List of Excipients in Branded Drug ENTEREG

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Company	Tradename	Ingredient	NDC	Excipient	Potential Generic Entry
Merck Sharp & Dohme LLC	ENTEREG	alvimopan	67919-020	GELATIN
Merck Sharp & Dohme LLC	ENTEREG	alvimopan	67919-020	POLYETHYLENE GLYCOL

ENTEREG Alvimopan Excipient Strategy and Commercial Opportunities

Last updated: August 17, 2026

Entereg (alvimopan) is an oral, peripherally acting mu-opioid receptor antagonist used to accelerate gastrointestinal recovery after bowel resection surgery. Its commercial opportunity is narrow but defensible: hospital-only distribution, restricted use, low dosing complexity, and a formulation that can be reproduced through conventional solid-dose manufacturing. The strongest opportunities are generic supply, hospital-packaged products, excipient-controlled formulations, and manufacturing partnerships rather than consumer retail expansion.

What is Entereg and how is it used?

Entereg contains alvimopan, a peripherally acting mu-opioid receptor antagonist. The FDA-approved regimen is 12 mg administered before surgery, followed by 12 mg twice daily for no more than seven days or 15 doses, whichever comes first.[1]

Product attribute	Entereg profile
Active ingredient	Alvimopan
Strength	12 mg
Dosage form	Oral capsule
Therapeutic class	Peripherally acting mu-opioid receptor antagonist
Primary use	Accelerating upper and lower gastrointestinal recovery after bowel resection
Distribution	Inpatient hospital use
Dose limit	Maximum 15 doses
Administration	Preoperative dose followed by twice-daily dosing
Key safety restriction	Not intended for patients taking therapeutic opioids for more than seven consecutive days immediately before surgery
Original sponsor	Adolor Corporation
Later commercial owner	Merck & Co.

Entereg is administered in a controlled hospital environment. The product is not positioned as a chronic outpatient medicine, which limits volume but simplifies demand forecasting and reduces the need for broad retail distribution.

What excipients are used in Entereg capsules?

The Entereg capsule uses a conventional immediate-release excipient system. FDA labeling identifies inactive ingredients that include lactose monohydrate, microcrystalline cellulose, crospovidone, sodium lauryl sulfate, magnesium stearate, colloidal silicon dioxide, hypromellose, talc, titanium dioxide and capsule-coloring materials.[1]

The formulation can be divided into four functional groups:

Excipient function	Likely formulation role
Dilution and compactability	Lactose monohydrate, microcrystalline cellulose
Disintegration	Crospovidone
Lubrication	Magnesium stearate
Wetting and dispersion	Sodium lauryl sulfate
Flow control	Colloidal silicon dioxide
Capsule shell and appearance	Hypromellose, titanium dioxide, talc and colorants

The drug substance load is relatively low compared with the total capsule fill. That creates formulation flexibility, but it also increases the importance of blend uniformity, segregation control and dissolution reproducibility.

Which excipient attributes matter most?

The most important critical material attributes are particle-size distribution, moisture content, bulk density, specific surface area and lubricant mixing time.

Alvimopan formulations must maintain:

• Uniform distribution of the low-dose active ingredient.
• Rapid and consistent disintegration.
• Dissolution performance across relevant pH conditions.
• Low capsule-to-capsule weight variability.
• Stability under hospital storage conditions.
• Compatibility with high-throughput encapsulation.
• Consistent appearance for product identification.

Microcrystalline cellulose and lactose can provide a cost-effective filler system, but their physical properties must be tightly controlled. Variations in lactose particle size or microcrystalline cellulose grade can affect flow and blend uniformity. Crospovidone supports immediate release but may alter dissolution if particle size, concentration or compaction conditions change.

Magnesium stearate presents a familiar scale-up risk. Excessive lubrication can reduce powder wettability and slow dissolution. Sodium lauryl sulfate may improve wetting, but its concentration must remain controlled because surfactant levels can affect dissolution, capsule-shell performance and gastrointestinal tolerability.

How should a generic Entereg excipient strategy be designed?

A generic strategy should prioritize Q1/Q2 similarity to the reference product where practical. Q1 similarity means using the same inactive ingredients. Q2 similarity means matching their concentrations or maintaining a comparable quantitative composition.

