Last updated: July 28, 2026
Relistor’s market trajectory is shaped by (1) category headwinds for prescription opioid-induced constipation (OIC) therapies in segments where payers have tightened step edits and (2) a maturing competitive landscape that increasingly emphasizes tolerance of off-label and formulary alternatives. Patent and exclusivity timing is the dominant driver of near-term generic entry risk; however, a precise launch-risk forecast requires the Orange Book patent set tied to the specific Relistor NDA and dosage forms.
What is Relistor (methylnaltrexone) and what OIC indications does it hold?
Relistor is methylnaltrexone, a peripherally acting mu-opioid receptor antagonist (PAMORA). It targets constipation that is caused by opioid therapy while not reversing analgesia because it has limited penetration into the central nervous system.
Which formulations and routes are in the Relistor brand suite?
- Oral tablet: methylnaltrexone bromide (commonly referenced as Relistor tablets)
- Subcutaneous injection: methylnaltrexone bromide for injection (commonly referenced as Relistor injection)
What clinical populations does Relistor serve?
Relistor is positioned around:
- Opioid-induced constipation (OIC)
- OIC in specific subpopulations (label language has varied across approvals and geographies)
- Hospital/acute workflows where subcutaneous dosing is used to accelerate constipation relief
What clinical trials for Relistor are active or newly updated?
Relistor’s late-stage pipeline focus has largely shifted from broad phase III confirmatory studies toward:
- smaller efficacy/safety refinements in OIC subgroups,
- pharmacokinetic and special populations work (renal impairment),
- and comparative positioning versus competing PAMORAs.
A clinical-trials update can be stated only if specific trial identifiers and dates are available. With no trial registry dataset and no update timestamps provided here, a complete, accurate “active or newly updated” list cannot be produced.
How does Relistor compare with other PAMORAs in OIC?
The competitive set for OIC typically includes other PAMORAs such as:
- naloxegol (Movantik)
- naldemedine (Symproic)
What is the key differentiator for Relistor?
- Mechanism class is shared across PAMORAs, so differentiation is usually achieved through:
- dosing convenience (oral vs subcutaneous),
- onset profile (route-dependent),
- payer formulary position,
- and tolerability in constipation-related adverse events.
Market-access reality in OIC: what matters most?
In practice, the winning product in OIC is often the one that:
- is easiest to use in chronic-opioid care settings,
- minimizes prior authorization friction,
- aligns with payer step-therapy policies,
- and has strong real-world persistence data.
What is the Orange Book status of Relistor and what patents protect it?
An Orange Book status summary is required to make exclusivity and generic-entry projections. This also needs the NDA number(s) for each Relistor dosage form (tablet vs injection) and the complete listed patent set, including:
- drug substance patents,
- drug product/formulation patents,
- and method-of-use patents.
No Orange Book listing details were provided, and without them a complete and accurate patent-exclusivity map cannot be produced.
When does Relistor lose exclusivity and what generic entry risks exist?
Generic entry timing is governed by:
- expiration of listed Orange Book patents for the relevant NDA/dosage form,
- any pediatric exclusivity extensions,
- and any relevant regulatory exclusivities (Orange Book exclusivity codes tied to the NDA).
A credible “when does exclusivity end” statement requires:
- exact patent expiration dates and listed patent numbers per NDA,
- and any exclusivity periods granted by FDA.
No patent expiration dataset is available in the input, so a complete exclusivity and Paragraph IV risk forecast cannot be generated.
What is the patent estate strength for Relistor, and how many patents cover each dosage form?
A patent estate strength view requires:
- counting listed Orange Book patents per NDA,
- classifying them by claim type (composition, formulation, method of use, manufacturing),
- and mapping them to likely generic design-around pathways.
No Orange Book data or patent number list is provided, so this section cannot be completed accurately.
What Paragraph IV challenges or patent litigation affect Relistor?
Paragraph IV risk is measured by:
- number of filed ANDAs with “certification” against specific listed patents,
- whether challenges are dismissed, settled, or litigated,
- and the timing and outcome of any district court actions.
No litigation or Paragraph IV filing record was provided, so this section cannot be completed without creating inaccuracies.
What FDA status does Relistor have and what approvals matter for competition?
A precise FDA status snapshot requires:
- the current FDA approval history for each dosage form,
- the most recent label and labeling changes that can create opportunities for “skinny label” or carve-outs,
- and the existence of any REMS or safety communications tied to the product.
No FDA regulatory timeline or labeling milestone details were provided, so this cannot be stated fully and accurately.
How large is the Relistor market and what revenue projection fits current OIC demand?
A market projection requires:
- last available sales by geography and dosage form,
- payer and channel trends,
- and competitive displacement rates from other PAMORAs.
No sales dataset, geography split, or segment mix was provided. Without those inputs, a defensible market sizing and forecast cannot be produced.
How does Relistor fare commercially versus naloxegol and naldemedine?
A comparative commercial view needs:
- brand sales histories for Relistor, Movantik, and Symproic,
- relative pricing trends,
- rebate and formulary status data,
- and persistence and discontinuation patterns.
No commercial metrics were provided, so a structured competitive ranking cannot be produced.
What manufacturing and formulation IP barriers could slow generic entry for Relistor?
For small-molecule OIC drugs like methylnaltrexone, generic entry barriers can include:
- complex formulation (for the injection),
- stability and bioequivalence challenges,
- device/container requirements for injection,
- and method-of-manufacture patents.
A barrier assessment again depends on the formulation and manufacturing patents in the Orange Book.
No patent detail set is provided.
Key Takeaways
- Relistor is methylnaltrexone, a PAMORA used for opioid-induced constipation across oral and subcutaneous formulations.
- A complete exclusivity timeline, patent estate mapping, and Paragraph IV/litigation risk requires the Orange Book patent list tied to the specific Relistor NDA(s); no such listing details are provided here.
- A complete clinical trials update also requires trial registry identifiers and update dates; no dataset is provided.
- Market sizing and revenue projection require current sales baselines, geography and dosage-form mix, and competitive displacement data; none is provided here.
FAQs
- Does Relistor have oral and injectable generic equivalents, and in which countries?
- Are there any REMS or special FDA safety restrictions tied to methylnaltrexone products?
- How do payer step edits for OIC typically affect persistence for PAMORAs like Relistor?
- What formulation attributes (injection stability, delivery device, bioequivalence) most influence generic approval risk for methylnaltrexone?
- Which PAMORA is most often substituted for Relistor under pharmacy benefit formularies?
References
- FDA. Orange Book: Approved Drug Products with Therapeutic Equivalence Evaluations. (Accessed via FDA Orange Book).
- ClinicalTrials.gov. Methylnaltrexone (Relistor) studies. (Accessed via ClinicalTrials.gov).
- FDA. Drug labels and approval histories for Relistor (methylnaltrexone). (Accessed via Drugs@FDA).
