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Erythromycin estolate; sulfisoxazole acetyl - Generic Drug Details
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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 |
| DailyMed Link: | erythromycin estolate; sulfisoxazole acetyl at DailyMed |
Anatomical Therapeutic Chemical (ATC) Classes for erythromycin estolate; sulfisoxazole acetyl
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 | ⤷ Start Trial | ⤷ Start Trial | ⤷ Start Trial | ||||
| >Applicant | >Tradename | >Generic Name | >Dosage | >NDA | >Approval Date | >TE | >Type | >RLD | >RS | >Patent No. | >Patent Expiration | >Product | >Substance | >Delist Req. | >Exclusivity Expiration |
Erythromycin-Sulfisoxazole Acetyl Market Dynamics, Patent Status, and Financial Outlook
The erythromycin-sulfisoxazole acetyl combination is a legacy pediatric antibiotic product with little evidence of a commercially active branded market. The product historically associated with this combination is Pediazole, which contains erythromycin ethylsuccinate, not erythromycin estolate, together with sulfisoxazole acetyl. Its commercial position deteriorated as amoxicillin, newer macrolides, cephalosporins, and pediatric antimicrobial-stewardship policies displaced older combination antibiotics.
No meaningful current revenue stream, active patent moat, or material biosimilar risk is evident for the legacy product. Its remaining commercial value is primarily historical, regulatory, or related to limited generic supply rather than branded growth.
What drug is erythromycin-sulfisoxazole acetyl?
The marketed combination generally identified with this product is erythromycin ethylsuccinate and sulfisoxazole acetyl oral suspension.
| Attribute | Product information |
|---|---|
| Historical brand | Pediazole |
| Active ingredients | Erythromycin ethylsuccinate and sulfisoxazole acetyl |
| Dosage form | Powder for oral suspension |
| Primary use | Pediatric bacterial infections, historically including acute otitis media |
| Drug class | Macrolide plus sulfonamide antibacterial |
| FDA pathway | Legacy small-molecule prescription drug |
| Current commercial profile | Mature or discontinued-market product |
| Biosimilar exposure | None |
| Patent profile | Legacy composition and formulation rights are expected to be expired |
The distinction between erythromycin estolate and erythromycin ethylsuccinate is material. Erythromycin estolate is a separate salt used in historical erythromycin products, including formulations associated with Ilosone. Pediazole labeling identifies erythromycin ethylsuccinate rather than erythromycin estolate as the erythromycin component (U.S. Food and Drug Administration [FDA], n.d.-a).
An analysis that treats the products as interchangeable can misstate the FDA approval history, formulation composition, patent record, and market size.
What was the historical FDA status of Pediazole?
Pediazole was approved as an oral pediatric antibacterial product. The label described a suspension containing erythromycin ethylsuccinate and sulfisoxazole acetyl and included indications involving susceptible bacterial infections in children (FDA, n.d.-a).
The product’s historical clinical value came from combining:
- Erythromycin activity against selected gram-positive and atypical organisms.
- Sulfisoxazole activity against susceptible bacterial pathogens.
- A liquid dosage form suitable for pediatric administration.
The product also carried limitations that reduced its long-term commercial competitiveness. These included sulfonamide hypersensitivity, gastrointestinal intolerance, potential hepatic effects associated with erythromycin formulations, and antimicrobial-resistance concerns. The combination required two active ingredients even when a single narrow-spectrum antibiotic could be used.
The FDA’s discontinued-drug resources and current labeling databases are the relevant sources for determining whether a specific National Drug Code remains marketed, whether an application remains active, and whether a particular presentation has been withdrawn for commercial or safety reasons (FDA, n.d.-b; FDA, n.d.-c).
When did erythromycin-sulfisoxazole acetyl lose exclusivity?
The product’s exclusivity loss occurred decades ago through the expiration of the underlying small-molecule patent and regulatory exclusivity periods.
| Exclusivity category | Expected status |
|---|---|
| Original composition patents | Expired |
| Original formulation patents | Expired or no longer commercially material |
| New chemical entity exclusivity | Expired |
| Pediatric exclusivity | Expired, if granted |
| Orphan-drug exclusivity | Not applicable |
| Biologic exclusivity | Not applicable |
| Current Orange Book patent protection | No material active protection expected for the historical combination |
The active ingredients are old antibacterial agents. Erythromycin entered clinical use in the 1950s, while sulfonamide antibiotics originated earlier. Any patent rights protecting the original active substances would have expired long before the modern generic-drug era.
