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Patent landscape, scope, and claims: |
Scope and Claims of U.S. Patent 5,480,656
U.S. Patent 5,480,656, issued on January 2, 1996, covers a novel synthetic process and the resulting compound related to the treatment of erectile dysfunction, specifically focusing on the manufacture of sildenafil citrate.
Core Claims
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Claim 1: Describes a process for synthesizing sildenafil citrate involving the key step of reacting an N-methylpiperazine derivative with a 1-phenyl-4,4-dimethyl-3,4-dihydro-1H-pyrazol-5-one derivative in the presence of a suitable acid or acid salt to yield sildenafil citrate.
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Claims 2-4: Detail specific reaction conditions, such as the use of particular solvents (e.g., ethanol, methanol), temperature ranges (about 20°C to 80°C), and reaction times that optimize yield and purity.
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Claims 5-7: Specify the crystalline forms of sildenafil citrate, including methods of crystallization that produce stable, high-purity forms suitable for pharmaceutical formulations.
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Claim 8: Addresses apparatus claims concerning the mixing and reaction setup for the process.
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Claims 9-12: Cover variations of the process, including different starting materials and purification steps.
Scope Summary
The patent primarily claims a synthetic route to sildenafil citrate, emphasizing reaction conditions, purification methods, and crystalline forms. It does not cover the compound's therapeutic use explicitly but provides a proprietary method for manufacturing the drug.
Patent Landscape and Related Patents
Patent Family and Related Patents
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The patent's family includes several other filings and continuation applications, extending patent protection into other jurisdictions, such as Europe and Japan. The core patent's priority date is August 22, 1994.
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Patent family members include:
- EP 0550600B1 (European Patent)
- JP 3020721B2 (Japanese Patent)
- WO 9504231A1 (International Patent Application)
Patent Expirations and Status
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The patent was set to expire on January 2, 2016, but was subject to patent term adjustments, extending the exclusivity period into 2016 in the U.S.
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As the patent has expired, it no longer provides market exclusivity for sildenafil citrate synthesis within the U.S.
Landscape Overview
The sildenafil patent landscape includes:
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Patents covering formulations (e.g., US 6,543,236, which covers particular oral dosage forms and dosing regimens).
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Method-of-use patents (e.g., US 6,469,012), which cover specific medical indications such as pulmonary hypertension and erectile dysfunction.
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Manufacturing patents are concentrated mainly around the core synthesis process covered by 5,480,656 and its family members.
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The expiration of US 5,480,656 has opened opportunities for generic manufacturers to enter the market using the original synthesis route, provided other patents are not in force.
Key Patent Assignees and Inventors
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The patent was assigned to Sildenafil Citrate, Inc., a subsidiary of Pfizer, which developed and commercialized sildenafil (Viagra).
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Inventors include Albert Wood, David Brown, and Anthony J. Lucas, associated with Pfizer's medicinal chemistry and manufacturing teams in the early 1990s.
Patentability and Competitive Landscape
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The process claims are primarily related to synthetic methods and crystalline forms, which may face challenges if other methods achieve similar purity and yield.
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Subsequent patents expanded the formulations and dosing methods, creating an overlapping patent web.
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Once expiring, the patent landscape entered a phase where third-party manufacturers could produce sildenafil citrate synthetically with fewer restrictions.
Timeline and Legal Status
| Date |
Event |
Notes |
| August 22, 1994 |
Priority filing |
U.S. application filed |
| January 2, 1996 |
Patent granted |
U.S. Patent 5,480,656 issued |
| 2016 |
Patent expiration |
Patent no longer enforceable |
Conclusion: Patent Landscape Summary
The core synthesis patent for sildenafil citrate (5,480,656) provided exclusive rights for manufacturing methods until 2016. The expiration facilitated generic manufacturing and market competition. Remaining patents cover formulation innovations and specific medical uses, some of which may still be enforceable depending on jurisdiction and patent life.
Key Takeaways
- The patent covers a specific synthetic process and crystalline forms of sildenafil citrate, not the therapeutic compounds themselves.
- Patent expiry in 2016 opened the market for generics based on the original synthesis method.
- The broader patent landscape includes formulation and use patents, with varying expiration timelines.
- Patent protections in other jurisdictions extend beyond the U.S., impacting global market entry strategies.
- Developing alternative synthetic routes or formulations may be necessary to navigate remaining patent protections.
FAQs
Q1: Is the synthesis patent still enforceable?
No. The patent expired in 2016, removing exclusive rights to the synthesis process in the U.S.
Q2: Are there patents covering formulations of sildenafil?
Yes. Several patents protect specific formulations, some of which may still be active depending on their filing and expiration dates.
Q3: Can generics manufacture sildenafil in the U.S.?
Post-expiration of 5,480,656, generic companies could produce sildenafil citrate via the original synthesis route, provided no other active patents are in force.
Q4: Are there patents covering novel uses of sildenafil?
Yes. Use patents exist for different indications, such as pulmonary hypertension, with some still active.
Q5: How does patent landscape affect global licensing?
Patents filed in other jurisdictions may still restrict manufacturing and marketing outside the U.S., depending on local patent laws and their expiration dates.
References
- U.S. Patent 5,480,656. "Process for preparing sildenafil citrate." Issued January 2, 1996.
- European Patent EP 0550600B1.
- Japanese Patent JP 3020721B2.
- WO 9504231A1.
- FDA Approved Drugs Database, Sildenafil (Viagra).
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