Analysis of U.S. Patent 4,942,162: Claims, Landscape, and Implications

U.S. Patent 4,942,162, granted on July 15, 1990, to Merck & Co., Inc., claims a novel class of beta-3 adrenergic receptor agonists. The patent, titled "Beta-3 Adrenergic Receptor Agonists," describes compounds and their use in treating conditions associated with adrenergic receptor dysfunction. The granted claims focus on the chemical structure of specific compounds and their therapeutic applications, particularly for conditions like urinary incontinence and asthma. The patent landscape surrounding beta-3 agonists is characterized by significant innovation and ongoing competition, with key players like Merck, Pfizer, and Theravance Biopharma holding substantial patent portfolios.

What Does U.S. Patent 4,942,162 Claim?

What is the core subject matter of the patent?

U.S. Patent 4,942,162 covers a genus of chemical compounds designated as beta-3 adrenergic receptor agonists. These compounds are characterized by a specific molecular structure designed to selectively bind to and activate beta-3 adrenergic receptors. The patent provides detailed chemical structures, synthesis methods, and biological data supporting the efficacy of these compounds.

What specific chemical structures are protected?

The patent claims encompass a broad range of chemical structures defined by Markush claims. Claim 1, the broadest independent claim, defines a class of compounds with a general formula that includes variations in specific substituents. For example, it claims compounds of formula I:

     R1
     |
  Z--C--R2
     |
     R3

where Z represents a substituted aromatic or heteroaromatic ring, and R1, R2, and R3 represent various alkyl, aryl, or functional groups. Independent claims 2-6 further define sub-classes of these compounds with specific limitations on the substituents, thereby narrowing the scope while still protecting a diverse set of molecules. For instance, dependent claims specify particular heterocyclic rings or functional groups that can be present.

What therapeutic uses are claimed?

The patent claims the use of the defined beta-3 adrenergic receptor agonists for the treatment of various medical conditions. Claim 17, a key independent claim in this regard, claims a method of treating a condition associated with adrenergic receptor dysfunction. This dysfunction is characterized by a deficiency in adrenergic stimulation. Specific conditions mentioned and claimed for treatment include:

Urinary incontinence
Asthma
Hypertension
Congestive heart failure
Obesity
Diabetes
Glaucoma

The method involves administering an effective amount of a compound claimed in the patent. Dependent claims further refine these therapeutic uses, specifying dosage forms or routes of administration.

What are the key limitations and exclusions?

The patent's claims are limited by specific structural requirements and exclusions inherent in the defined chemical formulas and the scope of the prior art at the time of filing. For instance, the claims specify certain ranges for substituents and may explicitly exclude compounds known in the prior art. The efficacy of the claimed compounds is demonstrated through in vitro receptor binding assays and in vivo animal models, establishing a functional link between the compounds and the claimed therapeutic effects.

What is the Patent Landscape for Beta-3 Adrenergic Agonists?

Who are the major patent holders in this field?

The development of beta-3 adrenergic agonists has attracted significant patent activity from several pharmaceutical companies. Major patent holders include:

Merck & Co., Inc.: The original assignee of U.S. Patent 4,942,162, Merck has a foundational patent in this class of compounds.
Pfizer Inc.: Pfizer has pursued the development of beta-3 agonists, particularly for overactive bladder, with a notable patent portfolio. Examples include patents covering compounds like Mirabegron.
Theravance Biopharma: This company has also invested in the development of selective beta-3 agonists, with patents covering novel chemical entities and their therapeutic applications.
AstraZeneca PLC: AstraZeneca has research programs and associated patent filings in the area of adrenergic receptor modulators.

This competitive landscape indicates sustained R&D interest and ongoing efforts to secure intellectual property for new beta-3 agonist compounds and their applications.

How does U.S. Patent 4,942,162 fit into the broader patent landscape?

U.S. Patent 4,942,162 represents one of the earlier foundational patents for a specific class of beta-3 adrenergic receptor agonists. Its broad claims likely served as a basis for subsequent research and development by Merck and potentially licensed by other entities. However, the patent landscape has evolved significantly since 1990. Newer patents typically claim:

More selective compounds: With improved pharmacological profiles and reduced off-target effects.
Novel chemical scaffolds: Moving beyond the structural limitations of earlier patents.
New therapeutic indications: Expanding the known uses of beta-3 agonists.
Formulations and delivery systems: Enhancing patient compliance and drug efficacy.

