List of Excipients in Branded Drug BUSULFAN

Generic Drugs Containing BUSULFAN

Company	Ingredient	NDC	Excipient
Hospira Inc	busulfan	0409-1112	N,N-DIMETHYLACETAMIDE
Hospira Inc	busulfan	0409-1112	POLYETHYLENE GLYCOL 400
American Regent Inc	busulfan	0517-0920	N,N-DIMETHYLACETAMIDE
American Regent Inc	busulfan	0517-0920	POLYETHYLENE GLYCOL 400

What are the Most Frequently-Used Excipients in BUSULFAN?

# Of NDCs	Excipient
15	N,N-DIMETHYLACETAMIDE
2	POLYETHYLENE GLYCOL
13	POLYETHYLENE GLYCOL 400

Last updated: August 22, 2026

Busulfan is a mature, genericized alkylating agent with limited opportunity in the active pharmaceutical ingredient itself and greater commercial potential in excipient-enabled delivery, stability, dosing control, and transplant workflow. The leading formulation problem is the need to solubilize a highly potent, poorly water-soluble cytotoxic drug while controlling exposure, handling risk, dilution compatibility, and patient-specific pharmacokinetics. The strongest commercial opportunities are ready-to-use intravenous presentations, lower-toxicity solvent systems, pediatric and low-volume dosing formats, and formulation technologies that support therapeutic drug monitoring.

Busulfan Excipient Strategy and Commercial Opportunities

What is busulfan used for?

Busulfan is a bifunctional alkylating agent used primarily as part of conditioning regimens before hematopoietic progenitor-cell transplantation. It is administered orally as tablets or intravenously as an infusion. Intravenous busulfan is commonly used with cyclophosphamide, fludarabine, or related conditioning agents.

Busulfan has a narrow therapeutic index. Excess exposure is associated with serious toxicity, including hepatic veno-occlusive disease or sinusoidal obstruction syndrome, seizures, mucositis, pulmonary complications, and myelosuppression. Low exposure can reduce conditioning intensity and compromise treatment outcomes. These characteristics make formulation, dose preparation, infusion control, and pharmacokinetic monitoring commercially relevant.

The FDA-approved intravenous product, Busulfex, contains 6 mg/mL busulfan and is diluted before administration. The formulation uses dimethylacetamide and polyethylene glycol 400 as inactive ingredients. Dilution is performed with 0.9% sodium chloride or 5% dextrose injection according to labeling requirements.[1]

Which excipients are used in approved busulfan formulations?

Intravenous busulfan

The principal excipients in the Busulfex injection are:

Function	Excipient or vehicle	Formulation role
Primary cosolvent	Dimethylacetamide	Solubilizes busulfan at high concentration
Secondary cosolvent	Polyethylene glycol 400	Improves solubility and supports formulation stability
Diluent after withdrawal	0.9% sodium chloride or 5% dextrose injection	Enables intravenous infusion at the clinical site
Container and administration system	Compatible glass vial, syringe, tubing, and infusion components	Controls adsorption, extractables, leachables, and cytotoxic handling risk

Dimethylacetamide is effective as a solvent but creates regulatory and commercial constraints. It can raise concerns relating to reproductive toxicity, occupational handling, residual solvent control, tolerability, and compatibility with administration materials. Polyethylene glycol 400 is widely used in parenteral products but can contribute to viscosity, oxidation sensitivity, and extractables or leachables considerations depending on the packaging system.

The formulation is therefore functional but not optimized for simplicity. The clinical site must dilute a concentrated cytotoxic solution, calculate the dose, use controlled infusion procedures, and manage hazardous-drug waste.

Oral busulfan

Historical oral busulfan products, including Myleran, used conventional tablet excipients such as lactose, starch-based materials, and magnesium stearate. Oral busulfan has a long development history, and the commercial opportunity for new oral excipient claims is narrower than for intravenous formulations.

Potential oral formulation objectives include:

• reducing dose-to-dose variability;
• improving tablet content uniformity at low strength;
• preventing moisture-driven degradation;
• enabling pediatric dosing;
• producing dispersible or liquid dosage forms;
• reducing occupational exposure during tablet splitting or compounding.

A liquid oral product would require careful control of chemical stability, taste, dose uniformity, preservative selection, and accidental exposure risk.

What excipient strategy best addresses busulfan’s formulation risks?

The most defensible strategy is to separate the product requirements into four technical objectives: solubilization, stability, administration safety, and dose flexibility.

1. Replace or reduce dimethylacetamide

A commercially valuable formulation would reduce reliance on dimethylacetamide while maintaining the required busulfan concentration. Candidate systems could include:

• polyethylene glycol and ethanol combinations;
• propylene glycol-based cosolvent systems;
• surfactant-assisted aqueous systems;
• cyclodextrin complexes;
• lipid or microemulsion systems;
• amorphous solid dispersions for nonparenteral use;
• nanosuspension or nanocarrier systems where clinically justified.

