Rivaroxaban for treatment of suspected or confirmed heparin-induced thrombocytopenia study

Essentials Heparin-induced thrombocytopenia (HIT) is a thrombogenic condition that is difficult to treat. We evaluated rivaroxaban as a treatment option in patients with suspected or confirmed HIT. One patient had recurrent thrombosis and 9/10 patients with thrombocytopenia had platelet recovery. Rivaroxaban may be an effective and safe treatment option for HIT.

SUMMARY

Background Rivaroxaban is a direct oral anti-Xa inhibitor that has the potential to greatly simplify treatment of heparin-induced thrombocytopenia (HIT). Objectives To evaluate the efficacy and safety of rivaroxaban in this patient population, we conducted a multicenter, single-arm, prospective cohort study of patients with suspected or confirmed HIT. Patients/Methods Twenty-two consecutive adults with suspected or confirmed HIT received rivaroxaban 15 mg bid until a local HIT assay result was available. Participants with a positive local assay result continued rivaroxaban 15 mg bid until platelet recovery (or until day 21 if they had acute thrombosis at study entry), then stepped down to rivaroxaban 20 mg daily until day 30. Results and Conclusions The primary outcome measure, incidence of new symptomatic, objectively-confirmed venous and arterial thromboembolism at 30 days, occurred in one HIT-positive participant (4.5%; 95% confidence interval [CI], 0-23.5%) and one HIT-positive participant required limb amputation despite platelet recovery. Platelet recovery was achieved in nine out of 10 HIT-positive patients with thrombocytopenia. Rivaroxaban appears to be effective for treating patients with confirmed HIT, although the small number of patients enrolled limits precision.

Distinguishing between anti-platelet factor 4/heparin antibodies that can and cannot cause heparin-induced thrombocytopenia

BACKGROUND

Many patients exposed to heparin develop antibodies against platelet factor 4 (PF4) and heparin, yet only those antibodies that activate platelets cause heparin-induced thrombocytopenia (HIT). Patients who produce anti-PF4/heparin antibodies without developing HIT either have antibodies that do not cause platelet activation or produce pathogenic antibodies at levels that are insufficient to cause HIT. Understanding the differences between anti-PF4/heparin antibodies with and without HIT will improve test methods and reduce overdiagnosis.

AIMS

To investigate the presence of low levels of platelet-activating antibodies in patients investigated for HIT who had anti-PF4/heparin antibodies but failed to cause platelet activation in the (14) C-serotonin release assay (SRA).

MATERIALS/METHODS

We developed a platelet activation assay similar to the SRA using exogenous PF4 without added heparin (PF4-SRA). This assay was able to detect low levels of platelet-activating antibodies. We used this PF4-SRA to test for platelet-activating antibodies in patients investigated for HIT.

RESULTS

The PF4-SRA detected platelet-activating antibodies in seven (100%) of seven SRA-positive sera even after the samples were diluted until they were no longer positive in the standard SRA. Platelet-activating antibodies were detected in 14 (36%) of 39 patients who had anti-PF4/heparin antibodies but tested negative in the SRA and did not have clinical HIT. The clinical diagnosis of HIT was confirmed by chart review and concordant with the SRA results.

CONCLUSIONS

A subset of heparin-treated patients produce subthreshold levels of platelet-activating anti-PF4/heparin antibodies that do not cause HIT. An increase in the titer of these pathogenic antibodies, along with permissive clinical conditions, could lead to HIT.

Severe bleeding events in adults and children with primary immune thrombocytopenia: a systematic review

BACKGROUND

The burden of severe bleeding in adults and children with immune thrombocytopenia (ITP) has not been established.

OBJECTIVES

To describe the frequency and severity of bleeding events in patients with ITP, and the methods used to measure bleeding in ITP studies.

PATIENTS/METHODS

We performed a systematic review of all prospective ITP studies that enrolled 20 or more patients. Two reviewers searched Medline, Embase, CINAHL and the Cochrane registry up to May 2014. Overall weighted proportions were estimated using a random effects model. Measurement properties of bleeding assessment tools were evaluated.

