Last updated: September 6, 2026
Enasidenib mesylate, marketed as Idhifa by Bristol Myers Squibb, is an oral IDH2 inhibitor approved for adults with relapsed or refractory acute myeloid leukemia (AML) carrying an IDH2 mutation. The product established a targeted treatment category but has remained a niche commercial asset because of its narrow biomarker-defined population, competition from broader AML therapies, confirmatory-trial setbacks, and limited label expansion.
Bristol Myers Squibb’s publicly reported Idhifa revenue declined from approximately $89 million in 2021 to $82 million in 2022 and approximately $70 million in 2023. The product’s commercial outlook weakened after the IDHENTIFY confirmatory trial failed to demonstrate a statistically significant overall-survival benefit. U.S. regulatory and market status therefore carries greater risk than the original accelerated approval suggested.
What is enasidenib mesylate and how does it work?
Enasidenib mesylate is the mesylate salt of enasidenib, an oral small-molecule inhibitor of mutant isocitrate dehydrogenase 2, or IDH2. IDH2 mutations can create the oncometabolite 2-hydroxyglutarate, which disrupts normal myeloid differentiation. Enasidenib reduces mutant IDH2 activity and can promote differentiation of malignant myeloid cells.
The drug is administered orally at 100 mg once daily. Its principal approved use has been adult patients with relapsed or refractory AML who have an IDH2 mutation identified by an FDA-authorized test.[1]
| Attribute |
Enasidenib mesylate |
| Brand |
Idhifa |
| Active ingredient |
Enasidenib |
| Molecular target |
Mutant IDH2 |
| Dosage form |
Oral tablets |
| Standard dose |
100 mg once daily |
| Initial U.S. approval |
August 1, 2017 |
| FDA pathway |
Accelerated approval |
| Primary indication |
Relapsed or refractory AML with an IDH2 mutation |
| Original sponsor |
Celgene |
| Current commercial owner |
Bristol Myers Squibb |
| Primary market |
United States |
The clinical value proposition is strongest in patients who have exhausted intensive chemotherapy, hypomethylating agents, venetoclax-based therapy, or transplantation options. The commercial limitation is that IDH2 mutations occur in only a minority of AML patients, generally around 8% to 12% depending on the population and testing method.[2]
What is the FDA regulatory status of Idhifa?
The FDA granted accelerated approval in 2017 based primarily on response data from Study AG221-C-001. The approval covered adults with relapsed or refractory AML with an IDH2 mutation after prior therapy.
The label includes important differentiation-syndrome risks. This potentially serious adverse event can involve fever, weight gain, edema, pulmonary infiltrates, hypotension, renal dysfunction, and other inflammatory findings. The label also identifies leukocytosis, tumor lysis syndrome, and embryo-fetal toxicity as material risks.[1]
The required confirmatory IDHENTIFY trial compared enasidenib with conventional care regimens in older patients with relapsed or refractory IDH2-mutated AML. The study did not meet its primary overall-survival endpoint.[3] The result reduced the probability of meaningful label expansion and increased the risk that the accelerated approval could face regulatory review.
FDA milestone timeline
| Date |
Event |
| August 2017 |
FDA grants accelerated approval for relapsed or refractory IDH2-mutated AML |
| 2018 |
Celgene continues U.S. commercialization and post-approval development |
| 2019 |
Bristol Myers Squibb acquires Celgene |
| 2021 |
IDHENTIFY confirmatory study fails to show a significant overall-survival benefit |
| 2022-2024 |
Commercial value remains constrained by narrow use, competition, and confirmatory-trial uncertainty |
The regulatory status should be distinguished from a conventional full approval supported by a positive randomized survival trial. Enasidenib’s original U.S. indication was built on response and durability data under the accelerated-approval framework.
How has enasidenib revenue changed over time?
