erythromycin estolate; sulfisoxazole acetyl - Profile

What are the generic drug sources for erythromycin estolate; sulfisoxazole acetyl and what is the scope of freedom to operate?

Erythromycin estolate; sulfisoxazole acetyl is the generic ingredient in one branded drug marketed by Lilly and is included in one NDA. Additional information is available in the individual branded drug profile pages.

Summary for erythromycin estolate; sulfisoxazole acetyl

US Patents:	0
Tradenames:	1
Applicants:	1
NDAs:	1

US Patents and Regulatory Information for erythromycin estolate; sulfisoxazole acetyl

Applicant	Tradename	Generic Name	Dosage	NDA	Approval Date	TE	Type	RLD	RS	Patent No.	Patent Expiration	Product	Substance	Delist Req.	Exclusivity Expiration
Lilly	ILOSONE SULFA	erythromycin estolate; sulfisoxazole acetyl	SUSPENSION;ORAL	050599-001	Sep 29, 1989		DISCN	No	No

Erythromycin Estolate and Sulfisoxazole Acetyl: Patent Landscape and Market Fundamentals

Last updated: February 19, 2026

This analysis examines the patent landscape and market fundamentals for erythromycin estolate and sulfisoxazole acetyl, two established antibiotic compounds. The review focuses on existing patent protections, regulatory status, and market demand to inform potential R&D and investment decisions.

What is the Patent Status of Erythromycin Estolate and Sulfisoxazole Acetyl?

Erythromycin estolate and sulfisoxazole acetyl are both well-established pharmaceutical compounds. As of the current analysis, the foundational patents protecting their initial discovery and synthesis have long expired.

• Erythromycin Estolate: Erythromycin itself is a macrolide antibiotic. The estolate form is a salt derivative designed to improve oral absorption. The original patents for erythromycin and its derivatives, including the estolate form, expired decades ago. Generic manufacturing is prevalent.

  • Key Patents: No active primary composition of matter patents are in force for erythromycin estolate. Any remaining patent protection would likely pertain to specific, novel manufacturing processes, novel formulations with improved delivery, or new therapeutic uses. A search of the USPTO patent database reveals no active patents specifically claiming erythromycin estolate as a new chemical entity.
  • Exclusivity: Market exclusivity for erythromycin estolate is primarily driven by regulatory exclusivities granted for new drug applications (NDAs) or supplemental NDAs (sNDAs) if new indications or formulations were approved. Given the age of the compound, these would have expired.

• Sulfisoxazole Acetyl: Sulfisoxazole is a sulfonamide antibiotic. The acetyl derivative is a prodrug that is hydrolyzed in vivo to the active sulfisoxazole. Similar to erythromycin estolate, the foundational patents for sulfisoxazole and its acetylated form have expired.

  • Key Patents: No active primary composition of matter patents are in force for sulfisoxazole acetyl. Any extant patent protection would be limited to specific manufacturing processes, advanced formulations, or novel combination therapies. A review of major patent databases shows no active patents claiming sulfisoxazole acetyl as a distinct new compound.
  • Exclusivity: Regulatory exclusivities associated with sulfisoxazole acetyl approvals have also long expired.

What are the Current Regulatory and Market Approvals?

Both erythromycin estolate and sulfisoxazole acetyl have a long history of regulatory approval for various bacterial infections. Their approval status is critical for understanding their current market position and any potential for new indications.

• Erythromycin Estolate:

  • FDA Approval: Erythromycin estolate has been approved by the U.S. Food and Drug Administration (FDA) for the treatment of various bacterial infections. It is commonly indicated for respiratory tract infections, skin and soft tissue infections, and certain sexually transmitted diseases caused by susceptible microorganisms.
  • Indications: Common approved indications include infections caused by Streptococcus pyogenes, Streptococcus pneumoniae, Staphylococcus aureus, Mycoplasma pneumoniae, and Chlamydia trachomatis.
  • Dosage Forms: Available in oral formulations such as tablets and suspensions.
  • Market Entry Date: The estolate salt of erythromycin gained FDA approval in the early 1960s, indicating a mature product lifecycle.

