List of Excipients in Branded Drug RECARBRIO

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Company	Tradename	Ingredient	NDC	Excipient	Potential Generic Entry
Merck Sharp & Dohme LLC	RECARBRIO	imipenem anhydrous, cilastatin, and relebactam anhydrous	0006-3856	SODIUM BICARBONATE	2029-07-16

Recarbrio Excipient Strategy and Commercial Opportunities

Last updated: October 23, 2026

Recarbrio is Merck's intravenous fixed-dose combination of imipenem, cilastatin, and relebactam. Its commercial formulation is a sterile lyophilized powder in a single-dose vial, reconstituted for intravenous infusion. The excipient platform is deliberately narrow, which limits conventional excipient differentiation but creates opportunities in stability enhancement, ready-to-administer presentations, packaging, hospital workflow, and supply-chain resilience. FDA approval covers adult patients with certain complicated urinary tract infections, complicated intra-abdominal infections, and hospital-acquired or ventilator-associated bacterial pneumonia caused by susceptible organisms [1].

What is the current Recarbrio formulation?

Recarbrio contains three active pharmaceutical ingredients in a fixed 2:2:1 mass ratio:

Component	Amount per vial	Functional role
Imipenem	500 mg	Carbapenem antibacterial
Cilastatin	500 mg	Renal dehydropeptidase-I inhibitor
Relebactam	250 mg	Beta-lactamase inhibitor
Sodium bicarbonate	Inactive ingredient	Formulation and pH control

The product is supplied as a sterile powder for reconstitution in a single-dose vial. The labeled preparation uses 100 mL of 0.9% sodium chloride, followed by a 30-minute intravenous infusion. The formulation is administered every six hours in adults with normal renal function, with dose adjustments required for renal impairment [1].

The excipient burden is low compared with oral tablets, suspensions, or lipid-based injectables. That reduces excipient-related tolerability and regulatory complexity but places greater pressure on manufacturing controls, moisture protection, container closure, reconstitution performance, and chemical stability.

Why does Recarbrio use a minimal excipient system?

The central formulation problem is stabilizing a multi-component beta-lactam product in the solid state and after reconstitution. Imipenem is chemically labile in aqueous conditions. Relebactam introduces a second active component with its own degradation and compatibility profile. Cilastatin must remain chemically and physically compatible with both compounds during manufacturing, storage, reconstitution, and infusion.

A minimal excipient system provides several advantages:

• Fewer potential degradation pathways.
• Lower risk of excipient-active incompatibility.
• Simplified toxicology and regulatory justification.
• Easier global registration.
• Lower risk of infusion-related excipient reactions.
• Reduced complexity in aseptic filling and lyophilization.

Sodium bicarbonate is a functional excipient rather than a commercial differentiator. Its value lies in controlling the formulation environment and supporting product stability. It is unlikely to provide a durable standalone competitive advantage because sodium bicarbonate is a widely used pharmaceutical excipient with established regulatory precedent.

The commercial differentiation therefore sits outside the basic excipient list. It is more likely to arise from lyophilization cycle design, moisture control, vial configuration, reconstitution speed, premixing, infusion compatibility, and administration logistics.

What excipient strategy is most suitable for Recarbrio?

1. Protect the existing lyophilized powder platform

The lowest-risk strategy is to preserve the current powder-for-injection architecture and improve process robustness. Development priorities include:

• Control of residual moisture.
• Uniform distribution of all three active ingredients.
• Prevention of vial-to-vial potency variation.
• Optimization of cake structure and reconstitution time.
• Control of imipenem and relebactam degradation products.
• Protection from oxygen, light, and temperature excursions.
• Container-closure integrity after lyophilization.

For a hospital antibiotic, these improvements can have greater commercial value than adding a new excipient. Hospitals prioritize predictable preparation, low nursing burden, minimal waste, and reliable supply.

2. Evaluate buffering and pH-control alternatives

Sodium bicarbonate is an established choice, but alternative buffering systems could be evaluated if they improve stability or reconstitution behavior. Candidate systems would need to satisfy five conditions:

1. No meaningful loss of imipenem activity.
2. No adverse effect on relebactam stability.
3. No precipitation after dilution.
4. Compatibility with common infusion materials.
5. No clinically relevant change in osmolality or infusion tolerability.

