Eltrombopag

Introduction Overview

Generic Name

eltrombopag

Brand Name

Promacta

Dosage Form

Film-coated tablets and oral suspension

Drug Class

Platelet-stimulating agents, Thrombopoietin receptor agonists

Pharmacokinetics

Absorption:
Eltrombopag is administered orally and exhibits variable absorption influenced by food and divalent cations. Peak plasma concentrations are typically reached 2 to 6 hours post-dose. The drug should be taken on an empty stomach, at least 1 hour before or 2 hours after meals, as concurrent ingestion of calcium-rich foods or supplements significantly decreases absorption by chelation. This interaction necessitates specific timing relative to meals and supplements containing aluminum, calcium, magnesium, or iron to maintain optimal bioavailability.

Distribution:
Eltrombopag demonstrates extensive plasma protein binding (>99%), primarily to albumin and alpha-1-acid glycoprotein, which limits its volume of distribution to approximately 117 liters. It does not appreciably cross the blood-brain barrier but distributes effectively in the systemic circulation and bone marrow, targeting thrombopoietin receptors on hematopoietic cells. The plasma half-life supports once-daily oral dosing.

Metabolism:
Eltrombopag undergoes hepatic metabolism predominantly via glucuronidation mediated by UDP-glucuronosyltransferase enzymes and oxidation primarily by cytochrome P450 CYP1A2 and CYP2C8 pathways. Metabolism is influenced by liver function; patients with hepatic impairment require dose adjustments. No active metabolites have been identified. The drug's metabolic pathway has low potential for significant cytochrome P450-mediated drug interactions, but caution is warranted when co-administered with drugs affecting hepatic enzymes.

Elimination:
The elimination of eltrombopag occurs mainly via fecal excretion of metabolites, with negligible renal clearance. Approximately 59% of an oral dose is excreted through feces and around 31% in urine as metabolites. The terminal half-life ranges from 21 to 32 hours in healthy subjects, facilitating once-daily dosing. Impaired hepatic function may alter clearance, necessitating careful monitoring and dose modification to avoid toxicity.

Dosage Forms

Available Dosage Forms:
- Film-coated tablets available in 12.5 mg, 25 mg, 50 mg, 75 mg, and 100 mg strengths.
- Oral suspension powder for reconstitution with water.

Dosages for Adults and Adolescents:
- For severe aplastic anemia (first-line):
- Adults: 150 mg once daily (75 mg once daily in patients of Asian ancestry).
- Refractory severe aplastic anemia: initial dose 50 mg once daily, titrated up to 150 mg; 25 mg initial dose for Asian ancestry patients.
- For immune thrombocytopenic purpura (ITP):
- Adults: 50 mg once daily (25 mg for East Asian ancestry).
- Maximum 75 mg daily.
- For thrombocytopenia in hepatitis C patients:
- Initial dose 25 mg once daily, maximum 100 mg once daily, adjusted to maintain platelet counts sufficient to initiate and maintain antiviral therapy.
- Pediatric patients:
- ITP ages 1 to 5 years: 25 mg once daily.
- ITP ages 6 and above: 50 mg once daily (25 mg for East Asian ancestry).
- Aplastic anemia:
- 2 to 5 years: 2.5 mg/kg once daily (1.25 mg/kg for Asian ancestry).
- 6 to 11 years: 75 mg once daily (37.5 mg for Asian ancestry).
- 12 years and older: 150 mg once daily (75 mg for Asian ancestry).

Specific Patient Populations:
- Patients of Asian ancestry require approximately half the dosage compared to non-Asian patients due to increased plasma concentrations.
- Dosing adjustments based on platelet count response are necessary.
- Promacta tablets must be swallowed whole; crushing or chewing is discouraged.
- Oral suspension must be mixed only with cool or cold water and used immediately; prepared doses expire within 30 minutes.
- Frequent monitoring of blood counts, liver function, and ophthalmologic examination for cataracts are recommended, especially in long-term use.

