Eltrombopag

• Immune Thrombocytopenia (ITP)
• Chronic Hepatitis C Thrombocytopenia
• Severe Aplastic Anemia
• Low Platelet Count

Eltrombopag is a thrombopoietin receptor agonist used to increase platelet production in various conditions including chronic immune thrombocytopenia (ITP), chronic hepatitis C-associated thrombocytopenia, and severe aplastic anemia. This oral medication stimulates megakaryocyte growth and differentiation.

Mechanism of Action

Eltrombopag is a small molecule, non-peptide thrombopoietin receptor (TpoR/c-MPL) agonist. It binds to the transmembrane domain of the TpoR, distinct from the binding site of endogenous thrombopoietin (TPO), and activates intracellular signaling pathways (JAK/STAT, MAPK) that promote megakaryocyte proliferation and differentiation from bone marrow progenitor cells. This leads to increased platelet production. Unlike recombinant TPO, eltrombopag does not compete with endogenous TPO and may have additive effects. In aplastic anemia, eltrombopag may also stimulate hematopoietic stem cells through direct and indirect mechanisms.

Available Formulations

Eltrombopag is available as film-coated tablets (12.5 mg, 25 mg, 50 mg, 75 mg) and as a powder for oral suspension (12.5 mg and 25 mg packets). The medication should be taken on an empty stomach (1 hour before or 2 hours after a meal). Food, especially dairy products and calcium-fortified foods, significantly reduces absorption. Metal cation-containing products should be separated by at least 4 hours.

Medical Uses

Eltrombopag is FDA-approved for chronic immune thrombocytopenia (ITP) in adults and pediatric patients 1 year and older with insufficient response to corticosteroids, immunoglobulins, or splenectomy; thrombocytopenia in patients with chronic hepatitis C to allow initiation and maintenance of interferon-based therapy; and severe aplastic anemia in patients with insufficient response to immunosuppressive therapy. It is also approved as first-line treatment for severe aplastic anemia in combination with standard immunosuppressive therapy.

Dosing Guidelines

For ITP in adults, start at 50 mg once daily (25 mg for East Asian patients), adjusting dose to achieve target platelet count (≥50,000/µL); maximum dose is 75 mg daily. For hepatitis C-associated thrombocytopenia, start at 25 mg daily, titrating to target platelet count needed for antiviral therapy. For severe aplastic anemia, doses up to 150 mg daily are used. Dose adjustments are based on platelet response. East Asian patients may have higher drug exposure and should start at reduced doses.

Important Safety Information

Eltrombopag carries a boxed warning for hepatotoxicity, including severe and potentially life-threatening cases. Liver function tests should be monitored before and during therapy; dose reduction or discontinuation may be required. The medication may increase thrombotic/thromboembolic risk in patients with chronic liver disease. Eltrombopag is only available through a restricted distribution program (PROMACTA CARES) for hepatitis C patients. Cataracts have developed in rodent studies; regular ophthalmologic monitoring is recommended.

Drug Interactions

Polyvalent cation-containing products (antacids, calcium, iron, magnesium, aluminum, zinc, selenium) significantly reduce eltrombopag absorption; administer 4 hours apart. Eltrombopag inhibits OATP1B1 and BCRP transporters, potentially increasing levels of substrates (rosuvastatin, methotrexate, topotecan). CYP2C8 and CYP1A2 metabolize eltrombopag; lopinavir/ritonavir may reduce levels. Monitor closely when used with other drugs affecting hepatic transporters.

Where Thrombopoietin Receptor Agonists Fit

Immune thrombocytopenia is treated in stages, and eltrombopag belongs to the second. Initial treatment aims to stop platelet destruction quickly — corticosteroids such as prednisone, with immunoglobulin added when a count has to be raised within hours. That approach cannot continue indefinitely, and when the count falls again as steroids are withdrawn the choice becomes a longer-term strategy: a thrombopoietin receptor agonist, an immunosuppressant, or splenectomy.

Agonists such as eltrombopag and the injectable romiplostim work differently from everything that precedes them. Rather than suppressing the immune attack, they raise production enough to outrun it. Two consequences are worth explaining at the outset. The effect lasts only while the drug is taken, although a minority of patients hold a safe count after a careful taper. And the goal is not a normal platelet count but a count high enough to prevent bleeding, because pushing higher adds clotting risk without adding benefit. Choosing between the oral and the injectable agent usually comes down to whether a patient prefers a daily tablet with dietary restrictions or a weekly injection without them.

The Absorption Problem That Explains Most Failures

More than anything else, eltrombopag fails because of what is taken with it. Polyvalent cations bind the drug and prevent it being absorbed, and the list is longer than most patients expect: dairy of any kind, calcium-fortified juices and cereals, multivitamins, iron tablets, calcium and magnesium supplements, zinc, and antacids. A patient who takes the tablet with breakfast rather than away from food, or who has quietly added a supplement, shows a count that has stopped responding and is often escalated to a higher dose when the real fix is timing. The instruction works better written out as a daily routine — a fixed hour when nothing else is taken — than as a rule to remember.

Liver testing is the other fixed commitment. Enzymes and bilirubin are checked before treatment and at intervals during it, and a rise may mean interrupting or lowering the dose rather than stopping permanently. Counts are checked frequently while the dose is being found and less often once it is settled, and a count is always rechecked after the drug is stopped, because a rebound drop below the starting level can occur. Patients are told which bleeding warrants a same-day call and which can wait. The MedlinePlus eltrombopag monograph and the NHLBI overview of thrombocytopenia describe the condition and the treatment for patients, and our hematology team manages the dose finding and the laboratory schedule.

Special Populations

Eltrombopag may cause fetal harm based on animal data; women should use effective contraception during treatment. It is unknown whether eltrombopag is excreted in human breast milk; breastfeeding is not recommended. Safety and efficacy have been established in pediatric patients 1 year and older for ITP. Elderly patients do not require dose adjustment but may be at increased thromboembolic risk. Dose reduction is not required for renal impairment. Reduce initial dose to 25 mg daily in patients with hepatic impairment (ITP) and avoid use in hepatitis C patients with hepatic decompensation.