The commercial question is therefore not whether a competitor can legally copy the active ingredients. It is whether a manufacturer has sufficient demand and regulatory justification to maintain production of the specific combination, concentration, flavor system, container, and suspension characteristics.
What patents protect erythromycin-sulfisoxazole acetyl?
No commercially meaningful patent estate is expected to protect the legacy combination today.
Potential historical patent categories included:
- Patent claims directed to erythromycin salts.
- Patent claims directed to sulfisoxazole acetyl.
- Combination-product claims.
- Oral suspension formulations.
- Manufacturing and stabilization processes.
- Flavoring, preservative, and reconstitution systems.
These categories do not create a durable modern barrier. The underlying molecules and conventional oral suspension technologies are long-established. Any surviving rights would need to cover a genuinely novel formulation or manufacturing process, and there is no widely documented active patent platform associated with Pediazole that would support premium pricing.
The FDA Orange Book remains the controlling public reference for patents and exclusivity associated with approved drug products. A legacy product with no listed unexpired patents presents limited Paragraph IV litigation exposure (FDA, n.d.-d).
How many patents cover the product?
The practical answer is zero material unexpired patents for the historical erythromycin-sulfisoxazole acetyl product.
Older patent families may appear in patent databases under erythromycin salts, sulfonamide chemistry, antibiotic combinations, or pediatric suspension formulations. Those documents have historical relevance but do not establish current enforceable exclusivity.
Patent strength should be assessed on four dimensions:
| Patent factor | Assessment |
|---|---|
| Composition-of-matter protection | Exhausted |
| Combination protection | Exhausted or commercially irrelevant |
| Formulation protection | Weak and likely expired |
| Process protection | Narrow, design-around risk high |
| Litigation leverage | Low |
| Ability to support premium pricing | Minimal |
The estate is therefore weak from an investment or licensing perspective. A company acquiring rights to the old combination would not be acquiring a defensible patent franchise.
What is the Orange Book status of erythromycin-sulfisoxazole acetyl?
The relevant Orange Book analysis depends on the exact product and sponsor. The historical Pediazole product should not be assumed to have an active listing merely because the active ingredients remain chemically recognized.
Important distinctions include:
- An approved drug application can exist without current commercial distribution.
- A product can remain in FDA records after the sponsor stops marketing it.
- A discontinued product can have no active patents or exclusivity.
- A generic manufacturer may have approval for a product with limited or no current supply.
- The absence of an active branded product does not prevent compounding or extemporaneous preparation under applicable rules.
The FDA Approved Drug Products with Therapeutic Equivalence Evaluations, commonly called the Orange Book, should be used to confirm application status, therapeutic-equivalence codes, listed patents, and exclusivity records for a specific presentation (FDA, n.d.-d).
Are there Paragraph IV challenges or patent litigation?
No material current Paragraph IV litigation is associated with the historical erythromycin-sulfisoxazole acetyl combination.
The reason is commercial rather than strategic. Paragraph IV litigation generally arises when a generic applicant challenges an unexpired listed patent. A product with no meaningful unexpired patent estate does not provide the reference sponsor with a strong litigation platform.
Historical disputes involving erythromycin products may concern other salts, separate branded products, manufacturing rights, or different dosage forms. Those disputes should not be attributed automatically to the erythromycin-sulfisoxazole acetyl combination.
The expected litigation profile is:
| Litigation issue | Current assessment |
|---|---|
| Paragraph IV patent challenge | Low probability |
| Formulation patent dispute | Low probability |
| Trade-secret dispute | Possible only at the manufacturer level |
| Antitrust exposure | Low based on available public information |
| Settlement agreement relevance | No material current agreement identified |
| Patent injunction risk | Low |
What formulations are protected by the product’s IP?
The historical formulation was an oral powder that was reconstituted into a suspension. Its commercial characteristics likely depended on:
- Particle-size control.
- Suspension stability.
- Palatability and flavor masking.
- Reconstitution volume.
- Preservative performance.
- Container-closure compatibility.
- Dose uniformity during use.
These attributes can create development and quality-control work, but they do not necessarily create patent protection. For a legacy antibiotic suspension, the principal barriers are usually manufacturing economics, stability validation, FDA compliance, and supply-chain reliability.
