List of Excipients in Branded Drug HUMULIN N

Company	Tradename	Ingredient	NDC	Excipient	Potential Generic Entry
Physicians Total Care Inc	HUMULIN N	insulin human	54868-1429	GLYCERIN
Physicians Total Care Inc	HUMULIN N	insulin human	54868-1429	HYDROCHLORIC ACID
Physicians Total Care Inc	HUMULIN N	insulin human	54868-1429	METACRESOL
Physicians Total Care Inc	HUMULIN N	insulin human	54868-1429	PHENOL
Physicians Total Care Inc	HUMULIN N	insulin human	54868-1429	PROTAMINE SULFATE
Physicians Total Care Inc	HUMULIN N	insulin human	54868-1429	SODIUM HYDROXIDE
Physicians Total Care Inc	HUMULIN N	insulin human	54868-1429	SODIUM PHOSPHATE, DIBASIC

HUMULIN N Excipient Strategy and Commercial Opportunities

Last updated: August 10, 2026

Humulin N is a recombinant human insulin isophane suspension, commonly called NPH insulin, marketed by Eli Lilly. Its commercial differentiation depends less on the insulin molecule, which is mature, and more on suspension stability, protamine complexation, preservative control, container compatibility, injection usability, and manufacturing consistency. The strongest excipient opportunities are therefore platform opportunities for NPH and other injectable suspensions rather than standalone opportunities tied to Humulin N.

What excipients are used in Humulin N?

Humulin N contains insulin human isophane and excipients that control suspension formation, tonicity, preservation, pH, and chemical stability.

Component	Functional role	Commercial relevance
Protamine sulfate	Complexes with insulin to create an intermediate-acting suspension	Core NPH performance attribute; major formulation constraint
Zinc oxide	Provides zinc ions that support insulin association and crystal or particle formation	Affects particle morphology, redispersibility, and release profile
Sodium phosphate dibasic	Buffering agent	Controls pH and formulation stability
Glycerin	Tonicity and formulation aid	Supports injection tolerability and physical stability
Phenol	Antimicrobial preservative	Important for multidose vial and pen presentations
Water for injection	Vehicle	Required for parenteral administration
Hydrochloric acid or sodium hydroxide	pH adjustment	Controls final formulation pH

The U.S. prescribing information identifies glycerin, protamine sulfate, phenol, sodium phosphate dibasic, zinc oxide, and water as inactive ingredients in Humulin N. The formulation pH is generally maintained near neutrality, within the range specified in the product labeling. [1]

Why protamine is commercially important

Protamine is the defining excipient in NPH insulin. It binds insulin and produces a depot after subcutaneous administration. The resulting absorption is slower than that of soluble human insulin but less prolonged than that of many modern basal insulin analogs.

Protamine creates several development constraints:

• Particle size must remain within a controlled distribution.
• The suspension must redisperse after storage.
• Shaking must not cause excessive foaming or aggregation.
• The formulation must deliver a consistent dose after resuspension.
• Protamine content must remain tightly controlled.
• Container surfaces must not selectively adsorb insulin or alter particle behavior.

A manufacturer that improves these attributes without materially changing the clinical profile could create value in manufacturing efficiency, device usability, or lifecycle management.

What formulation is protected by Humulin N?

The commercially relevant formulation is an aqueous suspension of recombinant human insulin complexed with protamine and associated with zinc. The product is supplied in vials and prefilled delivery systems, including KwikPen presentations in the U.S. market.

The formulation is designed to provide intermediate-duration insulin activity. Patients must resuspend the product before injection. The label instructs users to roll and invert the vial or pen until the suspension appears uniformly cloudy or milky. [1]

The main technical protection areas are:

1. Insulin-protamine complexation.
   The ratio, mixing conditions, and process sequence can affect particle formation and release.

2. Zinc-mediated association.
   Zinc concentration and local precipitation conditions influence insulin particle structure.

3. Suspension rheology.
   Viscosity and sedimentation behavior affect dose uniformity and ease of resuspension.

4. Preservative compatibility.
   Phenol must control microbial growth without materially increasing insulin degradation or causing unacceptable injection-site reactions.

5. Container closure and device compatibility.
   Vial glass, elastomer components, cartridge materials, and pen mechanisms can influence adsorption, extractables, dose delivery, and stability.