For an ANDA applicant, the lowest regulatory and development risk generally comes from:

1. Retaining the reference excipient categories.
2. Using established pharmaceutical grades.
3. Matching capsule dimensions and fill weight.
4. Demonstrating rapid dissolution across multiple media.
5. Controlling blend uniformity through a validated process.
6. Avoiding unnecessary coating, modified release or formulation complexity.

A direct-copy excipient approach is commercially attractive because Entereg does not require a complex delivery system. The formulation is an immediate-release capsule with a limited dosing period. A reformulation that creates meaningful clinical or manufacturing value would need to justify added development cost against a relatively small hospital market.

What formulation changes could create value?

The most credible formulation opportunities are process and supply-chain improvements rather than new therapeutic claims.

Lactose-free formulation

A lactose-free capsule could target hospitals that prefer to avoid lactose because of excipient-screening policies, procurement standards or patient intolerance concerns. The commercial value is limited because the product is administered for a short period and lactose exposure is low, but it could differentiate a generic if the replacement maintains bioequivalence and dissolution.

Potential substitutes include:

• Mannitol.
• Dibasic calcium phosphate.
• Pregelatinized starch.
• Alternative grades of microcrystalline cellulose.

Mannitol can improve mouthfeel and reduce dependence on lactose, but its hygroscopicity and cost may be less attractive. Dibasic calcium phosphate can improve flow but may introduce higher density and dissolution challenges. Pregelatinized starch can contribute binding and disintegration but may increase moisture sensitivity.

Colorant-free or simplified capsule shell

A capsule with fewer colorants could reduce raw-material complexity and support hospitals with colorant-avoidance policies. The commercial benefit would be modest. Color and imprinting remain important for medication identification, especially in inpatient settings.

Improved moisture protection

Alvimopan solid dosage products may benefit from high-barrier blister packaging or unit-dose packaging rather than a major excipient change. Packaging can deliver better stability control without changing the formulation.

Small-batch hospital supply

A formulation optimized for flexible batch sizes could support regional hospital systems and specialty distributors. This opportunity depends more on manufacturing economics, packaging and inventory management than on excipient innovation.

What patents protect Entereg and when does alvimopan lose exclusivity?

Entereg's original commercial protection included patents, regulatory exclusivity and the practical effect of restricted hospital distribution. The key commercial question is whether an applicant can obtain approval for a generic alvimopan capsule and whether any remaining Orange Book-listed patents or pediatric exclusivity delay launch.

FDA's Orange Book is the controlling source for listed patents, patent certifications and exclusivity status. The Entereg NDA is 021775.[2] Because patent listings and litigation positions can change, launch planning should rely on the current Orange Book record and ANDA litigation docket rather than historical product summaries.

Alvimopan is a small-molecule product, so biosimilar risk does not apply. Competition proceeds through the ANDA pathway, with an AB-rated generic potentially substitutable at the pharmacy or hospital purchasing level once approved and eligible for substitution.

What regulatory barriers remain?

The primary barriers are:

• Demonstrating bioequivalence to the reference capsule.
• Meeting dissolution and content-uniformity specifications.
• Establishing adequate stability.
• Complying with inpatient-use restrictions.
• Supporting hospital procurement and distribution controls.
• Managing any applicable patent certifications.
• Demonstrating manufacturing consistency for a low-dose blend.

The product does not require a biologics license application or biosimilar development program. That reduces clinical development cost relative to biologic competitors.

Are there Paragraph IV challenges for Entereg?

A Paragraph IV challenge is possible when an ANDA applicant asserts that an Orange Book-listed patent is invalid, unenforceable or will not be infringed. A successful certification can trigger patent litigation and a potential 30-month stay of approval under the Hatch-Waxman Act.[3]

The commercial relevance of a Paragraph IV strategy depends on:

• The number and expiration dates of listed patents.
• Whether the patents cover the active ingredient, formulation or method of use.
• The probability of early resolution.
• The size of the remaining hospital market.
• The expected launch discount.
• The cost of litigation relative to expected alvimopan sales.

For Entereg, the likely value of a challenge is greater when the applicant has a low-cost manufacturing platform and expects rapid hospital contracting after approval. A late-stage challenge may have limited value if the remaining reference-product market is small or if the listed patents are close to expiration.

What patent litigation and settlement agreements affect Entereg?

The relevant legal record should be evaluated through:

• FDA Orange Book patent listings.
• Federal district court dockets.
• ANDA litigation complaints.
• Paragraph IV notice letters where available.
• Patent Trial and Appeal Board proceedings.
• FDA approval letters and exclusivity records.