Mechanism Of Action

Eltrombopag is a small molecule thrombopoietin receptor (TPO-R) agonist that stimulates megakaryocyte proliferation and differentiation, thereby enhancing platelet production. It binds selectively to the transmembrane domain of the TPO receptor, also known as c-Mpl, which is located on hematopoietic stem cells and megakaryocytes. This non-competitive binding at the transmembrane site differs from endogenous thrombopoietin, which binds at the extracellular domain, allowing eltrombopag to activate the receptor independently and synergistically.

Upon binding, eltrombopag triggers intracellular signaling cascades, primarily activating the JAK-STAT pathway, leading to transcription of genes involved in cell survival, proliferation, and differentiation. Additionally, it stimulates the MAP kinase and PI3 kinase pathways, which further contribute to megakaryocyte maturation and platelet release into circulation. This mechanism enables platelet count increases in patients with thrombocytopenia.

Clinical implications of this mechanism include the capacity to elevate platelet counts in patients with chronic immune thrombocytopenia (ITP), hepatitis C-associated thrombocytopenia, and aplastic anemia, improving hemostasis and reducing bleeding risk. Importantly, eltrombopag’s unique binding permits its use alongside endogenous thrombopoietin, as it does not downregulate the receptor or compete for the same site.

Comparatively, eltrombopag differs from other TPO receptor agonists such as romiplostim, a peptide mimetic administered parenterally, by its oral bioavailability and distinct receptor interaction. This profile confers clinical advantages in patient convenience and pharmacological synergy.

Research has demonstrated that eltrombopag can facilitate multilineage hematopoiesis beyond platelets in aplastic anemia, reflecting possible effects on hematopoietic stem cells. However, continuous monitoring for clonal evolution and potential progression to myelodysplastic syndromes is essential given the proliferative stimulus imparted by eltrombopag.

Pharmacological Actions

Acts as a thrombopoietin receptor agonist stimulating platelet production.
Promotes megakaryocyte proliferation and differentiation in bone marrow.
Increases circulating platelet counts to reduce bleeding risk in thrombocytopenic patients.
Enhances multilineage hematopoiesis in aplastic anemia beyond just platelet lineage.
Non-competitive binding to the transmembrane domain of the thrombopoietin receptor.
Activates intracellular signaling pathways including JAK-STAT, MAP kinase, and PI3 kinase.
Oral bioavailability distinguishes it from peptide-based thrombopoietin mimetics.
Facilitates continuation or initiation of antiviral therapy in hepatitis C patients by raising platelet counts.
Does not compete with endogenous thrombopoietin, allowing additive effects.
Potential proliferative effect on hematopoietic stem cells necessitating monitoring for clonal evolution.
Modulates hematopoiesis without direct immunosuppression.
Protects against bleeding complications associated with low platelet counts.
Has a dose-dependent effect on platelet counts with titration based on clinical response.
Does not restore normal platelet counts but maintains counts sufficient to avoid bleeding.

Therapeutic Or Clinical Uses

Treatment of chronic immune thrombocytopenia (ITP) in adults and children one year and older refractory to other therapies.
Increase of platelet counts in hepatitis C patients undergoing interferon and ribavirin therapy to enable treatment continuation.
Management of aplastic anemia in adults and children aged 2 years and older in combination with other immunosuppressive therapies.
Used to reduce risk of bleeding in patients with thrombocytopenia due to ITP or aplastic anemia when other treatments have failed.
Facilitates initiation and maintenance of antiviral therapy in hepatitis C patients with thrombocytopenia.
Not indicated for treatment of thrombocytopenia from causes other than ITP, aplastic anemia, or hepatitis C therapy.
Not approved for treatment of myelodysplastic syndromes.
Employed primarily to maintain platelet counts between 50 and 200 x 10^9/L to minimize bleeding risks.
Off-label use may exist, but clinical evidence supports the approved indications.
Useful in patients who have undergone splenectomy but have persistent thrombocytopenia.
Provides an alternative to platelet transfusion for some patients.
Supports hematologic recovery in aplastic anemia, reducing transfusion dependence.
Used under specialist hematology supervision with regular monitoring.
Helps prevent bleeding complications without restoring normal platelet function.
Improves quality of life by reducing bleeding episodes and associated morbidity.

