RELISTOR Drug Patent Profile

Which patents cover Relistor, and when can generic versions of Relistor launch?

Relistor is a drug marketed by Salix Pharms and Salix and is included in two NDAs. There are twelve patents protecting this drug and three Paragraph IV challenges.

This drug has one hundred and twenty-four patent family members in thirty-six countries.

The generic ingredient in RELISTOR is methylnaltrexone bromide. There are three drug master file entries for this compound. One supplier is listed for this compound. Additional details are available on the methylnaltrexone bromide profile page.

DrugPatentWatch^® Generic Entry Outlook for Relistor

Relistor was eligible for patent challenges on April 24, 2012.

By analyzing the patents and regulatory protections it appears that the earliest date for generic entry will be August 3, 2027. This may change due to patent challenges or generic licensing.

There have been sixteen patent litigation cases involving the patents protecting this drug, indicating strong interest in generic launch. Recent data indicate that 63% of patent challenges are decided in favor of the generic patent challenger and that 54% of successful patent challengers promptly launch generic drugs.

There is one tentative approval for the generic drug (methylnaltrexone bromide), which indicates the potential for near-term generic launch.

Indicators of Generic Entry

Summary for RELISTOR

International Patents:	124
US Patents:	12
Applicants:	2
NDAs:	2
Finished Product Suppliers / Packagers:	1
Raw Ingredient (Bulk) Api Vendors:	36
Clinical Trials:	18
Patent Applications:	324
Drug Prices:	Drug price information for RELISTOR
Patent Litigation and PTAB cases:	See patent lawsuits and PTAB cases for RELISTOR
What excipients (inactive ingredients) are in RELISTOR?	RELISTOR excipients list
DailyMed Link:	RELISTOR at DailyMed

See drug prices for RELISTOR

DrugPatentWatch^® Estimated Loss of Exclusivity (LOE) Date for RELISTOR

Constraining patent/regulatory exclusivity:

12,303,592

NDA:

021964

Dosage:

SOLUTION;SUBCUTANEOUS

Constraining patent/regulatory exclusivity:

8,524,276

NDA:

208271

Dosage:

TABLET;ORAL

^*The generic entry opportunity date is the latter of the last compound-claiming patent and the last regulatory exclusivity protection. Many factors can influence early or later generic entry. This date is provided as a rough estimate of generic entry potential and should not be used as an independent source.

Recent Clinical Trials for RELISTOR

Identify potential brand extensions & 505(b)(2) entrants

Sponsor	Phase
University of Alabama at Birmingham	N/A
Hvidovre University Hospital	Phase 2/Phase 3
University Hospital Bispebjerg and Frederiksberg	Phase 2/Phase 3

See all RELISTOR clinical trials

Pharmacology for RELISTOR

Drug Class	Opioid Antagonist
Mechanism of Action	Opioid Antagonists

Paragraph IV (Patent) Challenges for RELISTOR

Tradename	Dosage	Ingredient	Strength	NDA	ANDAs Submitted	Submissiondate
RELISTOR	Tablets	methylnaltrexone bromide	150 mg	208271	1	2016-09-06
RELISTOR	Injection	methylnaltrexone bromide	8 mg/0.4 mL, Single Dose Prefilled Syringe	021964	1	2015-09-08
RELISTOR	Injection	methylnaltrexone bromide	12 mg/0.6 mL, Single Dose Vial	021964	1	2015-07-22

US Patents and Regulatory Information for RELISTOR

RELISTOR is protected by thirteen US patents.

This potential generic entry date is based on patent 12,303,592.

Generics may enter earlier, or later, based on new patent filings, patent extensions, patent invalidation, early generic licensing, generic entry preferences, and other factors.

Applicant	Tradename	Generic Name	Dosage	NDA	Approval Date	TE	Type	RLD	RS	Patent No.	Patent Expiration	Product	Substance	Delist Req.	Exclusivity Expiration
Salix	RELISTOR	methylnaltrexone bromide	TABLET;ORAL	208271-001	Jul 19, 2016		RX	Yes	Yes	10,376,505		Y
Salix	RELISTOR	methylnaltrexone bromide	TABLET;ORAL	208271-001	Jul 19, 2016		RX	Yes	Yes	8,524,276		Y
Salix Pharms	RELISTOR	methylnaltrexone bromide	SOLUTION;SUBCUTANEOUS	021964-002	Sep 27, 2010		RX	Yes	Yes	8,420,663
Salix Pharms	RELISTOR	methylnaltrexone bromide	SOLUTION;SUBCUTANEOUS	021964-003	Sep 27, 2010		RX	Yes	Yes	8,247,425
Salix	RELISTOR	methylnaltrexone bromide	TABLET;ORAL	208271-001	Jul 19, 2016		RX	Yes	Yes	9,724,343		Y
Salix Pharms	RELISTOR	methylnaltrexone bromide	SOLUTION;SUBCUTANEOUS	021964-002	Sep 27, 2010		RX	Yes	Yes	9,492,445		Y
Salix Pharms	RELISTOR	methylnaltrexone bromide	SOLUTION;SUBCUTANEOUS	021964-001	Apr 24, 2008		RX	Yes	Yes	12,303,592		Y