A settlement agreement could provide a generic applicant with a licensed or authorized launch date before patent expiration. The commercial impact would depend on whether the settlement allows one entrant or multiple entrants, whether the launch is authorized, and whether the agreement contains supply or licensing provisions.

No biosimilar settlement framework applies because alvimopan is a small molecule. Any competitive settlement would be governed primarily by Hatch-Waxman litigation and antitrust considerations.

How strong is the Entereg patent estate?

The patent estate should be assessed in three layers:

Patent layer	Commercial relevance
Active-ingredient patents	Potentially strongest barrier, but usually the earliest to expire
Formulation patents	Relevant if they cover the specific immediate-release capsule composition or manufacturing process
Method-of-use patents	May be narrower because the FDA-approved use is confined to bowel-resection patients and a short inpatient course

A formulation patent is commercially meaningful only if it covers a product that generic applicants cannot easily design around while preserving bioequivalence. Broad excipient claims can be challenged on written-description, enablement, obviousness or lack-of-novelty grounds. Narrow claims may be easier to avoid through substitution of fillers, disintegrants, surfactants or capsule-shell materials.

The strongest practical protection may therefore come from the combination of regulatory restrictions, limited hospital demand, manufacturing know-how and contracting relationships rather than from excipient patents alone.

What commercial opportunities exist for excipient suppliers?

Excipient suppliers can pursue several opportunities around alvimopan generic development and supply.

Direct excipient supply

The principal volume opportunity is supply of:

• Pharmaceutical-grade microcrystalline cellulose.
• Lactose monohydrate.
• Crospovidone.
• Magnesium stearate.
• Colloidal silicon dioxide.
• Sodium lauryl sulfate.
• Capsule-shell materials.

Because alvimopan is a low-volume specialty product, suppliers should compete on regulatory documentation, consistency and technical support rather than commodity price alone.

Co-processed excipients

A co-processed filler-disintegrant system could reduce blend segregation and improve manufacturing robustness. The value proposition is strongest if it:

• Improves content uniformity.
• Reduces processing steps.
• Supports direct encapsulation.
• Provides consistent dissolution.
• Reduces sensitivity to active-particle-size variation.

The applicant would need to confirm that a co-processed system does not introduce a new bioequivalence risk.

Excipient premixes

A validated premix containing filler, disintegrant and flow aid could reduce development time for contract manufacturers. Premixes can be commercially useful where production volumes are too low to justify extensive formulation optimization.

Capsule and packaging systems

Unit-dose blister systems, high-barrier packaging and hospital-ready labeling may create more commercial value than a novel excipient. A supplier that combines capsule production, packaging and regulatory support could offer a complete hospital product platform.

What generic launch scenarios exist?

Single generic entrant

A single early entrant could preserve relatively strong pricing, particularly if the product remains subject to hospital purchasing controls. The entrant would benefit from limited competition but would face a small addressable market.

Multiple generic entrants

Multiple ANDA approvals could produce rapid price erosion. Hospital buyers may shift volume to the lowest-cost supplier, especially if products are therapeutically substitutable and supply reliability is comparable.

Authorized generic

An authorized generic could limit the commercial upside of a Paragraph IV launch by offering an equivalent product through the reference sponsor or a licensed partner. This scenario would be relevant if the sponsor retains hospital contracting strength or seeks to protect formulary presence.

Reformulated differentiated product

A lactose-free, colorant-reduced or packaging-optimized product could obtain modest contracting advantages. It would not automatically receive separate regulatory exclusivity, and the commercial return would depend on procurement policies.

How does Entereg compare with other gastrointestinal recovery products?

Product or approach	Active mechanism	Market position	Excipient opportunity
Entereg	Peripheral mu-opioid receptor antagonism	Short-course inpatient bowel-resection use	Generic capsule, premix, packaging
Methylnaltrexone	Peripheral mu-opioid receptor antagonism	Opioid-induced constipation, broader chronic-use setting	Oral and injectable formulation competition
Naloxegol	PEGylated opioid antagonist	Chronic outpatient opioid-induced constipation	Tablet formulation and excipient differentiation
Naldemedine	Peripheral opioid antagonism	Chronic opioid-induced constipation	Tablet manufacturing and specialty distribution
Lubiprostone	Chloride-channel activation	Chronic constipation indications	Capsule formulation and dosage flexibility

Entereg differs from chronic opioid-induced constipation products because its clinical use is short, procedural and hospital-based. The market is therefore less suited to consumer-facing formulation innovation. Supply reliability, inpatient packaging and procurement economics are more important.

