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2.  Ticlopidine- and clopidogrel-associated thrombotic thrombocytopenic purpura (TTP): review of clinical, laboratory, epidemiological, and pharmacovigilance findings (1989–2008) 
Thrombotic thrombocytopenic purpura (TTP) is a fulminant disease characterized by platelet aggregates, thrombocytopenia, renal insufficiency, neurologic changes, and mechanical injury to erythrocytes. Most idiopathic cases of TTP are characterized by a deficiency of ADAMTS13 (a disintegrin and metalloprotease, with thrombospondin-1-like domains) metalloprotease activity. Ironically, use of anti-platelet agents, the thienopyridine derivates clopidogrel and ticlopidine, is associated with drug induced TTP. Data were abstracted from a systematic review of English-language literature for thienopyridine-associated TTP identified in MEDLINE, EMBASE, the public website of the Food and Drug Administration, and abstracts from national scientific conferences from 1991 to April 2008. Ticlopidine and clopidogrel are the two most common drugs associated with TTP in FDA safety databases. Epidemiological studies identify recent initiation of anti-platelet agents as the most common risk factor associated with risks of developing TTP. Laboratory studies indicate that most cases of thienopyridine-associated TTP involve an antibody to ADAMTS13 metalloprotease, present with severe thrombocytopenia, and respond to therapeutic plasma exchange (TPE); a minority of thienopyridine-associated TTP presents with severe renal insufficiency, involves direct endothelial cell damage, and is less responsive to TPE. The evaluation of this potentially fatal drug toxicity can serve as a template for future efforts to comprehensively characterize other severe adverse drug reactions.
doi:10.1038/ki.2008.613
PMCID: PMC3500614  PMID: 19180126
drug-associated TTP; epidemiology; ADAMTS13
3.  Human Thrombomodulin Knockin Mice Reveal Differential Effects of Human Thrombomodulin on Thrombosis and Atherosclerosis 
Objective
We sought to develop a murine model to examine the antithrombotic and antiinflammatory functions of human thrombomodulin in vivo.
Methods and Results
Knockin mice that express human thrombomodulin from the murine thrombomodulin gene locus were generated. Compared with wild-type mice, human thrombomodulin knockin mice exhibited decreased protein C activation in the aorta (P < 0.01) and lung (P < 0.001). Activation of endogenous protein C following infusion of thrombin was decreased by 90% in knockin mice compared with wild-type mice (P < 0.05). Carotid artery thrombosis induced by photochemical injury occurred more rapidly in knockin mice (12 ± 3 minutes) than wild-type mice (31 ± 6 minutes; P < 0.05). No differences in serum cytokine levels were detected between knockin and wild-type mice after injection of endotoxin. When crossed with apolipoprotein E-deficient mice and fed a Western diet, knockin mice had a further decrease in protein C activation but did not exhibit increased atherosclerosis.
Conclusion
Expression of human thrombomodulin in place of murine thrombomodulin produces viable mice with a prothrombotic phenotype but unaltered responses to systemic inflammatory or atherogenic stimuli. This “humanized” animal model will be useful for investigating the function of human thrombomodulin under pathophysiological conditions in vivo.
doi:10.1161/ATVBAHA.111.236828
PMCID: PMC3202707  PMID: 21885846
thrombomodulin; protein C; inflammation; atherosclerosis; thrombosis
4.  Elevated Procalcitonin and C-Reactive Protein as Potential Biomarkers of Sepsis in a Subpopulation of Thrombotic Microangiopathy Patients 
Journal of clinical apheresis  2009;24(4):150-154.
Thrombotic microangiopathy (TMA) comprises a group of microvascular thrombosis syndromes associated with multiple pathogenic factors. Deficient activity of ADAMTS13 is a pathogenic factor in a subset of TMA patients that provides strong rationale for plasma exchange treatment. However, the subset of TMA patients with normal ADAMTS13 activity remains a heterogeneous group of patients in which the appropriate treatment is not well understood. In addition to the common forms of TMA thrombotic thrombocytopenic purpura and the hemolytic uremic syndrome, the differential diagnosis of TMA may include sepsis, autoimmune disorders, and disseminated intravascular coagulation. Optimal treatment of TMA depends on timely recognition of treatable pathogenic factors. We hypothesized that sepsis is a rapidly identifiable pathogenic factor in a subset of TMA patients. To test this hypothesis, we retrospectively measured the rapid biomarkers of sepsis C-reactive protein (CRP) and procalcitonin (PCT), in a repository of pre-treatment plasma samples from 61 TMA patients treated with plasma exchange. Levels were analyzed in 31 severely ADAMTS13-deficient and 30 ADAMTS13-normal patients. None of the 31 patients with severe deficiency of ADAMTS13 had elevated PCT. However, 11 of 30 (37%) non-ADAMTS13-deficient patient samples were strongly positive for PCT. These patient samples also had a >10-fold higher median CRP level than patients with normal PCT. We conclude that rapid assays may help identify sepsis in a subset of TMA patients.
