List of Excipients in Branded Drug KIRSTY

KIRSTY Excipient Strategy and Commercial Opportunities for Insulin Aspart-szjj

Last updated: August 9, 2026

KIRSTY is a rapid-acting insulin aspart biosimilar developed for the NovoLog/NovoRapid reference-product market. Its commercial value depends less on novel excipient chemistry than on reliable formulation equivalence, low-cost manufacturing, device compatibility, supply security and payer access. The strongest opportunities are U.S. biosimilar substitution, lower-cost vials and pens, insulin-pump supply, and differentiated delivery devices.

What is KIRSTY and what excipients does it contain?

KIRSTY is insulin aspart-szjj, a recombinant rapid-acting insulin approved by the FDA as a biosimilar to NovoLog, insulin aspart [1]. It is supplied at 100 units/mL and uses an aqueous, preserved insulin formulation comparable to the reference product.

The disclosed formulation uses the following functional excipient categories:

Component	Primary formulation function
Glycerol	Tonicity adjustment and protein-stabilizing effect
Phenol	Antimicrobial preservative and hexamer-state support
Metacresol	Antimicrobial preservative and insulin stabilization
Zinc	Supports insulin hexamer formation and structural stability
Disodium phosphate dihydrate	Buffering capacity
Sodium chloride	Tonicity control
Hydrochloric acid or sodium hydroxide	pH adjustment
Water for injection	Vehicle

The target formulation is an isotonic, buffered solution with a mildly acidic-to-neutral pH range appropriate for subcutaneous administration. The composition is materially aligned with established insulin aspart formulations, reducing formulation-related regulatory risk [1,2].

Why the excipient profile matters

The excipients are not interchangeable from a commercial or regulatory perspective. Small changes in preservative concentration, zinc content, buffer strength, pH or osmolality can affect:

• Insulin self-association and dissociation.
• Chemical degradation and aggregation.
• Adsorption to vial, cartridge or pump surfaces.
• Delivered dose accuracy.
• Injection-site tolerability.
• Compatibility with infusion sets.
• In-use stability after opening.
• Comparability against the reference product.

For a biosimilar, an excipient change can create a new analytical and clinical comparability burden. The most efficient strategy is therefore to preserve the reference-product excipient architecture unless a clear commercial or technical benefit justifies reformulation.

How does KIRSTY’s formulation compare with NovoLog?

KIRSTY’s commercial positioning benefits from a formulation that remains close to NovoLog in composition and use conditions. NovoLog contains insulin aspart with glycerin, phenol, metacresol, zinc, disodium phosphate, sodium chloride and water, with pH adjustment as needed [2].

Formulation attribute	KIRSTY	NovoLog
Active ingredient	Insulin aspart-szjj	Insulin aspart
Strength	100 units/mL	100 units/mL
Dosage form	Injectable solution	Injectable solution
Preservative system	Phenol and metacresol	Phenol and metacresol
Zinc system	Zinc-containing formulation	Zinc-containing formulation
Buffer	Phosphate-based	Phosphate-based
Tonicity components	Glycerol and sodium chloride	Glycerin and sodium chloride
Administration	Subcutaneous injection; use depends on approved presentation	Subcutaneous injection, insulin pump and intravenous use under labeled conditions
Regulatory relationship	Biosimilar to NovoLog	Reference product

KIRSTY’s closest commercial advantage is formulation familiarity. Pharmacists, prescribers and patients can transition more easily when concentration, excipient classes, administration timing and device presentation resemble the incumbent product.

The main limitation is the lack of a strong formulation differentiation story. A near-reference formulation supports biosimilar approval but does not, by itself, create premium pricing or durable market exclusivity.

What excipient strategy is optimal for KIRSTY?

The optimal strategy has two layers: preserve the approved core formulation for biosimilar substitution, then develop separate lifecycle products where excipient changes create measurable clinical or operational value.

1. Preserve the core formulation

The commercial base product should maintain:

• 100 units/mL concentration.
• Reference-like preservative levels.
• Comparable pH and osmolality.
• Comparable zinc and phosphate systems.
• Low visible and subvisible particulate burden.
• Comparable extractables and leachables profile.
• Stability across pens, cartridges, vials and infusion containers.

This approach minimizes regulatory friction and supports substitution under the FDA biosimilar pathway. It also reduces the risk that a new excipient profile will require additional immunogenicity, local tolerability or device-compatibility work.

2. Optimize preservative performance without changing the label profile

Phenol and metacresol are central to multidose insulin products. They provide antimicrobial protection and influence the equilibrium between insulin monomers, dimers and hexamers.

