Promacta (eltrombopag) is a prescription medication that boosts platelet production in people whose blood doesn’t make enough on its own. It has three FDA-approved uses: treating chronic immune thrombocytopenia (ITP) in adults and children, raising platelet counts in people with chronic hepatitis C so they can start antiviral therapy, and treating severe aplastic anemia alongside immune-suppressing medications.
How Promacta Works
Platelets are tiny blood cells that form clots to stop bleeding. Your body produces them in the bone marrow, guided by a signaling protein called thrombopoietin (TPO). Promacta mimics that signal. It binds to the same receptor that TPO uses, triggering bone marrow cells to ramp up platelet production. Unlike the body’s natural TPO, which attaches to the outside of the receptor, Promacta is a small molecule that binds at a different site within the cell membrane. This still activates the same internal machinery that tells the bone marrow to grow more platelet-producing cells.
Promacta also appears to work earlier in the production chain than some similar drugs, stimulating precursor cells and encouraging them to mature into the cells that eventually release platelets. Beyond its platelet effects, the drug has an unusual secondary property: it binds to iron inside and outside cells, effectively pulling iron out. This iron-chelating action is separate from its platelet-boosting role and may partly explain its usefulness in conditions like aplastic anemia, where bone marrow function is broadly impaired.
Chronic Immune Thrombocytopenia (ITP)
ITP is an autoimmune condition where the immune system mistakenly destroys platelets faster than the body can replace them. This leads to easy bruising, bleeding gums, and in severe cases, dangerous internal bleeding. Promacta is approved for adults and children with chronic ITP who haven’t responded well enough to other treatments, including steroids or surgical removal of the spleen.
Rather than suppressing the immune attack on platelets, Promacta takes the opposite approach: it pushes the bone marrow to produce platelets fast enough to outpace the destruction. For many patients, this means platelet counts rise to a safer range, reducing the risk of serious bleeding episodes. ITP was Promacta’s first approved indication and remains its most common use.
Severe Aplastic Anemia
Severe aplastic anemia (SAA) is a rare and serious condition where the bone marrow fails to produce enough blood cells of any type, not just platelets. People with SAA are vulnerable to infections, anemia, and uncontrolled bleeding. The standard treatment is a bone marrow transplant or, when that isn’t an option, a combination of drugs that suppress the immune system.
Promacta is used alongside those immune-suppressing drugs to help restore bone marrow function. In a pediatric trial published in Blood Advances, the combination produced an overall response rate of about 55% at 26 weeks across both newly diagnosed and relapsed patients. Among children who had relapsed or not responded to prior treatment, the response rate was higher, at roughly 71%. The results for transfusion independence were particularly striking: about 77% of patients who previously needed regular platelet transfusions no longer required them, and around 67% became independent of red blood cell transfusions as well.
These findings reflect what clinicians see in adults too. Promacta’s ability to stimulate early bone marrow precursor cells, combined with its iron-chelating properties, appears to give the failing marrow a broader boost than platelet production alone.
Thrombocytopenia With Chronic Hepatitis C
Some people with chronic hepatitis C develop low platelet counts as a complication of liver disease. This becomes a practical problem when they need interferon-based antiviral therapy, because interferon further suppresses platelet production. If counts drop too low, doctors have to reduce the antiviral dose or stop treatment altogether.
Promacta is approved to raise platelet counts in these patients specifically so they can begin and maintain interferon-based therapy. Treatment typically starts at 25 mg daily and is adjusted upward in small increments every two weeks until platelets reach a level that supports antiviral treatment, with a maximum dose of 100 mg daily. Once antiviral therapy ends, Promacta is stopped as well.
This indication comes with important caveats. In clinical trials, patients taking Promacta alongside antivirals had a higher rate of blood clots (3%) compared to placebo (1%), with most clots forming in the blood vessels around the liver. There was also an increased risk of serious liver complications: ascites and encephalopathy occurred in 7% of patients on Promacta plus antivirals versus 4% on placebo. Patients with low albumin levels or more advanced liver disease at the start were at greatest risk. Promacta has not been studied in combination with the newer direct-acting antiviral drugs used without interferon, so this indication applies specifically to interferon-based regimens.
Liver Monitoring Requirements
Promacta carries a boxed warning, the FDA’s most serious safety label, for the risk of liver damage. The drug can cause elevations in liver enzymes that, in rare cases, progress to significant liver injury. In hepatitis C trials, about 1% of patients experienced drug-induced liver injury.
Because of this risk, liver function tests are required before starting Promacta, every two weeks while the dose is being adjusted, and monthly once a stable dose is reached. If test results come back abnormal, they’re repeated within three to five days to confirm. Confirmed abnormalities trigger weekly monitoring until levels return to normal. Promacta is discontinued if liver enzyme levels rise to three times the upper limit of normal and continue climbing, persist for four or more weeks, or are accompanied by signs of liver problems like elevated bilirubin or symptoms of liver failure.
Blood Clot Risk
Raising platelet counts carries an inherent tension: too few platelets cause bleeding, but too many can cause clotting. Promacta can push platelet counts above the target range, increasing the risk of blood clots in veins or arteries. This risk is present across all three approved uses but is most closely studied in hepatitis C patients, where clots formed primarily in the portal venous system (the blood vessels feeding the liver). Your doctor will monitor platelet counts regularly and adjust the dose to keep them in a safe window.
How to Take Promacta
Promacta has unusually strict timing rules around food and other medications because certain minerals dramatically reduce how much of the drug your body absorbs. The medication should be taken on an empty stomach, at least one hour before or two hours after a meal. Dairy products and calcium-fortified juices require an even wider gap: at least two hours before or four hours after taking Promacta. The same four-hour separation applies to antacids, mineral supplements, and any product containing iron, calcium, aluminum, magnesium, selenium, or zinc.
If you do eat around the time of your dose, the meal should contain no more than 50 mg of calcium, which effectively rules out milk, yogurt, cheese, and most fortified foods. This makes timing a real daily consideration. Many patients find it easiest to take Promacta first thing in the morning on an empty stomach, then wait before eating breakfast.