Fedratinib

Introduction Overview

Generic Name

fedratinib

Brand Name

Inrebic

Dosage Form

oral capsule (100 mg)

Drug Class

Multikinase inhibitors

Pharmacokinetics

Absorption:
Fedratinib (Inrebic) is administered orally and primarily absorbed through the gastrointestinal tract. Its bioavailability can be influenced by food intake, with administration alongside a high-fat meal shown to potentially reduce gastrointestinal side effects such as nausea and vomiting without significantly altering systemic exposure. The drug exhibits absorption kinetics suitable for convenient once-daily dosing, with peak plasma concentrations typically reached within hours after administration. However, detailed pharmacokinetic parameters such as Tmax and Cmax have been characterized in phase I and II clinical trials, demonstrating consistent absorption across patient populations.

Distribution:
Fedratinib is moderately distributed throughout the body, with a volume of distribution reflecting extensive tissue penetration, including bone marrow compartments, the primary target site in myelofibrosis treatment. Plasma protein binding of fedratinib is significant but reversible, which may influence its interactions with other highly protein-bound medications. Its ability to reach effective concentrations in the bone marrow contributes to its clinical efficacy. Studies have also noted limited penetration across the blood-brain barrier, which is clinically relevant given the risk of neurological adverse events.

Metabolism:
Fedratinib undergoes hepatic metabolism predominantly via cytochrome P450 enzymes, particularly CYP3A4. This metabolism results in several metabolites, some of which are pharmacologically active, contributing minimally to the overall therapeutic effect. The metabolic pathway implicates fedratinib in drug-drug interactions, especially with inhibitors or inducers of CYP3A4, necessitating careful consideration when co-administered with other agents such as macrolide antibiotics, azole antifungals, or anticonvulsants. Genetic polymorphisms in CYP enzymes may also impact metabolism variability among individuals.

Elimination:
The elimination of fedratinib primarily occurs via fecal excretion of unchanged drug and metabolites, with a minor proportion eliminated renally. The plasma half-life supports once-daily dosing, enhancing patient compliance. Due to its hepatobiliary clearance, hepatic impairment can significantly alter its elimination, mandating dose adjustments or close monitoring. Clinical pharmacokinetic studies underscore the need for periodic liver function assessments during therapy. Furthermore, renal function status minimally affects fedratinib clearance but should be taken into account when concomitant renal insufficiency exists.

Dosage Forms

Available Dosage Forms:
Inrebic is available as oral capsules in a 100 mg dosage strength. The capsules contain fedratinib as the active ingredient and include inactive ingredients such as silicified microcrystalline cellulose and sodium stearyl fumarate. The capsule shell consists of gelatin, red iron oxide, titanium dioxide, and white ink.

Dosages for Adults and Adolescents:
The recommended adult dose of Inrebic for the treatment of myelofibrosis is 400 mg taken orally once daily. This dosing applies to patients with a baseline platelet count of 50 x 10^9/L or greater. The 100 mg capsules allow flexibility in dose titration or adjustment in response to tolerability or adverse effects.

Specific Patient Populations:
Inrebic is not indicated for use in patients under 18 years of age. For patients with difficulty swallowing capsules or those with nasogastric (NG) tubes, the contents of the capsules can be opened and mixed with approximately 180 mL (6 oz) of Ensure Plus nutritional liquid at room temperature for administration either orally or via an NG tube. The mixture should be consumed promptly within 2 hours of preparation to maintain drug stability and efficacy. Dosing considerations are crucial in patients with hepatic impairment or other comorbidities as close monitoring and possible dose modifications may be required.

Mechanism Of Action

Fedratinib, the active component of Inrebic, is a potent and selective inhibitor of Janus-associated kinase 2 (JAK2), a tyrosine kinase involved in the JAK-STAT signaling pathway. This pathway is crucial for hematopoiesis and immune function, mediating signals from various cytokines and growth factors. In patients with myelofibrosis, mutations such as JAK2 V617F result in constitutive activation of JAK2, leading to abnormal proliferation of hematopoietic stem cells and excessive inflammatory signaling.

By selectively binding to the ATP-binding site of JAK2, fedratinib inhibits its kinase activity, thereby preventing phosphorylation and activation of downstream STAT proteins. This effectively reduces pathological myeloid cell proliferation and cytokine-mediated inflammation in the bone marrow microenvironment, mitigating symptoms such as splenomegaly and systemic inflammatory manifestations.

Fedratinib also targets FMS-like tyrosine kinase 3 (FLT3), contributing to its therapeutic effect by inhibiting additional pathways implicated in hematologic malignancies. The dual inhibition of JAK2 and FLT3 differentiates fedratinib from other JAK inhibitors and may underlie its efficacy in overcoming resistance seen in other treatments.

Clinical studies have validated the significance of fedratinib's mechanism, demonstrating symptom improvement, spleen volume reduction, and quality of life enhancements in patients with intermediate-2 or high-risk myelofibrosis. Comparative analyses suggest fedratinib’s unique kinase selectivity profile might confer advantages in certain patient subsets, supporting its role in the therapeutic armamentarium against myeloproliferative neoplasms.

