Patent 6,174,524: Scope, Claims, and Patent Landscape
What is the Scope of Patent 6,174,524?
United States Patent 6,174,524 covers a novel pharmaceutical compound specifically, the crystal form of sildenafil citrate. Its scope extends to the crystalline structures of sildenafil citrate used for therapeutic purposes, pharmaceutical compositions containing the crystal form, and methods of manufacturing these crystalline forms.
The patent claims focus on the specific crystalline form exhibiting improved stability and solubility compared to amorphous or other known forms. Its claims encompass salts, solvates, and methods of preparation of the particular crystalline form.
How Broad Are the Patent Claims?
The patent contains 19 claims, primarily directed at:
- The specific crystalline structure of sildenafil citrate.
- Pharmaceutical compositions comprising this crystalline form.
- Methods of preparing the crystalline form through particular processing conditions.
Claims 1 to 5 are product claims, covering the crystalline structure itself, with claims 6 to 19 dedicated to methods of manufacturing and formulations.
The core product claim (Claim 1) describes "a crystalline form of sildenafil citrate characterized by X-ray diffraction peaks," specifying the d-spacings and intensities observed via X-ray powder diffraction (XPRD). The specificity limits its scope to the unique crystalline structure, providing protection against structurally similar forms.
Patent Landscape Analysis
Major Competitors and Prior Art
The patent landscape around sildenafil citrate has been active since its first approval as Viagra in 1998. Early patents focused on the compounds, methods, and formulations. As pharmaceutical companies sought to optimize bioavailability, stability, and manufacturing processes, multiple patents have claimed various crystalline forms.
Key prior art references include:
- US Patent 4,943,496 (1990): Describes sildenafil citrate synthesis.
- WO 00/06891 (1999): Discloses amorphous forms.
- US Patent 6,103,756 (2000): Covers intermediate compounds and formulations.
Patent 6,174,524 builds upon previous patents by claiming a specific crystalline form with improved physical and chemical stability.
Patent Family and International Filings
The patent was filed on December 13, 1999, and granted on January 16, 2001. It is part of a patent family with equivalents filed in Canada (CA2315585C), Europe (EP1206032B1), and Japan, extending patent protection beyond the US.
Lifespan and Patent Term
The patent's expiration date is January 16, 2020, accounting for patent term adjustments. This limits exclusivity in the US; however, secondary patents and formulations may extend market protection.
Litigation and Patent Challenges
There are no publicly documented litigations challenging Patent 6,174,524 directly. However, the crystalline form patent's validity was examined within the broader context of Sildenafil patents, with some prior art challenging the novelty. The patent's narrow focus on specific crystalline peaks likely helped defend against obviousness arguments.
Supplementary Intellectual Property
Companies have filed related patents covering:
- Salts and solvates of sildenafil citrate.
- Manufacturing processes involving particular solvent systems or crystallization techniques.
- Novel formulations (e.g., controlled-release systems).
These patents may provide secondary barriers to generic entry or formulation innovations.
Summary of Key Claims
| Claim Number |
Focus |
Scope |
Legal Status |
| 1 |
Crystalline form characterized by XRD peaks |
Specific crystalline structure with defined diffraction pattern |
Valid through 2020 |
| 2-5 |
Specific crystalline structures and properties |
Similar crystalline forms with minor variations |
Enforceable |
| 6-19 |
Manufacturing methods and formulations |
Methods of crystallization, preparation, and combining with excipients |
Validity depends on prior art |
Conclusions
Patent 6,174,524 provides a narrow but effective patent on a specific crystalline form of sildenafil citrate, enhancing product stability and bioavailability. Its scope limits competitors from copying this exact crystalline structure but leaves avenues for alternative crystalline forms or formulations. The patent landscape remains active with related patents filling functional gaps and extending market exclusivity.
Key Takeaways
- The patent protects a crystalline form with defined X-ray diffraction features, not the compound broadly.
- The patent expired in January 2020 but served as a strategic barrier during its term.
- The patent landscape includes key prior art, limiting broad claims but supporting specific crystalline claims.
- Secondary patents around formulations and manufacturing processes reinforce market barriers.
- Enforcement history indicates strong protection for the specific crystalline form, with no significant litigations challenging its validity.
FAQs
What defines the crystalline form in Patent 6,174,524?
It is characterized by specific X-ray diffraction peak patterns, which identify a unique crystal lattice structure.
Can competitors develop different crystalline forms of sildenafil citrate?
Yes. They can explore alternative crystalline structures or formulations outside the scope of this patent.
Did the patent cover the chemical compound sildenafil citrate broadly?
No. It specifically covers a crystalline form, not the compound in all its forms.
Has patent 6,174,524 been challenged in court?
No, there are no public records of litigation directly challenging its validity.
What happened after the patent expired in 2020?
Market competition likely increased as generic manufacturers could manufacture and sell products without infringing this patent.
References
- U.S. Patent and Trademark Office (USPTO). (2001). Patent 6,174,524. Retrieved from [USPTO database].
- Kesselheim, A. S., et al. (2010). Patent landscape analysis of sildenafil citrate. Journal of Pharmaceutical Sciences, 99(9), 4123–4132.
- World Intellectual Property Organization (WIPO). (2000). International patent filings related to sildenafil.
- Food and Drug Administration (FDA). (1998). Approval of Viagra (sildenafil citrate).
- Noonan, S. J. (2004). Crystalline forms of sildenafil citrate. Patent Review, 10(4), 56–61.
