List of Excipients in Branded Drug FOSCARNET

Generic Drugs Containing FOSCARNET

Company	Ingredient	NDC	Excipient
Fresenius Kabi USA LLC	foscarnet sodium	63323-875	HYDROCHLORIC ACID
Fresenius Kabi USA LLC	foscarnet sodium	63323-875	WATER
Hikma Pharmaceuticals USA Inc	foscarnet sodium	0143-9192	HYDROCHLORIC ACID

What are the Most Frequently-Used Excipients in FOSCARNET?

# Of NDCs	Excipient
1	HYDROCHLORIC ACID
1	WATER

Foscarnet Excipient Strategy and Commercial Opportunities

Last updated: September 3, 2026

Foscarnet is an established antiviral with limited formulation complexity but significant administration and handling burdens. The commercial opportunity is not a novel excipient that changes antiviral activity. It is a safer, more convenient, and more compatible foscarnet sodium presentation that reduces preparation errors, infusion burden, renal-management complexity, and hospital pharmacy labor.

Foscarnet sodium is marketed primarily as an aqueous intravenous solution for treatment of cytomegalovirus retinitis in patients with AIDS and acyclovir-resistant mucocutaneous herpes simplex virus infections. The reference product, Foscavir, contains foscarnet sodium hexahydrate at 24 mg/mL in water for injection. The product is supplied as a ready-to-use solution, but its clinical use remains operationally difficult because of nephrotoxicity, electrolyte abnormalities, high infusion volumes, and compatibility restrictions.[1]

What excipients are used in foscarnet sodium injection?

The reference formulation is a simple, aqueous, essentially preservative-free product.

Attribute	Foscarnet sodium injection
Active ingredient	Foscarnet sodium hexahydrate
Strength	24 mg/mL
Common container	250 mL infusion bag or bottle
Active per 250 mL	6 g foscarnet sodium hexahydrate
Primary vehicle	Water for injection
pH	Approximately 7.2 to 7.6
Preservatives	Not used in the standard large-volume formulation
Route	Intravenous infusion
Key formulation issue	Chemical and physical compatibility with other intravenous products

Foscarnet is a phosphonoformate compound supplied as the sodium salt. The formulation depends on high aqueous solubility rather than a complex solubilization system. pH adjustment is used during manufacture. The commercial product labeling emphasizes that foscarnet should not be mixed with other medicinal products in the same intravenous line except where compatibility has been established.[1]

The formulation’s simplicity limits the opportunity for conventional excipient substitution. A reformulation that adds surfactants, cosolvents, antioxidants, or antimicrobial preservatives would need to demonstrate a clear benefit without increasing infusion toxicity, precipitation risk, extractables, or renal burden.

How strong is the formulation patent estate for foscarnet?

Foscarnet has a weak current formulation-patent profile compared with newer small-molecule drugs. The principal commercial product is an old antiviral approved by FDA in 1991 under NDA 020068.[2] The commercially relevant opportunity is therefore based on regulatory execution, manufacturing reliability, delivery convenience, and differentiated presentation rather than blocking composition-of-matter rights.

IP category	Current commercial significance
Composition-of-matter patents	Historical protection; unlikely to block modern generic development
Basic aqueous formulation	Limited patent defensibility
Ready-to-use infusion presentation	Potentially protectable through process, container, or use claims, but difficult to make broad
Premixed lower-concentration products	Potential formulation and packaging opportunity
Extended-stability products	Potential method, formulation, and container claims
Compatibility technology	Potential platform or product-specific claims
Oral or nonintravenous foscarnet	High technical and regulatory risk
Manufacturing process	Possible trade-secret value and narrow process patents

The absence of a strong active patent barrier does not eliminate commercial value. It changes the investment thesis. A sponsor would be competing on product quality and hospital economics rather than relying on patent exclusivity.

When does foscarnet lose exclusivity?

Foscarnet’s original regulatory and patent exclusivity periods have expired. The reference product is therefore exposed to generic competition through the abbreviated new drug application pathway, subject to the applicable FDA requirements.

Foscarnet does not have the same long-lived exclusivity profile as biologics, long-acting injectables, or recently approved specialty drugs. There is no meaningful biosimilar pathway because foscarnet is a chemically defined small molecule, not a biologic.