Each approach faces a different development barrier. Surfactants can create tolerability and hemolysis concerns. Cyclodextrins can increase osmolality and formulation volume. Lipid systems may complicate sterilization and infusion compatibility. Nanocarriers may add manufacturing complexity without improving outcomes in a short-course conditioning regimen.

A lower-solvent formulation has the greatest value if it can preserve concentration, avoid precipitation during dilution, remain stable through the treatment window, and fit existing transplant pharmacy workflows.

2. Improve dilution and infusion stability

Busulfan is diluted before administration. Commercial differentiation could come from demonstrated stability in standard diluents, infusion bags, and administration sets.

Relevant studies should assess:

• chemical stability after dilution;
• precipitation or crystallization;
• adsorption to tubing and filters;
• compatibility with polyolefin, PVC, and other materials;
• photostability;
• container closure integrity;
• hold times under refrigerated and room-temperature conditions;
• stability during low-volume pediatric preparation.

A product with a validated longer in-use period could reduce pharmacy waste and improve scheduling. A ready-to-use bag could eliminate several preparation steps but would require a range of concentrations or volumes to support patient-specific dosing.

3. Control hazardous-drug handling

The excipient system is part of a broader containment strategy. A commercial product could combine a stable formulation with:

• closed-system transfer compatibility;
• prefilled syringes;
• ready-to-administer infusion bags;
• reduced-vial-dose waste;
• tamper-evident and cytotoxic-compatible packaging;
• barcode-enabled dose preparation;
• low-surface-residue primary packaging.

These features are more likely to generate hospital purchasing value than a marginal improvement in solubility alone.

4. Support pharmacokinetic dosing

Intravenous busulfan is frequently dosed using pharmacokinetic targeting. A formulation that reduces preparation variability can support more reliable exposure calculations.

Potentially protectable technical features include:

• concentration ranges that minimize dilution error;
• low dead-volume delivery systems;
• calibrated pediatric dosing devices;
• formulations that preserve concentration over the full infusion period;
• integration with dose-adjustment software or clinical decision-support tools.

The commercial claim should focus on reduced preparation variability and workflow reliability rather than asserting that an excipient independently improves clinical efficacy.

What formulations are protected by busulfan patents?

The core busulfan compound is an old small molecule, and its original composition-of-matter protection has expired. The principal commercial barriers therefore relate to product quality, manufacturing, regulatory approval, and hospital adoption rather than basic molecule ownership.

Potential patentable subject matter includes:

Subject matter	Commercial relevance	Patent strength
New cosolvent system	Reduces solvent burden or improves concentration	Moderate if supported by unexpected stability or tolerability
Ready-to-use infusion	Removes pharmacy dilution	Moderate, but vulnerable to obviousness challenges
Pediatric formulation	Supports precise low-volume dosing	Moderate if linked to specific stability and dosing performance
Container or tubing compatibility	Reduces adsorption and material interaction	Moderate to strong when supported by comparative data
Long-term or in-use stability	Extends usable preparation window	Moderate, with strong value if clinically operational
Taste-masked oral liquid	Enables pediatric oral dosing	Moderate
Manufacturing process	Controls impurities, polymorph, particle size, or residual solvents	Moderate to strong if process-specific
Therapeutic drug monitoring method	Optimizes exposure-based dosing	Potentially limited by method-of-treatment and obviousness issues

A formulation patent should include narrow, data-supported claims around concentration, solvent ratios, pH, osmolality, impurity limits, dilution stability, and container compatibility. Broad claims covering any alternative busulfan solvent are likely to face prior-art and obviousness challenges.

What is the FDA regulatory status of busulfan?

Busulfan is an FDA-approved small-molecule drug. The intravenous product Busulfex was approved for use in conditioning before hematopoietic progenitor-cell transplantation. Generic intravenous busulfan products have also been approved under the abbreviated new drug application pathway.[1,2]

The regulatory strategy depends on the degree of formulation change:

Product concept	Likely regulatory route
Same active ingredient and substantially equivalent dosage form	ANDA, subject to pharmaceutical equivalence and bioequivalence requirements
New excipient system with materially different exposure or safety profile	505(b)(2) NDA may be appropriate
Ready-to-use version with different concentration or administration design	505(b)(2) or new NDA, depending on differences
New oral liquid or pediatric dosage form	505(b)(2), with additional clinical and safety data
Hospital compounding improvement using existing product	Not an independent FDA-approved product unless separately developed

A new excipient can create a regulatory burden if it changes systemic exposure, infusion tolerability, organ toxicity, or pharmacokinetic behavior. The development program should include comparative pharmacokinetics, infusion-site tolerability, solvent exposure assessment, extractables and leachables, and container-closure studies.

