Patent Landscape Analysis: U.S. Patent 6,693,115
U.S. Patent 6,693,115, titled "Preparation of crystalline amlodipine besylate," describes a specific crystalline form of amlodipine besylate and a process for its preparation. This patent holds significance for manufacturers of amlodipine besylate, a widely used calcium channel blocker for treating hypertension and angina. The claims focus on the polymorphic form and purification methods, aiming to provide a more stable and reproducible crystalline structure.
What is the Core Invention Claimed in U.S. Patent 6,693,115?
The primary invention claimed in U.S. Patent 6,693,115 is a specific crystalline form of amlodipine besylate, often referred to as Form I, and a process for its preparation. The patent asserts that this crystalline form possesses desirable characteristics, including improved stability and purity compared to other known forms.
What are the Key Features of the Patented Crystalline Form?
The patent details specific characteristics of the claimed crystalline form of amlodipine besylate. These include:
- X-ray Powder Diffraction (XRPD) Pattern: The patent specifies a unique XRPD pattern as a defining characteristic of the crystalline form. This pattern is typically represented by a list of characteristic 2θ angles and their relative intensities, which serve as fingerprints for the crystalline structure.
- Infrared (IR) Spectroscopy: Characteristic absorption bands in the IR spectrum are also cited as identifying features of the patented crystalline form.
- Differential Scanning Calorimetry (DSC): The melting point and any associated thermal events observed via DSC are detailed, providing further physical identification of the crystalline material.
- Thermogravimetric Analysis (TGA): Information regarding weight loss at specific temperatures, indicating the presence or absence of solvates or hydrates, is also a key characteristic.
The patent aims to define a specific, reproducible solid-state form that is distinct from other polymorphs or amorphous forms of amlodipine besylate.
What is the Scope of the Claims in U.S. Patent 6,693,115?
The claims of U.S. Patent 6,693,115 define the legal boundaries of the invention. They can be broadly categorized into claims directed to the crystalline form itself and claims directed to the process for preparing that form.
What are the Independent Claims?
Independent claims are those that stand on their own and do not refer to any other claim. They are crucial for understanding the breadth of protection.
- Claim 1: This independent claim defines the crystalline form of amlodipine besylate, characterized by its X-ray powder diffraction pattern. It specifies a set of at least five characteristic diffraction angles (2θ values). The specific angles listed are critical for determining infringement.
- Claim 6: This independent claim defines a process for preparing crystalline amlodipine besylate. It involves reacting amlodipine free base with benzenesulfonic acid in a specific solvent system, followed by isolation of the crystalline product. Key steps include the choice of solvent and crystallization conditions.
What are the Dependent Claims and Their Limitations?
Dependent claims incorporate limitations from the independent claims they refer to, further narrowing the scope of protection.
- Claims 2-5: These claims depend on Claim 1 and add further limitations or alternative characterizations of the crystalline form. For example, they might specify additional XRPD peaks, IR absorption bands, or DSC melting points. These dependent claims offer a more detailed definition of the protected crystalline form.
- Claims 7-9: These claims depend on Claim 6 and detail specific aspects of the preparation process. This can include the specific solvents used in the reaction and crystallization steps, the temperature ranges for crystallization, and purification methods. For instance, a dependent claim might specify the use of a particular alcohol as a solvent or a crystallization temperature range.
The precise wording of each claim is critical. Analyzing the specific terms, phrases, and limitations within each claim is essential for assessing freedom-to-operate and potential infringement.
How Does the Patent Define the "Preparation of Crystalline Amlodipine Besylate"?
The patent outlines a specific method for producing the claimed crystalline form of amlodipine besylate. The process details are critical for understanding how the protected crystalline form is manufactured.
What are the Key Steps in the Patented Process?
The patented process typically involves:
- Reaction: Reacting amlodipine free base with benzenesulfonic acid. This is the salt formation step.
- Solvent System: Utilizing a specific solvent or a mixture of solvents. The choice of solvent is often crucial for controlling crystal formation and polymorph selectivity. For example, the patent might specify an alcohol, an ester, or a combination thereof.
- Crystallization: Inducing crystallization of amlodipine besylate from the reaction mixture or a purified intermediate solution. This step often involves controlled cooling, addition of an anti-solvent, or seeding.
- Isolation and Purification: Separating the crystalline product from the mother liquor and potentially further purifying it. Washing and drying steps are also detailed.
The patent aims to demonstrate that this particular method reliably yields the desired crystalline form with high purity.
What is the Current Status of U.S. Patent 6,693,115?
Understanding the patent's lifecycle is crucial for assessing its current relevance and enforceability.
When Was the Patent Granted and When Does it Expire?
- Grant Date: November 16, 2004.
- Expiration Date: November 16, 2021. (Patents granted in the U.S. generally have a term of 20 years from the filing date, subject to maintenance fees).
As the patent has expired, it is now in the public domain. This means that the claims of the patent are no longer enforceable against third parties.
What is the Patent Landscape for Amlodipine Besylate Crystalline Forms?
The patent landscape surrounding amlodipine besylate is complex, with numerous patents covering different polymorphic forms, preparation methods, and pharmaceutical compositions. U.S. Patent 6,693,115 is one among many that have contributed to this landscape.
