List of Excipients in Branded Drug FOSCARNET SODIUM

Generic Drugs Containing FOSCARNET SODIUM

Company	Ingredient	NDC	Excipient
Hikma Pharmaceuticals USA Inc	foscarnet sodium	0143-9192	HYDROCHLORIC ACID
Hikma Pharmaceuticals USA Inc	foscarnet sodium	0143-9192	WATER
Heritage Pharmaceuticals Inc d/b/a Avet Pharmaceuticals Inc	foscarnet sodium	23155-771	HYDROCHLORIC ACID
Heritage Pharmaceuticals Inc d/b/a Avet Pharmaceuticals Inc	foscarnet sodium	23155-771	WATER
Sagent Pharmaceuticals	foscarnet sodium	25021-189	HYDROCHLORIC ACID
Sagent Pharmaceuticals	foscarnet sodium	25021-189	WATER

What are the Most Frequently-Used Excipients in FOSCARNET SODIUM?

# Of NDCs	Excipient
7	HYDROCHLORIC ACID
7	WATER

Foscarnet Sodium Excipient Strategy and Commercial Opportunities

Last updated: August 3, 2026

Foscarnet sodium is an established, off-patent intravenous antiviral with a difficult formulation profile. The commercial opportunity is not a new active-ingredient patent position. It is improved delivery: ready-to-use presentations, lower-volume dosing, peripheral-infusion compatibility, renal-dose flexibility, supply reliability, and hospital-oriented packaging. The reference product, Foscavir, is an aqueous, preservative-free solution containing foscarnet sodium in water for injection at 24 mg/mL, with no conventional solubilizer or antimicrobial preservative disclosed in the formulation [1].

What is foscarnet sodium and how is it administered?

Foscarnet sodium is the sodium salt of phosphonoformic acid. It is a pyrophosphate analogue that inhibits viral DNA polymerase and HIV reverse transcriptase without requiring intracellular activation by viral kinases [1,2].

The FDA-approved product is administered intravenously for:

• Cytomegalovirus retinitis in patients with AIDS.
• Acyclovir-resistant mucocutaneous herpes simplex virus infection in immunocompromised patients [1].

The standard commercial concentration is 24 mg/mL of foscarnet, expressed as foscarnet sodium. Treatment requires substantial fluid volumes and prolonged intravenous administration. The label recommends administration through a central venous catheter when possible because the solution is hypertonic. Peripheral administration requires dilution [1].

What are the key formulation constraints?

Foscarnet sodium has four commercial formulation constraints:

1. High administered dose and infusion volume.
2. High osmolality, which limits peripheral administration.
3. Renal elimination and dose adjustment requirements.
4. Electrolyte-related toxicity, particularly hypocalcemia, hypomagnesemia, hypokalemia, and phosphate disturbances [1].

The formulation is aqueous and highly ionic. It does not require a lipid vehicle, complex solubilizer, or depot technology. The central technical problem is therefore not dissolution. It is safe delivery of a high-dose, hypertonic electrolyte-containing solution.

What excipients are used in Foscavir and generic foscarnet sodium?

The Foscavir label identifies water for injection as the inactive ingredient. The product is supplied as a clear, colorless, sterile solution containing 24 mg/mL foscarnet sodium [1].

Attribute	Foscavir reference product
Active ingredient	Foscarnet sodium
Strength	24 mg/mL foscarnet
Dosage form	Sterile intravenous solution
Primary excipient	Water for injection
Preservative	None disclosed
Buffer system	No separate buffer identified in the US label
Container opportunity	Single-use bottle or flexible bag
Administration	Intravenous infusion
Main compatibility issue	Do not mix with other medicines in the same infusion line unless compatibility is established

The absence of conventional excipients creates a low-complexity composition but does not eliminate development risk. A generic manufacturer must control pH, osmolality, assay, impurities, particulate matter, container interaction, and stability across the intended shelf life.

Why is an excipient-free strategy commercially relevant?

An excipient-free formulation offers several advantages:

• Lower risk of excipient-related hypersensitivity.
• Simplified qualitative and quantitative composition.
• Reduced risk of extractables and leachables from complex formulations.
• Easier global regulatory comparison with the reference product.
• Lower raw-material and manufacturing costs.
• Fewer intellectual-property vulnerabilities around novel excipient combinations.

The disadvantage is that the formulation has limited room to solve administration problems. Adding buffers, tonicity agents, or complexing agents can create new compatibility, toxicity, and bioequivalence questions.

What excipient strategies could improve foscarnet sodium products?

The strongest product strategies focus on administration rather than changing the pharmacology.