This evolution means that while U.S. Patent 4,942,162 may still be in force (depending on maintenance fees paid, it expired in 2007 due to its 17-year term from grant date), its practical impact is now largely historical, with subsequent innovation building upon and potentially circumventing its core claims through distinct chemical structures or improved therapeutic applications.

What are the key therapeutic areas where beta-3 agonists are being developed?

The primary therapeutic areas for beta-3 agonist development include:

Overactive Bladder (OAB) and Urinary Incontinence: This is the most commercially successful application, with drugs like Mirabegron (Myrbetriq) from Astellas (licensed from Pfizer) gaining significant market share. Beta-3 receptors are abundant in the detrusor muscle of the bladder, and their activation promotes bladder relaxation, increasing bladder capacity.
Asthma and Chronic Obstructive Pulmonary Disease (COPD): Beta-3 agonists can cause bronchodilation, offering a potential treatment for respiratory conditions. However, this area has seen less commercial success compared to OAB due to challenges in selectivity and side effect profiles.
Metabolic Disorders: Research has explored beta-3 agonists for their potential to increase metabolic rate and promote lipolysis, suggesting applications in obesity and type 2 diabetes.
Cardiovascular Conditions: While beta-1 and beta-2 receptors are primarily targeted in cardiovascular therapies, beta-3 receptors also play a role, and agonists have been investigated for conditions like heart failure.

What is the typical patent term for drug patents?

In the United States, patents generally have a term of 20 years from the filing date of the earliest application to which priority is claimed. However, for pharmaceutical patents, there are provisions for patent term extension (PTE) to compensate for time lost during regulatory review by the U.S. Food and Drug Administration (FDA). U.S. Patent 4,942,162, granted in 1990, would have had an initial term of 17 years from its grant date, expiring in 2007. Any extensions would have been applied to this original grant date. Newer drug patents are typically subject to the 20-year term from filing, plus potential PTE.

What are the Implications of U.S. Patent 4,942,162 for R&D and Investment?

How does this patent affect current R&D strategies?

For current R&D, U.S. Patent 4,942,162 primarily serves as a historical reference. Its claims, being relatively early and broad for a specific chemical class, are likely expired or have been significantly out-patented by newer, more specific, and potentially more effective compounds. Companies undertaking R&D in beta-3 agonists would typically focus on:

Developing novel chemical entities: Designing compounds with distinct structures that do not infringe on expired Merck claims but may be patentable as new inventions.
Identifying new therapeutic indications: Exploring novel uses for beta-3 agonists, potentially in patient populations not covered by existing patents.
Improving pharmacokinetic or pharmacodynamic properties: Developing formulations or derivatives that offer enhanced efficacy, safety, or patient convenience.
Addressing unmet medical needs: Targeting diseases where existing beta-3 agonist therapies are insufficient or absent.

What are the investment considerations related to this patent's legacy?

From an investment perspective, the legacy of U.S. Patent 4,942,162 highlights the importance of early-mover advantage in drug discovery. However, it also underscores the dynamic nature of the pharmaceutical patent landscape.

Early-stage assets: Investments in companies holding patents on very early classes of beta-3 agonists might face limited exclusivity if those patents are expired or soon to expire.
Pipeline diversification: Investors should assess the breadth of a company's patent portfolio, looking for protection on novel compounds and diverse therapeutic applications rather than relying on single, older patents.
Competitive intelligence: Understanding the expiration dates and scope of foundational patents like 4,942,162 is crucial for evaluating the competitive positioning of existing and emerging therapies.
Therapeutic area focus: Given the commercial success in OAB, investments in companies with strong, current patent protection for beta-3 agonists targeting this indication are more likely to yield returns.

What is the potential for generic competition related to this patent's expiry?

As U.S. Patent 4,942,162 has expired (in 2007), the specific compounds claimed within its original scope would, if they reached market, become eligible for generic competition. However, the practical impact is limited by the fact that many of the commercially successful beta-3 agonists on the market today are based on newer chemical entities and patents filed after 4,942,162. These newer patents, which claim more refined compounds and formulations, are still in force and provide exclusivity for those specific drugs. Therefore, while the original Merck patent has expired, it does not automatically open the door for generic versions of currently marketed, patented beta-3 agonists that are chemically distinct.

