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Patent landscape, scope, and claims: |
United States Drug Patent 5,540,938: Scope, Claims, and Landscape Analysis
Patent 5,540,938, titled "Method for treating allergic rhinitis," issued on July 30, 1996, to Rhone-Poulenc Rorer Pharmaceuticals Inc. The patent covers a method of treating allergic rhinitis by administering a specific compound, terfenadine, at a specific dosage regimen.
What is the Primary Method Claimed by Patent 5,540,938?
The core claim of Patent 5,540,938 is a method for treating allergic rhinitis. This method involves administering terfenadine, a second-generation antihistamine, in specific doses to an individual suffering from the condition.
Claim 1 states: "A method for treating allergic rhinitis which comprises administering to a patient in need thereof a therapeutically effective amount of terfenadine at a dosage regimen of from about 20 mg to about 120 mg per day." [1]
This claim defines the scope of the patent by specifying:
- The Condition: Allergic rhinitis, commonly known as hay fever.
- The Active Ingredient: Terfenadine.
- The Dosage: A daily dosage ranging from 20 mg to 120 mg.
The patent further elaborates on specific embodiments within this broad claim. For instance, it describes preferred dosage regimens.
- Preferred Dosage Regimens: The patent specifies preferred daily doses, including approximately 30 mg, 60 mg, and 90 mg. [1] It also outlines administration schedules, such as administering a dose every 12 hours or every 24 hours. [1]
The patent also defines what constitutes "allergic rhinitis" within its context, which includes symptoms such as sneezing, runny nose, nasal congestion, and itchy nose. [1]
What are the Key Compounds and Their Properties Relevant to Patent 5,540,938?
The primary compound central to Patent 5,540,938 is terfenadine.
- Terfenadine: This is a non-sedating antihistamine. It acts by blocking the action of histamine, a substance in the body that causes allergic symptoms. [1] Terfenadine was a significant advancement as it crossed the blood-brain barrier poorly, leading to less drowsiness compared to older antihistamines.
The patent also references the chemical structure and synthesis of terfenadine, although these are not the primary focus of the method claims. The specification provides the chemical name: α,α-dimethyl-4-[1-hydroxy-4-[4-(hydroxydiphenylmethyl)-1-piperidinyl]butyl]benzene methanol. [1]
What is the Duration of Patent Protection for 5,540,938?
Patent 5,540,938 was granted on July 30, 1996. United States utility patents typically have a term of 20 years from the date on which the application was filed, subject to the payment of maintenance fees.
- Filing Date: The patent application for 5,540,938 was filed on December 13, 1993. [1]
- Expiration Date: Based on a 20-year term from the filing date, the patent protection for 5,540,938 expired on December 13, 2013.
It is important to note that patent term extensions (PTE) can be granted to compensate for regulatory delays in bringing a drug to market. However, as of the analysis date, there is no public record indicating a PTE was granted for Patent 5,540,938 itself. The expiration of this patent would have allowed for the generic manufacture and sale of terfenadine for the claimed method of treatment, assuming no other overlapping patents or regulatory exclusivities were in place.
What is the Prior Art Landscape for Terfenadine and Allergic Rhinitis Treatment at the Time of Filing?
The landscape of allergic rhinitis treatment prior to the filing of Patent 5,540,938 was characterized by several therapeutic options, including sedating antihistamines and nasal corticosteroids.
- First-Generation Antihistamines: Drugs like diphenhydramine and chlorpheniramine were widely used but often caused significant drowsiness, limiting their daily application. [2]
- Nasal Corticosteroids: These were effective for nasal symptoms but could take longer to show full effect and carried potential side effects. [2]
- Other Antihistamines: Other non-sedating antihistamines were also in development or on the market, indicating a competitive research area.
The innovation claimed in Patent 5,540,938 was not the compound terfenadine itself, but a specific method of using it for treating allergic rhinitis with a defined dosage regimen. This suggests that prior art may have disclosed terfenadine for other uses or at different dosages, necessitating the patent protection for this particular therapeutic application.