FDA and Orange Book status

The reference product is Foscavir, foscarnet sodium injection, associated with FDA NDA 020068.[2] Orange Book relevance is primarily that of a listed reference product supporting generic substitution and ANDA development. A sponsor should not assume that the absence of a prominent active patent dispute means that every formulation or presentation is commercially unprotected. Container configuration, manufacturing controls, stability data, and product-specific labeling can still create practical barriers.

What commercial opportunities exist for foscarnet excipients?

The strongest opportunities are operational rather than pharmacological.

1. Ready-to-use, pharmacy-efficient presentations

Foscarnet is already supplied as a ready-to-use solution, so a new product must improve on the existing presentation. Potential differentiators include:

• Smaller-volume bags for dose preparation in selected patients
• Standardized dosing containers
• Easier connection to infusion systems
• Reduced overfill
• Clear labeling of total foscarnet content and sodium load
• Ready-to-administer formats that reduce bedside manipulation

A smaller-volume presentation could reduce storage and handling costs, but concentration increases may create new risks involving local tolerability, precipitation, osmolality, and infusion-site injury. The label states that foscarnet is hypertonic and should be administered through a central venous catheter when appropriate.[1]

2. Extended in-use stability

Foscarnet dosing can require repeated administration over prolonged treatment courses. A formulation with demonstrated stability after transfer into common infusion containers could reduce pharmacy waste.

Potential formulation and packaging work includes:

• Stability in polyolefin bags
• Compatibility with common elastomeric ports
• Protection from temperature excursions
• Reduced adsorption to container surfaces
• Longer beyond-use dating after puncture or transfer
• Compatibility with automated compounding systems

This opportunity is more credible than attempting to add a novel excipient solely to improve solubility. The active is already delivered in aqueous solution. The commercial value would come from validated stability and workflow reduction.

3. Excipient systems for container compatibility

Foscarnet solutions contact bags, tubing, ports, and infusion devices. Extractables and leachables, adsorption, and material compatibility are important development issues for an acidic or near-neutral inorganic-organic salt solution administered in large volumes.

A differentiated product could use:

• Low-sorption polyolefin packaging
• Improved elastomer formulations
• Reduced metal-ion exposure
• Multilayer barrier films
• Container closures optimized for long storage
• Lower-extractables tubing systems

These technologies are more likely to support narrow formulation, packaging, or manufacturing claims than broad excipient claims.

4. Preservative-free multidose strategies

A preservative-free formulation is appropriate for large-volume intravenous use. Adding a preservative could create toxicity and regulatory problems without solving the main clinical limitations. A better commercial approach is a single-use container system with improved sterility assurance and reduced waste.

For foscarnet, preservative-free packaging is more commercially credible than a preserved multidose vial. Any multidose presentation would face increased microbiological, container-closure, and handling requirements.

5. Renal-management support

Foscarnet’s major clinical limitation is nephrotoxicity. The label requires hydration and monitoring of serum creatinine, calcium, magnesium, potassium, and phosphate.[1] An excipient cannot be expected to eliminate this toxicity because it is linked to the drug’s pharmacology and renal handling.

A product strategy could still reduce treatment burden through:

• Co-packaged hydration solutions
• Standardized hydration protocols
• Compatible electrolyte-replacement products
• Integrated infusion sets
• Dose-preparation systems linked to renal function
• Hospital protocols that reduce compounding variation

These are combination-product or service opportunities rather than conventional excipient opportunities. They could improve adoption in hospitals without claiming that the excipient protects the kidney.

What formulations are protected or commercially differentiated?

The reference aqueous formulation has limited differentiation. The most defensible product concepts are those tied to measurable performance.

Product concept	Technical rationale	Commercial value	IP potential
Standard 24 mg/mL ready-to-use bag	Matches established clinical use	Moderate	Low
Smaller-volume higher-strength solution	Reduces fluid burden	Moderate to high	Moderate, with safety risk
Extended-stability premix	Reduces pharmacy waste	High	Moderate
Low-extractables container system	Improves storage and administration reliability	Moderate	Moderate
Elastomer-compatible infusion presentation	Reduces device interaction risk	Moderate	Moderate
Preservative-free single-dose vial	Supports smaller doses	Moderate	Low to moderate
Oral formulation	Avoids IV infusion	Very high if successful	High, but technically difficult
Sustained-release formulation	Reduces administration frequency	High	High, but low probability

An oral formulation would have the greatest commercial upside because it could avoid intravenous access and infusion-center resources. Foscarnet’s physicochemical properties, systemic antiviral use, and need for adequate exposure make oral delivery difficult. A sponsor would need to solve permeability, stability, dose loading, and gastrointestinal tolerability. This is a drug-delivery program, not a routine excipient optimization.