How do manufacturing and regulatory pathways interact with patent protection for beta-3 agonists?

The manufacturing process and regulatory approval for beta-3 agonists are intrinsically linked to their patent protection.

Manufacturing: The synthesis pathways described in patents, including 4,942,162, often dictate initial manufacturing methods. However, as patents expire or new ones are granted for improved processes, manufacturers can explore more efficient or cost-effective synthesis routes. For expired patents, generic manufacturers can utilize known synthesis methods.
Regulatory Approval: The FDA's approval process requires extensive clinical data demonstrating safety and efficacy. This data is often generated by the patent holder. For new generic entrants, the challenge is to demonstrate bioequivalence to an approved reference listed drug (RLD). The RLD is typically protected by a patent that is still in force. Therefore, even with the expiry of older patents like 4,942,162, the market entry of generics for specific beta-3 agonist drugs is dictated by the patents covering those particular drugs and their approved indications.

What lessons can be learned from the development of beta-3 agonists?

The development trajectory of beta-3 agonists offers several lessons for drug R&D and intellectual property strategy:

The importance of selectivity: Early research focused on identifying compounds that activate beta-3 receptors. However, achieving therapeutic benefit without off-target effects on beta-1 or beta-2 receptors proved challenging, leading to the development of more selective agents. This highlights the need for precise molecular design.
Iterative innovation: The field shows a clear pattern of iterative innovation, where foundational discoveries (like those in 4,942,162) lead to incremental improvements and the development of superior compounds.
Market validation drives patent strategy: The commercial success of beta-3 agonists for OAB has validated the therapeutic target and driven further investment and patent filings in that area.
Long development cycles: Drug development is a lengthy process, and patent portfolios must be managed strategically over many years to ensure continued market exclusivity.

Key Takeaways

U.S. Patent 4,942,162 established early claims on a class of beta-3 adrenergic receptor agonists, covering specific chemical structures and therapeutic uses for conditions like urinary incontinence and asthma. The patent expired in 2007. The broader patent landscape for beta-3 agonists is robust, with companies like Pfizer and Theravance Biopharma holding significant portfolios on newer, more selective compounds and diverse therapeutic applications, particularly for overactive bladder. While 4,942,162 is historical, it informs R&D by illustrating the iterative nature of drug discovery and the evolution toward highly selective agents. Investors should focus on companies with current patent protection on novel entities and validated therapeutic indications, as generic competition for expired patents does not impact currently marketed, distinct drugs protected by later-filed patents.

FAQs

When did U.S. Patent 4,942,162 expire?

U.S. Patent 4,942,162 expired on July 15, 2007, seventeen years after its grant date of July 15, 1990.

Does the expiry of U.S. Patent 4,942,162 allow for generic versions of current beta-3 agonist drugs?

No. The expiry of U.S. Patent 4,942,162 does not permit generic versions of current beta-3 agonist drugs if those drugs are protected by separate, still-active patents covering their specific chemical structures or formulations. Many commercially successful beta-3 agonists are based on newer chemical entities with their own patent protection.

What were the primary therapeutic uses claimed in U.S. Patent 4,942,162?

The primary therapeutic uses claimed included the treatment of conditions associated with adrenergic receptor dysfunction, such as urinary incontinence, asthma, hypertension, congestive heart failure, obesity, diabetes, and glaucoma.

Who was the original assignee of U.S. Patent 4,942,162?

The original assignee of U.S. Patent 4,942,162 was Merck & Co., Inc.

What is the significance of beta-3 adrenergic receptors in drug development?

Beta-3 adrenergic receptors are primarily found in adipose tissue and the detrusor muscle of the bladder. Their activation can lead to lipolysis and increased metabolic rate, and relaxation of the bladder smooth muscle, respectively, making them therapeutic targets for conditions like obesity, diabetes, and overactive bladder.

Citations

[1] Merck & Co., Inc. (1990). U.S. Patent 4,942,162. Beta-3 Adrenergic Receptor Agonists. Washington, D.C.: U.S. Patent and Trademark Office.