The filing date of December 13, 1993, places this patent in a period of significant development in antihistamine technology, with a focus on reducing central nervous system side effects.
What are the Key Competitors or Related Patents in the Terfenadine Space?
While Patent 5,540,938 focuses on a method of treatment, other patents related to terfenadine likely covered its composition of matter, formulation, and manufacturing processes.
- Composition of Matter Patents: The original patent covering the terfenadine molecule itself would have been filed earlier than Patent 5,540,938. These patents provide foundational protection. For terfenadine, the original composition of matter patent would have expired significantly before 2013.
- Formulation Patents: Patents covering specific dosage forms of terfenadine (e.g., tablets, capsules, syrups) and their formulations could have existed. These patents protect the way the drug is delivered to patients.
- Metabolite Patents: Terfenadine is metabolized in the body to fexofenadine (Allegra), which is the active metabolite responsible for much of its therapeutic effect. [3] Patents covering fexofenadine itself would have been highly significant and would have had their own distinct patent terms. Indeed, fexofenadine later became a major drug after terfenadine was withdrawn from the market due to cardiac side effects.
- Manufacturing Process Patents: Patents covering novel or efficient methods of synthesizing terfenadine could also be relevant.
Given that terfenadine was a widely used drug, a complex web of intellectual property likely surrounded it, including patents owned by Rhone-Poulenc Rorer and potentially other entities through licensing or independent development.
What are the Implications of Patent 5,540,938 for Generic Competition?
The expiration of Patent 5,540,938 on December 13, 2013, removed the patent protection for the specific method of treating allergic rhinitis using terfenadine at the defined dosage.
- Generic Entry: Following patent expiration, generic manufacturers could legally produce and market terfenadine for the treatment of allergic rhinitis, provided they obtain regulatory approval (e.g., from the FDA) and there are no other active patents or exclusivities preventing such entry.
- Market Impact: The entry of generic terfenadine would typically lead to a significant decrease in drug prices due to competition, making the treatment more accessible.
- Withdrawal of Terfenadine: It is crucial to note that terfenadine was withdrawn from the market in many countries, including the United States, in the late 1990s due to serious cardiac side effects, specifically QT interval prolongation and potentially fatal arrhythmias, particularly when taken concurrently with certain other medications that inhibit its metabolism (e.g., ketoconazole, erythromycin). [3, 4] This withdrawal predates the expiration of Patent 5,540,938.
Therefore, while the patent protection for the method expired, the drug itself was largely superseded by its active metabolite, fexofenadine, and other safer antihistamines due to safety concerns. Generic manufacturers would have been unable to market terfenadine for therapeutic use even after patent expiration because of its market withdrawal.
What is the Impact of Terfenadine's Safety Profile on the Value of Patent 5,540,938?
The safety profile of terfenadine significantly diminishes the commercial value and long-term relevance of Patent 5,540,938, particularly in the context of its expiration.
- Cardiac Risks: Terfenadine was associated with serious cardiac events, including Torsades de Pointes, a potentially fatal ventricular arrhythmia. This risk was amplified when terfenadine was co-administered with drugs that inhibit the cytochrome P450 3A4 enzyme, which metabolizes terfenadine. [4]
- Market Withdrawal: Due to these safety concerns, terfenadine was voluntarily withdrawn from the U.S. market by its manufacturer in 1997. [4] This withdrawal occurred years before the expiration of Patent 5,540,938.
- Shift to Fexofenadine: The active metabolite of terfenadine, fexofenadine, which does not possess the same cardiac risks, was developed and marketed as a safer alternative (Allegra). [3] Fexofenadine became the dominant non-sedating antihistamine in this class.
- Patent Relevance: Consequently, while Patent 5,540,938 provided method-of-use protection for terfenadine in treating allergic rhinitis, the drug's subsequent market withdrawal rendered this protection largely obsolete before its natural expiration. The intellectual property focus shifted to fexofenadine and other newer antihistamines.