Idhifa has been a small commercial product within the Bristol Myers Squibb oncology portfolio. Public company filings indicate a downward revenue trajectory after an early period of market establishment.
| Fiscal year |
Reported Idhifa sales, approximately |
| 2021 |
$89 million |
| 2022 |
$82 million |
| 2023 |
$70 million |
Bristol Myers Squibb reports product sales through annual filings and investor materials. Exact presentation can vary by reporting period, currency treatment, and product-category disclosure.[4-6]
The decline from 2021 to 2023 was approximately 21%. That contraction is commercially significant because Idhifa did not develop into a platform product with multiple approved indications. Revenue depended heavily on a single mutation-defined AML indication.
What drove the financial trajectory?
Four factors shaped the product’s revenue performance:
-
Small eligible population. IDH2 mutations are present in a limited percentage of AML patients. The addressable population is smaller than for broad AML products or therapies used across multiple genetic subgroups.
-
Relapsed or refractory positioning. The product was initially directed to patients with advanced disease after prior treatment. This setting has high clinical need but limited treatment duration and substantial patient attrition.
-
Competitive treatment sequencing. Physicians can use azacitidine plus venetoclax, intensive chemotherapy, transplantation, clinical trials, and other targeted therapies depending on patient fitness and disease profile. Enasidenib competes for treatment position, not only for total AML patients.
-
Confirmatory-trial failure. The IDHENTIFY result weakened confidence in survival benefit and limited the likelihood of broadening the label into earlier-line treatment.
What is the commercial market for IDH2-mutated AML?
The relevant market is a narrow segment of the global AML therapeutics market. It is defined by disease status, prior therapy, mutation testing, patient fitness, treatment access, and physician preference.
Competitive landscape
| Therapy |
Target or mechanism |
Commercial relevance |
| Enasidenib |
Mutant IDH2 inhibitor |
Relapsed or refractory IDH2-mutated AML |
| Ivosidenib |
Mutant IDH1 inhibitor |
IDH1-mutated AML across selected treatment settings |
| Azacitidine plus venetoclax |
Hypomethylating agent plus BCL-2 inhibitor |
Broad frontline use in many unfit AML patients |
| Intensive chemotherapy |
Cytotoxic chemotherapy |
Fit patients, often with curative intent |
| Allogeneic transplant |
Cellular treatment |
Consolidation or salvage for selected patients |
| Clinical trials |
Variable |
Important in relapsed or molecularly defined disease |
Ivosidenib is the closest targeted comparator by mechanism, but it inhibits IDH1 rather than IDH2. The two products address separate molecular populations. Venetoclax-based regimens create the more important commercial pressure because they are used broadly in frontline AML and may influence later treatment sequencing.
The market has also shifted toward molecular testing at diagnosis and relapse. Greater testing supports identification of IDH2-mutated patients, but testing alone does not ensure treatment adoption. Physicians must weigh response probability, differentiation syndrome, cytopenias, infection risk, prior therapies, and transplant plans.
What patents protect enasidenib mesylate?
The principal U.S. composition-of-matter patent publicly associated with enasidenib is U.S. Patent No. 9,499,567, assigned to Agios Pharmaceuticals and licensed for development and commercialization through Celgene.[7] The patent covers substituted small molecules, including compounds associated with IDH2 inhibition.
| Patent category |
Publicly associated protection |
Commercial significance |
| Composition of matter |
U.S. Patent No. 9,499,567 |
Core molecule protection |
| Formulation and solid-state protection |
Additional family members and related filings may apply |
Potentially relevant to tablet manufacture and follow-on products |
| Method of use |
IDH2-mutated malignancies and AML treatment claims |
May affect label-specific generic or branded competition |
| Regulatory exclusivity |
Accelerated-approval framework |
Separate from patent term |
The reported expiration date for the core U.S. patent is in 2033, subject to terminal disclaimers, patent-term adjustment, patent-term extension, and the scope of issued claims.[7] A patent expiration date does not by itself establish the first legally available generic launch date. Generic entry also depends on Orange Book listings, Paragraph IV litigation, settlements, regulatory approval, and any applicable pediatric or patent-term extensions.
How strong is the enasidenib patent estate?
The estate has a potentially valuable composition-of-matter anchor because a valid, enforceable core compound patent can block direct substitution until expiry. Its strength is reduced by the product’s modest revenue base and by the possibility that generic manufacturers may challenge the patent well before 2033.
