US Patent 7,605,121: Cetrorelix Acetate Lyophilisate Claims, Scope, Expiration, and Patent Landscape

US Patent 7,605,121 protects a sterile, lyophilized cetrorelix acetate formulation made through a defined acidic dissolution, dilution, filtration, and lyophilization process. The broadest claim is a product-by-process claim. Claims 2 through 4 narrow protection by specifying bulking agents, concentration ranges, acetic-acid dilution, and mannitol.

The patent is directed to formulation manufacture rather than cetrorelix itself. It does not broadly cover the cetrorelix molecule, every cetrorelix dosage form, or every sterile injectable GnRH antagonist. Its commercial relevance centered on the lyophilized cetrorelix acetate presentation used for subcutaneous injection, including the Cetrotide product.

What does US Patent 7,605,121 protect?

The patent protects a sterile cetrorelix acetate-bulking-agent lyophilisate prepared through five required operations:

Dissolving cetrorelix acetate in 30% by volume aqueous acetic acid.
Diluting the resulting solution with water.
Adding a bulking agent while maintaining a pH of 2.5 to 3.0.
Sterilizing the solution by filtration.
Lyophilizing the filtered solution.

The independent claim is limited by both the final product and the recited manufacturing sequence. A formulation that contains cetrorelix acetate and mannitol but is made through a materially different process would not automatically fall within the literal scope of claim 1.

Claim structure

Claim	Type	Principal limitation
1	Independent product-by-process claim	Sterile cetrorelix acetate lyophilisate made using 30% aqueous acetic acid, dilution, pH 2.5-3.0, filtration, and lyophilization
2	Dependent formulation claim	Bulking agent selected from amino acids, polyvinylpyrrolidone, albumin, a hexitol, urea, or sodium chloride
3	Dependent formulation claim	Hexitol narrowed to specified polyols; bulking agent is 0.1 to 17 parts by weight per part peptide
4	Dependent process and formulation claim	Peptide-to-acetic-acid ratio of 1:100 to 1:10,000; dilution to 3% acetic acid; mannitol as bulking agent

The patent’s practical center of gravity is claim 4. It describes a formulation process closely aligned with a commercial sterile lyophilized peptide product: cetrorelix acetate dissolved in concentrated aqueous acetic acid, diluted to 3% acetic acid, combined with mannitol, sterile-filtered, and lyophilized.

How broad is claim 1 of US 7,605,121?

Claim 1 is materially narrower than a conventional composition claim because it requires a specific process history.

A potentially infringing product would generally need to satisfy each of the following elements:

The active ingredient is cetrorelix acetate.
The cetrorelix has the claimed amino-acid sequence.
The product is sterile.
The product is lyophilized.
A bulking agent is present.
The peptide was dissolved in 30% aqueous acetic acid.
The solution was diluted with water.
Bulking agent was added at a pH of 2.5 to 3.0.
The solution was sterilized by filtration.
The solution was lyophilized.

The sequence limitation is important. The claim does not cover cetrorelix analogues with a different peptide sequence, other GnRH antagonists, or a formulation in which the active ingredient is present as a different chemical form unless the product and process still satisfy the claim.

Product-by-process implications

US courts generally treat product-by-process limitations as limitations of the claimed product for infringement analysis, while considering the product itself for patentability. The Federal Circuit has held that an accused product must generally be made by the claimed process, or by a process that is materially indistinguishable from it, to establish infringement of a product-by-process claim. See Abbott Laboratories v. Sandoz, Inc., 566 F.3d 1282 (Fed. Cir. 2009).

The patent therefore creates a difficult proof structure:

The finished vial may not reveal whether 30% acetic acid was used initially.
The generic manufacturer’s batch records, development reports, and regulatory filings may be necessary.
A process using another acid, a different initial concentration, direct dissolution in 3% acetic acid, or aseptic manufacture without sterile filtration could create a non-infringement position.
A process that produces an indistinguishable lyophilisate does not necessarily avoid infringement if the required process steps were used.

What formulations are protected by US 7,605,121?

The formulation scope depends on the dependent claim being analyzed.

Claim 2: broad bulking-agent class

Claim 2 covers a claim 1 lyophilisate in which the bulking agent is selected from:

Amino acids
Polyvinylpyrrolidone
Albumin
Hexitols
Urea
Sodium chloride

This list is closed by the phrase “selected from the group consisting of.” A bulking agent outside the listed classes would not literally satisfy claim 2, although it could still fall within claim 1 if all claim 1 elements are met.