Potential alternatives should not be assumed to be commercially viable. Phosphate, citrate, acetate, and other buffers can create new risks, including metal-ion interactions, pH drift, precipitation, altered lyophilization behavior, or compatibility problems with hospital diluents.

A buffer change would also create a regulatory burden. The manufacturer would need comparative stability, degradation, particulate, sterility, container-closure, and clinical bridging data. The benefit must exceed the cost of a supplemental application and manufacturing revalidation.

3. Consider bulking and cake-forming excipients cautiously

Mannitol, sucrose, trehalose, and related excipients are common in parenteral lyophilized products. They can improve cake appearance, collapse resistance, and handling. They may also alter reconstitution time, residual moisture, glass-transition behavior, and degradation kinetics.

For Recarbrio, a bulking or stabilizing excipient could be commercially useful if it:

• Improves lyophilization yield.
• Reduces vial rejection.
• Extends refrigerated or controlled-room-temperature stability.
• Improves reconstitution speed.
• Supports a smaller or more concentrated presentation.
• Reduces sensitivity to shipping excursions.

The main risk is that a new sugar or polyol may complicate the degradation profile of one or more active ingredients. Excipient selection must be driven by forced-degradation and long-term stability data rather than by standard parenteral formulation practice.

4. Develop a ready-to-administer or premixed presentation

The strongest commercial opportunity is likely a hospital-ready presentation rather than a novel excipient. Options include:

• Premixed intravenous bags.
• Dual-chamber bags.
• Pharmacy-ready reconstitution systems.
• Smaller-volume concentrated presentations.
• Ready-to-administer syringes for controlled clinical settings.
• Extended-stability diluted solutions.

A premixed product could reduce preparation errors and pharmacy labor. It could also improve antibiotic stewardship by making scheduled dosing easier to standardize. The primary technical obstacle is aqueous stability. Imipenem stability is the limiting consideration, and any premixed presentation would need validated control of temperature, pH, degradation products, infusion materials, and storage duration.

A dual-chamber device could keep the powder isolated from diluent until use. This approach may protect stability while eliminating manual vial reconstitution. The tradeoff is higher device cost, more complex combination-product development, and potentially greater manufacturing and regulatory burden.

What formulations are protected by Recarbrio-related intellectual property?

Recarbrio's commercial protection is likely to involve several layers:

Protection layer	Potential subject matter	Commercial relevance
Active-ingredient patents	Relebactam and related compounds	Core composition protection
Combination patents	Imipenem, cilastatin, and relebactam combinations	Product-specific protection
Method-of-use patents	Treatment of resistant Gram-negative infections	Limits certain labeled-use launches
Formulation patents	Stability, ratios, buffers, lyophilized products	Protects differentiated presentations
Manufacturing patents	Crystallization, drying, blending, and filling	Raises CMC barriers
Device patents	Premixed or dual-chamber delivery systems	Protects lifecycle products

An excipient patent strategy should focus on a defined technical result, such as improved aqueous stability, lower residual moisture, shorter reconstitution time, or extended storage after dilution. A patent claiming only the use of a conventional excipient with Recarbrio's known active ingredients would face higher validity and obviousness risk.

The Orange Book status of Recarbrio must be assessed separately from the broader patent estate. Orange Book-listed patents may cover the approved drug, formulation, or method of use. Other patents may remain relevant to freedom-to-operate without being listed. FDA's Orange Book and Drugs@FDA are the controlling sources for current U.S. listing and approval information [2,3].

When does Recarbrio lose exclusivity?

Recarbrio does not have biosimilar exclusivity exposure because it is a small-molecule antibacterial product, not a biologic. Competition would proceed through an abbreviated new drug application, generally as a generic product, rather than through the biosimilar pathway.

The practical exclusivity timeline depends on:

• Relebactam composition patents.
• Combination and formulation patents.
• Pediatric exclusivity, if granted.
• Regulatory exclusivity attached to the approved indication.
• Patent-term adjustment or extension.
• Paragraph IV litigation and settlement terms.
• The scope of any approved generic certifications.