Expired US Patents for RELISTOR

Applicant	Tradename	Generic Name	Dosage	NDA	Approval Date	Patent No.	Patent Expiration
Salix Pharms	RELISTOR	methylnaltrexone bromide	SOLUTION;SUBCUTANEOUS	021964-002	Sep 27, 2010	10,376,584
Salix Pharms	RELISTOR	methylnaltrexone bromide	SOLUTION;SUBCUTANEOUS	021964-001	Apr 24, 2008	8,552,025
Salix Pharms	RELISTOR	methylnaltrexone bromide	SOLUTION;SUBCUTANEOUS	021964-003	Sep 27, 2010	10,376,584
Salix Pharms	RELISTOR	methylnaltrexone bromide	SOLUTION;SUBCUTANEOUS	021964-001	Apr 24, 2008	9,669,096
Salix	RELISTOR	methylnaltrexone bromide	TABLET;ORAL	208271-001	Jul 19, 2016	6,559,158
Salix Pharms	RELISTOR	methylnaltrexone bromide	SOLUTION;SUBCUTANEOUS	021964-003	Sep 27, 2010	8,552,025
Salix Pharms	RELISTOR	methylnaltrexone bromide	SOLUTION;SUBCUTANEOUS	021964-002	Sep 27, 2010	8,552,025

EU/EMA Drug Approvals for RELISTOR

Company	Drugname	Inn	Product Number / Indication	Status	Generic	Biosimilar	Orphan	Marketing Authorisation	Marketing Refusal
Bausch Health Ireland Limited	Relistor	methylnaltrexone bromide	EMEA/H/C/000870Treatment of opioid-induced constipation in advanced-illness patients who are receiving palliative care when response to usual laxative therapy has not been sufficient.	Authorised	no	no	no	2008-07-01

International Patents for RELISTOR

When does loss-of-exclusivity occur for RELISTOR?

Based on analysis by DrugPatentWatch, the following patents block generic entry in the countries listed below:

Argentina

Australia

Brazil

Canada

Chile

China

Colombia

Costa Rica

Ecuador

Eurasian Patent Organization

European Patent Office

Georgia, Republic of

Guatemala

Hong Kong

Hungary

Israel

Japan

Malaysia

Mexico

Morocco

New Zealand

Peru

Philippines

Poland

Russian Federation

Singapore

South Africa

South Korea

Spain

Taiwan

Tunisia

Ukraine

Generics may enter earlier, or later, based on new patent filings, patent extensions, patent invalidation, early generic licensing, generic entry preferences, and other factors.

See the table below for additional patents covering RELISTOR around the world.

Country	Patent Number	Title	Estimated Expiration
Australia	2004229463	Pharmaceutical formulations containing methylnaltrexone
Australia	2010202824	Pharmaceutical formulations containing methylnaltrexone
Australia	2013203378	Pharmaceutical formulations containing methylnaltrexone
Brazil	PI0409133	formulações farmacêuticas contendo metilnaltrexona
Canada	2521379	FORMULATIONS PHARMACEUTIQUES CONTENANT DE LA METHYLNALTREXONE (PHARMACEUTICAL FORMULATIONS CONTAINING METHYLNALTREXONE)
Canada	2811272	FORMULATIONS PHARMACEUTIQUES CONTENANT DE LA METHYLNALTREXONE (PHARMACEUTICAL FORMULATIONS CONTAINING METHYLNALTREXONE)
China	104383542	PHARMACEUTICAL FORMULATIONS CONTAINING METHYLNALTREXONE

RELISTOR (methylnaltrexone bromide) market dynamics and financial trajectory: exclusivity, competition, and revenue risks

Last updated: July 21, 2026

RELISTOR (methylnaltrexone bromide) has a limited prescription footprint tied to opioid-induced constipation (OIC) and refractory constipation, with revenue driven by branded persistence post-launch and then exposed to generic substitution. Commercial performance has been constrained by shrinking OIC share as managed-care formularies, pathway shifts, and payer restrictions favored alternative OIC classes and by long-tail use that is sensitive to prior authorization and step edits.

What is RELISTOR (methylnaltrexone) used for, and how does demand translate into market dynamics?

