Banderanko, Nicholas

Abstract Thrombotic thrombocytopenic purpura (TTP) is a microvascular occlusive disorder characterized by systemic aggregation of platelets, thrombocytopenia, and mechanical injury to erythrocytes. Between 30% and 80% of TTP cases are associated with ADAMTS13 deficiency. Thienopyridine-derivative anti-platelet agents, ticlopidine and clopidogrel, are the drugs most commonly associated with TTP. The structures differ only by a carboxymethyl side-chain and have no common metabolites. Since 2002, our R01 research project has focused on evaluating thienopyridine-associated TTP. Herein, we present the final results. Clinical and laboratory data were obtained from case reports, the FDA’s MedWatch program, a Japanese national reference laboratory for ADAMTS13 assays, and apheresis centers at Duke University, University of North Carolina, Northwestern University, and the Mayo Clinic. Epidemiologic data for rate estimation for thienopyridine-associated TTP among persons who receive cardiac stents were obtained from international cardiology laboratories. Pharmacovigilance information was obtained from package inserts for the drugs. Most thienopyridine-associated TTP cases are associated with two weeks or more of ticlopidine rather than clopidogrel, are immune-mediated involving neutralizing antibodies to ADAMTS13, resolve with therapeutic plasma exchange (TPE), and have spontaneous relapses. Less frequently, cases are associated with clopidogrel, occur within days of drug initiation, may be a direct result of endothelial cell damage, are less responsive to TPE, and are less likely to recur. Thienopyridine-associated TTP patients with severe deficiency of ADAMTS13 activity have a different profile than those with normal ADAMTS13 levels. Among thienopyridine-associated TTP patients who have ADAMTS13 deficiency, TPE is usually performed for a few days and patients recover without detectable organ damage. In contrast, among thienopyridine-associated TTP patients who do not have ADAMTS13 deficiency, several weeks of TPE is required for recovery, and 30% mortality rates have been reported. Despite similar chemical structures, ticlopidine- and clopidogrel-associated TTP probably occur by different mechanisms and have different clinical presentations and expected outcomes. Clinical Characteristics Onset Platelet Count <20,000 (%) Creatinine ≤2 mg/dl (%) Neurologic Symptoms (%) Mortality With TPE/Without TPE (%) Relapse *p < 0.05 ticlopidine 10%* <2 weeks; 90% 2-12 weeks 84* 28* 28 15/44 Occasional clopidogrel 74%*≤2 weeks; 26% > 2 weeks 60* 55* 32 28/33 Rare Epidemiology, Pharmacovigilance & Basic Science Incidence (cases per treated patients) Safety ADAMTS13 Activity (%) ADAMTS13 Antibodies (%) ticlopidine 1:1,600 “Black Box” warning <10* 90* clopidogrel 1:100,000 package insert warning 50–100* 10*

Abstract Background: The Surveillance, Epidemiology & Risk Factors for TTP (SERF-TTP) study is the largest prospective cohort of idiopathic TTP cases to date. Methods: Patients with first episode of idiopathic TTP were enrolled at 11 sites in the US. Exclusion criteria include solid organ or allogeneic stem cell transplant, anti-neoplastic therapy or malignancy. All patients underwent therapeutic plasma exchange (TPE). Remission is defined as platelet count >150,000/mm3. ADAMTS13 activity was measured by fluorescence resonance energy transfer assay (FRETS-vWF73, Peptides Int.). ADAMTS13 inhibitor was assessed by ELISA (Technozym ADAMTS13 INH ELISA, Technoclone) and functional inhibition of normal ADAMTS13 activity (modified FRETS). Differences between the groups was evaluated by Chi-square test, t-test or Fisher’s exact test. Results: Complete data is available for 57 cases. 84% were female & median age was 42. ADAMTS13 was severely deficient (<10%) in 53%, moderate (10–50%) in 8%, & normal (>50%) in 39%. Adverse events were frequent & most commonly include citrate toxicity and allergic reactions. Long-term followup was available for 56 patients, and overall relapse rate was 25% with median time to relapse of 11 months. The relapse rate was 41% in patients with severe ADAMST13 deficiency & 0% in patients with normal ADAMTS13 activity (p=0.0077). Conclusions: Severe ADAMTS13 deficiency does not define all cases of idiopathic TTP, yet is associated with a unique syndrome characterized by severe thrombocytopenia, normal renal function, presence of ADAMTS13 neutralizing autoantibodies & high risk of relapse. Non-ADAMTS13 deficient idiopathic TTP has clinical features similar to thrombotic microangiopathies associated with stem cell transplant or drugs such as quinine, yet has a better than expected overall survival after TPE. There is likely an alternate disease mechanism for this cohort, possibly immunologic, which may be responsive to TPE and warrants further study. ADAMTS13 < 10% n=30 ADAMTS13 > 50% n=22 p-value * t-test, ** Fisher’s Exact Test, # Chi-Square Test Presenting Labs Hemoglobin (mean) 8.5 9.2 0.22* Platelet count (mean x10^9/L) 19 57 <0.0005* Serum creatinine (mean) 1.33 3.9 0.0012* ADAMTS13 antibody (neutralizing & non-neutralizing) % 100 63.6 0.0004** ADAMTS13 neutralizing antibody % 83 35 .0003# Presenting Symptoms Neurologic symptoms present 45 52.4 0.23# Diarrhea 23 30.4 0.79# Infection 40 43.5 0.79# Past Medical History Connective Tissue Disease % 10 8.5 0.28# Family history of TTP % 0 4.6 0.11# Remission Labs Hemoglobin (mean) 12.2 8.5 0.16* Platelet count (mean x10^9/L)) 169 152 0.15* Serum creatinine (mean) 1.02 3.7 0.0009* Outcomes Therapy-related Adverse events % 71 55 0.24# Time (days) to remission (plt > 150,000) 9.7 9.2 0.89* Early remission (< 8 days) % 73 57 0.20# 30 day Exacerbation rate % 35 28 0.63# 30 day Survival % 96.6 90.0 0.56** Long-term Relapse % 41 0 0.0077**