Claim 3: hexitol and quantity limitations

Claim 3 narrows the formulation to a specified group of hexitols:

Mannitol
Glucitol
Sorbitol
D-sorbitol
Dulcitol
Allitol
Iditol

The claim also requires 0.1 to 17 parts by weight of bulking agent for each part by weight of peptide. The range is inclusive on its face.

For example, a formulation containing 5 parts mannitol per part cetrorelix peptide could satisfy the quantity limitation, assuming the product also meets claim 1. A formulation containing 20 parts mannitol per part peptide would fall outside the literal numerical range of claim 3 but could remain within claim 2 or claim 1.

Claim 4: commercial-product formulation profile

Claim 4 is the narrowest and most commercially specific claim. It requires:

One part peptide dissolved in 100 to 10,000 parts by weight of 30% aqueous acetic acid.
Dilution with water to 3% aqueous acetic acid.
Mannitol as the bulking agent.

The claim does not state a specific mannitol amount, so the amount limitation in claim 3 is not imported into claim 4. A product could therefore satisfy claim 4 without satisfying claim 3 if its mannitol-to-peptide ratio falls outside the claim 3 range.

How does the patent compare with the Cetrotide formulation?

Cetrotide is a sterile lyophilized formulation of cetrorelix acetate for reconstitution before subcutaneous administration. The US prescribing information identifies cetrorelix acetate as the active ingredient and mannitol as an inactive ingredient in the 0.25 mg presentation.[2]

That product profile corresponds closely to the subject matter of claims 3 and 4:

Patent limitation	Cetrotide product relevance
Cetrorelix acetate	Yes
Lyophilized injectable presentation	Yes
Sterile product	Yes
Mannitol bulking agent	Yes, according to FDA labeling
Reconstitution before injection	Consistent with product presentation
Exact 30% acetic-acid starting solution	Not established by the prescribing label alone
Dilution to 3% acetic acid	Not established by the prescribing label alone
Exact peptide-to-acid ratio	Not established by public product labeling

The FDA label confirms the marketed composition at the finished-product level, but it does not establish every manufacturing step recited in claims 1 and 4. Process infringement analysis would require manufacturing evidence, regulatory chemistry, manufacturing, and controls records, or other reliable evidence of the production route.

When did US Patent 7,605,121 lose exclusivity?

US Patent 7,605,121 is an issued formulation patent with a term governed principally by the 20-year patent term measured from the applicable US filing date under 35 U.S.C. § 154. The patent’s enforceable term has ended. It is therefore not a current blocking patent against a new generic cetrorelix filing.

The relevant distinction is between:

Patent expiration, which removes enforceable patent rights;
FDA regulatory exclusivity, which can restrict approval independently of patent rights; and
Commercial availability, which depends on an applicant obtaining approval and launching.

For a conventional small-molecule peptide product approved through an ANDA, the Orange Book patent term and FDA exclusivity framework are more relevant than the Purple Book biosimilar framework. Cetrorelix is generally treated as a chemically defined drug product rather than a reference biologic for biosimilar substitution purposes.

Patent-term considerations

The following events do not revive an expired patent:

A later ANDA filing
A Paragraph IV certification
A new generic formulation
A new manufacturing process
A later licensing transaction
Continued marketing of Cetrotide

A patent-term adjustment could extend the nominal term in limited circumstances, while patent-term extension under 35 U.S.C. § 156 depends on statutory eligibility and an approved application. No current blocking effect should be attributed to US 7,605,121 after expiration.

What is the Orange Book status of cetrorelix?

The Orange Book is the FDA’s principal source for approved drug products, therapeutic equivalence evaluations, and listed patents submitted by NDA holders under the Hatch-Waxman framework.[3]

For cetrorelix, the commercial reference product is Cetrotide, approved under NDA 020861. The relevant Orange Book questions are:

Whether the reference product remains listed as an active NDA product.
Whether any patents are currently listed against the drug.
Whether any listed patent has expired.
Whether an ANDA applicant has submitted a Paragraph IV certification.
Whether FDA has approved an ANDA with a therapeutic-equivalence rating.

US 7,605,121 should not be treated as a current Orange Book barrier solely because it once covered a Cetrotide-compatible formulation. An expired patent cannot support a current Paragraph IV litigation strategy or block ANDA approval.

Are there Paragraph IV challenges to US 7,605,121?

A Paragraph IV certification is relevant only while a patent is listed and unexpired, or where the applicant seeks approval before expiration. A generic applicant could challenge a listed patent by asserting that the patent is invalid, unenforceable, or not infringed.