RELISTOR is a peripherally acting mu-opioid receptor antagonist (PAMORA). It is used for:

• OIC in adult patients with chronic non-cancer pain who have had insufficient response to laxative(s)
• OIC in adult patients with advanced illness (e.g., cancer) who require opioid analgesics and have had insufficient response to laxative(s)
• Refractory constipation in patients with advanced illness (historically reflected in labeling across geographies)

Which patient segments create the highest commercial value?

• Chronic non-cancer pain with inadequate laxative response is the most stable prescription channel.
• Advanced illness patients skew more episodic but can sustain repeat use around opioid regimen changes.
• The largest demand sensitivity is payer policy: OIC is often managed with step therapy and requires documentation of laxative failure.

How do PAMORAs compete for OIC share?

PAMORAs compete within a crowded OIC market that also includes:

• Osmotic and stimulant laxatives (first-line and step-therapy options)
• Other PAMORAs (e.g., naloxegol, naldemedine)
• Prescription agents outside PAMORA class (in some formularies)

For RELISTOR, differentiation has been largely clinical positioning (rapid onset, route options historically), but payer and pharmacy benefit design increasingly favor newer, formulary-preferred products. That shifts gross-to-net erosion and limits sales growth even where clinical adoption persists.

When did RELISTOR lose exclusivity, and what does that imply for revenue?

Key dynamic: The brand’s long-term trajectory follows the typical pattern for older, small-molecule brands in OIC: branded revenues peak then trend downward as generic methylnaltrexone enters and as rebates/contracting intensify in competitive segments.

• The practical timeline is that RELISTOR’s effective market protection ended once composition and method protections and any market exclusivity (if applicable in the U.S.) were exhausted and generic approvals became possible.
• After generic entry, RELISTOR’s remaining revenue becomes increasingly dependent on contract wins and patient-specific prescriber preferences rather than sustained new-to-brand growth.

How does generic entry affect net revenue specifically?

In OIC, formularies often shift from open coverage to:

• Preferred generic or preferred PAMORA class
• Prior authorization that targets higher-cost brands
• Quantity and duration limits

That produces:

• Price compression across channels
• Increased pharmacy claims variability
• Loss of new prescriptions, with brand retention mostly among patients stabilized on RELISTOR or those for whom alternative agents fail

What patents protect RELISTOR, and how do they shape generic entry risks?

RELISTOR is a well-established small-molecule product. The patent estate for methylnaltrexone typically includes:

• Composition-of-matter protection
• Specific pharmaceutical formulations (including dosage forms and salts)
• Potential method-of-use claims tied to OIC indications and dosing regimens
• Manufacturing and process-related claims

Market impact: once core composition and formulation protections expire, generic entry becomes less a question of technical feasibility and more a question of regulatory pathway timing and payer contracting.

How do formulation and method patents affect competition?

Even after composition expiration, residual exclusivity can persist if:

• A specific formulation (e.g., injection vs oral) is separately protected
• A method-of-use claim is still enforceable for a labeled indication
• Pediatric or other narrow exclusivity applies in the relevant jurisdiction

Once those are cleared, generic and authorized generics move market pricing and volume.

What is the Orange Book status of RELISTOR, and where does it matter financially?

Orange Book listings generally reflect:

• Approved drug products
• Active ingredients
• Patent numbers and expiration dates associated with those products

Financial relevance: Orange Book status informs:

• The likelihood and timing of Paragraph IV challenges
• The expected availability of generic equivalents in key channels
• The risk profile for brand holders’ remaining revenue

Once Orange Book protections tied to key dosage forms expire, payers accelerate substitution, accelerating revenue decline.

What generic entry risks exist for RELISTOR (methylnaltrexone), and what happens to market share?

Risk profile after exclusivity: high. Methylnaltrexone is a mature small molecule, and when patent barriers fall:

• Pharmacy substitution often occurs quickly through PBM formularies
• Wholesale demand shifts to the lowest acquisition cost product unless contracts protect the brand
• Market share transitions to generics and, in parallel, to newer PAMORAs depending on payer preference

How does PBM contracting change after generic launch?

Expect:

• Elevated rebates for brand retention attempts
• Narrowing of brand inclusion to specific plan types
• Increased use of step edits (e.g., OTC laxative trial requirement)
• Switch triggers to preferred alternatives

How does RELISTOR compare with naloxegol and naldemedine in the OIC payer model?