Ready-to-use flexible infusion bags

A flexible bag can reduce pharmacy compounding and preparation time. It can also reduce manipulation errors in hospital pharmacies. A commercial product could be supplied in multiple dose volumes, such as:

Presentation concept	Commercial purpose
250 mL	Lower-dose or partial-course administration
500 mL	Standard institutional use
1,000 mL	High-dose treatment and reduced handling
Patient-specific bags	Renal-adjusted dosing and ambulatory infusion

The principal development issues are bag permeability, water loss, oxygen transmission, seal integrity, and extractables. Polyolefin systems are more attractive than PVC where compatibility and plasticizer concerns are material, but the final choice requires stability data.

Diluted, lower-concentration products

A lower-concentration presentation could target peripheral administration. This is commercially attractive because it may reduce central-line dependence in selected patients. It also creates a potential hospital product differentiated by nursing convenience.

The tradeoff is higher infusion volume. A diluted product may be easier on the vein but more burdensome for fluid-restricted patients. The commercial value depends on whether the label supports peripheral administration and whether the product can maintain chemical and microbiological stability after dilution.

Concentrated products for central-line use

A more concentrated product could reduce infusion volume for patients with fluid restrictions. This approach would likely worsen peripheral tolerability and would remain dependent on central venous access. It has a narrower target market but may be relevant for intensive-care and transplant settings.

Increasing concentration also raises risks involving precipitation, viscosity, local tissue injury, and container compatibility. A concentration increase is therefore a higher-risk formulation program than a packaging or presentation change.

Preservative-free multi-dose alternatives

Foscarnet is used in severely immunocompromised patients. A preservative-free presentation is commercially preferable. A multi-dose container could reduce waste but would create a higher microbiological-control burden and may be unattractive for a product used in small patient populations.

A single-dose, ready-to-use package is more consistent with the clinical setting and with the reference product’s positioning.

Hospital admixture and compounding systems

A manufacturer could supply a pharmacy-ready concentrate with validated dilution instructions, or a closed-system transfer-compatible package. The opportunity is operational rather than pharmacological. It may support premium pricing if it reduces preparation labor and medication-error risk.

The product would need robust compatibility data with commonly used diluents and infusion materials. The label warns against simultaneous administration with other drugs through the same line because of compatibility concerns [1].

What stability and compatibility issues affect foscarnet sodium?

Foscarnet sodium products require a stability program covering:

• Assay and degradation products.
• pH drift.
• Osmolality.
• Visible and subvisible particles.
• Container closure integrity.
• Light exposure.
• Freeze-thaw stress.
• In-use stability after opening or dilution.
• Compatibility with infusion bags, tubing, filters, and catheters.

The reference label states that Foscavir should be stored at controlled room temperature and protected from freezing. Crystallization or precipitation after freezing would be a material commercial risk for cold-chain distribution and hospital storage [1].

A formulation developer should evaluate:

• Sodium and phosphate interactions.
• Calcium- and magnesium-containing solutions.
• Common IV diluents, including 0.9% sodium chloride and dextrose solutions.
• PVC and non-PVC tubing.
• In-line filters.
• Adsorption to infusion components.
• Compatibility after dilution at room temperature and under refrigeration.

A label-supported compatibility package can become a practical competitive advantage even when no patent protection exists.

What FDA regulatory status does foscarnet sodium have?

Foscarnet sodium is an FDA-approved antiviral administered by intravenous infusion. Foscavir was approved under NDA 019862 for CMV retinitis in patients with AIDS, with later labeling covering acyclovir-resistant HSV infection [1].

The product has no conventional small-molecule new-drug exclusivity remaining. The active ingredient and original clinical uses are longstanding. Current commercial competition is therefore primarily governed by generic drug approval, manufacturing capacity, supply reliability, institutional contracting, and formulation differentiation.

Is foscarnet sodium an Orange Book patent opportunity?

The principal commercial opportunity is not an Orange Book patent strategy. The original active-ingredient and basic-use positions are historically old, and any original patent terms would have expired before the current market.

The FDA Orange Book should be reviewed for current patent and exclusivity listings associated with the relevant NDA and dosage form. The absence of a listed patent does not prevent a manufacturer from seeking approval, but it means that a new formulation would need its own patent claims to create a meaningful regulatory delay or litigation position [3].

Potential patentable subjects include:

• A defined concentration range with demonstrated stability.
• A specific flexible-bag material and closure system.
• A validated diluted formulation stable for a specified in-use period.
• A peripheral-infusion formulation with controlled osmolality.
• A dosing presentation linked to renal function.
• A closed-system pharmacy preparation method.
• A formulation that limits precipitation or particulate formation.
• A combination package containing foscarnet and renal-monitoring or electrolyte-replacement components, subject to patentability and regulatory relevance.

Broad claims covering foscarnet sodium in water are unlikely to provide a strong modern composition position. Narrow claims tied to measurable performance attributes are more defensible.

