-term adjustments

Any foreign counterpart with a different filing date, terminal disclaimer, supplementary protection certificate, or regulatory extension must be assessed separately.

Key Takeaways

U.S. Patent 5,413,999 covers a broad family of HIV protease inhibitors and narrower indinavir-related compounds.
Claims 1 through 7 are chemical compound claims, with claim 1 as the broad Markush genus and claim 7 directed to a specific depicted compound.
Claims 8 through 10 cover pharmaceutical compositions.
Claims 11 through 13 cover treatment of AIDS, HIV infection, and HIV protease inhibition.
The patent is associated with indinavir, the active ingredient in Crixivan.
The patent expired in September 2012.
No biosimilar pathway applies because indinavir is a small molecule.
Current generic entry risk is primarily regulatory, technical, and commercial rather than based on Patent 5,413,999.
Separate patents would need to be reviewed for formulations, solid forms, manufacturing processes, and foreign markets.

FAQs

Does U.S. Patent 5,413,999 cover indinavir sulfate?

Yes. The patent is associated with indinavir-related HIV protease inhibitor compounds and pharmaceutically acceptable salts, including the sulfate salt used in Crixivan.

Can a company still sue a generic manufacturer under U.S. Patent 5,413,999?

No. The patent expired in September 2012 and cannot provide current exclusionary rights against a new U.S. generic product.

Was indinavir protected by biologic exclusivity?

No. Indinavir is a chemically synthesized small molecule. Its regulatory pathway was the NDA and ANDA system, not the biologic license application and biosimilar system.

Are Crixivan formulation patents still enforceable?

Patents listed for Crixivan must be reviewed individually. The formulation and composition claims of U.S. Patent 5,413,999 are expired, but a separate patent with a later expiration date would require independent analysis.

Is a generic indinavir product commercially attractive?

The absence of the expired patent barrier does not create strong commercial opportunity by itself. Indinavir faces competition from newer antiretroviral therapies, lower treatment demand, manufacturing complexity, and potentially limited reference-product and market-access advantages.

References

United States Patent and Trademark Office. (1995). U.S. Patent No. 5,413,999: HIV protease inhibitors. U.S. Department of Commerce.
U.S. Food and Drug Administration. (1996). Crixivan (indinavir sulfate) approval history and prescribing information. FDA.
U.S. Food and Drug Administration. (2024). Approved drug products with therapeutic equivalence evaluations. FDA, Center for Drug Evaluation and Research.
U.S. Food and Drug Administration. (2024). Orange Book: Approved drug products with therapeutic equivalence evaluations. FDA, Center for Drug Evaluation and Research.
U.S. Code, 35 U.S.C. § 154. Patent term.
U.S. Code, 21 U.S.C. § 355(j). Abbreviated new drug applications and patent certifications.

Country	Patent Number	Estimated Expiration	Supplementary Protection Certificate	SPC Country	SPC Expiration
Austria	163926	⤷ Start Trial
Austria	230610	⤷ Start Trial
Australia	2819992	⤷ Start Trial
Australia	5921394	⤷ Start Trial
Australia	659234	⤷ Start Trial
>Country	>Patent Number	>Estimated Expiration	>Supplementary Protection Certificate	>SPC Country	>SPC Expiration

Details for Patent: 5,413,999

Summary for Patent: 5,413,999