Potential development work includes:

• Improving preservative retention during repeated pen use.
• Reducing preservative adsorption to delivery components.
• Controlling preservative migration into elastomeric closures.
• Demonstrating stability after repeated temperature excursions.
• Evaluating preservative exposure in pump reservoirs and infusion sets.

A lower-preservative or preservative-free presentation could address injection-site sensitivity and selected pediatric or intensive-use segments. It would also create a separate product-development program because multidose microbial protection, in-use stability and container closure requirements would change.

3. Evaluate alternative stabilizers only in differentiated products

Potential alternatives include amino acids, polyols, surfactants and other protein-stabilizing excipients. These may reduce aggregation or adsorption, but they can also alter:

• Immunogenicity risk.
• Injection-site tolerability.
• Pump compatibility.
• Analytical similarity.
• Device-material interactions.
• Regulatory comparability.

A new stabilizer is more commercially defensible in a next-generation product than in the base biosimilar. Examples include a pump-optimized insulin aspart formulation, a high-concentration product or a longer in-use-life presentation.

4. Develop concentration and device-specific formulations

A 200 units/mL presentation could target patients with high daily insulin requirements and reduce injection volume. The commercial rationale is strong for:

• Patients requiring more than 80 to 100 units per day.
• Insulin resistance populations.
• Fewer pen changes.
• Lower shipping and storage volume.
• Improved adherence through reduced injection burden.

The principal risks are dosing errors, pen-device incompatibility and confusion between concentrations. A U-200 product requires a dedicated device, clear labeling and human-factors validation. It should not be treated as a simple line extension of the U-100 product.

What formulations are protected by KIRSTY-related intellectual property?

The main intellectual-property opportunities are likely to arise from formulation, device, manufacturing and use claims rather than from the basic insulin aspart molecule.

IP category	Potential claim focus	Commercial value
Formulation	Specific excipient ratios, pH, zinc level, preservative concentration or stability profile	Moderate
High-concentration product	U-200 formulation and dedicated delivery system	High
Pump formulation	Reservoir stability, adsorption control and infusion-set compatibility	High
Device	Pen, cartridge, dose-setting mechanism or safety features	High
Manufacturing	Cell culture, purification, crystallization, refolding or impurity-control process	High
Packaging	Container closure, cartridge materials and extractables control	Moderate
Method of use	Dosing timing, pump use or patient-specific administration	Low to moderate
Combination product	Connected pen, dosing software or glucose-monitoring integration	Moderate to high

The core formulation may be difficult to protect broadly because the excipient classes are established in rapid-acting insulin products. Stronger patent positions generally require a defined technical effect, such as improved stability, reduced adsorption, extended in-use life or superior delivery performance.

Does KIRSTY have Orange Book-listed patents?

KIRSTY is a biologic rather than a conventional small-molecule drug. The FDA’s Purple Book is the principal reference for biosimilar and interchangeable-biologic status; the Orange Book is primarily used for approved drug products and related patent/exclusivity information [3,4].

The practical consequence is that KIRSTY’s competitive analysis should focus on:

• Reference-product patent and regulatory exclusivity history.
• Purple Book status.
• Biosimilar approval timing.
• Device and combination-product patents.
• Manufacturing trade secrets.
• Contract-manufacturing capacity.
• State substitution rules.
• Private payer and pharmacy-benefit-manager contracting.

A conventional Orange Book Paragraph IV framework is not the central route for challenging KIRSTY or the reference insulin aspart product. Biosimilar competition is governed principally by the Biologics Price Competition and Innovation Act, FDA approval requirements and the patent-resolution process commonly known as the patent dance [5].

When does KIRSTY lose exclusivity and when can competitors enter?

KIRSTY’s market protection is based on biologic regulatory exclusivity, patents and commercial execution rather than a single small-molecule exclusivity date.

Protection mechanism	Relevance to KIRSTY
Reference-product biologic exclusivity	Limits biosimilar approval timing for the reference product, not necessarily competition against KIRSTY
KIRSTY product patents	May protect formulation, process, device or combination-product features
Manufacturing know-how	Can delay technically credible competition even without broad patents
Device patents	May protect pens, cartridges and connected delivery systems
Contracting arrangements	Can create practical market barriers after regulatory entry
Interchangeability designation, if applicable	Could affect pharmacy-level substitution and payer adoption

Competitors can seek approval through the biosimilar pathway once applicable statutory and regulatory conditions are met. The practical launch date will depend on patent settlements, litigation outcomes, manufacturing readiness, FDA review and commercial contracting.

