List of Excipients in Branded Drug HUMULIN

Company	Tradename	Ingredient	NDC	Excipient	Potential Generic Entry
A-S Medication Solutions	HUMULIN	insulin human	50090-0352	GLYCERIN
A-S Medication Solutions	HUMULIN	insulin human	50090-0352	HYDROCHLORIC ACID
A-S Medication Solutions	HUMULIN	insulin human	50090-0352	METACRESOL
A-S Medication Solutions	HUMULIN	insulin human	50090-0352	PHENOL

Humulin Excipient Strategy and Commercial Opportunities in Human Insulin Formulations

Last updated: September 24, 2026

Humulin is Eli Lilly’s human insulin portfolio, including regular insulin, NPH insulin, premixed 70/30 insulin and concentrated U-500 regular insulin. Its excipient strategy is built around chemical stability, zinc-mediated insulin association, antimicrobial preservation, suspension control and, for NPH products, protamine-based intermediate action. Commercial opportunities are strongest in preservative systems, low-volume concentrated delivery, excipient-quality supply, insulin-device compatibility and follow-on insulin formulations.

What products and formulations does Humulin include?

Humulin products use recombinant human insulin and differ mainly by insulin concentration, crystallization state, protamine content, zinc content, preservatives and delivery format.

Product	Insulin type	Concentrations	Principal formulation function
Humulin R	Regular human insulin	U-100, U-500	Shorter-acting soluble insulin
Humulin N	NPH human insulin	U-100	Intermediate-acting protamine suspension
Humulin 70/30	70% NPH and 30% regular human insulin	U-100	Premixed intermediate and short-acting insulin
Humulin R U-500	Regular human insulin	U-500	High-concentration insulin for patients requiring large daily doses

Humulin R U-500 contains five times the insulin concentration of U-100 regular insulin. The concentration reduces injection volume for patients with severe insulin resistance but increases the commercial importance of dose-conversion controls, pen design, syringe compatibility and medication-error mitigation.[1]

What excipients are used in Humulin?

The principal excipients and formulation aids reported in U.S. prescribing information include:

Excipient or formulation component	Primary function in Humulin formulations
Metacresol	Antimicrobial preservative and formulation stabilizer
Phenol	Preservative, particularly in selected concentrated or premixed formulations
Glycerin	Tonicity and solvent adjustment
Zinc oxide	Promotes insulin association and helps control pharmacokinetic release
Dibasic sodium phosphate	Buffering and pH control
Protamine sulfate	Forms the NPH insulin complex and slows absorption
Hydrochloric acid and sodium hydroxide	pH adjustment
Water for injection	Vehicle

The exact composition differs by product, concentration and presentation. Product-specific labeling controls the authoritative excipient list.[1-4]

How does Humulin’s excipient strategy work?

Humulin’s formulation platform uses excipients to manage four technical requirements: insulin stability, physical state, absorption rate and multidose-container microbiological protection.

Zinc and insulin association

Zinc promotes association of insulin molecules into larger assemblies. In soluble regular insulin, zinc contributes to formulation stability and influences dissociation after subcutaneous injection. In NPH insulin, zinc works with protamine to create a suspension with delayed absorption.

This gives zinc salts commercial importance beyond simple mineral content. Suppliers must meet pharmaceutical-grade purity requirements, control trace metals and demonstrate lot-to-lot consistency. Zinc oxide also must remain compatible with pH adjustment, container materials and long-term storage conditions.

Protamine and NPH release control

Protamine sulfate is the defining excipient for NPH insulin. It binds insulin and produces a suspension that is absorbed more slowly than soluble regular insulin. The commercial value of protamine is tied to particle-size control, suspension uniformity, resuspendability and reproducible pharmacokinetics.

Protamine creates manufacturing and quality-control burdens. NPH suspensions require controlled mixing, settling studies, agitation instructions and container-performance testing. Variability in protamine characteristics can affect particle formation and dose uniformity.

Metacresol and phenol preservation

Multidose insulin vials and pens require antimicrobial protection after repeated access. Metacresol is a central preservative in Humulin products. Phenol is present in certain formulations and can contribute to both preservation and insulin self-association.

