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
Patent Litigation and PTAB cases:	See patent lawsuits and PTAB cases for RELISTOR

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.

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			Y
Salix	RELISTOR	methylnaltrexone bromide	TABLET;ORAL	208271-001	Jul 19, 2016		RX	Yes	Yes			Y
Salix Pharms	RELISTOR	methylnaltrexone bromide	SOLUTION;SUBCUTANEOUS	021964-002	Sep 27, 2010		RX	Yes	Yes
Salix Pharms	RELISTOR	methylnaltrexone bromide	SOLUTION;SUBCUTANEOUS	021964-003	Sep 27, 2010		RX	Yes	Yes
Salix	RELISTOR	methylnaltrexone bromide	TABLET;ORAL	208271-001	Jul 19, 2016		RX	Yes	Yes			Y
Salix Pharms	RELISTOR	methylnaltrexone bromide	SOLUTION;SUBCUTANEOUS	021964-002	Sep 27, 2010		RX	Yes	Yes			Y

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

Honduras

Hong Kong

Hungary

Israel

Japan

Malaysia

Mexico

Morocco

New Zealand

Norway

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)

RELISTOR (methylnaltrexone bromide) investment scenario and fundamentals analysis: exclusivity, patent estate, FDA status, pricing pressure, and generic entry risk

Last updated: July 29, 2026

RELISTOR is a branded methylnaltrexone product used for opioid-induced constipation (OIC) and is also a legacy branded franchise with limited near-term growth levers. The investment profile is dominated by (1) expiring patent and regulatory exclusivity headwinds, (2) small-molecule generic penetration risk typical for older NCE/old-generation branded products, and (3) constrained demand growth due to mature OIC alternatives and payer switching. The practical upside for investors is tied to residual brand strength, channel placement, and any remaining lifecycle protections, not to platform innovation.

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What is RELISTOR (methylnaltrexone bromide) used for and what are the core demand drivers?

RELlSTOR is a peripherally acting mu-opioid receptor antagonist approved for constipation in specific opioid-use settings.

Key indication scope (US)

• Opioid-induced constipation in adults with chronic non-cancer pain who have had inadequate relief with laxative(s).
• Opioid-induced constipation in adults with advanced illness (cancer) who require opioid pain management and have had inadequate relief with laxative(s).
• (US labeling also includes pediatric-adjacent language in some contexts historically, but the core US branded franchise is adult-based.)

Fundamentals that move sales

• OIC prevalence and opioid prescribing trends: slower opioid growth and substitution toward different pain regimens reduces addressable market tailwinds.
• Payer formularies and step edits: RElistor competes against lactulose, polyethylene glycol, stimulant laxatives, and newer OIC agents. Payers generally favor lower-cost options unless RElistor retains formulary positioning.
• Route of administration: injectable convenience can support adherence where oral options fail, but it is less elastic than oral brands for broad access.
• Safety and tolerability: peripherally acting antagonist profile tends to limit central opioid antagonism concerns, but GI adverse events and patient selection still matter.

Commercial interpretation

• Mature OIC category = limited incremental demand creation.
• Brand economics = driven by rebate intensity and net price, not by volume expansion.
• Investor sensitivity = high to formulary losses and generic price resets.

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What is the Orange Book status of RELISTOR (methylnaltrexone bromide) and what does it imply for generic entry timing?

Direct answer: The “Orange Book status” determines whether ANDA filers can challenge patents and at what point exclusivity ends. For legacy small molecules like methylnaltrexone, the practical generic risk often accelerates once the last listed patents expire and any unexpired exclusivity periods lapse.

Investment implication

• When patents listed for a drug are gone, generic entry tends to become a question of manufacturing and regulatory readiness rather than IP.
• If patents are still listed for a specific dosage form or use, Paragraph IV challenges become the main event timing risk.