• Sulfisoxazole Acetyl:

  • FDA Approval: Sulfisoxazole acetyl is also FDA-approved for treating a range of bacterial infections, particularly urinary tract infections (UTIs) and certain types of bacterial conjunctivitis.
  • Indications: Approved for infections caused by susceptible microorganisms, including strains of E. coli, Proteus mirabilis, and Streptococcus species. It is often used in combination therapy or for patients with specific contraindications to other antibiotic classes.
  • Dosage Forms: Primarily available in oral liquid formulations and ophthalmic preparations.
  • Market Entry Date: Sulfisoxazole itself was approved in the 1950s, with the acetyl derivative also having a long history of FDA approval.

What is the Market Demand and Competitive Landscape?

The market demand for both erythromycin estolate and sulfisoxazole acetyl is characterized by their established nature, generic availability, and competition from newer, broader-spectrum antibiotics.

• Erythromycin Estolate:

  • Market Size: The global market for erythromycin estolate is relatively stable but mature. Demand is sustained by its cost-effectiveness and established efficacy against specific pathogens. However, it faces significant competition from other macrolides (e.g., azithromycin, clarithromycin) and other antibiotic classes with broader spectra or improved pharmacokinetic profiles.
  • Competition:
    • Within Macrolides: Azithromycin and clarithromycin are dominant due to their more convenient dosing regimens and broader coverage against some atypical pathogens.
    • Other Classes: Fluoroquinolones and cephalosporins represent significant competition for many indicated infections.
  • Pricing: As a generic drug, erythromycin estolate is priced competitively, making it a cost-effective option, particularly in resource-limited settings or for specific indications where resistance to newer agents is a concern.
  • Resistance Trends: Increasing bacterial resistance to macrolides, including erythromycin, is a growing concern that can impact its use.

• Sulfisoxazole Acetyl:

  • Market Size: The market for sulfisoxazole acetyl is also mature and primarily driven by specific niches, particularly pediatric UTIs and ophthalmic infections. The overall market size is smaller compared to erythromycin estolate.
  • Competition:
    • UTIs: Competition is intense from trimethoprim-sulfamethoxazole, nitrofurantoin, and fluoroquinolones.
    • Ophthalmic Infections: Competition comes from broad-spectrum ophthalmic antibiotics like fluoroquinolones and aminoglycosides.
  • Pricing: Sulfisoxazole acetyl is a low-cost generic option. Its use is often dictated by susceptibility testing and physician preference for specific indications where it remains effective.
  • Resistance Trends: Resistance to sulfonamides is variable, and judicious use is necessary to preserve efficacy.

What are the Potential R&D and Investment Opportunities?

Given the expired primary patents and generic status of both compounds, opportunities lie in innovation around formulation, new indications, or combination therapies.

• Erythromycin Estolate:

  • Novel Formulations:
    • Extended-Release: Development of extended-release formulations to improve patient compliance and potentially reduce dosing frequency.
    • Topical/Transdermal Delivery: Investigating novel topical or transdermal delivery systems for localized infections, potentially minimizing systemic exposure and side effects.
    • Nanoformulations: Encapsulation in nanoparticles could improve bioavailability, target drug delivery, or enhance penetration into biofilms.
  • New Indications:
    • Drug-Resistant Organisms: Re-evaluating efficacy against emerging drug-resistant strains where older antibiotics may retain activity.
    • Non-Bacterial Applications: Exploring potential anti-inflammatory or immunomodulatory properties that have been reported for macrolides, although this is highly speculative and would require extensive preclinical and clinical research.
  • Combination Therapies:
    • Synergistic Combinations: Investigating combinations with other antibiotics or non-antibiotic agents to enhance efficacy or overcome resistance mechanisms.

• Sulfisoxazole Acetyl:

  • Improved Formulations:
    • Pediatric Formulations: Developing more palatable or easier-to-administer liquid formulations for pediatric use.
    • Ophthalmic Innovations: Creating novel ophthalmic delivery systems (e.g., sustained-release implants, preservative-free formulations) to improve efficacy and patient comfort for eye infections.
  • New Indications:
    • Specific Pathogen Niches: Identifying specific bacterial infections where sulfisoxazole acetyl demonstrates superior activity or a better safety profile compared to alternatives, potentially based on emerging resistance patterns.
    • Combination Therapy: Exploring synergistic combinations with other agents for complex infections, such as multi-drug resistant UTIs.
  • Prodrug Strategies: Investigating novel prodrug forms of sulfisoxazole with improved pharmacokinetics or targeted delivery, though this is a high-risk, high-reward area.

What is the Manufacturing and Supply Chain Landscape?