Side Or Adverse Effects

Nausea and diarrhea are among the most common gastrointestinal side effects.
Headache and fatigue frequently reported during therapy.
Anemia, evidenced by low red blood cells causing pallor and tiredness.
Elevation of liver enzymes and hepatotoxicity requiring regular liver function monitoring.
Serious risk of thromboembolic events including stroke, deep vein thrombosis, and pulmonary embolism due to excessive platelet counts.
Vision changes, including tunnel vision, eye pain, or halos around lights indicating possible cataract formation.
Bruising and bleeding episodes may paradoxically occur during treatment or after discontinuation.
Hypersensitivity reactions including rash, hives, swelling, and difficulty breathing (rare).
Confusion and fatigue as manifestations of liver dysfunction or hepatic encephalopathy.
Right upper quadrant abdominal pain associated with hepatotoxicity.
Possible increase in risk of clonal evolution to myelodysplastic syndrome or acute leukemia with prolonged use in specific populations.
Pain or burning during urination reported in some patients.
Diarrhea and vomiting indicating gastrointestinal intolerance.
Cough and fever may develop as nonspecific symptoms.
Laboratory abnormalities including abnormal bone marrow morphology.

Precautions

Use with caution in patients with pre-existing liver disease; monitor liver function tests regularly.
Avoid use in patients with myelodysplastic syndrome or pre-existing hematologic malignancies due to risk of progression to leukemia.
Adjust dosing in patients of East or Southeast Asian ancestry due to increased plasma drug exposure.
Monitor platelet counts closely to avoid thrombocytosis and associated thrombotic complications.
Take the medication on an empty stomach and avoid concomitant intake with calcium-rich foods or supplements.
Use effective contraception during treatment and for at least 7 days after stopping due to potential fetal harm.
Avoid breastfeeding while receiving eltrombopag therapy.
Patients with history of cataracts should have periodic ophthalmologic evaluation during therapy.
Avoid concomitant use with antacids or supplements containing polyvalent cations within 2 hours before or 4 hours after dosing.
Discontinuation may lead to rebound thrombocytopenia and increased bleeding risk; monitor closely.
Be vigilant for signs of blood clots and report symptoms promptly.
Dose adjustments should be guided by platelet count response to minimize adverse effects.
Use caution in patients with history of blood clots or hypercoagulable states.
Patients should avoid activities that increase bleeding risk especially during and up to 4 weeks after cessation.
Ensure adherence to monitoring schedules for blood counts, liver function, and eye examination.

Warnings

Risk of hepatotoxicity and liver function abnormalities; immediate medical attention required for signs of liver injury.
Increased risk of thromboembolic events with excessive platelet counts, including strokes and deep vein thrombosis.
Do not use in patients with myelodysplastic syndrome or pre-existing blood cancers due to potential for malignant progression.
Risk of bleeding may increase transiently after stopping treatment; careful monitoring for at least 4 weeks post-therapy is essential.
Avoid intake with dairy products or calcium-containing substances close to dosing time to prevent reduced efficacy.
Use with ribavirin and interferon treatment in chronic hepatitis C may heighten risk of liver problems.
Call your doctor immediately if signs of liver dysfunction occur: nausea, upper abdominal pain, confusion, jaundice.
Potential for serious allergic reactions including anaphylaxis exists.
Patients of East Asian descent require lower dosing due to increased sensitivity and higher plasma concentrations.
Risk of vision changes and cataract development; periodic ophthalmologic assessments recommended.
Pregnancy category indicates potential fetal harm; contraindicated in pregnancy.
Concomitant use with certain medications can reduce drug effectiveness and should be carefully managed.
Dose-dependent side effects necessitate careful titration and ongoing surveillance.
Use caution in patients who have undergone splenectomy, as platelet responses may differ.
Avoid use in patients with conditions causing thrombocytopenia other than the approved indications.