Preservative selection affects:

• Antimicrobial effectiveness
• Injection-site tolerability
• Container-closure compatibility
• Extractables and leachables
• Protein aggregation
• Long-term stability
• Device priming and residual-volume behavior

Preservative concentration is therefore part of the product’s critical quality profile. A replacement preservative cannot be treated as a simple substitution because changes may alter insulin aggregation, adsorption to surfaces or immunogenicity risk.

Glycerin and tonicity

Glycerin supports tonicity and contributes to the physicochemical environment of the insulin solution. Tonicity adjustment must be balanced against viscosity, injection force, device performance and patient tolerability.

For concentrated U-500 products, the excipient environment has greater commercial relevance because a smaller injection volume contains a larger insulin dose. Any change in viscosity or surface tension can affect pen delivery, needle performance and dose accuracy.

What excipient opportunities exist for Humulin and follow-on insulin products?

The most credible opportunities are specialized rather than broad-volume commodity substitution.

High-purity zinc systems

Pharmaceutical zinc suppliers can compete on:

• Low trace-metal burden
• Tight particle-size distribution
• Low endotoxin profile
• Consistent dissolution behavior
• Compatibility with insulin aggregation
• Supply resilience across manufacturing sites

A supplier that can support insulin-specific quality-by-design packages may gain an advantage over a general pharmaceutical mineral supplier.

Protamine sulfate optimization

Protamine is a higher-value opportunity because NPH and premixed insulin depend on its release-control function. Potential development areas include:

• Tighter molecular-weight distribution
• Improved suspension uniformity
• Reduced aggregation
• Better resuspendability
• Lower bioburden and endotoxin
• More consistent insulin-protamine complexation

A new protamine source would face significant comparability requirements. Demonstrating chemical equivalence alone would not establish equivalent insulin release behavior.

Preservative systems with improved tolerability

Metacresol and phenol are established excipients, but alternative antimicrobial systems could support differentiated products if they maintain insulin stability and meet parenteral safety requirements.

Potential commercial claims could involve:

• Lower preservative exposure per dose
• Better tolerability in high-frequency use
• Reduced container interaction
• Improved compatibility with prefilled pens
• Longer in-use stability

These opportunities are technically difficult because the preservative can influence the protein product itself. A formulation change would likely require extensive stability, immunogenicity, device and clinical comparability data.

Low-volume and high-concentration insulin

Humulin R U-500 demonstrates the commercial value of concentration as a formulation strategy. Additional opportunities may involve:

• Higher-concentration human insulin
• Concentrated premixes
• Large-dose delivery systems
• Pen platforms with enhanced dose safeguards
• Insulin formulations optimized for patients with severe insulin resistance

The opportunity is linked to device engineering. Concentration alone has limited value if the delivery system does not prevent dosing errors or support accurate administration.

What FDA regulatory issues affect Humulin excipient changes?

Humulin is an insulin biologic subject to biologics regulation. FDA moved insulin products from the Federal Food, Drug, and Cosmetic Act drug framework to the Public Health Service Act biologics framework on March 23, 2020.[5]

FDA pathways for follow-on insulin

A follow-on insulin sponsor may pursue:

1. A 351(a) biologics license application for a new insulin product.
2. A 351(k) biosimilar or interchangeable biosimilar application referencing an approved insulin.
3. A formulation or device change through a supplement if the sponsor owns the underlying product license.

Excipient changes can affect the level of evidence required. A minor manufacturing adjustment may be handled through comparability data, while a new preservative, protamine source or release-control system may require broader analytical and clinical support.

What does interchangeability mean for insulin?

Interchangeability is a regulatory designation under the biosimilar pathway. It concerns substitution at the pharmacy level under applicable law and does not mean that every formulation or delivery system is identical.

For insulin, the assessment may include:

• Primary structure
• Higher-order structure
• Aggregation
• Potency
• Receptor binding
• Impurity profile
• Immunogenicity
• Pharmacokinetic and pharmacodynamic similarity
• Device performance where relevant

An excipient strategy that changes absorption or stability can create a larger comparability burden than a change limited to packaging materials.

What is the Orange Book and Purple Book status of Humulin?

Humulin’s current regulatory position should be analyzed through biologic reference-product and Purple Book concepts rather than treating the portfolio like a conventional small-molecule drug listed solely through Orange Book patents.