Payer preference often follows:

• Formulary position and contract rebates
• Dosing simplicity and patient adherence
• Clinical differentiation for hard-to-treat subgroups
• Safety and tolerability profiles as interpreted in payer criteria

RELISTOR competes in a market where newer oral PAMORAs have expanded usage. That shifts the center of gravity:

• Away from branded methylnaltrexone in plans that prefer the newer PAMORA class
• Toward generic substitution in plans that still cover methylnaltrexone but do not sustain brand pricing

What FDA pathway and regulatory status dynamics shape RELISTOR’s commercialization?

RELISTOR is an FDA-approved prescription product with established labeling. After generic approvals, the FDA regime primarily impacts:

• Eligibility of generics via abbreviated pathways
• Label comparability and interchangeability
• Post-approval labeling updates that can alter medical necessity criteria

Commercial consequence: regulatory stability can preserve existing brand cohorts, but it does not stop generic price pressure once exclusivity ends.

What patent litigation and settlements have affected RELISTOR commercialization?

As a market matter, RELISTOR’s patent and exclusivity structure is typical for an older small-molecule brand: once the principal barriers expire, litigation becomes less frequent, and generics focus on timely market access and payer contracting.

Commercial takeaway: in late-stage products, litigation timing tends to matter for narrow windows of exclusivity but is rarely sufficient to reverse long-term volume erosion once substitution is structurally enabled.

What is the revenue trajectory for RELISTOR, and what variables drive it?

A realistic revenue trajectory for RELISTOR post-exclusivity is dominated by:

1. Generic substitution and price erosion
2. OIC market shrinkage in specific channels due to preferential coverage of other PAMORAs
3. Net-to-gross pressures from higher rebates in competitive OIC formularies
4. Patient and prescriber switching behavior after new-to-brand loss
5. Contract cycles with PBMs and health systems

Where does RELISTOR still hold commercial traction?

• Patients already stable on methylnaltrexone after prior treatment failures
• Formularies where methylnaltrexone remains a covered PAMORA option without immediate substitution requirements
• Specific prescriber practice patterns and hospital procurement policies where drug acquisition costs drive product selection

What manufacturing and supply-chain issues matter for RELISTOR’s financial performance?

For established injectables, the recurring commercial risk is supply continuity. If supply constraints occur, payers and providers may:

• Switch patients to alternative PAMORAs
• Reduce inventory of the brand and its generics
• Lock in alternative product usage patterns that later persist even after supply normalizes

This can magnify revenue declines once exclusivity ends.

What geographic coverage and international competition risks exist for RELISTOR?

OIC management is global, and methylnaltrexone faces:

• Generic competition in jurisdictions with earlier patent expirations
• Parallel competitive pressure from local and international PAMORAs
• National payer reimbursement models that may favor specific PAMORAs

Net effect: revenue in each market becomes increasingly dependent on local formulary inclusion rather than broad brand protection.

How strong is the patent estate for RELISTOR versus generic and biosimilar substitution threats?

RELISTOR faces:

• Generic substitution threat (primary)
• Limited relevance of biosimilar risk because it is a small molecule, not a biologic

Patent-estate strength is thus evaluated against generic entry barriers:

• Composition-of-matter remaining life
• Formulation-specific remaining claims tied to product versions that drive payer decisions
• Enforceable method-of-use claims for labeled indications

Once those are exhausted, generic substitution becomes the dominant driver of revenue decline.

Key Takeaways

• RELISTOR’s market dynamics are anchored to OIC payer policy, step-therapy requirements, and PBM contract outcomes.
• Revenue trajectory follows a post-exclusivity pattern for mature small molecules: branded sales compress first through contracting, then through generic substitution.
• Competition is not only from generics of methylnaltrexone but also from newer PAMORAs that increasingly win formulary positions.
• Remaining brand value depends on contract retention, patient stability, and supply continuity rather than growth.

FAQs

1. How do PBM step edits for opioid-induced constipation affect RELISTOR persistence vs switching to naloxegol or naldemedine?
2. Does RELISTOR injection versus other dosage forms face different patent-driven competition timing?
3. What drives net price erosion for RELISTOR after generic methylnaltrexone launches?
4. How do FDA labeling updates for OIC indications influence coverage criteria and brand demand?
5. What supply disruptions risk patient switching away from RELISTOR and toward alternative PAMORAs even after normalization?

References

1. FDA Orange Book. “Methylnaltrexone Bromide” (RELISTOR listings). U.S. Food and Drug Administration. https://www.accessdata.fda.gov/scripts/cder/daf/
2. FDA Drug Approval Package / Labeling for RELISTOR (methylnaltrexone bromide). U.S. Food and Drug Administration. https://www.accessdata.fda.gov/scripts/cder/daf/
3. U.S. FDA. Guidance for Industry: ANDAs and generic drug substitution framework. U.S. Food and Drug Administration. https://www.fda.gov/

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