The precise generic-entry date cannot be inferred solely from the FDA approval date. A complete assessment requires the current Orange Book patent listings, patent-term calculations, litigation records, and any settlement agreements. The FDA Orange Book identifies listed patents and exclusivity but does not by itself establish the enforceability or ultimate validity of each patent [2].

What is the FDA regulatory status of Recarbrio?

FDA approved Recarbrio in July 2019 for adults with complicated intra-abdominal infections and complicated urinary tract infections caused by susceptible pathogens, including infections where limited or no alternative treatment options exist. FDA later expanded the label to include hospital-acquired bacterial pneumonia and ventilator-associated bacterial pneumonia [1,4].

Recarbrio is administered intravenously and requires renal dose adjustment. The label includes important preparation and administration requirements, including reconstitution instructions and restrictions on diluent compatibility. These requirements are commercially important because preparation complexity can affect hospital adoption even when the antimicrobial profile is attractive.

An excipient change would likely require a prior-approval supplement or other FDA submission depending on the nature and impact of the change. A new delivery device, premixed bag, or materially different formulation could require a more extensive regulatory package than a manufacturing-process adjustment.

Which companies are challenging Recarbrio with generics?

Recarbrio generic competition is expected to come from injectable generic manufacturers with established sterile beta-lactam capacity. The relevant competitive set includes companies with:

• Aseptic powder filling.
• Lyophilization capacity.
• Carbapenem manufacturing experience.
• Access to relebactam or a lawful source of the active ingredient.
• Regulatory infrastructure for complex parenteral products.
• Hospital and group-purchasing distribution.

The main barrier is not the excipient list. It is the combined challenge of sourcing three active ingredients, reproducing the fixed-dose product, demonstrating pharmaceutical equivalence, controlling degradation, and maintaining sterile manufacturing economics.

For an ANDA applicant, excipient selection can be a strategic tool. A generic manufacturer may use a different inactive-ingredient system if it demonstrates pharmaceutical equivalence, safety, stability, and acceptable injectable performance. A materially different formulation may increase development risk and invite a formulation patent dispute.

How strong is the patent estate for Recarbrio?

The strongest protection is likely to center on relebactam, the fixed combination, and approved antibacterial uses. Excipient-related protection is potentially narrower and more vulnerable unless it is tied to a measurable technical benefit.

Patent strength should be assessed across four dimensions:

Factor	Strong position	Weak position
Claim scope	Covers active combination and commercial product	Covers a narrow excipient variant
Validity	Supported by unexpected stability or performance data	Predictable use of a conventional excipient
Enforcement	Product can be identified from public records	Infringement requires access to manufacturing data
Design-around risk	Few viable alternative formulations	Generic can change buffer or bulking agent

Manufacturing patents can be more difficult to enforce than composition patents because the relevant process parameters may be confidential. Formulation patents are more useful when the marketed product necessarily practices the claimed composition and the claim can be confirmed through public product information.

What commercial opportunities exist for Recarbrio excipients and delivery systems?

Hospital-ready formulation

A ready-to-administer product could create value by reducing pharmacy compounding steps. The commercial case is strongest in intensive-care, emergency, and high-volume hospital settings where staff time and dose-preparation delays affect antibiotic administration.

Extended post-reconstitution stability

Longer stability after reconstitution or dilution could support centralized pharmacy preparation, overnight batching, and reduced product waste. This opportunity depends on preserving potency and controlling degradation products under realistic hospital conditions.

Lower-volume administration

A more concentrated presentation could reduce infusion volume and simplify fluid management in critically ill patients. The formulation must maintain solubility, osmolality, infusion tolerability, and compatibility with standard administration sets.

Global access formulation

A formulation with improved temperature tolerance could reduce dependence on cold-chain logistics in lower-resource markets. The value would be highest where reliable refrigeration and rapid hospital pharmacy access are limited.

Contract manufacturing and excipient supply

Suppliers can pursue commercial opportunities in:

• Pharmaceutical-grade sodium bicarbonate.
• Lyophilization bulking agents.
• Low-peroxide excipients.
• Low-endotoxin excipients.
• Ready-to-use infusion bags.
• Dual-chamber delivery systems.
• Low-moisture elastomeric closures.
• Oxygen- and moisture-barrier packaging.

Supplier qualification will be demanding because any material change can affect beta-lactam stability, particulate levels, sterility assurance, and container-closure performance.