The FDA’s Purple Book identifies licensed biological products and reference-product relationships. Insulin products approved under the biologics framework may be relevant to biosimilar and interchangeable-biosimilar competition.[6]

Patent protection is only one part of Humulin’s exclusivity profile. Relevant barriers may include:

• Biologic regulatory exclusivity
• Manufacturing know-how
• Formulation process controls
• Device and combination-product claims
• Trademark and brand recognition
• Distribution scale
• Insulin supply reliability
• Clinical interchangeability data
• Contracting and formulary access

Publicly available product labeling does not establish a complete current patent estate for every Humulin presentation. A definitive patent-by-patent freedom-to-operate analysis requires a current review of FDA listings, USPTO records, court dockets and applicable patent assignments.

How strong is the patent estate for Humulin excipients and formulations?

The commercial defensibility of Humulin is likely stronger in manufacturing and product-system know-how than in basic excipient composition claims.

Formulation patents

Potential claim categories include:

• Defined insulin-to-zinc ratios
• Protamine-insulin particle characteristics
• Preservative concentrations
• pH and buffer ranges
• Concentrated insulin formulations
• Stability profiles
• Suspension behavior
• Container-closure systems
• Prefilled pen assemblies

Older human-insulin formulation claims may face expiration or validity challenges. Later patents covering delivery devices, manufacturing controls, concentrated presentations or specific formulation improvements can remain commercially relevant even when foundational insulin patents are no longer enforceable.

Manufacturing and trade-secret barriers

Insulin manufacturing is difficult to replicate at commercial scale. Barriers include:

• Recombinant expression and precursor processing
• Folding and disulfide-bond control
• Removal of host-cell impurities
• Zinc and protamine complexation
• Sterile filtration and filling
• Suspension uniformity
• In-use stability
• Pen and vial compatibility

These capabilities can protect market position even where composition-of-matter patent protection is limited.

Which companies challenge Humulin and the human-insulin market?

Competition comes from several categories rather than a single direct generic substitute.

Competitive category	Examples	Commercial effect
Other human insulin products	Novo Nordisk human insulin products	Direct competition in regular, NPH and premix segments
Insulin analogs	Insulin lispro, aspart, glargine, detemir and degludec	Compete on convenience, timing and glycemic control
Biosimilar insulin	Insulin glargine biosimilars such as Semglee and Rezvoglar	Establish biosimilar substitution and pricing pressure
Authorized or unbranded insulin	Lilly and other manufacturer channels	Reduces brand-price separation
Delivery devices	Disposable pens, reusable pens, pumps and syringes	Shifts value from molecule to administration system

Semglee became the first interchangeable biosimilar insulin product designated by FDA in 2021.[7] Rezvoglar later received interchangeable biosimilar approval for insulin glargine.[8] These products do not directly establish biosimilarity to Humulin because insulin glargine is a different insulin molecule from human insulin, but they increase competitive pressure on insulin pricing and payer expectations.

What generic entry risks exist for Humulin?

The main entry risks are price erosion, formulary substitution, unbranded product expansion and device-enabled switching.

Generic and biosimilar launch scenarios

Scenario	Likely commercial consequence
Follow-on U-100 regular insulin	Pressure on vial and pen pricing
Follow-on NPH insulin	Competition based on price and supply reliability
Follow-on 70/30 insulin	Contracting pressure in premix channels
Follow-on U-500 insulin	Higher regulatory and device-safety burden, but greater value per patient
Unbranded Humulin-equivalent supply	Brand-price erosion without full therapeutic displacement
New concentrated human insulin	Potential niche competition in severe insulin resistance

U-500 has higher switching friction because dosing errors can cause severe hypoglycemia. A competing product would need a clear presentation, compatible delivery device and strong pharmacy communication. That raises launch costs but also creates a barrier against casual substitution.

What licensing and partnering opportunities exist?

Publicly disclosed Humulin-specific excipient licensing arrangements are not established by the product labels cited here. Commercial opportunities are more likely to arise through supplier, contract-development and device partnerships.