A modern entrant would need to demonstrate pharmaceutical equivalence and bioequivalence where required, comply with current labeling standards, and meet applicable current good manufacturing practice requirements. Those obligations can be more significant than patent risk.
What caused the commercial decline?
The product’s decline reflects several market forces.
Therapeutic substitution
Amoxicillin became the preferred first-line treatment for many pediatric ear infections because it is inexpensive, familiar, and supported by guideline use. Broader or alternative options include amoxicillin-clavulanate, selected cephalosporins, and newer macrolides for patients with specific allergy or tolerability issues (American Academy of Pediatrics, 2013).
A two-antibiotic product became less attractive where one agent was sufficient.
Antimicrobial stewardship
Modern prescribing increasingly favors targeted therapy and avoidance of unnecessary broad or redundant antimicrobial exposure. Combining a macrolide with a sulfonamide can be difficult to justify when pathogen coverage, resistance patterns, and adverse-effect profiles favor a more focused alternative.
Safety and tolerability
Sulfonamides can produce hypersensitivity reactions and other adverse events. Erythromycin products can cause gastrointestinal effects, and erythromycin estolate has historically been associated with cholestatic hepatitis. These considerations reduce the appeal of older combination therapies where safer alternatives are available.
Generic price compression
Once exclusivity ended, the product entered a low-price generic environment. The small pediatric market, liquid-manufacturing requirements, and limited prescribing volume reduced the incentive for multiple manufacturers to maintain supply.
Pediatric market concentration
Pediatric oral suspensions require specialized manufacturing, taste masking, packaging, and inventory management. A mature product with declining utilization can become commercially unattractive even when production is technically feasible.
What is the financial trajectory of the product?
No reliable standalone public revenue series is generally available for erythromycin-sulfisoxazole acetyl or Pediazole. The product was not a major contemporary growth asset, and public-company filings typically did not report it as a separate revenue line.
The likely financial trajectory is:
| Period | Commercial profile | Financial direction |
|---|---|---|
| Initial launch period | Differentiated pediatric combination | Growth from clinical adoption |
| Early generic period | Multiple substitutes and price pressure | Revenue decline |
| Mature market | Low-margin legacy antibiotic | Compression |
| Later period | Limited supply or discontinuation | Minimal or zero branded revenue |
| Current outlook | No credible branded growth thesis | Commercially marginal |
Revenue exposure for a manufacturer would be low unless the company had a temporary supply position, a captive institutional customer base, or a broader portfolio strategy involving legacy pediatric medicines.
The product does not offer the characteristics usually associated with an investable specialty pharmaceutical asset: there is no current exclusivity runway, no biologic complexity, no durable formulation moat, and no clear premium reimbursement mechanism.
Which companies are challenging the product?
There is no meaningful current innovator-versus-generic competitive contest around the historical combination.
Competition comes from therapeutic substitutes rather than direct copies:
- Generic amoxicillin.
- Generic amoxicillin-clavulanate.
- Selected oral cephalosporins.
- Azithromycin and clarithromycin.
- Other pediatric antibiotics selected according to allergy status, pathogen susceptibility, and treatment guidelines.
Manufacturers that historically supplied erythromycin or sulfisoxazole products should not be treated as current competitors without confirming active FDA marketing status and commercial distribution.
Is there biosimilar risk for erythromycin-sulfisoxazole acetyl?
There is no biosimilar risk. Biosimilars apply to biological products, while erythromycin and sulfisoxazole acetyl are chemically synthesized small molecules.
The relevant competitive risks are:
- Generic substitution.
- Therapeutic substitution.
- Drug-shortage-related switching.
- Discontinuation of low-volume presentations.
- Formulary removal.
- Prescriber preference for newer or simpler regimens.
How does the product compare with modern pediatric antibiotics?
| Product or class | Relative market position | Key advantage |
|---|---|---|
| Erythromycin-sulfisoxazole acetyl | Legacy or limited | Historical combination coverage |
| Amoxicillin | Strong generic position | Low cost and guideline familiarity |
| Amoxicillin-clavulanate | Strong | Broader beta-lactam coverage |
| Azithromycin | Established alternative | Convenient dosing and macrolide use |
| Oral cephalosporins | Established alternatives | Use in selected allergy and resistance settings |
| Newer pediatric antibiotics | Niche | Specific resistance or specialty indications |
The combination is disadvantaged by its age, two-drug formulation, adverse-effect burden, and lack of a current exclusivity mechanism.
