Eltrombopag

MECHANISM OF ACTION

Eltrombopag is a thrombopoietin receptor agonist (TPO-RA) that binds to the transmembrane domain of the thrombopoietin (c-Mpl) receptor on megakaryocyte precursors in the bone marrow. This binding stimulates the proliferation and differentiation of megakaryocytes, leading to an increased production of platelets.

PHARMACOKINETICS

Absorption 

Eltrombopag is orally administered and rapidly absorbed, reaching peak plasma concentrations (Cmax) within 2 to 6 hours after a dose. Its oral bioavailability is affected by food and divalent cations—co-administration with calcium-, magnesium-, aluminum-, or iron-containing foods or supplements can significantly reduce absorption.

Distribution

Eltrombopag is highly bound to plasma proteins (≥99%), mainly albumin, which limits its free circulating concentration. It has a moderate volume of distribution, indicating that it largely remains in the plasma with limited tissue penetration.

Metabolism

Eltrombopag is primarily metabolized in the liver through glucuronidation, oxidation, and minor cytochrome P450 (CYP1A2 and CYP2C8) pathways. Its metabolites are mostly inactive, and hepatic metabolism is essential for drug clearance and maintaining safe plasma levels.

Elimination

Eltrombopag is eliminated primarily via feces (≈59%) and to a lesser extent via urine (≈31%), mostly as metabolites rather than unchanged drug. Its terminal half-life ranges from 21 to 32 hours, allowing for once-daily oral dosing.

PHARMACODYNAMICS

Eltrombopag is a thrombopoietin receptor agonist (TPO-RA) that stimulates platelet production by binding to the c-Mpl receptor on megakaryocyte precursors in the bone marrow. This leads to a dose-dependent increase in platelet counts, helping prevent bleeding in conditions like chronic immune thrombocytopenia (ITP), aplastic anemia, and hepatitis C–related thrombocytopenia. Its effects are gradual, usually seen within 1–2 weeks of therapy, and platelet levels return toward baseline after discontinuation, reflecting its reversible and controllable action.

ADMINISTRATION

Eltrombopag is administered orally as a tablet, usually once daily. To ensure optimal absorption, it should be taken on an empty stomach or at least 2 hours before or 4 hours after meals containing calcium, dairy products, or other minerals.

DOSAGE AND STRENGTH

Eltrombopag is available as 25 mg, 50 mg, and 75 mg oral tablets. For chronic immune thrombocytopenia (ITP), adults typically start with 50 mg once daily, which can be adjusted up to 75 mg based on platelet response, while children receive 25–50 mg daily depending on body weight. In severe aplastic anemia, the recommended dose is 150 mg once daily as part of combination therapy.

DRUG INTERACTIONS

Eltrombopag can interact with other medications through chelation and liver metabolism. Co-administration with divalent cations such as calcium, magnesium, iron, or aluminum can reduce its absorption, while drugs metabolized by CYP1A2 or CYP2C8 may be affected by its use.

FOOD INTERACTIONS

Eltrombopag absorption is significantly reduced by foods or supplements containing divalent cations such as calcium, magnesium, iron, or aluminum. To ensure optimal absorption, it should be taken on an empty stomach or at least 2 hours before or 4 hours after meals containing these minerals.

CONTRAINDICATIONS

Eltrombopag is contraindicated in patients with a known hypersensitivity to the drug or its components, those with severe liver disease or active hepatic impairment, and individuals with uncontrolled high platelet counts due to the risk of thrombosis.

SIDE EFFECTS

• Headache 

• Nausea and vomiting 

• Fatigue 

• Diarrhea 

• Abdominal pain 

• Muscle or joint pain 

• Elevated liver enzymes

TOXICITY

Toxicity from Eltrombopag can occur with excessive dosing or prolonged use, leading to hepatotoxicity, excessive platelet production, and thrombotic events. Liver injury is a significant concern, as indicated by elevated liver enzymes, and overproduction of platelets may increase the risk of blood clots.