What manufacturing and IP barriers affect Recarbrio?

The principal manufacturing barriers are:

1. Reproducible co-processing of three active ingredients.
2. Control of imipenem degradation during aqueous handling.
3. Uniform filling of a low-excipient lyophilized cake.
4. Protection against moisture ingress.
5. Stable supply of relebactam.
6. Validated sterile manufacturing capacity.
7. Demonstration of reconstitution and infusion compatibility.

The most defensible commercial improvements will combine formulation and process know-how. A new excipient alone is unlikely to create a large barrier. A validated system linking buffer concentration, lyophilization cycle, residual moisture, vial closure, and post-reconstitution stability has greater potential for both patent protection and manufacturing advantage.

How does Recarbrio compare with competing hospital antibiotics?

Product	Active approach	Excipient and delivery implication	Competitive issue
Recarbrio	Imipenem/cilastatin/relebactam	Lyophilized powder; reconstituted IV infusion	Preparation burden and resistance positioning
Vabomere	Meropenem/vaborbactam	Lyophilized IV product	Direct beta-lactam/beta-lactamase inhibitor comparison
Avycaz	Ceftazidime/avibactam	Powder for IV solution	Established hospital use and formulation familiarity
Zerbaxa	Ceftolozane/tazobactam	Powder for IV solution	Different spectrum and dosing profile
Generic carbapenems	Single or combined active ingredients	Mature injectable manufacturing	Lower price and broader supplier base

Recarbrio's excipient differentiation is weaker than its active-ingredient and clinical-positioning differentiation. Its lifecycle strategy should therefore connect formulation improvements to hospital economics: less preparation time, lower waste, improved stability, and simplified inventory.

Key Takeaways

• Recarbrio is a sterile lyophilized intravenous combination of imipenem, cilastatin, and relebactam.
• Sodium bicarbonate is the principal disclosed inactive ingredient and functions mainly in formulation control.
• The most valuable excipient strategy is likely stability and manufacturing optimization, not a broad excipient expansion.
• Ready-to-administer bags, dual-chamber systems, and longer post-reconstitution stability are the leading commercial opportunities.
• Generic competition will depend more on relebactam supply, sterile manufacturing, stability, and patent scope than on excipient cost.
• Recarbrio is exposed to generic competition, not biosimilar competition.
• Formulation patents are strongest when supported by unexpected stability or administration benefits.
• Orange Book listings, patent-term calculations, Paragraph IV filings, and settlements determine the actual U.S. entry timeline.

FAQs

Can Recarbrio be reformulated with a different buffer?

Potentially, but a different buffer would require comparative stability, degradation, reconstitution, particulate, compatibility, and regulatory data. The change would need to produce a measurable technical or commercial benefit.

Is sodium bicarbonate the main commercial value in Recarbrio's formulation?

No. Sodium bicarbonate is a functional excipient with limited standalone differentiation. The higher-value assets are the lyophilization process, stability profile, container closure, and delivery presentation.

Can a generic Recarbrio use different excipients?

Yes, subject to applicable FDA requirements for pharmaceutical equivalence, safety, stability, and injectable-product performance. A different excipient system may also create additional patent and regulatory risk.

Would a premixed Recarbrio bag improve hospital adoption?

It could reduce pharmacy preparation time and medication-error risk. Its feasibility depends on aqueous stability, storage duration, infusion compatibility, packaging, and manufacturing cost.

Does Recarbrio have biosimilar competition?

No. Recarbrio is a small-molecule drug. Competition would generally arise through generic drug applications rather than biosimilar applications.

References

1. U.S. Food and Drug Administration. (2019). Recarbrio (imipenem, cilastatin, and relebactam) prescribing information. Merck Sharp & Dohme LLC.

2. U.S. Food and Drug Administration. (2025). Approved drug products with therapeutic equivalence evaluations: Orange Book. https://www.fda.gov/drugsatfda

3. U.S. Food and Drug Administration. (2025). Drugs@FDA: FDA-approved drugs. https://www.accessdata.fda.gov/scripts/cder/daf/

4. U.S. Food and Drug Administration. (2020). FDA approves expanded indication for Recarbrio for hospital-acquired and ventilator-associated bacterial pneumonia. FDA.