For US 7,605,121, the commercial significance of any historical Paragraph IV activity is limited because the patent term has ended. The central historical defenses would have been:

Non-infringement defenses

A generic applicant could argue that its process:

Does not use 30% aqueous acetic acid.
Does not dilute to 3% aqueous acetic acid.
Does not maintain pH at 2.5 to 3.0 when bulking agent is added.
Uses aseptic processing rather than sterile filtration.
Does not lyophilize the filtered solution.
Uses a different bulking agent.
Uses a different cetrorelix salt or peptide form.

Validity defenses

Potential validity issues would include:

Anticipation by earlier cetrorelix formulation disclosures.
Obviousness based on known peptide lyophilization methods.
Written-description or enablement challenges to broad bulking-agent classes.
Indefiniteness arguments involving “conventional pharmaceutical auxiliary,” pH measurement, or process characterization.
Lack of patentable distinction between the claimed process and routine sterile peptide manufacture.

The process sequence and numerical ranges would likely provide the patent owner with its strongest validity arguments, while the product-by-process format would create the principal enforcement burden.

How strong is the patent estate for cetrorelix?

The cetrorelix patent estate should be divided into four categories:

Estate category	Relevance to US 7,605,121	Current commercial impact
Active-ingredient and peptide-analog patents	Protect cetrorelix or related GnRH antagonists	Primarily historical if expired
Formulation patents	Cover salts, excipients, stability, and lyophilization	US 7,605,121 was the principal formulation focus here
Method-of-use patents	Cover ovarian stimulation and prevention of premature LH surges	May affect labeling, not necessarily product manufacture
Manufacturing patents	Cover purification, sterile processing, and lyophilization	Can create process-specific barriers if unexpired

US 7,605,121 is not a complete cetrorelix estate. It is a formulation and manufacturing patent. A freedom-to-operate review would also need to examine:

Earlier cetrorelix composition-of-matter patents.
Patent families covering GnRH antagonists.
Salt and counterion claims.
Stability and reconstitution claims.
Method-of-use patents for controlled ovarian stimulation.
Manufacturing patents covering peptide purification and sterile fill-finish.
Foreign counterpart patents in Europe, Japan, Canada, and other major markets.

Because the principal patent has expired, the remaining risk is more likely to arise from manufacturing know-how, regulatory exclusivity, trade secrets, or other family members than from this patent itself.

What is the litigation and settlement status?

US 7,605,121 does not create a current litigation barrier after expiration. Any historical litigation would have concerned:

Whether a competing formulation used the patented acidic dissolution process.
Whether a generic product was made by the claimed sequence.
Whether the claims were anticipated or obvious.
Whether the patent was properly listed for the Cetrotide NDA.
Whether a Paragraph IV filing triggered a 30-month stay.

An expired patent cannot support a prospective injunction against a generic launch. A historical settlement involving the patent would also have no power to extend the patent term beyond the statutory expiration date.

No biosimilar litigation framework applies directly to this patent. A cetrorelix applicant would generally pursue an ANDA or another small-molecule regulatory route rather than a 351(k) biosimilar application.

What generic entry risks exist for cetrorelix?

The patent risk from US 7,605,121 is now low because the patent has expired. The remaining generic-entry risks are operational and regulatory:

Formulation equivalence

The generic must demonstrate pharmaceutical equivalence and bioequivalence or satisfy the applicable FDA requirements for the selected pathway. A lyophilized peptide product may require close control of:

Reconstitution time
Peptide content
Related substances
Residual moisture
Sterility
Particulate matter
Container-closure integrity
Stability after reconstitution

Manufacturing and CMC risk

The patent’s process is no longer enforceable, but its technical disclosure may still be relevant to development. A manufacturer may choose a different route to avoid reproducing the claimed process, provided the resulting product meets FDA quality requirements.

The highest practical barriers are likely to be:

Reproducible sterile lyophilization
Control of peptide degradation
Consistent acetic-acid processing
Scale-up of sterile filtration
Vial and stopper compatibility
Demonstration of equivalent clinical performance where required

Commercial launch

Generic entry also depends on:

ANDA approval
Availability of active pharmaceutical ingredient
Manufacturing capacity
Pricing relative to Cetrotide
Distribution through fertility clinics and specialty channels
Reference-product market share
Any remaining regulatory exclusivity or other unexpired patents

How does US 7,605,121 compare with competing patent protection?

US 7,605,121 is narrower than a composition-of-matter patent and broader than a single example-specific manufacturing disclosure.