6. Manufacturing control.
   Insulin biosynthesis, purification, crystallization, aseptic filling, and suspension homogenization create process barriers even when composition is known.

When does Humulin N lose exclusivity?

Humulin N's principal product and formulation patents are understood to be long expired. The product was first approved in the 1980s, and the original composition and manufacturing patents would not provide meaningful current-term exclusivity in the United States.

The commercial protection profile is therefore based on:

• Manufacturing know-how.
• Regulatory approval history.
• Brand recognition.
• Supply reliability.
• Device presentation.
• Quality systems.
• Distribution contracts.
• Switching friction among patients and prescribers.

Humulin N does not have the exclusivity profile of a newly approved biologic. Traditional small-molecule patent analysis is also incomplete because insulin products are biologics and may be subject to the Biologics Price Competition and Innovation Act framework. FDA transitioned certain insulin products from the Federal Food, Drug, and Cosmetic Act to the Public Health Service Act on March 23, 2020. [2]

What is the FDA regulatory status of Humulin N?

Humulin N is an FDA-approved insulin human isophane product. It is indicated to improve glycemic control in adults and children with diabetes mellitus. [1]

Regulatory item	Status
Active ingredient	Insulin human isophane
Product type	Intermediate-acting recombinant human insulin suspension
U.S. sponsor	Eli Lilly and Company
U.S. route	Subcutaneous injection
Main presentations	Vials and prefilled pen systems
FDA regulatory framework	Biologic under the Public Health Service Act after the 2020 transition
Interchangeability status	No automatic interchangeability should be assumed without checking the current FDA designation
Orange Book relevance	Limited compared with conventional small-molecule products; biologic reference-product and biosimilar records are more relevant

The FDA Purple Book is the principal database for licensed biological products and biosimilar or interchangeable designations. [3] A product's presence in the Purple Book does not, by itself, resolve all formulation, device, manufacturing, or state substitution questions.

How many patents cover Humulin N?

No meaningful current U.S. patent estate can be identified from the mature product history alone. The commercially important patents associated with recombinant human insulin, NPH formulations, and related manufacturing methods were primarily filed decades ago and would generally have expired.

Current risk analysis should distinguish three categories:

Patent category	Relevance to Humulin N
Original insulin sequence or recombinant production patents	Generally expired or commercially weak for Humulin N
NPH composition patents	Generally mature and unlikely to block a conventional copy
Later device, cartridge, packaging, or process patents	May affect a particular presentation or manufacturing route

A competitor could still encounter active patents covering:

• A specific pen mechanism.
• Cartridge geometry.
• Needle shielding.
• Dose-setting systems.
• Container closure components.
• Automated manufacturing equipment.
• Novel suspension stabilization methods.
• Combination products involving monitoring or delivery software.

Those rights would not necessarily block a vial-based or independently designed presentation.

Are there Paragraph IV challenges to Humulin N?

Paragraph IV litigation is primarily associated with abbreviated new drug applications for small-molecule products under the Hatch-Waxman Act. Humulin N is a biologic product, so a conventional generic Paragraph IV pathway is not the central regulatory route.

A competing insulin product would more likely use:

• A biosimilar application under section 351(k) of the Public Health Service Act.
• A separate biologics license application under section 351(a).
• An applicable abbreviated pathway if FDA determines that the product falls within a different regulatory category.

The absence of a conventional Paragraph IV framework does not eliminate litigation risk. Disputes may instead involve patent lists, patent dance procedures, manufacturing patents, device patents, trade secrets, or state substitution rules under the biosimilar framework. [2,4]

What biosimilar and competitive risks exist for Humulin N?

Humulin N competes with other NPH insulin products, including Novolin N from Novo Nordisk. It also competes clinically with longer-acting basal insulin products such as insulin glargine, insulin detemir, and insulin degludec.