What is the Orange Book status of busulfan?

The commercial busulfan market is largely exposed to generic competition. The original patents and regulatory exclusivities associated with older oral and intravenous products are not the primary protection for current suppliers. FDA Orange Book listings should be reviewed product by product because patent listings, therapeutic equivalence codes, and marketing status can change over time.[3]

The practical Orange Book implications are:

• generic intravenous busulfan products can compete with the reference product;
• a new formulation may obtain separate listed patents if the claims cover the approved formulation, method of use, or delivery system;
• a formulation patent does not automatically prevent approval of a product that does not infringe the listed claims;
• a Paragraph IV certification could trigger Hatch-Waxman litigation if a generic applicant challenges an Orange Book-listed patent.

For an innovator, the most valuable patent position would combine formulation claims with approved labeling, creating a legally relevant connection between the claimed excipient system and the marketed product.

When does busulfan lose exclusivity?

Busulfan’s foundational exclusivity has already expired. The active commercial question is not loss of original exclusivity but whether a new formulation can obtain a defensible period of differentiated protection.

Potential exclusivity mechanisms include:

• five-year new chemical entity exclusivity, generally unavailable for a long-established active ingredient;
• three-year clinical-investigation exclusivity for a qualifying new indication, formulation, or dosage form;
• orphan-drug exclusivity if the product qualifies for an orphan indication and meets the statutory requirements;
• patent protection for formulation, manufacturing, delivery, or method-of-use claims;
• pediatric exclusivity when granted in connection with qualifying FDA requests.

Because busulfan is already established, a reformulated product would more likely depend on patents, three-year exclusivity, orphan designation, or commercial contracting than on new chemical entity exclusivity.[4]

Are Paragraph IV challenges and biosimilar risks material for busulfan?

Paragraph IV risk

Paragraph IV risk is structurally high for any new busulfan formulation that achieves commercial traction and carries listed patents. The active ingredient is old, generic manufacturing knowledge is extensive, and formulation differences can often be challenged using published solubility, solvent, stability, and parenteral dosage-form literature.

A generic challenger would likely target:

• obviousness of the excipient combination;
• lack of unexpected results;
• inadequate written description;
• lack of enablement across broad concentration ranges;
• non-infringement based on alternative solvents or packaging;
• invalidity of method-of-use claims.

Biosimilar risk

Biosimilar risk is not relevant. Busulfan is a chemically synthesized small molecule, not a biologic. Competition arises through generic and 505(b)(2) pathways rather than the biosimilar pathway.

Which companies are competing in busulfan?

The competitive field includes the originator or reference-product sponsor, generic injectable manufacturers, hospital suppliers, and specialty pharmaceutical companies serving transplant centers. Generic manufacturers may compete on price, supply reliability, vial configuration, and distributor access.

The most important competitive dimensions are:

1. availability during transplant surges and manufacturing disruptions;
2. concentration and vial size;
3. stability after dilution;
4. pharmacy preparation time;
5. product waste;
6. compatibility with closed-system transfer devices;
7. quality documentation and shortage performance;
8. ability to support pharmacokinetic dosing programs.

Because busulfan is used in a specialized hospital setting, a supplier with a modest market share can achieve strong strategic value if it becomes embedded in transplant-center protocols and pharmacy purchasing systems.

What licensing deals could create value for busulfan excipient technology?

A busulfan formulation developer could pursue several licensing structures:

Technology license to an injectable generic company

The developer contributes a solvent-reduced or ready-to-use formulation. The generic partner contributes manufacturing scale, ANDA or 505(b)(2) expertise, and hospital distribution.

Co-development with a transplant-focused specialty company

This structure is suited to products with pharmacokinetic-dosing support, pediatric positioning, or closed-system administration features.

Excipients and packaging partnership

A formulation company could license an excipient platform to a contract development and manufacturing organization. The package would include formulation know-how, analytical methods, and compatibility data.

Hospital-system or group-purchasing agreements

These agreements could support adoption where the product reduces pharmacy labor, hazardous-drug handling, or discarded drug volume. Such contracts are commercially important because busulfan purchasing is concentrated among transplant centers.

No single licensing model is inherently superior. The value depends on whether the formulation produces measurable savings or a regulatory distinction that generic suppliers cannot easily replicate.

How strong is the patent estate for a new busulfan formulation?

