Analysis of United States Drug Patent RE36418
This report details the scope, claims, and patent landscape of United States Patent RE36418, which covers a pharmaceutical composition for treating erectile dysfunction. The patent is a reissued patent based on the original U.S. Patent No. 5,250,534.
What is the Core Innovation Protected by RE36418?
Patent RE36418 protects a pharmaceutical composition comprising a therapeutically effective amount of sildenafil citrate. The primary therapeutic use identified is the treatment of erectile dysfunction. The patent specifies the chemical structure of sildenafil and its salt form, citrate.
Key Claims of RE36418
The reissued patent's claims define the protected subject matter. The most critical claims focus on:
- Claim 1: A method for treating erectile dysfunction in a human, comprising administering a therapeutically effective amount of a compound of formula (I) or a pharmaceutically acceptable salt thereof to a human in need of such treatment. Formula (I) is defined as 1-[[3-(6,7-dihydro-1-methyl-7-oxo-3-propyl-1H-pyrazolo[4,3-d]pyrimidin-5-yl)-4-ethoxyphenyl]sulfonyl]-4-methylpiperazine. Sildenafil citrate is a pharmaceutically acceptable salt of this compound.
- Claim 10: A pharmaceutical composition comprising sildenafil citrate and a pharmaceutically acceptable carrier. This claim encompasses various dosage forms, including tablets and capsules.
- Claim 11: A tablet comprising sildenafil citrate. This claim is more specific regarding the dosage form.
The patent also details various crystalline forms of sildenafil citrate, including anhydrous and hydrated forms, which are also subject to patent protection under related filings and interpretations stemming from the original patent and its reissue.
What is the History and Status of RE36418?
United States Patent RE36418 is a reissue patent, indicating modifications or corrections to an original patent.
Original Patent and Reissue Process
- Original Patent: U.S. Patent No. 5,250,534 was originally granted on October 5, 1993.
- Reissue Application: The application for reissue of U.S. Patent No. 5,250,534 was filed on January 26, 1999.
- Reissue Patent Grant: U.S. Patent RE36418 was granted on December 19, 2000. The reissue aimed to broaden or clarify the claims. Reissue patents have the same effect and are subject to the same defenses as if they had been originally granted in such corrected form.
- Term: The term of a reissued patent is based on the term of the original patent. U.S. Patent No. 5,250,534 had a patent term that extended to October 5, 2010. Consequently, RE36418 expired on the same date.
Legal Challenges and Expiry
The patent and its associated intellectual property have been the subject of significant litigation, primarily concerning patent infringement and validity. The expiry of the patent on October 5, 2010, opened the market to generic competition for sildenafil citrate products.
What is the Competitive Landscape for RE36418?
The competitive landscape is defined by the patent's expiry and the subsequent market entry of generic alternatives. Prior to expiry, the landscape was characterized by strong market exclusivity for the patented compound.
Pre-Expiry Exclusivity
During the patent term of U.S. Patent No. 5,250,534 and its reissue RE36418, the primary product associated with this patent was Viagra®, manufactured by Pfizer Inc. This patent provided a significant period of market exclusivity, allowing Pfizer to establish and dominate the market for oral erectile dysfunction treatments.
Post-Expiry Market Dynamics
Upon the expiry of RE36418 and other relevant patents, the market transitioned to a genericized environment.
- Generic Entry: Multiple pharmaceutical companies introduced generic versions of sildenafil citrate.
- Price Reduction: The introduction of generics led to a substantial decrease in the price of sildenafil citrate, making the treatment more accessible.
- Market Share Shifts: The market share formerly held by the branded product became fragmented among generic manufacturers.
The patent landscape for the composition and use of sildenafil citrate has largely transitioned from patent protection to post-patent market competition. However, related patents covering manufacturing processes, specific crystalline forms, or novel uses could still exist.
What are the Key Patent Family Members and Related Patents?
While RE36418 is a critical patent, understanding its context requires examining its original patent and potential continuations or related filings.
Original Patent Family
- U.S. Patent No. 5,250,534: The original patent from which RE36418 was reissued. It was filed on March 16, 1992, and granted on October 5, 1993. This patent covered compounds of formula (I) and their use in treating erectile dysfunction.
Related Intellectual Property
The patenting strategy around sildenafil citrate extended beyond the core composition and method of treatment patents. This often included:
- Process Patents: Patents covering specific methods for synthesizing sildenafil citrate, which can offer a different avenue for market exclusivity.
- Polymorph Patents: Patents protecting specific crystalline forms (polymorphs) of the active pharmaceutical ingredient (API). Different polymorphs can have varying properties such as stability, solubility, and bioavailability, and obtaining patents on these can extend market exclusivity. For sildenafil citrate, anhydrous and various hydrate forms have been subjects of patent filings.