Product	Manufacturer	Insulin type	Commercial position
Humulin N	Eli Lilly	Human insulin isophane	Established NPH brand
Novolin N	Novo Nordisk	Human insulin isophane	Direct branded NPH competitor
Insulin glargine products	Multiple manufacturers	Long-acting insulin analog	Basal alternative with different dosing profile
Insulin degludec	Novo Nordisk	Ultra-long-acting insulin analog	Premium basal alternative
Follow-on and biosimilar insulin products	Multiple companies	Varies	Price and access pressure

The strongest direct competitive threat is price-based substitution between Humulin N and other NPH products. The broader threat is therapeutic migration toward long-acting analogs, which may offer more predictable pharmacokinetics or simpler dosing despite higher acquisition costs.

What commercial opportunities exist for Humulin N excipients?

1. Improved redispersibility

A supplier could develop excipient systems that reduce settling and shorten the time required to achieve uniform resuspension. The commercial value would be highest in:

• Prefilled pens.
• High-volume markets with limited cold-chain reliability.
• Patient populations with dexterity limitations.
• Formulations intended to reduce handling errors.

Any change would need to preserve the pharmacokinetic behavior of NPH insulin and demonstrate dose uniformity across the product shelf life.

2. Lower-preservative or alternative-preservative systems

Phenol is effective and established, but preservatives can create tolerability, extractables, and compatibility considerations. Potential opportunities include:

• Reduced phenol concentration.
• Alternative antimicrobial systems.
• Container systems that reduce microbial ingress.
• Single-dose or lower-use-volume presentations.

The opportunity is constrained by the need to demonstrate antimicrobial effectiveness, sterility assurance, chemical stability, and device compatibility.

3. Protamine alternatives

Protamine replacement is technically difficult because it is central to NPH pharmacology. Potential development areas include:

• Recombinant protamine.
• More consistent protamine fractions.
• Synthetic polyelectrolytes that create a comparable insulin depot.
• Modified protein or peptide complexing agents.

A true replacement would likely alter the product's clinical and regulatory profile. It would require extensive comparability and pharmacokinetic evaluation rather than a simple excipient substitution.

4. Zinc and particle-engineering systems

Zinc source, concentration, and processing conditions can affect insulin particle formation. Commercial opportunities include:

• Tighter particle-size control.
• Reduced aggregation.
• Improved storage stability.
• More reproducible release after injection.
• Lower batch-to-batch variability.

These opportunities may be protectable through process patents, particle specifications, formulation ranges, or manufacturing know-how.

5. Container and device compatibility

Excipient suppliers can create value without changing the formulation by improving the primary container system. Relevant areas include:

• Low-adsorption cartridge materials.
• Elastomer closures with lower extractables.
• Improved suspension visibility.
• Reduced residual volume.
• More reliable pen dose delivery.
• Materials compatible with phenol-containing insulin suspensions.

Device-related improvements may be commercially stronger than composition changes because they can improve adherence and reduce administration errors while preserving the established formulation.

What manufacturing and intellectual-property barriers affect market entry?

A conventional NPH formulation is difficult to block through expired composition patents, but it remains difficult to manufacture consistently. Key barriers include:

• Recombinant insulin production at commercial scale.
• Removal of host-cell proteins and process impurities.
• Correct folding and disulfide-bond formation.
• Control of desamido and other degradation products.
• Protamine-insulin particle engineering.
• Aseptic processing.
• Long-term stability testing.
• Device filling and dose accuracy.
• Validation of cold-chain handling.
• Demonstration of comparable clinical performance.

Trade secrets may be more important than patents. A competitor may be able to reproduce the listed ingredients yet fail to match sedimentation, redispersibility, particle morphology, impurity profile, or dose uniformity.

Which companies are challenging the Humulin N market?

Eli Lilly and Novo Nordisk are the principal branded human-insulin competitors. The market also includes biosimilar, follow-on, contract manufacturing, and regional insulin producers.

The competitive landscape is shaped by:

• Government reimbursement and tender systems.
• Reliance on vial versus pen presentations.
• Access to insulin manufacturing capacity.
• Biosimilar or follow-on approval requirements.
• Device ownership and licensing.
• Regional procurement contracts.
• Insulin affordability initiatives.

In the United States, the commercial opportunity is more likely to involve lower-cost supply, authorized or follow-on biologic strategies, and manufacturing partnerships than a new conventional NPH composition.

What licensing opportunities exist around Humulin N?