The commercial relevance of formulation and method-of-use patents is more limited than the core molecule patent. A generic applicant may seek approval with a label that omits patented uses, subject to the Hatch-Waxman framework. Formulation patents are more effective when they cover technically necessary tablet characteristics rather than optional excipients or easily avoided manufacturing parameters.
What is the Orange Book status of enasidenib?
Idhifa is an FDA-approved small-molecule drug and falls within the Hatch-Waxman framework rather than the biologics biosimilar pathway. Orange Book-listed patents, if active, can support certification-based patent litigation against an abbreviated new drug application applicant.[8]
A complete commercial assessment requires distinguishing:
- patents listed for the reference product;
- patents with claims covering the active ingredient;
- patents covering the approved formulation;
- method-of-use patents;
- pediatric exclusivity;
- patent-term extension;
- patents removed, expired, disclaimed, or delisted.
No material biosimilar risk applies to enasidenib mesylate because it is not a biologic. The relevant threat is generic competition through an ANDA, potentially accompanied by a Paragraph IV certification.
When does enasidenib lose exclusivity?
The core U.S. patent is publicly reported to expire in 2033, but commercial exclusivity could end earlier through a successful Paragraph IV challenge or settlement. Generic applicants can file before patent expiration and litigate whether the patent is invalid, unenforceable, or not infringed.
The main timing scenarios are:
| Scenario |
Potential market effect |
| No successful challenge |
Generic launch generally deferred until relevant patent barriers expire |
| Paragraph IV settlement |
Entry date depends on negotiated terms |
| Core patent invalidated |
Early generic entry becomes possible |
| Narrow label carve-out |
Generic may enter for unprotected uses while branded use claims remain litigated |
| Regulatory withdrawal or indication change |
May reduce market value without eliminating patent rights |
Because Idhifa sales are comparatively low, the expected value of a lengthy patent challenge may be limited unless the challenger sees manufacturing synergies, international sales potential, or a broader opportunity in IDH2-targeted therapy.
What patent litigation and settlement risks affect Idhifa?
The commercial record does not show a high-profile generic settlement comparable with major blockbuster medicines. The primary legal risk is a future ANDA Paragraph IV challenge directed at the core composition patent or any listed formulation patent.
Potential litigation issues include:
- claim construction for the enasidenib chemical structure;
- validity challenges based on obviousness or written description;
- enablement;
- infringement by a generic active pharmaceutical ingredient;
- patent-term calculations;
- regulatory carve-outs for method-of-use claims;
- damages and injunction standards.
The strongest litigation position would normally come from a valid composition patent with claims that directly cover the generic active ingredient. Method-of-use litigation is more dependent on the generic label and the prescriber’s actual use.
What manufacturing and geographic barriers protect enasidenib?
Enasidenib is a synthetic small molecule, so it does not have the manufacturing complexity associated with monoclonal antibodies, cell therapies, or viral-vector products. Manufacturing barriers are still material in three areas:
-
Active pharmaceutical ingredient control. The manufacturer must reproduce the required chemical route, impurity profile, polymorph or solid-state characteristics, and analytical controls.
-
Tablet formulation. Bioequivalence, dissolution, stability, and control of degradation products are required for ANDA approval.
-
Global regulatory filings. Patent status, data exclusivity, product registration, and use of brand names differ by jurisdiction.
The United States remains the most important patent and regulatory market. Europe, Japan, Canada, and other markets may have different supplementary protection certificates, national patent outcomes, reimbursement terms, and launch timing. A U.S. patent expiry therefore does not establish a global generic launch date.
How does enasidenib compare with ivosidenib?
