The Food and Drug Administration has approved the first drug specifically indicated for the treatment of adults with acquired thrombotic thrombocytopenic purpura (aTTP), a rare and potentially life-threatening blood clotting disorder. The drug, caplacizumab-yhdp (Cablivi), was approved under priority review and received orphan drug designation, a special status granted to drugs that treat rare diseases. Caplacizumab-yhdp is a von Willebrand factor-directed antibody fragment; it inhibits the interaction of von Willebrand factor with platelets, reducing von Willebrand factor-mediated platelet adhesion and platelet consumption. It is prescribed in combination with plasmapheresis and immunosuppressive therapy.

Cancer, HIV, lupus, infections, and pregnancy can all trigger the onset of aTTP, which occurs when the body mistakenly makes antibodies that suppress the activity of an enzyme that inhibits certain blood clotting factors. This disorder produces low platelet counts (thrombocytopenia), small areas of bleeding under the skin (purpura), low red blood cell counts, and hemolytic anemia. In response, blood clots form in small blood vessels throughout the body, which can have serious consequences if blood flow to the brain, heart, or other major organs is compromised. Onset of aTTP episodes occurs rapidly, lasting days to months, and relapses are possible. The main treatment for aTTP is daily plasmapheresis to remove the antibodies.

In a clinical trial of 145 patients, participants were randomized to receive either standard care (plasmapheresis and immunosuppressants) plus placebo or standard care plus caplacizumab-yhdp. Platelet counts increased sooner in those receiving caplacizumab-yhdp than in those on standard care alone. Fewer patients treated with caplacizumab-yhdp experienced aTTP-related death or recurrence of aTTP during the treatment period or at least one treatment-emergent major thrombotic event. Relapses were also significantly lower in the treatment group than in the standard care group.

Caplacizumab-yhdp carries a warning that severe bleeding can occur with use, although the most common adverse effects (seen in 15% of patients) are headache and minor bleeding from the nose or gums. Combination therapy with anticoagulants can increase the risk of serious bleeding.

Caplacizumab-yhdp should be administered when plasmapheresis is started. The first dose is given as an iv bolus, and subsequent doses are given subcutaneously in the abdomen. Because the drug comes as a powder requiring reconstitution, nurses should teach patients how to prepare the drug and administer it. The injection site should be rotated among the abdominal quadrants. The area around the navel should be avoided. For specifics on dosing and administration, see the drug's labeling. Nurses should also educate patients on the risk of bleeding from the nose and mouth; if significant bleeding occurs, the patient's health care provider should be notified. To read the complete prescribing information for caplacizumab-yhdp, go to http://www.accessdata.fda.gov/drugsatfda_docs/label/2019/761112s000lbl.pdf.