Rare patients treated with a thienopyridine may develop thrombotic thrombocytopenic purpura (TTP). There are at least 2 mechanisms of occurrence which influences management and outcome.
Thienopyridines include clopidogrel, prasugrel and ticlopidine. They interfere with platelet function by acting as antagonists to the platelet adenosine diphosphate receptor.
Patients with TTP present with thrombocytopenia and reduced levels of ADAMTS13.
There are 2 types of TTP associated with thienopyridines. One is immune (with presence of an autoantibody) and one is nonimmune.
Feature
Immune
Nonimmune
often associated with
ticlopidine
clopidogrel
ADAMTS13 activity
< 15%
> 15%
onset after start of thienopyridine
more than 2 weeks (late)
2 weeks or less (early)
thrombocytopenia
severe
mild
renal function
often normal
often abnormal
autoantibody to ADAMTS13
present
absent
plasma exchange
improves outcome
did not improve outcome
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