doi:10.1002/jca.20205
PMCID: PMC2750870  PMID: 19591197
Thrombotic microangiopathy (TMA); sepsis; C-reactive protein (CRP); procalcitonin (PCT); ADAMTS13
5.  Ticlopidine-, Clopidogrel-, and Prasugrel-Associated Thrombotic Thrombocytopenic Purpura: A 20-Year Review from the Southern Network on Adverse Reactions (SONAR) 
Thienopyridine-derivatives (ticlopidine, clopidogrel, and prasugrel) are the primary antiplatelet agents. Thrombotic thrombocytopenic purpura (TTP) is a rare drug-associated syndrome, with the thienopyridines being the most common drugs implicated in this syndrome. We reviewed 20 years of information on clinical, epidemiologic, and laboratory findings for thienopyridine-associated TTP. Four, 11, and 11 cases of thienopyridine-associated TTP were reported in the first year of marketing of ticlopidine (1989), clopidogrel (1998), and prasugrel (2010), respectively. As of 2011, the FDA received reports of 97 ticlopidine-, 197 clopidogrel-, and 14 prasugrel-associated TTP cases. Severe deficiency of ADAMTS-13 (a disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13) was present in 80% and antibodies to 100% of these TTP patients on ticlopidine, 0% of the patients with clopidogrel-associated TTP (p < 0.05), and an unknown percentage of patients with prasugrel-associated TTP. TTP is associated with use of each of the three thienopyridines, although the mechanistic pathways may differ.
doi:10.1055/s-0032-1328894
PMCID: PMC3804561  PMID: 23111862
thrombotic thrombocytopenic purpura; ticlopidine; clopidogrel; prasugrel; adverse event
6.  Two Mechanistic Pathways for Thienopyridine-Associated Thrombotic Thrombocytopenic Purpura 
Objectives
We sought to describe clinical and laboratory findings for a large cohort of patients with thienopyridine-associated thrombotic thrombocytopenic purpura (TTP).
Background
The thienopyridine derivatives, ticlopidine and clopidogrel, are the 2 most common drugs associated with TTP in databases maintained by the U.S. Food and Drug Administration (FDA).
Methods
Clinical reports of TTP associated with clopidogrel and ticlopidine were identified from medical records, published case reports, and FDA case reports (n = 128). Duration of thienopyridine exposure, clinical and laboratory findings, and survival were recorded. ADAMTS13 activity (n = 39) and inhibitor (n = 30) were measured for a subset of individuals.
Results
Compared with clopidogrel-associated TTP cases (n = 35), ticlopidine-associated TTP cases (n = 93) were more likely to have received more than 2 weeks of drug (90% vs. 26%), to be severely thrombocytopenic (84% vs. 60%), and to have normal renal function (72% vs. 45%) (p < 0.01 for each). Compared with TTP patients with ADAMTS13 activity >15% (n = 13), TTP patients with severely deficient ADAMTS13 activity (n = 26) were more likely to have received ticlopidine (92.3% vs. 46.2%, p < 0.003). Among patients who developed TTP >2 weeks after thienopyridine, therapeutic plasma exchange (TPE) increased likelihood of survival (84% vs. 38%, p < 0.05). Among patients who developed TTP within 2 weeks of starting thienopyridines, survival was 77% with TPE and 78% without.
Conclusions
Thrombotic thrombocytopenic purpura is a rare complication of thienopyridine treatment. This drug toxicity appears to occur by 2 different mechanistic pathways, characterized primarily by time of onset before versus after 2 weeks of thienopyridine administration. If TTP occurs after 2 weeks of ticlopidine or clopidogrel therapy, therapeutic plasma exchange must be promptly instituted to enhance likelihood of survival.
doi:10.1016/j.jacc.2007.04.093
PMCID: PMC3167088  PMID: 17868804

Results 1-6 (6)