When does foscarnet sodium lose exclusivity?

Foscarnet sodium has already lost practical exclusivity for the active ingredient and core therapeutic uses. There is no commercially relevant small-molecule patent cliff comparable to a recently launched branded medicine.

Exclusivity category	Current commercial assessment
Active-ingredient patent	Historical protection expired
Basic formulation protection	Historical protection expired or not commercially controlling
FDA new-drug exclusivity	Expired
Orphan-drug exclusivity	Not a current barrier to generic entry for the established indications
Biosimilar exclusivity	Not applicable
Formulation-specific patents	Possible only if separately developed and listed or asserted
Generic entry	Legally available subject to FDA approval and market supply

A new applicant would generally pursue an ANDA if it can demonstrate pharmaceutical equivalence and bioequivalence or otherwise satisfy the applicable FDA requirements. An NDA 505(b)(2) pathway could be considered for a materially different formulation, concentration, administration route, or delivery system.

Are there Paragraph IV challenges for foscarnet sodium?

Paragraph IV litigation is not the principal risk profile for the legacy foscarnet market. A Paragraph IV certification applies when an ANDA applicant challenges a listed patent. If no relevant patent is listed for the reference product, the applicant would not need to create a Paragraph IV case around an expired core product position.

A new formulation patent could change that analysis. If an innovator obtains and lists an eligible patent for a qualifying formulation or method, an ANDA applicant could face:

• Paragraph IV certification.
• A 45-day period for patent litigation after notice.
• A potential 30-month stay of approval if litigation is timely filed, subject to statutory exceptions.
• Product-specific settlement negotiations.
• A launch decision based on patent validity, infringement, and damages exposure [4].

For a foscarnet product, the more likely disputes would concern formulation, container, dilution, or administration claims rather than the active ingredient.

What patent strength does a foscarnet sodium formulation have?

Patent strength is likely moderate to weak for broad composition claims and stronger for narrowly demonstrated delivery improvements.

Claim type	Likely strength
Foscarnet sodium as an antiviral	Weak; historically known
Foscarnet sodium in water for injection	Weak unless tied to a novel technical result
Specific pH and concentration range	Moderate if supported by stability and safety data
Peripheral-infusion formulation	Moderate if clinically validated
Ready-to-use bag system	Moderate, but vulnerable to design-around
Dilution and in-use stability method	Moderate if technically specific
Renal-dose presentation	Moderate to weak unless linked to a novel device or workflow
Manufacturing process	Moderate if it solves a reproducible impurity or particulate problem

Patent value will depend on whether hospitals consider the improvement necessary rather than merely convenient. A ready-to-use bag may generate commercial value without producing strong exclusionary rights.

Which companies are likely to challenge or compete with foscarnet sodium?

Competition is likely to come from generic injectable manufacturers, hospital-contract suppliers, and specialty distributors rather than from biotechnology companies developing biosimilars.

Relevant competitor categories include:

• ANDA sponsors of foscarnet sodium injection.
• Established sterile-injectable manufacturers.
• Contract development and manufacturing organizations with high-containment or sterile-liquid capacity.
• Specialty pharmaceutical companies supplying infectious-disease hospitals.
• Pharmacy-compounding providers and institutional outsourcing facilities.

The market is small relative to major anti-infective categories. That can reduce the number of competitors, but it also increases dependence on each supplier. A manufacturer with reliable sterile capacity can obtain disproportionate hospital share during shortages or discontinuations.

What commercial opportunities exist for foscarnet sodium?

Supply-secure generic injection

The lowest-risk opportunity is a standard 24 mg/mL generic with dependable supply, multiple vial or bag sizes, and competitive hospital pricing. The main barriers are sterile manufacturing economics and limited annual demand.

Ready-to-administer hospital product

A ready-to-use bag can command a premium if it reduces pharmacy labor, preparation time, and waste. The product should support barcode medication administration, clear dose labeling, and standard infusion-pump workflows.

Renal-dose packaging

Foscarnet requires renal-function-based dose adjustment. A product line with several standardized dose volumes could reduce bedside calculation and preparation errors. The commercial opportunity is strongest if the presentations align with common institutional protocols.

Ambulatory infusion

An ambulatory formulation could target home infusion and outpatient infectious-disease treatment. The main requirements are stability after connection, manageable infusion volume, pump compatibility, and clear handling instructions.

Geographic licensing

Foscarnet products may fit licensing arrangements in markets where branded supply is limited or generic registration is incomplete. The strongest licensing proposition would combine:

• Existing sterile manufacturing.
• Regional regulatory registrations.
• Stability data in local packaging.
• Hospital distribution.
• Supply guarantees.
• Pharmacovigilance capability.