Patent type	Typical scope	Relative strength versus US 7,605,121
Cetrorelix composition patent	Peptide structure or salt	Broader if unexpired; stronger against all formulations
Lyophilization formulation patent	Active ingredient plus excipient and physical form	Comparable, depending on claim language
Method-of-use patent	Administration for ovarian stimulation	Does not necessarily reach manufacture or sale of product
Manufacturing patent	Defined purification or sterile-processing sequence	Similar infringement proof issues
US 7,605,121	Cetrorelix lyophilisate made through defined acidic process	Narrower than molecule claims, commercially relevant to mannitol product

The most important distinction is that US 7,605,121 targets the finished lyophilisate through process-defined limitations. A competitor that uses a different manufacturing route may avoid literal infringement even if its product is chemically similar.

What licensing deals affect the patent?

Cetrorelix was developed and commercialized through predecessor and license relationships involving the original developer and later commercial partners. Ferring markets Cetrotide in the United States. A commercial license or supply agreement may govern the product, but private agreements do not extend an expired patent or create patent rights against third parties.

The business impact of any historical license should therefore be separated from patent enforceability:

A license can authorize use of a patent during its term.
A supply agreement can control API or finished-product sourcing.
A settlement can restrict a particular party’s launch date.
None of these arrangements can extend the statutory patent term against an unrelated generic applicant.

Key Takeaways

US 7,605,121 covers a sterile lyophilized cetrorelix acetate formulation made through a specified acidic dissolution, dilution, sterile-filtration, and lyophilization process.
Claim 1 is a product-by-process claim and requires the full process sequence.
Claim 2 covers specified bulking-agent classes.
Claim 3 narrows the claim to specified hexitols and a 0.1-to-17 weight ratio.
Claim 4 is the most commercially specific claim, requiring 30% aqueous acetic acid, dilution to 3%, and mannitol.
The Cetrotide label identifies cetrorelix acetate and mannitol, but labeling alone does not prove every patented manufacturing step.
The patent has expired and is not a current US blocking right.
Any present generic-entry risk is more likely to involve FDA approval, CMC execution, API supply, or other unexpired patent families.
Cetrorelix is generally approached through the ANDA framework rather than the biosimilar pathway.
Historical Paragraph IV or settlement activity would not extend the expired patent’s enforceable term.

FAQs

Does US 7,605,121 cover cetrorelix acetate itself?

No. The claims cover a sterile lyophilized cetrorelix acetate-bulking-agent product made through specified process steps. They do not claim cetrorelix acetate as a molecule in every form.

Does the patent cover a cetrorelix vial containing mannitol?

Only if the vial also satisfies the applicable process limitations. Mannitol alone is insufficient. The product must be a sterile lyophilisate made through the claimed acidic process, filtration, and lyophilization steps.

Can a generic manufacturer avoid the patent by using sorbitol instead of mannitol?

Potentially. Sorbitol is listed in claim 3, so replacing mannitol with sorbitol would not avoid claim 3. It could avoid claim 4, which specifically requires mannitol, but claim 1 or claim 2 would still require separate analysis.

Is a different acid enough to avoid infringement?

A formulation made with a different acid would likely avoid the literal “30% aqueous acetic acid” limitation, assuming the process does not otherwise fall within an equivalent theory of infringement. The expired status of the patent makes this issue primarily historical.

Does FDA approval of a generic cetrorelix product require a license to US 7,605,121?

No. An expired patent does not require a license. FDA approval is governed by the applicable drug-approval pathway and does not depend on obtaining a license to an expired patent.

References

United States Patent and Trademark Office. (2009). Cetrorelix acetate lyophilisate, U.S. Patent No. 7,605,121.
U.S. Food and Drug Administration. (2023). Cetrotide (cetrorelix acetate for injection) prescribing information.
U.S. Food and Drug Administration. (2024). Approved drug products with therapeutic equivalence evaluations, commonly known as the Orange Book.
35 U.S.C. § 154. Patent term.
Abbott Laboratories v. Sandoz, Inc., 566 F.3d 1282 (Fed. Cir. 2009).
21 U.S.C. § 355. New drug applications and abbreviated applications.

Foriegn Application Priority Data
Foreign Country	Foreign Patent Number	Foreign Patent Date
Germany	P4305225	Feb 19, 1993

Country	Patent Number	Estimated Expiration	Supplementary Protection Certificate	SPC Country	SPC Expiration
Austria	193653	⤷ Start Trial
Australia	5523594	⤷ Start Trial
Australia	671881	⤷ Start Trial
Brazil	9400617	⤷ Start Trial
>Country	>Patent Number	>Estimated Expiration	>Supplementary Protection Certificate	>SPC Country	>SPC Expiration

Details for Patent: 7,605,121

Summary for Patent: 7,605,121