The manufacturing of erythromycin estolate and sulfisoxazole acetyl is well-established, with a global supply chain dominated by generic manufacturers.

• Erythromycin Estolate:

  • Manufacturing: Active pharmaceutical ingredient (API) manufacturing is widely distributed, with significant production capacity in Asia (India, China) and some in Europe. The synthesis is a multi-step process starting from fermentation products.
  • Formulation: Finished dosage forms are manufactured by numerous generic pharmaceutical companies worldwide.
  • Supply Chain: The supply chain is generally robust, though subject to the same global pressures as other pharmaceutical ingredients, including raw material sourcing, geopolitical events, and shipping logistics.
  • Quality Control: Manufacturers must adhere to strict Good Manufacturing Practices (GMP) standards set by regulatory bodies like the FDA and EMA.

• Sulfisoxazole Acetyl:

  • Manufacturing: API manufacturing is also concentrated in regions with established chemical and pharmaceutical manufacturing capabilities. The synthesis involves acetylation of sulfisoxazole.
  • Formulation: Generic companies produce the finished dosage forms, including oral liquids and ophthalmic solutions.
  • Supply Chain: Similar to erythromycin estolate, the supply chain is global and subject to typical industry challenges.
  • Quality Control: GMP compliance is mandatory for all manufacturers.

Key Takeaways

• Both erythromycin estolate and sulfisoxazole acetyl are mature pharmaceutical compounds with expired foundational patents.
• Market exclusivity is limited to any remaining regulatory exclusivities for specific formulations or indications, which are likely also expired given the age of the drugs.
• Generic competition is the primary market dynamic, leading to price sensitivity and stable, albeit mature, market demand.
• Erythromycin estolate faces competition from newer macrolides and other antibiotic classes, while sulfisoxazole acetyl's market is primarily in pediatric UTIs and ophthalmic infections.
• Opportunities for R&D and investment lie in novel formulations, identification of new indications (potentially against resistant strains), and synergistic combination therapies.
• Manufacturing is well-established globally, with a robust but typical pharmaceutical supply chain.

Frequently Asked Questions

1. Are there any patentable aspects for erythromycin estolate or sulfisoxazole acetyl beyond their original composition of matter? Patents can be obtained for novel manufacturing processes, unique formulations that offer a significant therapeutic advantage (e.g., improved bioavailability, extended release, reduced side effects), or new therapeutic uses that are not obvious extensions of known uses.

2. What is the current global resistance profile for bacteria targeted by erythromycin estolate and sulfisoxazole acetyl? Resistance to erythromycin (and other macrolides) has been increasing globally, particularly among Gram-negative bacteria and some Gram-positive pathogens like Staphylococcus aureus. Sulfonamide resistance is also present but can vary by geographic region and specific bacterial species. Detailed susceptibility data is crucial for current clinical use.

3. What is the typical lifecycle stage of a drug like erythromycin estolate or sulfisoxazole acetyl? These drugs are in the mature or decline phase of their lifecycle. Their primary revenue streams are from established generic markets. Further growth is unlikely without significant innovation in formulation, indication, or combination therapy.

4. What regulatory hurdles exist for developing new formulations or indications for these older drugs? Developing new formulations requires demonstrating bioequivalence or therapeutic equivalence to the innovator product, along with proving safety and efficacy for the specific formulation and intended use. New indications require rigorous clinical trials to demonstrate safety and efficacy in the target patient population, following established FDA or EMA guidelines.

5. What are the primary drivers for continued demand for these older antibiotics in the current market? Continued demand is driven by their cost-effectiveness as generic alternatives, their established efficacy against specific pathogens where resistance to newer agents may not yet be prevalent, and their role in specific patient populations (e.g., pediatrics, pregnant women where certain newer agents are contraindicated) or as second-line treatments.

Citations

[1] U.S. Food & Drug Administration. (n.d.). Drugs@FDA. Retrieved from https://www.accessdata.fda.gov/scripts/cder/daf/ [2] World Health Organization. (2022). Global action plan on antimicrobial resistance 2016-2020. Retrieved from https://www.who.int/publications/i/item/9789241512036 [3] U.S. Patent and Trademark Office. (n.d.). PatFT and AppFT Databases. Retrieved from https://www.uspto.gov/patents/search [4] European Medicines Agency. (n.d.). European public assessment reports (EPARs). Retrieved from https://www.ema.europa.eu/en/medicines/human/assessments