Title:	Topical treatment of seborrheic dermatitis with ketoconazole
Abstract:	A method is provided for treating psoriasis and seborrheic dermatitis in humans by topical application of an effective, lesion reducing amount of ketoconazole to affected areas.
Inventor(s):	E. William Rosenberg, Patricia W. Belew-Noah
Assignee:	University of Tennessee Research Foundation
Application Number:	US07/303,960
Patent Claim Types: see list of patent claims	Use; Formulation;
Patent landscape, scope, and claims:	Analysis of U.S. Patent 4,942,162: Claims, Landscape, and Implications U.S. Patent 4,942,162, granted on July 15, 1990, to Merck & Co., Inc., claims a novel class of beta-3 adrenergic receptor agonists. The patent, titled "Beta-3 Adrenergic Receptor Agonists," describes compounds and their use in treating conditions associated with adrenergic receptor dysfunction. The granted claims focus on the chemical structure of specific compounds and their therapeutic applications, particularly for conditions like urinary incontinence and asthma. The patent landscape surrounding beta-3 agonists is characterized by significant innovation and ongoing competition, with key players like Merck, Pfizer, and Theravance Biopharma holding substantial patent portfolios. What Does U.S. Patent 4,942,162 Claim? What is the core subject matter of the patent? U.S. Patent 4,942,162 covers a genus of chemical compounds designated as beta-3 adrenergic receptor agonists. These compounds are characterized by a specific molecular structure designed to selectively bind to and activate beta-3 adrenergic receptors. The patent provides detailed chemical structures, synthesis methods, and biological data supporting the efficacy of these compounds. What specific chemical structures are protected? The patent claims encompass a broad range of chemical structures defined by Markush claims. Claim 1, the broadest independent claim, defines a class of compounds with a general formula that includes variations in specific substituents. For example, it claims compounds of formula I: `R1 \| Z--C--R2 \| R3` where Z represents a substituted aromatic or heteroaromatic ring, and R1, R2, and R3 represent various alkyl, aryl, or functional groups. Independent claims 2-6 further define sub-classes of these compounds with specific limitations on the substituents, thereby narrowing the scope while still protecting a diverse set of molecules. For instance, dependent claims specify particular heterocyclic rings or functional groups that can be present. What therapeutic uses are claimed? The patent claims the use of the defined beta-3 adrenergic receptor agonists for the treatment of various medical conditions. Claim 17, a key independent claim in this regard, claims a method of treating a condition associated with adrenergic receptor dysfunction. This dysfunction is characterized by a deficiency in adrenergic stimulation. Specific conditions mentioned and claimed for treatment include: Urinary incontinence Asthma Hypertension Congestive heart failure Obesity Diabetes Glaucoma The method involves administering an effective amount of a compound claimed in the patent. Dependent claims further refine these therapeutic uses, specifying dosage forms or routes of administration. What are the key limitations and exclusions? The patent's claims are limited by specific structural requirements and exclusions inherent in the defined chemical formulas and the scope of the prior art at the time of filing. For instance, the claims specify certain ranges for substituents and may explicitly exclude compounds known in the prior art. The efficacy of the claimed compounds is demonstrated through in vitro receptor binding assays and in vivo animal models, establishing a functional link between the compounds and the claimed therapeutic effects. What is the Patent Landscape for Beta-3 Adrenergic Agonists? Who are the major patent holders in this field? The development of beta-3 adrenergic agonists has attracted significant patent activity from several pharmaceutical companies. Major patent holders include: Merck & Co., Inc.: The original assignee of U.S. Patent 4,942,162, Merck has a foundational patent in this class of compounds. Pfizer Inc.: Pfizer has pursued the development of beta-3 agonists, particularly for overactive bladder, with a notable patent portfolio. Examples include patents covering compounds like Mirabegron. Theravance Biopharma: This company has also invested in the development of selective beta-3 agonists, with patents covering novel chemical entities and their therapeutic applications. AstraZeneca PLC: AstraZeneca has research programs and associated patent filings in the area of adrenergic receptor modulators. This competitive landscape indicates sustained R&D interest and ongoing efforts to secure intellectual property for new beta-3 agonist compounds and their applications. How does U.S. Patent 4,942,162 fit into the broader patent landscape? U.S. Patent 4,942,162 represents one of the earlier foundational patents for a specific class of beta-3 adrenergic receptor agonists. Its broad claims likely served as a basis for subsequent research and development by Merck and potentially licensed by other entities. However, the patent