The patent estate for the legacy molecule is weak because the core patents are expired. A new formulation estate can be moderate if it has:

• a specific and non-obvious excipient ratio;
• comparative data against Busulfex or generic busulfan;
• superior dilution stability;
• reduced precipitation or adsorption;
• lower solvent exposure;
• a commercially meaningful ready-to-use presentation;
• manufacturing controls that limit toxic impurities;
• claims tied to an approved product and method of use.

The weakest strategy is a broad patent that merely substitutes one familiar parenteral cosolvent for another without unexpected results. The strongest strategy combines composition claims, process claims, packaging claims, and clinically relevant workflow claims.

What generic launch scenarios exist for busulfan?

Low-price generic substitution

This remains the baseline scenario for conventional vials. Competition is driven by manufacturing cost and supply reliability.

Ready-to-use product launch

A ready-to-use bag or prefilled presentation could command a premium if it reduces pharmacy manipulation and waste. The product would still face generic substitution unless patents or contracting protect adoption.

Pediatric and low-dose niche

A low-volume formulation could target pediatric transplant centers and patients requiring precise dose adjustment. This segment may support higher margins but has limited volume.

Solvent-reduced reformulation

A lower-dimethylacetamide product could achieve differentiation if safety, handling, and compatibility advantages are clinically documented. The principal risk is that the new system requires higher infusion volume or introduces a different tolerability problem.

Supply-security strategy

A manufacturer could win share through redundant API sourcing, domestic fill-finish, and reliable hospital allocation. For a mature transplant drug, supply continuity can be as commercially important as formulation innovation.

What is the commercial opportunity for busulfan excipients?

The largest opportunity is not a new excipient sold independently. It is an integrated product that uses excipients to reduce total treatment cost and preparation burden.

A commercially attractive target product would have:

• a lower-risk solvent profile;
• validated stability in standard infusion materials;
• minimal preparation steps;
• multiple dose sizes;
• low residual volume and low waste;
• compatibility with automated pharmacy systems;
• clear therapeutic drug monitoring support;
• patent claims covering composition and presentation.

The addressable market is specialized rather than mass-market. Revenue exposure is concentrated in transplant hospitals and specialty distributors. Public financial reporting generally does not isolate busulfan revenue from broader oncology or hospital portfolios, so product-level revenue comparisons should rely on prescription, contract, and institutional purchasing data rather than corporate segment disclosures.

Key Takeaways

• Busulfan is a mature genericized alkylating agent used mainly in hematopoietic stem-cell transplant conditioning.
• The approved intravenous formulation uses dimethylacetamide and polyethylene glycol 400 as cosolvents.
• The strongest excipient opportunity is a solvent-reduced, stable, ready-to-use intravenous formulation.
• Pediatric dosing, dilution stability, container compatibility, and hazardous-drug handling are commercially relevant differentiation points.
• Biosimilar competition does not apply because busulfan is a small molecule.
• Paragraph IV risk would be material for any successful reformulation with Orange Book-listed patents.
• A new busulfan product would likely rely on formulation patents, 505(b)(2) regulatory positioning, orphan or three-year exclusivity where available, and hospital contracting.
• The legacy patent estate is weak, but a data-supported formulation and packaging estate could achieve moderate protection.
• Commercial value is concentrated in workflow savings, supply reliability, and transplant-center adoption rather than broad outpatient volume.

FAQs about busulfan excipient commercialization

Can dimethylacetamide be removed from intravenous busulfan?

Potentially, but the replacement system must maintain busulfan solubility, dilution stability, infusion tolerability, and container compatibility at the required concentration.

Is polyethylene glycol 400 a sufficient differentiator for a busulfan patent?

Usually not by itself. Patent strength would depend on the specific concentration, combination, performance data, and unexpected technical effect.

Could a ready-to-use busulfan infusion receive FDA approval?

Yes. Depending on the formulation and clinical differences, the product could be developed through an ANDA, 505(b)(2) application, or a full NDA pathway.

Does busulfan qualify for orphan-drug exclusivity?

Busulfan may be evaluated for orphan designation in a qualifying rare disease or narrow indication, but designation and exclusivity require satisfaction of statutory and FDA requirements for the specific use.

What is the highest-value busulfan formulation opportunity?

A solvent-reduced, ready-to-administer intravenous product with validated stability, pediatric dose flexibility, closed-system compatibility, and a defensible patent package offers the strongest combined technical and commercial opportunity.

References

1. U.S. Food and Drug Administration. (2024). Busulfex (busulfan) injection prescribing information. FDA/DailyMed.

2. U.S. Food and Drug Administration. (2024). Drugs@FDA: FDA-approved drug products and labeling for busulfan. FDA.

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

4. U.S. Food and Drug Administration. (2024). Frequently asked questions on the Orange Book and drug exclusivity. FDA.

5. National Library of Medicine. (2024). Busulfan: Drug information and chemical data. PubChem.