This is a multicenter, randomized, double-blind, parallel, placebo-controlled phase II clinical study. It is planned to recruit 74 patients with acquired thrombotic thrombocytopenic purpura (TTP). To evaluate the efficacy and safety of Anfibatide as an adjuvant therapy for plasma exchange in patients with acquired TTP.

The study will consist of 3 periods: screening(up to 7 days), treatment and follow-up(up to 3 months). Subjects are assigned in a 1:1 ratio to Anfibatide or placebo during plasma exchange with the use of a computerized randomization schedule. The administration is 5 IU/60kg intravenous infusion and 0.002 IU/kg/h continuous intravenous infusion. Plasma exchange as the main treatment method is performed daily on the 5th day of solstice and then adjusted to every other day. Fresh frozen plasma（FFP）and cryoprecipitate-reduced plasma are preferred. Subjects will receive the study drug immediately after daily plasma exchange.

Inclusion Criteria:

1. Female and male subjects with 18 years of age or older.
2. Subjects with diagnosis of TTP.
3. Necessitating plasma exchange.
4. Obtained, signed and dated informed consent.

Exclusion Criteria:

1. Platelet count greater or equal to 100*10^9/μL.
2. Severe heart, liver and kidney dysfunction, including those with glutamic-pyruvic transaminase ≥ 5xULN，glomerular filtration rate <30ml/min.
3. Uncontrolled severe active infection.
4. Known congenital TTP.
5. Subjects with malignant tumors in the past 5 years.
6. Other diseases that cause microangiopathy hemolytic anemia and thrombocytopenia, such as disseminated intravascular coagulation (DIC), antiphospholipid antibody syndrome, hemolytic uremic syndrome, malignant hypertension, and transplant-related microangiopathy.
7. Pregnant or lactating women. Subjects of reproductive age, are unable to use effective contraceptive methods during the study period.
8. Severe active bleeding or progressive aggravation of bleeding symptoms.
9. Subjects who have received plasmapheresis during the treatment of the onset of the disease.
10. Subject is participating in other clinical stuy or is less than 3 months away from the end of previous clinical study.
11. Subject who have participated in other clinical trials related to Anfibatide.
12. Severe or life threatening clinical condition other than TTP that would impair participation in the trial.
13. Life expectation less than 1 week.
14. Known to be allergic to the drugs or ingredients in the study.
15. Inability to follow programme requirements and procedures.
16. Subjects who are not eligible to participate in this clinical study as determined by the investigator.