Contraindication

Known hypersensitivity to eltrombopag or any formulation components.
Patients with myelodysplastic syndrome due to risk of worsening disease and progression to leukemia.
Pregnant women due to potential teratogenic effects on the fetus.
Patients with thrombocytopenia not related to ITP, hepatitis C therapy, or aplastic anemia.
Severe hepatic impairment where drug metabolism may be significantly affected without clear benefits.
Breastfeeding women, as eltrombopag may be excreted in human milk and cause adverse effects in infants.
Use in patients with active or uncontrolled thrombotic disorders unless benefits outweigh risks.
Concurrent use with certain antacids or supplements contraindicated if dosing intervals cannot be maintained.

Drug Interactions

Antacids containing calcium, magnesium, or aluminum can reduce eltrombopag absorption; separate doses by 2 hours before or 4 hours after.
Oral supplements containing calcium, iron, magnesium, selenium, or zinc interact similarly; dosing separation necessary.
Concomitant use with anticoagulants such as warfarin, apixaban, clopidogrel, enoxaparin may increase bleeding or thrombotic risk; monitor accordingly.
Statins including atorvastatin, pravastatin, rosuvastatin, simvastatin may have altered plasma levels when co-administered.
CYP1A2 and CYP2C8 inhibitors or inducers may impact metabolism, although clinically significant interactions are limited.
Ribavirin and interferon antiviral therapy combined with eltrombopag increases risk of hepatotoxicity.
No significant interactions reported with most common medications but close monitoring advised when initiating or stopping concurrent therapy.
Caution with other platelet-modifying agents to prevent additive thrombotic risks.
Vitamin or mineral supplements should be managed to avoid impacting eltrombopag bioavailability.
Avoid grapefruit juice due to potential for enzyme-mediated metabolic interactions (theoretical).
Use of immunosuppressive agents in aplastic anemia should consider overlapping toxicities.
Drugs altering gastric pH may influence eltrombopag dissolution and absorption.
Frequent labs recommended to monitor for interaction-related adverse effects during co-administration.
Potential for interference with laboratory coagulation tests during treatment.

Preparations Of The Drug

Film-coated tablets in strengths of 12.5 mg, 25 mg, 50 mg, 75 mg, and 100 mg for oral administration.
Oral suspension powder for reconstitution with cold water, designed for pediatric or patients unable to swallow tablets.
Tablets composed of eltrombopag olamine active ingredient with inactive ingredients including magnesium stearate, mannitol, microcrystalline cellulose, povidone, and sodium starch glycolate.
Tablet coatings utilize FD&C colorants (Blue No. 2 aluminum lake for 50 mg, Yellow No. 6 aluminum lake for 25 mg, Iron Oxide pigments for 75 mg), hypromellose, polyethylene glycol, and polysorbate 80 to ensure stability and masking taste.
Oral suspension requires preparation immediately prior to administration and should be discarded if not used within 30 minutes to ensure potency.
Storage at room temperature protected from moisture and heat recommended for all formulations.
Tablets should be kept in original containers with desiccant to maintain integrity.
Dosing syringes or appropriate measuring devices provided for oral suspension to ensure accuracy.
No generic versions branded under Promacta currently, but eltrombopag is available generically.
The drug is distributed commercially by Novartis Pharmaceuticals Corporation.
Medication guides accompany each packaging to instruct on dosing, administration, and precautions.
Formulations are designed to maintain consistent release and absorption characteristics for daily dosing convenience.