Enasidenib and ivosidenib are differentiated primarily by mutation target.
| Metric |
Enasidenib |
Ivosidenib |
| Target |
IDH2 |
IDH1 |
| Brand |
Idhifa |
Tibsovo |
| Developer origin |
Agios/Celgene |
Agios |
| AML population |
IDH2-mutated |
IDH1-mutated |
| Main commercial limitation |
Small IDH2 population and confirmatory-trial failure |
Mutation-defined population and competing AML regimens |
| Biologic exclusivity risk |
None |
None |
| Generic pathway |
ANDA |
ANDA |
Ivosidenib has benefited from development across more than one disease setting, including selected newly diagnosed AML patients and cholangiocarcinoma. Enasidenib’s commercial profile has been narrower, leaving it more exposed to weak treatment duration and limited label expansion.
What generic launch risks exist for enasidenib?
The most likely long-term threat is a direct generic enasidenib product after resolution of core patent barriers. Risk increases if:
- Idhifa sales remain below the level needed to support aggressive litigation;
- the active ingredient is commercially straightforward to synthesize;
- the Orange Book contains few enforceable formulation patents;
- the FDA accepts an ANDA with a permissible label carve-out;
- the core composition patent is narrowed or invalidated.
A generic launch would likely produce rapid price erosion because the product is an oral small molecule with no biologic interchangeability barriers. The revenue impact would depend on whether the branded product retains specialist prescribing, patient-support programs, or contractual access advantages.
Key Takeaways
- Enasidenib mesylate is an oral mutant IDH2 inhibitor marketed as Idhifa for relapsed or refractory IDH2-mutated AML.
- Bristol Myers Squibb’s reported Idhifa revenue declined from approximately $89 million in 2021 to about $70 million in 2023.
- The product’s market is constrained by a small biomarker-defined population and competition from venetoclax-based regimens, transplantation, chemotherapy, and clinical trials.
- The FDA granted accelerated approval in 2017, but the IDHENTIFY confirmatory trial failed to show a significant overall-survival benefit.
- U.S. Patent No. 9,499,567 is the principal publicly associated composition patent, with reported expiration in 2033, subject to statutory adjustments and legal challenges.
- Enasidenib has generic, not biosimilar, exposure.
- The product’s financial risk is driven more by market contraction and regulatory uncertainty than by immediate biosimilar competition.
- A future Paragraph IV challenge could materially shorten effective exclusivity if the core patent is invalidated or a settlement permits early entry.
FAQs About Enasidenib Mesylate
Is enasidenib mesylate the same as Idhifa?
Yes. Idhifa is the branded product containing enasidenib mesylate, the mesylate salt form of enasidenib.
Does enasidenib treat IDH1-mutated AML?
No. Enasidenib targets mutant IDH2. Ivosidenib is the principal approved IDH1-targeted comparator.
Is enasidenib a chemotherapy drug?
No. It is an oral targeted small-molecule inhibitor. Its clinical effect is associated with differentiation of malignant myeloid cells rather than conventional cytotoxic chemotherapy.
Can a generic manufacturer launch before 2033?
Potentially. A generic applicant could challenge the relevant patents through a Paragraph IV certification, obtain approval after a successful challenge, or reach a settlement allowing entry before the reported core-patent expiry.
Why did Idhifa sales remain relatively low?
The product addresses a narrow IDH2-mutated AML population, is primarily used in relapsed or refractory disease, competes with multiple treatment strategies, and did not obtain the expected commercial benefit from a positive confirmatory survival result.
References
- U.S. Food and Drug Administration. (2024). Idhifa (enasidenib) prescribing information.
- U.S. Food and Drug Administration. (2017). FDA approves IDHIFA for relapsed or refractory acute myeloid leukemia.
- Bristol Myers Squibb. (2021). IDHENTIFY phase 3 study of Idhifa did not meet primary endpoint in relapsed or refractory IDH2 mutant AML.
- Bristol Myers Squibb. (2022). 2021 annual report.
- Bristol Myers Squibb. (2023). 2022 annual report.
- Bristol Myers Squibb. (2024). 2023 annual report.
- U.S. Patent and Trademark Office. (2018). U.S. Patent No. 9,499,567, substituted 2-oxo-1,2-dihydropyridine compounds and methods of use.
- U.S. Food and Drug Administration. (2024). Approved drug products with therapeutic equivalence evaluations, 44th edition.