How to use Orange Book in diligence

• Identify each listed active ingredient strength, dosage form, and patent type:
  • Drug substance patents (composition of matter)
  • Drug product patents (formulation)
  • Method-of-use patents (indications)
• Map each to:
  • Expiration date
  • Any pediatric exclusivity extensions (when applicable)
  • Whether exclusivity is tied to the NDA or to an approval pathway category

Expected diligence outcome for RELISTOR-style franchises

• If Orange Book shows no unexpired exclusivity and no unexpired patents, ANDA launches tend to occur on a near-regular schedule after expiration.
• If there is at least one unexpired formulation or method-of-use patent, launch may be delayed by settlement or ongoing litigation.

(No Orange Book listing data was provided in the prompt; without the specific Orange Book table entries and expiration dates, a complete, accurate patent-expiry timeline for RELISTOR cannot be produced.)

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What patents protect RELISTOR and how strong is the patent estate?

Direct answer: A drug’s patent estate strength is measured by the number of listed patents that remain unexpired, the coverage breadth (composition, formulation, method-of-use), and whether patents are staggered or concentrated around a single expiry window.

How investors should score the estate

• Coverage count: number of distinct, unexpired patents listed for each dosage form/strength.
• Claim dependency: whether method-of-use claims can be “designed around” by limiting patient population or changing labeling.
• Litigation posture: whether prior generic filings indicate sustained risk or implied settlement.

Typical investor conclusion for legacy methylnaltrexone franchises

• If composition-of-matter and method-of-use protections are largely expired, the remaining value is limited to formulation/product-specific patents or exclusivity.
• If there are still active formulation/product patents, generics may delay or enter only with design-around modifications and carve-outs.

(No patent numbers, assignees, or expiration dates were provided. Producing a complete strength assessment without those specifics would risk inaccuracy.)

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When does RELISTOR lose exclusivity and what are the key FDA exclusivity triggers?

Direct answer: Exclusivity loss is driven by:

• Patent expiration for listed patents in the Orange Book
• Any statutory exclusivities (5-year NCE, 3-year new clinical investigations, 7-year orphan, pediatric exclusivity when applicable)
• NDA-specific exclusivity tied to the initial approval and subsequent supplements

Investment timing logic

• If patents drive exclusivity (most common for legacy brands), the “hard” date is the last listed patent expiration.
• If statutory exclusivity is the binding constraint, the “hard” date is exclusivity expiry plus the generic filing strategy that anticipates it.
• For a small molecule with mature approval history, the probability weight shifts toward patent expiry rather than statutory exclusivity.

(No exact exclusivity expiry dates were provided; a date-specific timeline cannot be produced accurately.)

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What patent litigation affects RELISTOR, including Paragraph IV challenges and settlements?

Direct answer: Litigation affects investor risk by changing launch timing and by signaling whether generics expect enforceable remaining patents.

Diligence checklist

• Identify ANDA filings tied to methylnaltrexone dosage forms.
• For each Paragraph IV:
  • Filing date
  • Patents challenged
  • Country of filing is US via ANDA
  • Court, case number, and status
• Map settlements:
  • Design-around terms
  • Carve-out labeling changes
  • Entry-date stipulations
  • Royalty or supply arrangements

(No litigation records, case numbers, or settlement dates were provided. A complete litigation impact analysis requires those data.)

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What formulations are protected by RELISTOR patents and can generics design around them?

Direct answer: Formulation patents usually fall into:

• Compositions for stability, bioavailability, or manufacturability
• Dosage form specific protections (injectable solution properties, excipient systems)
• Device or delivery method claims (less common for simple injectable solutions unless tied to specific stability or formulation performance)

Generic design-around pathways

• Reformulation within acceptable stability and bioequivalence ranges
• Use of different excipient systems
• Narrowing label to avoid method-of-use infringement
• Manufacturing process changes if process patents exist (rare for older small molecules unless specifically claimed)

Investor relevance

• Formulation and process patents often make launch slower but not impossible.
• The key is whether patents are “blocking” with no feasible workaround for generic bioequivalence.

(No patent claim set or formulation patent coverage was provided.)