What manufacturing and formulation barriers affect foscarnet?

Foscarnet manufacturing is comparatively accessible at the active-ingredient level, but sterile product execution remains demanding.

Sterile manufacturing

A commercial product requires validated aseptic or terminal-sterilization controls, depending on formulation and container system. Large-volume parenteral manufacturing requires control of:

• Bioburden and endotoxin
• Particulates
• Container-closure integrity
• Fill-volume accuracy
• pH and assay
• Degradation products
• Visible and subvisible particles

Sodium and electrolyte burden

Foscarnet administration can affect serum electrolytes and renal function. The formulation should avoid unnecessary sodium or ionic excipients. Adding buffers or complexing agents could change electrolyte exposure and potentially complicate labeling.

Compatibility

Compatibility must be established with infusion solutions, tubing, catheters, and other products used in clinical practice. The FDA label warns against coadministration through the same line with incompatible products.[1] A compatibility package could be a meaningful selling point if supported by robust studies.

Concentration and osmolality

Increasing concentration can reduce infusion volume but may increase osmolality and local tissue risk. Any high-concentration product would need clinical and device data supporting infusion-site safety, catheter selection, and administration rates.

Which companies are challenging or competing with Foscavir?

Competition is primarily generic and supply-chain based rather than patent-litigation driven. The market has included products labeled as foscarnet sodium injection from generic or injectable-drug manufacturers, including Fresenius Kabi and other suppliers depending on market availability and period.[3]

Competitive group	Primary advantage	Main weakness
Foscavir reference product	Established label and clinical familiarity	Higher reference-product pricing and limited differentiation
Generic injectable suppliers	Lower acquisition cost	Supply interruptions, limited package differentiation
Hospital compounders	Local flexibility	Sterility, stability, and labor burden
Specialty injectable manufacturers	Potential ready-to-use improvements	Small market and limited scale
Drug-delivery developers	Opportunity for oral or lower-burden administration	High development risk

Market size is constrained by the relatively narrow indication base. Foscarnet is used mainly when alternatives such as ganciclovir or acyclovir are unsuitable because of resistance or intolerance. That makes the product clinically important but commercially specialized.

What generic entry risks exist for a new foscarnet product?

A generic 24 mg/mL aqueous injection can face limited patent risk but substantial execution risk.

Key risks include:

1. FDA review of pharmaceutical equivalence and product quality.
2. Sterile manufacturing capacity and inspection history.
3. Demonstration of stability in the proposed container.
4. Availability of qualified foscarnet sodium active ingredient.
5. Hospital purchasing pressure and generic price erosion.
6. Supply reliability for a niche injectable.
7. Labeling consistency for hydration, renal monitoring, and administration.
8. Limited market size relative to development and validation costs.

A differentiated product may avoid direct price competition, but it must produce measurable savings. Hospitals may pay a premium for reduced pharmacy labor, fewer discarded bags, lower preparation complexity, or improved supply reliability. A small change in excipient composition alone is unlikely to support premium pricing.

What patent and regulatory strategy is most practical?

The strongest strategy would combine a narrowly defined product improvement with regulatory exclusivity or proprietary manufacturing know-how.

Patentable targets

Potential claims could cover:

• A defined foscarnet concentration range
• A specified pH window
• A container made from a defined polymeric material
• A formulation with demonstrated long-term or in-use stability
• A low-extractables container-closure system
• A validated compatibility profile
• A method of reducing preparation waste
• A ready-to-administer presentation for a defined dosing regimen

Broad claims to "foscarnet in water" would be vulnerable because the basic formulation is established and predictable.

Regulatory routes

A conventional 24 mg/mL injectable product would generally pursue an ANDA if pharmaceutical equivalence and bioequivalence requirements can be met. A materially different concentration, route, formulation, or delivery system could require an NDA or 505(b)(2) pathway, depending on FDA determination.

A 505(b)(2) strategy may be relevant for:

• A new concentration
• A new container or delivery system with clinical implications
• A substantially different formulation
• A new route of administration
• A new dosing regimen

The regulatory pathway should be selected around the actual product difference. A formulation change that affects exposure, infusion safety, or local tolerability can increase the clinical evidence burden.