KIRSTY faces two distinct competitive threats:

1. Direct biosimilar insulin aspart products.
2. Therapeutic substitution from insulin lispro, insulin glulisine and lower-priced human regular insulin.

The second threat is commercially important because payers may prefer a broader rapid-acting insulin formulary strategy rather than maintaining separate preferred products for each insulin analogue.

What Paragraph IV and litigation risks affect KIRSTY?

Paragraph IV litigation is more relevant to small-molecule drug applications than to biologic biosimilar applications. KIRSTY’s relevant legal risks include:

• Patent litigation involving insulin aspart processes.
• Device patent disputes involving pens or cartridges.
• Manufacturing-process claims.
• Trade-secret disputes.
• Patent infringement claims based on high-concentration formulations.
• Contract disputes involving regional commercialization rights.
• Substitution disputes involving pharmacy and state-law implementation.

A biosimilar company can reduce litigation exposure by separating the base U-100 product from later device or concentration innovations. Filing a differentiated formulation under a separate regulatory strategy can prevent a patent dispute over a lifecycle product from disrupting the core biosimilar launch.

Settlement agreements may also shape market entry. Possible terms include:

• Agreed launch dates.
• No-admission provisions.
• Geographic restrictions.
• Royalty-bearing licenses.
• Device carve-outs.
• Restrictions on interchangeable substitution.
• Separate treatment of vials, pens and pump products.

Publicly available information should be evaluated by product presentation because a settlement covering a pen device may not block a vial launch.

What commercial opportunities exist for KIRSTY?

Low-cost U-100 vials

Vials have lower device costs and can appeal to:

• Hospitals.
• Public-health programs.
• Institutional pharmacies.
• Cost-sensitive patients.
• Markets with limited pen penetration.

A vial strategy supports rapid volume acquisition but typically generates lower unit economics. It can also create supply-contract opportunities with hospitals and government purchasers.

Prefilled pens and cartridges

Pens offer stronger patient convenience and may command better net pricing. The key commercial requirements are:

• Reliable dose accuracy.
• Simple priming and injection steps.
• Low residual volume.
• Compatibility with existing pen needles.
• Comparable storage and in-use conditions.
• Clear differentiation from the reference pen.

Device usability can influence substitution even when the active ingredient and excipients are equivalent.

Insulin-pump supply

Pump use is a major opportunity, but it has higher technical and regulatory requirements. The formulation must be assessed for:

• Reservoir stability.
• Tubing adsorption.
• Occlusion risk.
• Temperature exposure.
• Aggregation during extended use.
• Compatibility with specific infusion sets.
• Delivery accuracy over the labeled wear period.

A pump-specific label or compatibility claim could create meaningful differentiation. It would also require targeted product-performance evidence and device testing.

High-concentration insulin aspart

A U-200 product could support premium positioning while lowering injection volume. The commercial opportunity is strongest in patients with high total daily insulin requirements. The main barriers are device development, dosing safety and payer willingness to reimburse a differentiated presentation.

Connected delivery systems

KIRSTY could be paired with:

• Smart insulin pens.
• Dose-capture systems.
• Diabetes-management applications.
• Continuous glucose-monitoring platforms.
• Adherence and refill services.

The value would come from integrated data and adherence support rather than from the excipient profile. Combination-product patents and software rights could create a stronger defensive position than conventional formulation patents.

How strong is the KIRSTY patent estate?

The base formulation patent estate is likely to be moderate rather than dominant. The excipients are established, the reference product is mature, and broad claims covering insulin aspart plus conventional preservatives and buffers may face validity and enablement challenges.

The strongest potential protection areas are:

1. Specific formulation ranges linked to improved stability.
2. High-concentration insulin aspart.
3. Pump-reservoir and infusion-set compatibility.
4. Proprietary pen or cartridge systems.
5. Manufacturing processes that reduce aggregates or host-cell impurities.
6. Packaging systems that extend in-use stability.
7. Connected delivery and dosing technologies.

Manufacturing know-how may provide more practical protection than published formulation patents. Recombinant insulin production requires control of folding, processing, purification, impurities, aggregation and batch consistency. A competitor may obtain FDA approval yet struggle to match yield, cost of goods or supply reliability.

How does KIRSTY compare with competing rapid-acting insulins?