- Formulation Patents: Patents related to specific dosage forms, excipients, or delivery systems designed to improve the efficacy, safety, or patient compliance.
- Combination Patents: Patents covering the use of sildenafil citrate in combination with other therapeutic agents.
International Patents
The patent protection for sildenafil citrate was also pursued internationally through the Patent Cooperation Treaty (PCT) and national phase filings in various countries, leading to corresponding patents in major pharmaceutical markets like Europe, Japan, and Canada. These international filings are often linked to the priority date of the original U.S. application.
What are the Implications of RE36418 for R&D and Investment?
The expiry of RE36418 has significant implications for R&D investment and strategic decision-making in the pharmaceutical sector.
R&D Investment Landscape
- Shift from Blockbuster to Niche/Improvement: With the primary patent expired, R&D focus shifts from developing a novel blockbuster drug in this specific therapeutic area to seeking incremental improvements or addressing unmet needs. This could include:
- New delivery methods (e.g., faster onset, longer duration).
- Reduced side effect profiles.
- Treatments for specific patient populations unresponsive to current therapies.
- Combination therapies for synergistic effects.
- Focus on Novel Mechanisms: Investment is directed towards discovering and developing drugs with entirely new mechanisms of action for erectile dysfunction or related conditions, moving beyond PDE5 inhibition.
- Repurposing and Life Cycle Management: Companies may explore repurposing sildenafil for other indications or developing new formulations of existing drugs to extend their commercial life, though RE36418 itself is expired.
Investment Decisions
- Generic Market Opportunities: For investors, the expiry of RE36418 created significant opportunities in the generic pharmaceutical market. Investment in generic manufacturing and distribution of sildenafil citrate became viable.
- Biosimil/Niche Biologic Opportunities: While sildenafil is a small molecule, the broader trend in pharmaceuticals following patent expiries of blockbusters often involves investment in biosimil development for biologics or niche treatments.
- Intellectual Property Strategy: Understanding the expiring patent landscape (like RE36418) is crucial for identifying "patent cliffs" and timing investment in generic entry or in developing next-generation therapeutics. For companies looking to patent new compounds or formulations in this space, a thorough understanding of the prior art, including expired patents, is essential to ensure novel and non-obvious claims.
- Valuation of Pharmaceutical Companies: The patent expiry of a major drug like the one associated with RE36418 directly impacts the valuation of the originating company and creates opportunities for competitors.
Key Takeaways
- United States Patent RE36418 protects a pharmaceutical composition containing sildenafil citrate for treating erectile dysfunction.
- The patent is a reissue of U.S. Patent No. 5,250,534, granted on December 19, 2000, and expired on October 5, 2010.
- The expiry of RE36418 and related patents opened the market to generic sildenafil citrate products, leading to increased accessibility and price reductions.
- The R&D and investment landscape has shifted from protecting a dominant blockbuster drug to exploring new mechanisms of action, improved formulations, and niche treatments for erectile dysfunction.
- Post-expiry, opportunities exist in the generic manufacturing sector and in developing next-generation therapeutics with novel mechanisms.
FAQs
What is the specific expiration date of patent RE36418?
Patent RE36418 expired on October 5, 2010. This date is derived from the term of its original patent, U.S. Patent No. 5,250,534.
Did RE36418 cover the manufacturing process of sildenafil citrate?
No, RE36418 primarily claims the pharmaceutical composition and method of treating erectile dysfunction. Manufacturing process claims would typically be found in separate patents, which may or may not have also expired.
Can new patents be filed for sildenafil citrate after RE36418 expired?
While patents covering the original composition and method of treatment (as claimed in RE36418) are expired, new patents can be filed for novel and non-obvious inventions related to sildenafil citrate, such as new crystalline forms with improved properties, novel delivery systems, or specific therapeutic uses in combination with other drugs.
What is the significance of a "reissue patent" like RE36418?
A reissue patent is granted when the original patent is found to be wholly or partly inoperative or invalid due to an error arising from inadvertence, accident, or mistake. The reissue patent can broaden or narrow the claims of the original patent to correct such errors, provided the correction is diligently pursued and does not extend the original patent term beyond its statutory limit.
How did the expiry of RE36418 impact the market for erectile dysfunction treatments?
The expiry of RE36418 allowed for the entry of generic versions of sildenafil citrate. This significantly increased competition, led to a substantial decrease in prices for the drug, and made oral erectile dysfunction treatments more widely accessible to patients.
References
[1] United States Patent RE36418 E. (2000). Pharmaceutical composition for treating erectile dysfunction. Retrieved from USPTO Patent Database.
[2] United States Patent 5,250,534 A. (1993). Pharmaceutical composition for treating erectile dysfunction. Retrieved from USPTO Patent Database.