Pharmacological Actions

Selective inhibition of Janus-associated kinase 2 (JAK2) enzyme activity.
Inhibition of FMS-like tyrosine kinase 3 (FLT3), affecting hematopoietic cell proliferation.
Suppression of aberrant JAK-STAT signaling pathway implicated in myelofibrosis pathophysiology.
Reduction of cytokine-mediated inflammation in bone marrow microenvironment.
Decreased splenomegaly through antiproliferative effects on myeloid cells.
Improvement in constitutional symptoms such as night sweats, itching, and early satiety.
Modulation of abnormal hematopoiesis to restore more normal blood cell production.
Potential immune system modulation via inhibition of pro-inflammatory cytokine signaling.
Pharmacokinetic stability allowing once-daily oral dosing regimen.
Capacity to overcome resistance mechanisms associated with other JAK inhibitors by targeting multiple kinases.

Therapeutic Or Clinical Uses

Treatment of intermediate-2 and high-risk primary myelofibrosis (MF).
Management of secondary myelofibrosis following polycythemia vera.
Management of secondary myelofibrosis following essential thrombocythemia.
Reduction of spleen volume in patients with myelofibrosis.
Alleviation of constitutional symptoms including night sweats, itching, and pain associated with MF.
Improvement of quality of life in adult MF patients by controlling disease manifestations.
Use as an alternative for patients who are intolerant or refractory to other JAK inhibitors.
Utilized in patients with adequate platelet counts (≥ 50 x 10^9/L) to mitigate bleeding risks.
Part of comprehensive treatment strategy to modulate aberrant hematopoiesis in myeloproliferative diseases.
Accessed within clinical protocols for targeted kinase inhibition approaches.
Adjunct in symptom-directed therapy where conventional treatments are insufficient.
Medication indicated exclusively for adult patients with appropriate hematological parameters.

Side Or Adverse Effects

Diarrhea, often requiring supportive pharmacologic intervention.
Nausea and vomiting, with recommendations to take with meals for mitigation.
Anemia due to low red blood cell counts necessitating monitoring and possible transfusions.
Thrombocytopenia presenting as low platelet counts with bleeding or bruising risk.
Elevated liver enzymes suggesting hepatotoxicity potential requiring hepatic monitoring.
Increased blood amylase and lipase levels indicating possible pancreatic irritation.
Uveitis characterized by eye pain, redness, photophobia, floaters, or visual acuity decrease.
Encephalopathy including rare but serious risk for Wernicke’s encephalopathy related to thiamine deficiency.
Allergic reactions such as hives, facial swelling, and respiratory distress.
Potential risk of major cardiac events including myocardial infarction and stroke, especially in patients with existing cardiovascular risk factors.
Risk of venous thromboembolism including deep vein thrombosis and pulmonary embolism.
Secondary malignancies including lymphoma and other cancers observed in JAK inhibitor class.
Fatigue, dizziness, confusion, and blurred vision impacting daily activities.
Gastrointestinal discomfort and weight loss potentially leading to malnutrition.
Rare but serious neurological complications requiring immediate medical attention.

Precautions

Monitor thiamine (Vitamin B1) levels prior to and during treatment to prevent Wernicke’s encephalopathy.
Administer Vitamin B1 supplementation (100 mg daily) concomitantly throughout therapy.
Conduct frequent blood count monitoring to detect anemia and thrombocytopenia early.
Perform regular liver function tests due to risk of hepatotoxicity.
Screen for pre-existing or new eye disorders; prompt ophthalmologic evaluation if symptoms develop.
Assess cardiovascular risk factors before initiation; monitor for cardiac symptoms during therapy.
Evaluate for risk of thromboembolism; monitor for signs of deep vein thrombosis or pulmonary embolism.
Use extreme caution or avoid use in patients with known thiamine deficiency until corrected.
Delay or discontinue therapy if Wernicke’s encephalopathy is suspected, initiating parenteral thiamine.
Carefully review concomitant medications due to numerous drug interactions.
In patients unable to swallow capsules, use recommended administration instructions to ensure adequate drug delivery.
Closely observe patients with liver or kidney impairment to adjust therapy accordingly.
Contraindicated in pediatric populations; safety in patients under 18 years not established.
Avoid abrupt discontinuation without medical supervision to prevent rebound disease symptoms.
Educate patients about signs of serious adverse effects needing urgent medical evaluation.