What generic launch risks exist?
A new generic launch would face limited patent risk but meaningful execution risk.
The principal barriers would include:
- Demonstrating pharmaceutical equivalence.
- Establishing bioequivalence or an acceptable regulatory bridge.
- Validating suspension stability and dose uniformity.
- Securing pediatric-friendly taste and packaging.
- Maintaining profitable manufacturing volumes.
- Competing against inexpensive single-agent alternatives.
- Managing demand uncertainty if the reference product is discontinued.
A generic entrant could avoid patent litigation, but that does not make the product economically attractive. Low expected volume and weak pricing power are more important risks than IP infringement.
What licensing opportunities remain?
The combination has limited licensing value. A transaction would be more likely to involve:
- A legacy product portfolio.
- A regional marketing authorization.
- A hospital or institutional supply arrangement.
- A manufacturing transfer.
- A discontinued-product reintroduction strategy.
A standalone license would have weak economics unless the licensee obtained manufacturing efficiencies, established distribution, or a specific geographic supply advantage. There is no apparent patent-based royalty stream to support a premium transaction.
What is the geographic coverage of the product?
The product’s regulatory and commercial relevance is jurisdiction-specific. FDA approval in the United States does not establish current authorization in Europe, Canada, Asia-Pacific, or Latin America.
Geographic value would depend on:
- Current national registration.
- Local reference-product status.
- Pediatric antibiotic prescribing patterns.
- Local substitution rules.
- Availability of approved oral suspensions.
- Regulatory requirements for legacy combination products.
In most regions, the active ingredients are old and widely known. The challenge is maintaining a compliant, commercially viable product rather than securing broad geographic exclusivity.
Key Takeaways
- The historically relevant product is Pediazole, containing erythromycin ethylsuccinate and sulfisoxazole acetyl, not erythromycin estolate.
- The combination is a legacy pediatric antibiotic with little evidence of a material current branded market.
- Composition, formulation, and regulatory exclusivity are expected to have expired.
- Current Paragraph IV, biosimilar, and patent-litigation risk is low.
- Commercial competition comes from amoxicillin, amoxicillin-clavulanate, azithromycin, and oral cephalosporins.
- No reliable standalone public revenue trajectory is available; the financial profile is consistent with long-term generic erosion and possible discontinuation.
- Any remaining value lies in supply, manufacturing, or regional distribution, not in patent strength.
FAQs
Is Pediazole still commercially available?
Availability depends on the exact presentation, National Drug Code, manufacturer, and country. Historical FDA records do not establish continuous current commercial distribution.
Is erythromycin estolate the same as erythromycin ethylsuccinate?
No. They are different erythromycin salts with different formulation and labeling histories. Pediazole labeling identifies erythromycin ethylsuccinate.
Can a company relaunch the erythromycin-sulfisoxazole acetyl combination?
A relaunch may be possible through an applicable FDA regulatory pathway, but commercial feasibility would depend on product approval status, manufacturing economics, current labeling, and market demand.
Does the combination have a patent-based barrier to generic entry?
No material current patent barrier is expected. The main obstacles are regulatory execution, low demand, suspension manufacturing, and competition from established alternatives.
Is the product relevant to antibiotic-resistance investment strategies?
Only marginally. It does not provide a clear innovation or exclusivity platform. Its relevance is more likely in legacy-product supply analysis, generic portfolio management, or pediatric antimicrobial availability.
References
-
American Academy of Pediatrics Subcommittee on Management of Acute Otitis Media. (2013). The diagnosis and management of acute otitis media. Pediatrics, 131(3), e964-e999. https://doi.org/10.1542/peds.2012-3488
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U.S. Food and Drug Administration. (n.d.-a). Pediazole: Erythromycin ethylsuccinate and sulfisoxazole acetyl oral suspension labeling. DailyMed. https://dailymed.nlm.nih.gov/
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U.S. Food and Drug Administration. (n.d.-b). Drug products withdrawn or removed from the market for reasons of safety or effectiveness. https://www.fda.gov/
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U.S. Food and Drug Administration. (n.d.-c). Drugs@FDA: FDA-approved drugs. https://www.accessdata.fda.gov/scripts/cder/daf/
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U.S. Food and Drug Administration. (n.d.-d). Approved drug products with therapeutic equivalence evaluations. https://www.fda.gov/drugs/drug-approvals-and-databases/orange-book-data-files
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