The value of licensing will be constrained by the small patient population and limited ability to sustain high development costs.

What manufacturing and intellectual-property barriers exist?

The principal barriers are operational:

• Sterile aqueous manufacturing.
• High-quality control for ionic solutions.
• Container-closure compatibility.
• Particulate and crystallization control.
• Scale-up without pH or osmolality drift.
• Reliable supply of sterile containers and closures.
• Regulatory documentation for diluted and ready-to-use presentations.

The active ingredient itself is unlikely to create a significant manufacturing moat. A manufacturer may still encounter process know-how issues involving impurity control, filtration, filling, and long-term stability.

A defensible commercial package would combine a standard generic with proprietary presentation claims, validated compatibility data, differentiated packaging, and supply reliability. Patent protection alone is unlikely to justify the program.

How does foscarnet sodium compare with competing antiviral delivery strategies?

Product strategy	Foscarnet sodium	Acyclovir or ganciclovir alternatives
Main use	Resistant CMV or HSV infections	Broader first-line or alternative antiviral use
Administration	Intravenous	Oral and intravenous options vary
Core formulation	Aqueous injectable	Often broader dosage-form options
Main toxicity concern	Renal and electrolyte toxicity	Drug-specific hematologic, renal, or neurologic toxicity
Excipient opportunity	Delivery volume, osmolality, packaging	Oral bioavailability, sustained release, solubility
Patent opportunity	Narrow formulation and device claims	Often broader lifecycle-management options
Commercial market	Specialized and relatively small	Larger or more diversified

Foscarnet’s clinical role limits volume but increases the value of reliable access. A formulation that improves administration without compromising renal monitoring may be more commercially relevant than a modest cost reduction.

Key Takeaways

• Foscarnet sodium is an established, off-patent intravenous antiviral with no biosimilar pathway.
• Foscavir uses a simple aqueous formulation with water for injection as the disclosed inactive ingredient.
• The main formulation problems are hypertonicity, large infusion volumes, renal-dose variability, and electrolyte toxicity.
• Ready-to-use bags, renal-dose presentations, validated dilution systems, and ambulatory-infusion packaging are the strongest commercial opportunities.
• Broad patents on foscarnet sodium or foscarnet in water are unlikely to be strong. Narrow claims tied to stability, osmolality, container systems, or administration performance offer better prospects.
• Paragraph IV litigation is not the central market risk unless a new formulation patent is listed.
• Manufacturing reliability, sterile capacity, container compatibility, and hospital contracting are likely to matter more than core active-ingredient IP.
• A 505(b)(2) strategy may be appropriate for a materially differentiated presentation; a conventional ANDA is more suitable for a reference-matched injection.

FAQs

Is foscarnet sodium a biologic requiring a biosimilar application?

No. Foscarnet sodium is a chemically synthesized small molecule. Generic applicants would generally use an ANDA or, for a materially different product, an NDA pathway such as 505(b)(2), not a biosimilar application.

Can foscarnet sodium be formulated as an oral tablet?

An oral tablet would face major development and clinical challenges. The approved product is intravenous, and an oral program would require new pharmacokinetic, efficacy, safety, and formulation evidence. It would be a new product-development program rather than a simple generic lifecycle strategy.

Is a lyophilized foscarnet sodium product commercially attractive?

Probably not as a first-line strategy. Foscarnet is already supplied as an aqueous solution, and lyophilization would add reconstitution steps, packaging cost, and administration complexity. It could become relevant only if it produced a major stability or distribution advantage.

Could a foscarnet sodium product be sold in prefilled syringes?

A prefilled syringe is unlikely to be optimal for standard treatment because the administered dose and volume are large. It may have limited value for small-volume institutional preparation or specialized dosing, but flexible bags and pharmacy-ready containers are more commercially aligned with current use.

What is the strongest lifecycle-management opportunity for foscarnet sodium?

The strongest opportunity is a ready-to-use, preservative-free infusion system with validated renal-dose presentations, infusion compatibility, and improved pharmacy workflow. The commercial case depends on supply reliability and hospital adoption rather than exclusivity over the active ingredient.

References

1. U.S. Food and Drug Administration. (2023). Foscavir (foscarnet sodium) injection prescribing information. FDA/DailyMed.

2. De Clercq, E. (2003). Clinical potential of the acyclic phosphonate antivirals cidofovir, adefovir, and tenofovir in treatment of DNA virus and retrovirus infections. Clinical Microbiology Reviews, 16(4), 569-596.

3. U.S. Food and Drug Administration. (2024). Approved drug products with therapeutic equivalence evaluations: Orange Book. FDA.

4. U.S. Food and Drug Administration. (2024). Abbreviated new drug application submissions: Refuse-to-receive standards and Paragraph IV certification requirements. FDA.