Potential licensing targets include:

• Insulin manufacturing platforms.
• Recombinant protamine technology.
• Suspension stabilization systems.
• Pen and cartridge technologies.
• Low-adsorption packaging.
• Cold-chain stabilization.
• Digital dose-tracking systems.
• Regional distribution rights.
• Contract fill-finish capacity.

A licensing transaction centered only on the known Humulin N excipient formula would have limited defensibility because the formulation is mature. Stronger deal value would require one or more of the following:

1. An active patent family with meaningful remaining term.
2. Demonstrated manufacturing-cost reduction.
3. Improved device usability.
4. A regulatory pathway with lower development risk.
5. Access to constrained production capacity.
6. Documented improvement in stability or dose uniformity.

How strong is the Humulin N patent estate?

The legacy patent estate is weak as a current exclusivity barrier. The product's stronger assets are operational:

• Established regulatory status.
• Large-scale manufacturing capability.
• Quality history.
• Brand recognition.
• Distribution reach.
• Physician and patient familiarity.
• Device integration.

For a competitor, the principal risk is not a conventional composition patent. It is the combined cost and complexity of establishing a compliant insulin manufacturing platform and obtaining regulatory acceptance for a suspension with reliable clinical performance.

What generic launch scenarios exist for Humulin N?

Three launch scenarios are commercially plausible.

Low-cost NPH biologic entrant

A manufacturer launches a vial-based human insulin isophane product with a lower price. This approach has the lowest device complexity but remains dependent on manufacturing scale and payer access.

Follow-on product with pen presentation

A competitor offers a pen or cartridge system designed to match or improve Humulin N usability. Device patents, human-factors testing, and combination-product requirements increase development cost.

Premium improved-suspension product

A company develops a formulation with improved redispersibility, storage robustness, or reduced handling burden. This product may support differentiated pricing but would require stronger clinical and regulatory evidence.

Key Takeaways

• Humulin N is a mature NPH insulin product whose principal formulation patents are generally expired.
• Protamine sulfate and zinc oxide are the central excipient drivers of its intermediate-acting suspension.
• Phenol, glycerin, phosphate buffer, and container materials support preservation, tonicity, pH control, and stability.
• Conventional Paragraph IV analysis is less relevant because Humulin N is regulated as a biologic.
• Biosimilar, follow-on biologic, manufacturing, device, and trade-secret issues are more important entry considerations.
• The strongest commercial opportunities involve redispersibility, container compatibility, pen delivery, stability, manufacturing yield, and lower-cost supply.
• A new Humulin N-like composition would have limited patent value unless paired with active process, device, or formulation claims.
• Competitive pressure comes from Novolin N, follow-on insulin products, and migration to long-acting insulin analogs.

FAQs

Can an excipient change create a new Humulin N patent?

Yes. A new excipient system could support patent claims if it produces a novel and non-obvious formulation, stability profile, particle structure, or delivery result. A routine substitution of glycerin, buffer, or preservative would face a weaker patent position.

Is protamine sulfate the main barrier to copying Humulin N?

Protamine is a major technical barrier because it determines insulin complexation and release. The broader barrier is the integrated process covering recombinant insulin quality, particle engineering, aseptic filling, stability, and dose uniformity.

Can Humulin N be sold in a preservative-free presentation?

A preservative-free presentation may be possible in a single-dose container, but multidose vial or pen products require a microbial-control strategy. The change would require validation of sterility, in-use stability, container closure integrity, and usability.

Does Humulin N have an automatic generic substitution pathway?

No automatic generic substitution should be assumed. The applicable substitution rules depend on the product's FDA designation, biosimilar or interchangeable status, state law, and payer policy.

Which excipient opportunity has the highest commercial potential?

Improved suspension and delivery-system performance has the strongest potential. Redispersibility, dose consistency, cartridge compatibility, and reduced handling burden can create value without relying on a new insulin molecule.

References

1. Eli Lilly and Company. (2024). Humulin N prescribing information. U.S. Food and Drug Administration.

2. U.S. Food and Drug Administration. (2020). Transition plan for insulin and other biological products regulated under the Federal Food, Drug, and Cosmetic Act. FDA.

3. U.S. Food and Drug Administration. (2024). Purple Book: Database of licensed biological products. FDA.

4. U.S. Food and Drug Administration. (2024). Biosimilar and interchangeable biosimilar products. FDA.