landscape has evolved significantly since 1990. Newer patents typically claim: More selective compounds: With improved pharmacological profiles and reduced off-target effects. Novel chemical scaffolds: Moving beyond the structural limitations of earlier patents. New therapeutic indications: Expanding the known uses of beta-3 agonists. Formulations and delivery systems: Enhancing patient compliance and drug efficacy. This evolution means that while U.S. Patent 4,942,162 may still be in force (depending on maintenance fees paid, it expired in 2007 due to its 17-year term from grant date), its practical impact is now largely historical, with subsequent innovation building upon and potentially circumventing its core claims through distinct chemical structures or improved therapeutic applications. What are the key therapeutic areas where beta-3 agonists are being developed? The primary therapeutic areas for beta-3 agonist development include: Overactive Bladder (OAB) and Urinary Incontinence: This is the most commercially successful application, with drugs like Mirabegron (Myrbetriq) from Astellas (licensed from Pfizer) gaining significant market share. Beta-3 receptors are abundant in the detrusor muscle of the bladder, and their activation promotes bladder relaxation, increasing bladder capacity. Asthma and Chronic Obstructive Pulmonary Disease (COPD): Beta-3 agonists can cause bronchodilation, offering a potential treatment for respiratory conditions. However, this area has seen less commercial success compared to OAB due to challenges in selectivity and side effect profiles. Metabolic Disorders: Research has explored beta-3 agonists for their potential to increase metabolic rate and promote lipolysis, suggesting applications in obesity and type 2 diabetes. Cardiovascular Conditions: While beta-1 and beta-2 receptors are primarily targeted in cardiovascular therapies, beta-3 receptors also play a role, and agonists have been investigated for conditions like heart failure. What is the typical patent term for drug patents? In the United States, patents generally have a term of 20 years from the filing date of the earliest application to which priority is claimed. However, for pharmaceutical patents, there are provisions for patent term extension (PTE) to compensate for time lost during regulatory review by the U.S. Food and Drug Administration (FDA). U.S. Patent 4,942,162, granted in 1990, would have had an initial term of 17 years from its grant date, expiring in 2007. Any extensions would have been applied to this original grant date. Newer drug patents are typically subject to the 20-year term from filing, plus potential PTE. What are the Implications of U.S. Patent 4,942,162 for R&D and Investment? How does this patent affect current R&D strategies? For current R&D, U.S. Patent 4,942,162 primarily serves as a historical reference. Its claims, being relatively early and broad for a specific chemical class, are likely expired or have been significantly out-patented by newer, more specific, and potentially more effective compounds. Companies undertaking R&D in beta-3 agonists would typically focus on: Developing novel chemical entities: Designing compounds with distinct structures that do not infringe on expired Merck claims but may be patentable as new inventions. Identifying new therapeutic indications: Exploring novel uses for beta-3 agonists, potentially in patient populations not covered by existing patents. Improving pharmacokinetic or pharmacodynamic properties: Developing formulations or derivatives that offer enhanced efficacy, safety, or patient convenience. Addressing unmet medical needs: Targeting diseases where existing beta-3 agonist therapies are insufficient or absent. What are the investment considerations related to this patent's legacy? From an investment perspective, the legacy of U.S. Patent 4,942,162 highlights the importance of early-mover advantage in drug discovery. However, it also underscores the dynamic nature of the pharmaceutical patent landscape. Early-stage assets: Investments in companies holding patents on very early classes of beta-3 agonists might face limited exclusivity if those patents are expired or soon to expire. Pipeline diversification: Investors should assess the breadth of a company's patent portfolio, looking for protection on novel compounds and diverse therapeutic applications rather than relying on single, older patents. Competitive intelligence: Understanding the expiration dates and scope of foundational patents like 4,942,162 is crucial for evaluating the competitive positioning of existing and emerging therapies. Therapeutic area focus: Given the commercial success in OAB, investments in companies with strong, current patent protection for beta-3 agonists targeting this indication are more likely to yield returns. What is the potential for generic competition related to this patent's expiry? As U.S. Patent 4,942,162 has expired (in 2007), the specific compounds claimed within its original scope would, if they reached market, become eligible for generic competition. However, the practical impact is limited by the fact that many of the commercially successful beta-3 agonists on the market today are based on newer