Enasidenib

Introduction Overview

Generic Name

enasidenib

Brand Name

Idhifa

Dosage Form

oral tablet

Drug Class

Miscellaneous antineoplastics

Pharmacokinetics

Absorption:
Enasidenib is administered orally and is rapidly absorbed from the gastrointestinal tract. Studies show that peak plasma concentrations are typically achieved within 4 to 6 hours following oral administration. The bioavailability of enasidenib is sufficient to allow once-daily dosing, and food intake does not significantly affect its absorption, permitting administration with or without meals. Hydration is recommended to maintain optimal absorption and metabolism during therapy.

Distribution:
Enasidenib exhibits extensive plasma protein binding, primarily to albumin, which influences its volume of distribution. The drug distributes into bone marrow effectively, targeting leukemic cells harboring the IDH2 mutation. The volume of distribution supports its activity in hematopoietic tissues, ensuring therapeutic drug exposure at the site of leukemic cell proliferation. The drug’s distribution kinetics indicate low penetration into the central nervous system, consistent with its hematological target.

Metabolism:
Metabolism of enasidenib occurs predominantly in the liver through cytochrome P450 enzymes, particularly CYP3A4. The metabolic pathway involves oxidation to active metabolites, many of which retain inhibitory activity against the mutant IDH2 enzyme. Metabolic stability supports sustained pharmacodynamic effects with daily dosing. The drug’s metabolism can be influenced by concomitant medications that induce or inhibit CYP3A4, necessitating careful drug interaction monitoring.

Elimination:
Enasidenib and its metabolites are primarily eliminated via feces, with a minor proportion excreted renally. The elimination half-life supports once-daily dosing and allows for steady-state plasma concentrations within 15 days of initiation. Renal impairment does not appear to significantly affect drug clearance, but hepatic function should be monitored due to the extensive hepatic metabolism. Dose adjustments may be required in patients with significant hepatic impairment. Studies report that drug exposure remains consistent during prolonged therapy, supporting chronic dosing until disease progression or intolerance.

Dosage Forms

Available Dosage Forms:
- Oral tablet: 100 mg

Dosages for Adults and Adolescents:
- Usual adult dose for acute myeloid leukemia (AML) with IDH2 mutation is 100 mg once daily, administered orally, with or without food.
- Treatment is continued until disease progression or unacceptable toxicity occurs.
- For patients without progression or unacceptable toxicity, a minimum treatment duration of 6 months is recommended to allow for clinical response.

Specific Patient Populations:
- Patients must be selected based on presence of IDH2 mutations confirmed by an FDA-approved diagnostic test.
- No dosage adjustment is routinely required for renal impairment; however, caution is advised in hepatic impairment.
- Safety and efficacy in pediatric populations have not been established.
- Pregnancy is contraindicated; strict contraceptive measures are recommended for both males and females during treatment and for at least 2 months after the last dose due to teratogenic risk.
- Breastfeeding is not recommended during treatment and for 1 month after therapy completion.

Clinical guidelines emphasize adherence to the prescribed dosing schedule and advise against crushing, chewing, or breaking tablets to ensure drug integrity and absorption. Regular monitoring through laboratory testing is important to evaluate efficacy and toxicity during therapy.

Mechanism Of Action

Enasidenib (Idhifa) functions as a targeted molecular therapy specifically inhibiting the mutant isocitrate dehydrogenase-2 (IDH2) enzyme, which plays a pivotal role in the pathogenesis of certain acute myeloid leukemia (AML) subtypes. The IDH2 mutation leads to aberrant enzymatic activity resulting in the production of the oncometabolite 2-hydroxyglutarate (2-HG), which disrupts normal cellular differentiation processes.

By selectively inhibiting the mutant IDH2 enzyme, enasidenib decreases the levels of 2-HG, thereby restoring normal epigenetic regulation and promoting the differentiation of leukemic blasts into mature blood cells. This differentiation reverses the block in maturation characteristic of AML, decreasing the proliferation of immature leukemic cells and allowing restoration of healthy hematopoiesis.

At the cellular level, enasidenib modulates metabolic and epigenetic pathways impaired by the mutant IDH2. Its inhibition of mutant enzyme activity leads to normalization of methylation patterns and gene expression. This mechanism contrasts with conventional cytotoxic chemotherapy which primarily targets dividing cells; enasidenib's targeted approach offers a novel method to address mutated metabolic pathways in AML.

Clinical trials have demonstrated that enasidenib induces responses in patients with relapsed or refractory AML harboring IDH2 mutations, underscoring the clinical utility of targeting oncogenic metabolic enzymes. Comparative mechanisms exist with IDH1 inhibitors used in similar settings. Enasidenib’s differentiation-promoting effects contribute to its clinical profile and unique adverse effect, differentiation syndrome, a direct consequence of abrupt maturation of leukemic cells.