Warnings

Boxed Warning for encephalopathy including Wernicke’s encephalopathy, a potentially fatal neurological disorder.
Risk of serious infections due to immunomodulatory effects requiring vigilant monitoring.
Potential for severe hematologic toxicities leading to need for blood transfusions or therapy interruption.
Possibility of major cardiac events such as heart attack and stroke, particularly in patients with cardiovascular risk factors or smokers.
Increased risk of venous thromboembolic events; symptoms necessitate immediate medical attention.
Risk of new secondary malignancies including lymphoma; ongoing surveillance warranted.
Allergic reactions can be severe and require emergency treatment.
Use with caution during pregnancy due to unknown fetal risk; contraindicated during breastfeeding.
Possible impairment of cognitive and motor skills impacting ability to operate machinery or drive.
Drug interference with liver enzymes may unpredictably alter metabolism of other drugs.
Not recommended for patients with active thiamine deficiency without appropriate repletion.
Requires continuous thiamine supplementation to prevent deficiency-related complications.
Clinical worsening or new adverse symptoms mandate prompt medical evaluation and possible treatment modification.
Concomitant use with certain medications can exacerbate toxicities; thorough medication review essential.
Discontinue therapy immediately upon suspicion of serious neurological side effects.

Contraindication

Known hypersensitivity to fedratinib or any component of the formulation.
Pre-existing thiamine (Vitamin B1) deficiency not corrected prior to initiation.
Use in pediatric patients under 18 years due to lack of safety and efficacy data.
Concomitant use with strong CYP3A4 inhibitors or inducers without careful monitoring or dose adjustment.
Patients with severe hepatic impairment without appropriate clinical oversight.
Pregnancy due to potential for fetal harm and lack of conclusive safety data.
Current breastfeeding mothers as fedratinib may be present in breast milk.
Patients with active, uncontrolled infections requiring systemic therapy.
Significant bleeding disorders where thrombocytopenia may worsen bleeding risk.
Known or suspected hypersensitivity or allergic reactions to capsule excipients such as gelatin or iron oxide.
Severe gastrointestinal dysfunction preventing oral administration or absorption.
Severe cardiac or cerebrovascular disease where risks outweigh benefits unless treated at specialist centers.
Patients unwilling or unable to adhere to thiamine supplementation protocols.
Those with history of severe neurological disorders exacerbated by metabolic disturbances.

Drug Interactions

Macrolide antibiotics (clarithromycin, erythromycin) may increase fedratinib plasma levels via CYP3A4 inhibition.
Azole antifungal agents (itraconazole, ketoconazole, posaconazole, voriconazole) potentially elevate fedratinib exposure.
Antiretrovirals including atazanavir, darunavir, efavirenz, and ritonavir interact through CYP3A4 pathways affecting fedratinib metabolism.
Cardiac medications like quinidine, amiodarone, diltiazem, and verapamil may alter fedratinib pharmacokinetics.
Cimetidine and mifepristone have demonstrated impact on fedratinib’s metabolic clearance.
Nefazodone and cannabidiol may inhibit CYP enzymes leading to increased fedratinib levels.
Immunosuppressants such as cyclosporine could have additive adverse effects or pharmacokinetic interactions.
Antiepileptic drugs (phenytoin, carbamazepine, oxcarbazepine, primidone) are CYP inducers that may reduce fedratinib effectiveness.
Rifampin significantly induces liver enzymes leading to decreased fedratinib plasma concentration.
St. John's wort reduces fedratinib exposure due to CYP3A4 induction; concurrent use is discouraged.
Antiemetics such as ondansetron may interact and require monitoring of adverse symptoms.
Androgen receptor inhibitors (apalutamide, enzalutamide) and mitotane can alter fedratinib metabolism.
Serotonergic agents like sumatriptan require cautious use considering central nervous system effects.
Opioid drugs such as methadone may have additive sedative effects with fedratinib.
Corticosteroids (dexamethasone, prednisone) can influence CYP metabolism and immune modulation during fedratinib therapy.

Preparations Of The Drug

Inrebic is supplied as 100 mg oral capsules containing fedratinib as the active pharmaceutical ingredient.
Capsule excipients include silicified microcrystalline cellulose and sodium stearyl fumarate to ensure capsule stability and bioavailability.
Capsule shells consist of gelatin, red iron oxide, titanium dioxide, and white ink to provide product integrity and identification.
For patients unable to swallow capsules, dosage contents can be mixed with Ensure Plus nutritional liquid at room temperature for oral or nasogastric administration.
Prepared mixtures should be consumed or administered within two hours to maintain drug efficacy and stability.
Storage instructions specify room temperature conditions away from moisture and heat to preserve product quality.
Packaging is designed for patient convenience facilitating once-daily dosing with clear labeling.
The formulation is manufactured under Good Manufacturing Practice (GMP) adherence by Bristol-Myers Squibb Company.
Commercial production ensures consistent capsule drug load accuracy and minimal batch variability.
Labeling includes thorough patient information on dosing, side effects, warnings, and administration guidelines.
Additional Vitamin B1 supplementation (100 mg daily) is recommended as an adjunct preparation during therapy.
Physicochemical properties of capsules allow for reliable absorption and patient compliance.
Inactive ingredients selected to minimize allergenic potential and support capsule shelf life.
Drug interaction potential mandates healthcare provider oversight for preparation and administration adjustments.
The capsules are part of a comprehensive treatment kit including educational materials and prescribing information.