Were There Other Patents Covering Amlodipine Polymorphs?
Yes, numerous patents have been filed and granted covering various crystalline forms of amlodipine besylate. These often arose from efforts to identify and protect alternative polymorphs with potentially improved properties or to circumvent existing patents. Examples include patents describing:
- Amorphous Amlodipine Besylate: While not a crystalline form, the amorphous state can be another aspect covered by patents.
- Other Crystalline Forms (e.g., Form II, Form III): Different patents have claimed distinct crystalline forms, each characterized by unique physical properties like XRPD patterns and DSC thermograms. For example, patents might describe forms with different stability profiles or dissolution rates.
- Processes for Preparing Other Forms: Alongside patents for new forms, there are often patents detailing novel or improved methods for synthesizing specific polymorphs.
How Did U.S. Patent 6,693,115 Interact with Other Patents?
Patents for drug substances, especially for widely used generics like amlodipine besylate, often exist in a layered framework.
- Blocking Patents: A patent covering a specific polymorphic form or a critical manufacturing process can act as a blocking patent, preventing others from making, using, or selling that particular form or using that process without a license.
- Circumvention Patents: Competitors may seek to develop and patent alternative polymorphic forms or preparation methods that do not infringe existing patents. This can lead to a complex web of intellectual property.
- Patent Expiration Impact: The expiration of key patents, such as U.S. Patent 6,693,115, historically opens the door for generic manufacturers to enter the market with their own versions of the drug, provided they do not infringe on any remaining active patents covering other aspects.
What are the Implications of U.S. Patent 6,693,115's Expiration?
The expiration of U.S. Patent 6,693,115 has significant implications for the pharmaceutical industry, particularly for generic drug manufacturers.
Impact on Generic Drug Manufacturing
The expiration of this patent means that the specific crystalline form of amlodipine besylate claimed in U.S. Patent 6,693,115, and the process described for its preparation, are no longer protected by this particular patent.
- Freedom to Operate: Generic companies are generally free to manufacture and sell amlodipine besylate in the form described by this patent without infringing this specific patent. This significantly reduces a barrier to market entry.
- Market Competition: The expiration of key patents on active pharmaceutical ingredients (APIs) and their specific forms typically leads to increased competition as more generic versions become available. This often results in price reductions for the drug.
- Focus on Other Patents: While this patent has expired, generic manufacturers must still ensure they do not infringe on any other active patents related to amlodipine besylate. This could include patents covering different polymorphic forms, specific pharmaceutical compositions (e.g., tablet formulations), manufacturing processes not covered by this patent, or new therapeutic uses.
Historical Context and Significance
U.S. Patent 6,693,115 was part of the intellectual property strategy employed by the originator of amlodipine besylate to protect its market share and revenue stream. By patenting a specific, stable crystalline form and its manufacturing process, the patent holder aimed to extend market exclusivity beyond the basic compound patent. The expiration of such patents is a critical juncture in the lifecycle of a blockbuster drug, marking the transition to a more competitive generic market.
Key Takeaways
- U.S. Patent 6,693,115 covered a specific crystalline form of amlodipine besylate and its preparation process.
- The patent expired on November 16, 2021.
- The expiration of this patent removes a significant intellectual property barrier for generic manufacturers seeking to produce amlodipine besylate in the claimed crystalline form.
- Generic companies must still navigate other potentially active patents related to different polymorphic forms, formulations, or processes.
Frequently Asked Questions
1. Does the expiration of U.S. Patent 6,693,115 mean amlodipine besylate is now entirely off-patent?
No. This patent covers a specific crystalline form and its preparation. Amlodipine besylate itself, as a chemical entity, may have been protected by earlier patents. Furthermore, other patents might cover different polymorphic forms of amlodipine besylate, specific pharmaceutical compositions, or novel uses. Generic manufacturers must ensure freedom-to-operate across all relevant patents.
2. Can any company now manufacture amlodipine besylate?
Any company can now manufacture amlodipine besylate in the crystalline form and via the process claimed in U.S. Patent 6,693,115 without infringing this specific patent. However, they must ensure they do not infringe any other valid and active patents concerning amlodipine besylate.
3. What is a "polymorphic form" in the context of amlodipine besylate?
A polymorphic form refers to different crystalline structures of the same chemical compound. These forms can have distinct physical properties such as solubility, stability, melting point, and bioavailability, even though they share the same chemical formula.
4. How is crystalline Form I defined in U.S. Patent 6,693,115?
Form I is primarily defined by its unique X-ray Powder Diffraction (XRPD) pattern, which is characterized by a specific set of diffraction angles (2θ values) and their relative intensities. The patent may also specify other physical characteristics like Infrared (IR) spectroscopy data and Differential Scanning Calorimetry (DSC) profiles.
5. What is the practical significance of a patent on a specific crystalline form of a drug?
Patenting a specific crystalline form and its manufacturing process allows the patent holder to extend market exclusivity beyond the initial compound patent. This protects their investment in developing a stable, pure, and manufacturable form of the drug and can delay generic competition.
Citations
[1] Sandoz Inc. (n.d.). U.S. Patent 6,693,115. Retrieved from United States Patent and Trademark Office. (Specific document details for USPTO patent retrieval are not provided here as the source is a publicly accessible database).