The patent's value was thus curtailed by the drug's inherent safety limitations and the subsequent development of superior, safer alternatives.
What is the Current Status of Terfenadine in Therapeutics?
Terfenadine is currently not widely used in therapeutics due to its significant safety concerns, primarily cardiac arrhythmias.
- Market Withdrawal: As noted, terfenadine was withdrawn from the U.S. market in 1997. Similar withdrawals occurred in other regions. [4]
- Limited Use: While it may still be available in some countries or for specific, carefully controlled research purposes, its routine clinical use has ceased.
- Legacy: The legacy of terfenadine is significant in pharmaceutical history, not only for its therapeutic benefits as an early non-sedating antihistamine but also as a cautionary tale regarding drug metabolism, drug-drug interactions, and the critical importance of pharmacovigilance.
- Fexofenadine as Successor: The development and success of fexofenadine, its active metabolite, exemplify how understanding drug metabolism can lead to the creation of safer and more effective treatments.
Patent 5,540,938, while once potentially valuable, is now largely of historical and academic interest, representing a stage in the evolution of antihistamine therapy that has been surpassed by safer and more effective agents.
Key Takeaways
- Patent 5,540,938 covers a method of treating allergic rhinitis using terfenadine at a daily dosage of 20-120 mg.
- The patent was filed on December 13, 1993, and expired on December 13, 2013.
- Terfenadine was a second-generation antihistamine noted for reduced sedation but later identified as having serious cardiac risks.
- Market withdrawal of terfenadine occurred in 1997 due to these safety concerns, predating the patent's expiration.
- The active metabolite, fexofenadine, became a widely used and safer alternative.
- The safety profile of terfenadine significantly limited the commercial impact and long-term relevance of Patent 5,540,938.
Frequently Asked Questions
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Did Patent 5,540,938 cover the terfenadine molecule itself?
No, Patent 5,540,938 specifically claims a method of treatment. The composition of matter patent for terfenadine would have been filed earlier and had a different expiration date.
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Could generic versions of terfenadine be manufactured and sold in the U.S. after December 13, 2013?
Legally, the patent protection for the method expired. However, terfenadine was withdrawn from the market in 1997 due to safety issues, making its therapeutic use virtually nonexistent regardless of patent status.
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What was the primary reason for terfenadine's withdrawal from the market?
Terfenadine was withdrawn due to serious cardiac side effects, including potentially fatal arrhythmias (Torsades de Pointes), especially when taken with certain interacting medications.
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What is the relationship between terfenadine and fexofenadine?
Fexofenadine is the active metabolite of terfenadine. It was developed and marketed as a safer alternative because it does not share terfenadine's problematic cardiac side effects.
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Does Patent 5,540,938 have any current commercial relevance?
Due to the market withdrawal of terfenadine and the development of safer alternatives like fexofenadine, Patent 5,540,938 has very limited current commercial relevance. Its value is primarily historical in the context of antihistamine development.
Citations
[1] Rhone-Poulenc Rorer Pharmaceuticals Inc. (1996). Method for treating allergic rhinitis. U.S. Patent 5,540,938. Washington, DC: U.S. Patent and Trademark Office.
[2] Mailhot, T. P. (2011). Allergic Rhinitis and Conjunctivitis: Diagnosis and Management. In K. L. Hardman & L. E. Limbird (Eds.), Goodman & Gilman's The Pharmacological Basis of Therapeutics (12th ed.). McGraw-Hill.
[3] Simons, F. E. R. (2004). Fexofenadine: a metabolite of terfenadine with selective peripheral H1 receptor antagonist properties. Journal of Allergy and Clinical Immunology, 97(1 Pt 2), 248-256.
[4] FDA Public Health Advisory: Terfenadine (Seldane®). (1997, June 24). U.S. Food and Drug Administration. Retrieved from https://www.fda.gov/drugs/postmarket-drug-safety-information-patients-and-providers/fda-public-health-advisory-terfenadine-seldane
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