Pharmacological Actions

Selective inhibition of mutant isocitrate dehydrogenase-2 (IDH2) enzyme activity.
Reduction of the oncometabolite 2-hydroxyglutarate (2-HG) levels in leukemic cells.
Restoration of normal cellular differentiation pathways in hematopoietic progenitor cells.
Induction of maturation of malignant myeloblasts into functional blood cells.
Modulation of epigenetic and metabolic dysregulation associated with IDH2 mutations.
Inhibition of leukemic blast proliferation through differentiation rather than cytotoxicity.
Oral targeted therapy enabling sustained systemic exposure with once-daily dosing.
Potential to improve hematologic function and reduce transfusion dependence in AML patients.
Minimal central nervous system penetration, focusing action on bone marrow and blood.
Metabolized primarily by CYP3A4, enabling potential drug-drug interaction considerations.
Shown efficacy in relapsed or refractory acute myeloid leukemia with IDH2 mutations.
May cause differentiation syndrome as a pharmacodynamic consequence of its mechanism.
Improves patient outcomes in genetically defined subpopulations of AML.
Acts specifically on mutated metabolic enzymes rather than general cell proliferation.

Therapeutic Or Clinical Uses

Treatment of relapsed or refractory acute myeloid leukemia (AML) in adults with IDH2 mutations.
Management of AML patients with documented IDH2 gene mutations, confirmed via FDA-approved tests.
Therapy option for patients who have failed prior AML treatments.
Use in AML to promote differentiation and restore healthy blood cell production.
Adjunct in personalized medicine approaches targeting leukemic molecular abnormalities.
Part of molecularly targeted therapy regimens for hematologic malignancies.
Treatment to delay disease progression in IDH2-mutated AML cases.
Option for patients ineligible for intensive chemotherapy due to comorbidities or age.
Clinical tool to reduce leukemic cell burden through targeted enzyme inhibition.
Used in patients requiring a non-cytotoxic approach to AML management.
May be considered in clinical trial settings for combination therapies in AML.
Benefit in improving quality of life by reducing symptoms related to marrow failure.
Treatment aligned with genetic testing for precision oncology in hematology.
Potential role in maintenance therapy post induction in mutation-positive AML.
Therapeutic alternative in AML cases resistant to conventional chemotherapeutic agents.

Side Or Adverse Effects

Differentiation syndrome characterized by fever, cough, dyspnea, bone pain, rapid weight gain, and edema.
Nausea and vomiting, potentially severe and requiring supportive care.
Diarrhea occurring commonly, sometimes persistent during therapy.
Loss of appetite leading to weight changes and nutritional concerns.
Jaundice caused by hepatic involvement or drug-induced liver injury.
Dark urine and clay-colored stools indicating liver dysfunction.
Potential tumor lysis syndrome presenting with muscle cramps, weakness, and electrolyte disturbances.
Signs of hypokalemia or hypocalcemia such as tingling sensations around mouth and extremities.
Fatigue and generalized weakness related to hematologic effects.
Allergic reactions including rash, hives, and rare anaphylactic events.
Elevations in liver enzymes necessitating close monitoring of hepatic function.
Severe or ongoing vomiting and diarrhea potentially leading to dehydration.
Risk of low blood pressure in the context of differentiation syndrome or adverse effects.
Potential for infections due to immunosuppression secondary to AML and therapy.
Gastrointestinal disturbances requiring symptomatic management.

Precautions

Screen patients for IDH2 mutation using FDA-approved diagnostic tests prior to initiating therapy.
Monitor closely for signs and symptoms of differentiation syndrome, especially within the initial 10 days to 5 months of therapy.
Use barrier contraceptive methods during treatment and for at least 2 months after the last dose due to teratogenic risk.
Adjust treatment or discontinue if severe toxicity or signs of differentiation syndrome occur.
Avoid use in patients with known hypersensitivity to enasidenib or any formulation components.
Cautious use in patients with hepatic impairment; monitor liver function tests regularly.
Educate patients on importance of adherence to dosing schedule and not to crush or chew tablets.
Provide patient counseling on hydration to reduce risk of gastrointestinal adverse effects.
Avoid breastfeeding during treatment and for at least one month after completion.
Regular laboratory monitoring to assess treatment efficacy and detect adverse effects early.
Inform patients about potential symptoms indicative of serious side effects requiring urgent medical attention.
Monitor electrolytes and renal function to manage tumor lysis syndrome risk.
Assess fertility considerations and counsel patients accordingly before and during treatment.
Avoid concomitant strong CYP3A4 inducers or inhibitors without close monitoring.
Promptly investigate any new symptoms such as jaundice, swelling, or respiratory difficulty.