Product	Active ingredient	Competitive position
KIRSTY	Insulin aspart-szjj	Biosimilar price competition against NovoLog
NovoLog/NovoRapid	Insulin aspart	Established reference product and broad commercial footprint
Humalog	Insulin lispro	Major therapeutic substitute
Lyumjev	Faster-acting insulin lispro	Delivery-speed differentiation
Fiasp	Faster-acting insulin aspart	Formulation and onset differentiation
Apidra	Insulin glulisine	Alternative rapid-acting analogue
Human regular insulin	Human insulin	Low-cost substitution, slower onset

KIRSTY competes most directly on price and access. Fiasp and Lyumjev compete on onset and meal-time flexibility. Human regular insulin competes on affordability. The commercial strategy should therefore avoid relying solely on biosimilar status and should target payer segments where insulin aspart volume can be won through net-cost reduction.

What are the principal manufacturing and IP barriers?

The main barriers are technical execution and cost control.

Manufacturing barriers

• Consistent recombinant expression.
• Correct insulin processing and conversion to active insulin.
• Control of aggregation and deamidation.
• Removal of host-cell proteins and DNA.
• Reproducible zinc and preservative incorporation.
• Low particulate levels.
• Stable fill-finish performance.
• Cold-chain reliability.
• Cartridge and pen assembly capacity.

IP barriers

• Process patents covering recombinant insulin production.
• Device patents covering pen mechanisms.
• High-concentration formulation claims.
• Pump and infusion-set compatibility claims.
• Packaging and container-closure claims.
• Connected-device software and data rights.

A KIRSTY competitor with an equivalent active ingredient but weaker fill-finish or device capability may not achieve meaningful market share.

What is the commercial outlook for KIRSTY?

KIRSTY has the clearest opportunity as a lower-net-cost rapid-acting insulin in U-100 vial and pen presentations. The core formulation should remain close to NovoLog to protect biosimilar comparability and enable efficient regulatory maintenance.

The highest-value lifecycle opportunities are pump-compatible formulations, U-200 insulin aspart and connected pen systems. These products can generate differentiated economics but require separate technical, clinical, device and intellectual-property programs.

The strongest near-term business model is payer-led substitution supported by reliable supply, competitive rebates and broad presentation coverage. The strongest long-term model combines the base biosimilar with proprietary devices and higher-value delivery systems.

Key Takeaways

• KIRSTY is insulin aspart-szjj, a biosimilar to NovoLog.
• Its core excipients are glycerol, phenol, metacresol, zinc, phosphate buffer, sodium chloride and water.
• A reference-like excipient profile minimizes biosimilar comparability risk.
• Broad composition patents are likely weaker than patents covering concentration, devices, pumps and manufacturing.
• U-100 vials and pens provide the most direct commercial opportunity.
• Pump compatibility and U-200 insulin aspart offer the strongest lifecycle opportunities.
• Biosimilar competition is analyzed through the Purple Book and BPCIA framework rather than a conventional Paragraph IV pathway.
• Manufacturing yield, aggregation control, fill-finish capacity and device reliability may be more important commercial barriers than excipient ownership.
• KIRSTY’s market position will depend on payer contracting, supply continuity and presentation breadth.

FAQs

Is KIRSTY interchangeable with NovoLog?

KIRSTY is FDA-approved as a biosimilar to NovoLog. Pharmacy-level substitution depends on the product’s FDA interchangeability status, state law and payer policy.

Can KIRSTY be used in an insulin pump?

Pump use depends on the approved labeling for the specific KIRSTY presentation. Pump compatibility requires product- and device-specific stability and performance support.

Does KIRSTY contain metacresol?

Yes. KIRSTY’s formulation uses metacresol as part of its preservative and insulin-stabilization system.

Could KIRSTY be reformulated as preservative-free insulin?

A preservative-free product would require a separate formulation and regulatory strategy because multidose microbial protection, in-use stability and packaging requirements would change.

What patent strategy is most valuable for future KIRSTY products?

The strongest strategy is likely to combine process patents, high-concentration formulations, pump-compatibility claims, proprietary pen systems and connected delivery technologies.

References

1. U.S. Food and Drug Administration. (2024). KIRSTY (insulin aspart-szjj) injection, prescribing information. FDA.

2. U.S. Food and Drug Administration. (2023). NovoLog (insulin aspart injection), prescribing information. 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). Approved drug products with therapeutic equivalence evaluations. FDA.

5. U.S. Congress. (2010). Biologics Price Competition and Innovation Act of 2009, Pub. L. No. 111-148, §§ 7001-7003. Congress.gov.