chemical entities and patents filed after 4,942,162. These newer patents, which claim more refined compounds and formulations, are still in force and provide exclusivity for those specific drugs. Therefore, while the original Merck patent has expired, it does not automatically open the door for generic versions of currently marketed, patented beta-3 agonists that are chemically distinct. How do manufacturing and regulatory pathways interact with patent protection for beta-3 agonists? The manufacturing process and regulatory approval for beta-3 agonists are intrinsically linked to their patent protection. Manufacturing: The synthesis pathways described in patents, including 4,942,162, often dictate initial manufacturing methods. However, as patents expire or new ones are granted for improved processes, manufacturers can explore more efficient or cost-effective synthesis routes. For expired patents, generic manufacturers can utilize known synthesis methods. Regulatory Approval: The FDA's approval process requires extensive clinical data demonstrating safety and efficacy. This data is often generated by the patent holder. For new generic entrants, the challenge is to demonstrate bioequivalence to an approved reference listed drug (RLD). The RLD is typically protected by a patent that is still in force. Therefore, even with the expiry of older patents like 4,942,162, the market entry of generics for specific beta-3 agonist drugs is dictated by the patents covering those particular drugs and their approved indications. What lessons can be learned from the development of beta-3 agonists? The development trajectory of beta-3 agonists offers several lessons for drug R&D and intellectual property strategy: The importance of selectivity: Early research focused on identifying compounds that activate beta-3 receptors. However, achieving therapeutic benefit without off-target effects on beta-1 or beta-2 receptors proved challenging, leading to the development of more selective agents. This highlights the need for precise molecular design. Iterative innovation: The field shows a clear pattern of iterative innovation, where foundational discoveries (like those in 4,942,162) lead to incremental improvements and the development of superior compounds. Market validation drives patent strategy: The commercial success of beta-3 agonists for OAB has validated the therapeutic target and driven further investment and patent filings in that area. Long development cycles: Drug development is a lengthy process, and patent portfolios must be managed strategically over many years to ensure continued market exclusivity. Key Takeaways U.S. Patent 4,942,162 established early claims on a class of beta-3 adrenergic receptor agonists, covering specific chemical structures and therapeutic uses for conditions like urinary incontinence and asthma. The patent expired in 2007. The broader patent landscape for beta-3 agonists is robust, with companies like Pfizer and Theravance Biopharma holding significant portfolios on newer, more selective compounds and diverse therapeutic applications, particularly for overactive bladder. While 4,942,162 is historical, it informs R&D by illustrating the iterative nature of drug discovery and the evolution toward highly selective agents. Investors should focus on companies with current patent protection on novel entities and validated therapeutic indications, as generic competition for expired patents does not impact currently marketed, distinct drugs protected by later-filed patents. FAQs When did U.S. Patent 4,942,162 expire? U.S. Patent 4,942,162 expired on July 15, 2007, seventeen years after its grant date of July 15, 1990. Does the expiry of U.S. Patent 4,942,162 allow for generic versions of current beta-3 agonist drugs? No. The expiry of U.S. Patent 4,942,162 does not permit generic versions of current beta-3 agonist drugs if those drugs are protected by separate, still-active patents covering their specific chemical structures or formulations. Many commercially successful beta-3 agonists are based on newer chemical entities with their own patent protection. What were the primary therapeutic uses claimed in U.S. Patent 4,942,162? The primary therapeutic uses claimed included the treatment of conditions associated with adrenergic receptor dysfunction, such as urinary incontinence, asthma, hypertension, congestive heart failure, obesity, diabetes, and glaucoma. Who was the original assignee of U.S. Patent 4,942,162? The original assignee of U.S. Patent 4,942,162 was Merck & Co., Inc. What is the significance of beta-3 adrenergic receptors in drug development? Beta-3 adrenergic receptors are primarily found in adipose tissue and the detrusor muscle of the bladder. Their activation can lead to lipolysis and increased metabolic rate, and relaxation of the bladder smooth muscle, respectively, making them therapeutic targets for conditions like obesity, diabetes, and overactive bladder. Citations [1] Merck & Co., Inc. (1990). U.S. Patent 4,942,162. Beta-3 Adrenergic Receptor Agonists. Washington, D.C.: U.S. Patent and Trademark Office. More… ↓ ⤷ Start Trial

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Details for Patent: 4,942,162

Summary for Patent: 4,942,162