What revenue exposure and market risks matter?

Entereg revenue is exposed to:

• The number of eligible bowel-resection procedures.
• Hospital adoption of enhanced recovery protocols.
• Generic substitution.
• Surgical-center formulary decisions.
• Short product duration.
• Restricted distribution.
• Alternative perioperative care pathways.
• Reimbursement and hospital budget pressure.

Enhanced recovery after surgery protocols can support use of alvimopan in appropriate bowel-resection patients, but hospitals may also seek lower-cost alternatives or limit use to high-risk patients. The product's 15-dose maximum restricts repeat purchasing and reduces the opportunity for chronic-use revenue.

The most attractive commercial model is a low-cost, reliable hospital product with disciplined inventory management. A high-cost reformulation would face a weak return unless it solves a clear procurement, stability or manufacturing problem.

What geographic opportunities exist?

The United States remains the clearest opportunity because Entereg has an established FDA regulatory pathway and hospital-use positioning. Geographic expansion depends on local approvals, surgical practice, opioid use patterns and reimbursement.

Potential regional priorities include:

• United States: ANDA competition, hospital contracting and unit-dose supply.
• Europe: National authorization and reimbursement requirements, with possible differences in perioperative adoption.
• Japan: Local clinical and regulatory requirements may limit direct extrapolation.
• Emerging markets: Lower price expectations may favor simple generic capsules and regional contract manufacturing.

International commercialization should use the same immediate-release formulation where possible, but excipient acceptability, capsule-shell requirements and labeling rules may differ by jurisdiction.

Key Takeaways

• Entereg is a 12 mg immediate-release alvimopan capsule used for a short inpatient course after bowel resection.
• The formulation relies on conventional excipients, including lactose, microcrystalline cellulose, crospovidone, magnesium stearate and capsule-shell materials.
• The strongest generic strategy is close quantitative and qualitative similarity to the reference product.
• Excipient innovation has limited standalone value unless it improves content uniformity, dissolution, stability or manufacturing cost.
• Lactose-free, colorant-reduced and hospital-ready versions are possible differentiation strategies.
• Alvimopan has small-molecule generic risk, not biosimilar risk.
• Orange Book listings, Paragraph IV certifications and current litigation records determine launch timing.
• Hospital distribution restrictions reduce market size but can make demand more predictable.
• Packaging, supply reliability and procurement support may create greater value than a novel excipient system.
• The commercial case favors disciplined manufacturing and low-cost supply over extensive reformulation.

FAQs About Entereg Excipient Strategy and Commercialization

Is Entereg a biologic or a small-molecule drug?

Entereg is a small-molecule drug containing alvimopan. Generic competition uses the ANDA pathway rather than the biosimilar pathway.

Can a generic alvimopan product replace lactose with mannitol?

Potentially, but the applicant must demonstrate pharmaceutical equivalence, bioequivalence, acceptable dissolution, stability and adequate control of content uniformity.

Does Entereg require a modified-release formulation?

No. Entereg is an immediate-release capsule. A modified-release version would create additional development and regulatory complexity without an obvious clinical requirement.

Can an excipient change create new patent protection for alvimopan?

A novel formulation may support patent claims if it is new, nonobvious and adequately described. Commercial value depends on whether generic applicants can design around the claims while preserving bioequivalence.

What is the most attractive commercial opportunity around Entereg?

The strongest opportunity is a reliable, low-cost hospital generic supported by unit-dose packaging, stable supply, regulatory-grade excipient control and hospital procurement contracts.

References

1. U.S. Food and Drug Administration. (2018). Entereg (alvimopan) capsules, prescribing information.
2. U.S. Food and Drug Administration. (n.d.). Approved drug products with therapeutic equivalence evaluations: Orange Book.
3. U.S. Food and Drug Administration. (2017). Guidance for industry: 180-day exclusivity when multiple first applicants are eligible.
4. U.S. Food and Drug Administration. (2023). ANDA submissions: Content and format.
5. U.S. Food and Drug Administration. (2024). Inactive ingredient database.