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How does RELISTOR compare with other opioid-induced constipation therapies and what does that mean for market share?

Competitive set (US)

• Osmotic/stimulant laxatives and combinations
• Other OIC-specific agents (peripherally acting antagonists and newer mechanisms depending on label and payer preference)

Competitive dimensions

• Net price and rebate intensity: generics and formulary-favored agents cap premium pricing.
• Patient preference: injectables can be adopted for rescue therapy when oral laxatives fail.
• Adjudication by payers: step edits often reduce switching into higher-cost brands unless there is documented laxative failure.

Investor read-through

• Even without immediate generic entry, branded OIC sales tend to flatten when payers shift to lower-cost alternatives.
• Generic entry risk adds a price shock, compressing remaining gross margin.

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What generic entry risks exist for RELISTOR and what scenarios drive downside?

Direct answer: The downside scenario is early generic launch that triggers steep price erosion and rapid formulary movement.

Downside drivers

• Loss of remaining unexpired patent “hooks”
• ANDA approval readiness (bioequivalence and manufacturing scale)
• Payer contract renegotiation based on launch presence
• Channel inventory and reimbursement re-coding that compresses the transition period

Scenario framework for investors

• Best case: one or more remaining listed patents delay ANDA approval or keep generics off formularies through label design constraints.
• Base case: delayed but eventual generic entry after last patent expiry leads to predictable price erosion.
• Worst case: early resolution of disputes or broad patent weakness yields faster-than-expected launches and rapid net price decline.

(A scenario with dates and probabilities requires unexpired patent and litigation specifics.)

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What is the revenue exposure and what KPIs matter most for RELISTOR investors?

Investor KPIs

• US net sales and trend: quarter-over-quarter and MAT changes.
• Gross-to-net bridge: rebate, chargebacks, copay assistance burden.
• Script and patient persistence: injectables can show distinct persistence patterns.
• Formulary status:
  • Top payer placement
  • Number of covered lives under each tier
• Inventory and channel fill:
  • Generic anticipation can distort near-term demand.
• Margin sensitivity:
  • Small-molecule injectables can be margin-stable pre-entry but typically compress sharply post-generic.

Interpretation

• For an older branded OIC drug, the main value driver is whether the brand retains pricing power longer than expected through residual protection and contracting.

(No company financials or unit metrics were provided.)

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Key Takeaways

• RELISTOR’s investment fundamentals are primarily driven by residual IP and payer contracting dynamics typical of mature OIC branded products.
• The “decisive” diligence work for generic risk is Orange Book mapping to identify unexpired listed patents and exclusivities by dosage form/strength.
• Patent litigation and Paragraph IV events are the principal timing risk for generic entry. Without specific Orange Book listings and case records, a date-specific exclusivity calendar cannot be built reliably.
• Competitive pressure in OIC is structurally persistent due to payer step edits and the availability of lower-cost alternatives.
• The most actionable investor KPIs are net price (gross-to-net), payer/formulary retention, and formulary switching speed around any generic launch trigger.

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FAQs

1) What determines when methylnaltrexone generics can launch in the US?
Orange Book unexpired patents and any remaining exclusivity periods tied to the NDA approval and supplements.

2) Can a generic launch with a narrower labeling strategy for opioid-induced constipation?
If method-of-use patents are implicated, labeling carve-outs can be a design-around pathway, but the feasibility depends on the specific patent claim language.

3) Does formulation IP usually block generic entry or only slow it?
Formulation patents can delay approvals if they are directly infringed or cannot be designed around while maintaining bioequivalence.

4) What payer behaviors typically reduce branded OIC sales?
Formulary tiering, prior authorization, step edits, and switching incentives after preferred generic availability.

5) How do settlement agreements affect generic entry timing?
Settlements can set entry dates, restrict launch scope, or require label limitations, shifting timing from strict statutory/patent expiry to contract terms.

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References

No sources were provided in the prompt, and no Orange Book, litigation docket, or FDA label sources were included in the supplied information.