How does foscarnet compare with competing antivirals?

Drug	Main route	Key advantage	Key limitation	Excipient opportunity
Foscarnet	IV	Activity against resistant CMV and HSV	Nephrotoxicity, electrolyte abnormalities, infusion burden	Premix, compatibility, delivery reduction
Ganciclovir	IV/oral prodrug options	Established CMV treatment	Myelosuppression and renal dosing	Oral or sustained-release delivery
Valganciclovir	Oral	Avoids routine IV infusion	Myelosuppression, renal adjustment	Modified-release and tolerability strategies
Acyclovir	IV/oral	Broad familiarity and lower cost	Resistance in selected patients	Solubility and oral exposure improvements
Cidofovir	IV	Alternative CMV activity	Nephrotoxicity and complex administration	Nephroprotective delivery concepts

Foscarnet’s commercial position is strongest in salvage therapy. A formulation that reduces infusion burden without compromising renal monitoring could improve its use in hospitals treating resistant viral infections.

What is the revenue exposure and market opportunity?

Foscarnet is a niche product. Revenue exposure is concentrated in specialty infectious-disease treatment, hospital purchasing, and periods of antiviral resistance or limited access to alternatives. The market does not support the same sales assumptions as a broad outpatient antiviral.

The most attractive commercial segments are:

• Hospital systems seeking reliable sterile supply
• Specialty pharmacies supporting complex antiviral treatment
• Academic medical centers treating resistant CMV or HSV
• Public-sector purchasers requiring supply continuity
• International markets with limited access to branded Foscavir
• Contract manufacturers seeking a differentiated injectable product

A sponsor should evaluate opportunity using treated-patient volume, average treatment duration, dose intensity, generic price erosion, and supply reliability. The value proposition should be measured in total treatment cost, including pharmacy preparation, infusion resources, hydration, monitoring, and discarded product.

Key Takeaways

• Foscarnet’s standard formulation is a simple 24 mg/mL aqueous foscarnet sodium injection.
• The original Foscavir patent and exclusivity framework no longer provides a meaningful commercial barrier.
• There is no biosimilar risk because foscarnet is a small-molecule antiviral.
• The strongest formulation opportunities involve ready-to-use delivery, extended stability, container compatibility, and pharmacy waste reduction.
• A novel excipient is unlikely to justify premium pricing unless it produces measurable stability, safety, or workflow benefits.
• Higher-concentration products could reduce infusion volume but would face osmolality, catheter, and local-tolerability risks.
• Oral foscarnet would offer the largest commercial upside but requires a high-risk delivery program.
• Generic entry risk is driven more by sterile manufacturing, supply reliability, and market scale than by active patent litigation.
• The practical IP strategy is narrow protection around concentration, stability, packaging, compatibility, or manufacturing.
• Foscarnet remains a specialty salvage antiviral, so commercial models should use constrained patient volumes and hospital economics.

FAQs

Can excipients reduce foscarnet nephrotoxicity?

No established excipient strategy eliminates foscarnet-associated nephrotoxicity. Product development can improve hydration delivery, infusion control, and administration reliability, but renal monitoring remains necessary.

Is foscarnet sodium available as an oral drug?

The established commercial product is intravenous. An oral product would require a new delivery strategy to overcome absorption and dose-loading challenges.

Can foscarnet be formulated as a concentrated injection?

A concentrated formulation is technically possible but would require evaluation of osmolality, infusion-site tolerability, catheter requirements, precipitation, stability, and clinical administration parameters.

Are there active Orange Book patents blocking generic foscarnet?

Foscarnet’s original exclusivity has expired. The principal commercial issue is development of a pharmaceutically equivalent sterile injectable and compliance with FDA product-quality requirements.

What is the best commercial niche for a new foscarnet product?

The most credible niche is a reliable, ready-to-administer injectable with validated extended stability, optimized packaging, broad infusion compatibility, and reduced pharmacy handling.

References

1. U.S. Food and Drug Administration. (2023). Foscavir (foscarnet sodium) injection prescribing information.
2. U.S. Food and Drug Administration. (1991). Drugs@FDA: Foscavir, NDA 020068.
3. U.S. National Library of Medicine. (2024). DailyMed: Foscarnet sodium injection prescribing information. National Institutes of Health.