Warnings

Boxed warning for differentiation syndrome, which can be fatal if not promptly treated.
Risk of severe and potentially life-threatening adverse reactions including tumor lysis syndrome.
Potential for hepatotoxicity necessitating regular liver function monitoring.
Use in pregnant or breastfeeding women is contraindicated due to risk of fetal harm.
Risk of serious hypersensitivity reactions including anaphylaxis.
May cause fetal harm when administered to pregnant women; pregnancy testing required before initiation.
Use barrier contraception as hormonal contraceptives may be ineffective during treatment.
Drug interactions may alter enasidenib plasma levels, increasing toxicity risk.
Delay in cancer treatment may occur if severe adverse effects develop.
Infections may be worsened due to underlying disease and immunosuppression from therapy.
Gradual onset of differentiation syndrome may obscure diagnosis and delay treatment.
Patients should be informed that symptoms like fever, cough, and swelling require immediate medical evaluation.
Close clinical monitoring is necessary to manage blood count changes and other hematologic toxicities.
Potential for drug accumulation in hepatic impairment necessitates dose adjustments or discontinuation.
Avoid sudden discontinuation without medical oversight to prevent disease flare or progression.

Contraindication

Known hypersensitivity or allergy to enasidenib or any excipients in Idhifa tablets.
Pregnancy due to demonstrated teratogenicity and risk of fetal harm.
Women who are breastfeeding should not use enasidenib.
Patients unable to adhere to contraception recommendations during treatment.
Use in pediatric patients has not been established; safety and efficacy not confirmed.
Concomitant use with drugs contraindicated due to severe drug interactions affecting CYP3A4 metabolism.
Patients with uncontrolled severe hepatic impairment unless risk-benefit justifies use.
History of severe allergic reactions to structurally related compounds may be a relative contraindication.
Patients with active uncontrolled infections or severe immunosuppression requiring different management.
Known intolerance to other miscellaneous antineoplastic drugs may increase risk of adverse effects.
Concomitant active malignancies requiring incompatible therapies.
Patients with severe gastrointestinal malabsorption where oral absorption may be compromised.
Patients who cannot swallow oral tablets reliably or safely.
Previous severe reaction to targeted IDH inhibitors with cross-reactive potential.
Any condition where continued therapy would present unacceptable risk as determined by clinician.

Drug Interactions

Strong CYP3A4 inducers (e.g., rifampin, phenytoin) may decrease enasidenib plasma levels, lowering efficacy.
CYP3A4 inhibitors (e.g., ketoconazole, clarithromycin) may increase enasidenib exposure and toxicity risk.
Concomitant use with drugs prolonging QT interval requires caution and monitoring.
Potential interaction with drugs metabolized by UGT enzymes due to enasidenib's influence on metabolism.
Possible reduced effectiveness of hormonal contraceptives; barrier methods recommended.
Medications causing electrolyte imbalance may increase risk of cardiac adverse effects when combined.
Drugs affecting hepatic metabolism may alter enasidenib pharmacokinetics necessitating dose evaluation.
Co-administration with immunosuppressants may worsen bone marrow suppression.
Potential additive gastrointestinal side effects with agents causing nausea and vomiting.
Interference with laboratory tests related to liver function or hematology may occur.
Use caution with other antineoplastic agents that have overlapping toxicities.
Interactions with herbal supplements like St. John's Wort may affect enasidenib metabolism.
Monitor patients closely when initiating or discontinuing concomitant drugs affecting CYP enzymes.
Ensure complete medication reconciliation to identify potential interactions before treatment.
Adjust enasidenib dose as clinically indicated based on therapeutic drug monitoring or toxicity.

Preparations Of The Drug

Idhifa is supplied as oral tablets of 100 mg strength.
Tablets are intended for oral administration and should be swallowed whole.
Tablets are packaged with a moisture-absorbing desiccant to preserve stability.
Store Idhifa tablets at controlled room temperature, protected from moisture and heat.
Do not crush, chew, or break tablets to maintain intended release characteristics.
Original container packaging includes detailed dosing instructions and safety information.
No intravenous or alternative parenteral formulations are currently available.
Prescription-only medication requiring specialist oncology supervision.
Patient medication guides and counseling materials accompany dispensing.
Handling by healthcare professionals includes use of appropriate protective measures due to antineoplastic properties.
Disposal of unused drugs should follow hazardous waste guidelines appropriate for chemotherapy agents.
Availability may vary by region; generic formulations currently limited.
Medication should be kept out of reach of children and unauthorized persons.
Proper labeling includes warnings regarding teratogenicity and differentiation syndrome risk.
Pharmacy compounding is generally unnecessary due to commercial availability of tablets.