Potential transaction structures include:

• Exclusive supply of pharmaceutical-grade protamine
• Dual-source zinc or preservative agreements
• Co-development of concentrated insulin devices
• Licensing of suspension-control technology
• Contract manufacturing of follow-on human insulin
• Regional rights for biosimilar or interchangeable insulin products
• Excipient platform licensing for multidose protein injectables

The strongest assets would combine an excipient with validated insulin compatibility, scalable supply and regulatory documentation. A commodity excipient without insulin-specific data would have limited negotiating leverage.

How does Humulin compare with insulin analog products?

Humulin is generally differentiated by established human-insulin chemistry, broad clinical familiarity and lower-cost positioning. Analog products compete through pharmacokinetic convenience.

Attribute	Humulin human insulin	Rapid- or long-acting insulin analog
Molecular basis	Recombinant human insulin	Modified insulin sequence
Excipient role	Controls preservation, association and suspension	Same functions, often with different formulation requirements
Main differentiation	Cost, familiarity and established presentations	Timing, duration and dosing convenience
Key formulation opportunity	Protamine, concentration and preservation	Stabilization, absorption control and device delivery
Substitution risk	Price-driven and channel-driven	More dependent on clinical and formulary positioning

Excipient suppliers should therefore assess Humulin against both human-insulin competitors and analog products. A technology that improves multidose stability or concentrated delivery may have application across both categories.

Key Takeaways

• Humulin’s principal excipient system uses metacresol, phenol in selected products, glycerin, zinc, phosphate buffer, water and pH adjusters.
• Protamine sulfate is the critical release-control excipient for Humulin N and Humulin 70/30.
• Humulin R U-500 creates the clearest commercial opportunity for concentrated insulin delivery, dose safety and device integration.
• Excipient substitution is difficult because changes can alter aggregation, suspension behavior, pharmacokinetics, immunogenicity and device performance.
• FDA insulin competition is increasingly shaped by the 351(k) biosimilar pathway, although current biosimilar approvals have focused on insulin analogs rather than direct Humulin equivalents.
• Manufacturing know-how, supply reliability and device integration may provide stronger commercial barriers than legacy composition patents.
• The most attractive partnering targets are insulin-qualified protamine, high-purity zinc systems, preservative alternatives and concentrated-delivery technologies.

FAQs

Can metacresol be removed from Humulin formulations?

Removal may be possible only after demonstrating antimicrobial protection, insulin stability, container compatibility, in-use performance and product quality through an appropriate FDA regulatory pathway.

Why is protamine commercially important in NPH insulin?

Protamine binds insulin and creates the suspension responsible for delayed absorption. Its quality can affect particle formation, resuspendability and release consistency.

Does Humulin R U-500 have the same excipient strategy as U-100 regular insulin?

The products share core formulation concepts, but concentration, preservative content, device presentation and injection-volume requirements can differ. Product-specific labeling controls the comparison.

Are insulin excipients eligible for separate patent protection?

Yes. Patents may cover excipient ratios, pH ranges, insulin complexes, release characteristics, concentrated formulations, manufacturing processes or delivery devices. Patentability and enforceability depend on the specific claims and prior art.

Does an insulin biosimilar automatically compete with Humulin?

No. Biosimilarity is product-specific. An insulin glargine biosimilar competes with insulin glargine reference products, not automatically with recombinant human insulin products such as Humulin.

References

1. Eli Lilly and Company. (2024). Humulin R U-100 prescribing information. U.S. Food and Drug Administration.
2. Eli Lilly and Company. (2024). Humulin N prescribing information. U.S. Food and Drug Administration.
3. Eli Lilly and Company. (2024). Humulin 70/30 prescribing information. U.S. Food and Drug Administration.
4. Eli Lilly and Company. (2024). Humulin R U-500 prescribing information. U.S. Food and Drug Administration.
5. U.S. Food and Drug Administration. (2020). Insulin products and the transition of insulin products under the Federal Food, Drug, and Cosmetic Act.
6. U.S. Food and Drug Administration. (2024). Purple Book: Database of licensed biological products.
7. U.S. Food and Drug Administration. (2021). FDA approves first interchangeable biosimilar insulin product.
8. U.S. Food and Drug Administration. (2022). FDA approves interchangeable biosimilar insulin glargine product.