RESULTS

We identified 118 studies that reported bleeding (n = 10 908 patients). Weighted proportions for intracerebral hemorrhage (ICH) were 1.4% for adults (95% confidence interval [CI], 0.9-2.1%) and 0.4% for children (95% CI, 0.2-0.7%; P < 0.01), most of whom had chronic ITP. The weighted proportion for severe (non-ICH) bleeding was 9.6% for adults (95% CI, 4.1-17.1%) and 20.2% for children (95% CI, 10.0-32.9%; P < 0.01) with newly-diagnosed or chronic ITP. Methods of reporting and definitions of severe bleeding were highly variable in primary studies. Two bleeding assessment tools (Buchanan 2002 for children; Page 2007 for adults) demonstrated adequate inter-rater reliability and validity in independent assessments.

CONCLUSIONS

ICH was more common in adults and tended to occur during chronic ITP; other severe bleeds were more common in children and occurred at all stages of disease. Reporting of non-ICH bleeding was variable across studies. Further attention to ITP-specific bleeding measurement in clinical trials is needed to improve standardization of this important outcome for patients.

FcγRIIa proteolysis as a diagnostic biomarker for heparin-induced thrombocytopenia

BACKGROUND

A significant challenge in the management of heparin-induced thrombocytopenia (HIT) patients is making a timely and accurate diagnosis. The readily available enzyme immunoassays (EIAs) have low specificities. In contrast, platelet activation assays have higher specificities, but they are technically demanding and not widely available. In addition, ~ 10% of samples referred for HIT testing are initially classified as indeterminate by the serotonin release assay (SRA), which further delays accurate diagnosis. HIT is characterized by platelet activation, which leads to FcγRIIa proteolysis. This raises the possibility that identification of the proteolytic fragment of FcγRIIa could serve as a surrogate marker for HIT.

OBJECTIVES

To determine the specificity of platelet FcγRIIa proteolysis induced by sera from patients with HIT, and to correlate the results with those of the SRA.

METHODS/PATIENTS

Sera from HIT patients and control patients with other thrombocytopenic/prothrombotic disorders were tested for their ability to proteolyse FcγRIIa. The results were correlated with anti-platelet factor 4 (PF4)/heparin antibodies (EIA), and heparin-dependent platelet activation (SRA).

RESULTS

Only HIT patient samples (20/20) caused heparin-dependent FcγRIIa proteolysis, similar to what was shown by the SRA. None of the samples from the other patient groups or hospital controls caused FcγRIIa proteolysis. Among nine additional samples that tested indeterminate in the SRA, FcγRIIa proteolysis resolved five samples that had a positive anti-PF4/heparin EIA result; three had no FcγRIIa proteolysis, and two were shown to have heparin-dependent FcγRIIa proteolysis

CONCLUSIONS

This study suggests that heparin-dependent FcγRIIa proteolysis is at least as specific as the SRA for the diagnosis of HIT.

A systematic evaluation of laboratory testing for drug-induced immune thrombocytopenia

BACKGROUND

Drug-induced immune thrombocytopenia (DITP) can be confirmed by the demonstration of drug-dependent platelet antibodies in vitro; however, laboratory testing is not readily accessible and test methods are not standardized.

OBJECTIVE

To identify drugs with the strongest evidence for causing DITP based on clinical and laboratory criteria.

PATIENTS/METHODS

We developed a grading system to evaluate the quality of DITP laboratory testing. The 'DITP criteria' were: (i) Drug (or metabolite) was required for the reaction in vitro; (ii) Immunoglobulin binding was demonstrated; (iii) Two or more laboratories obtained positive results; and (iv) Platelets were the target of immunoglobulin binding. Laboratory diagnosis of DITP was considered definite when all criteria were met and probable when positive results were reported by only one laboratory. Two authors applied the DITP criteria to published reports of each drug identified by systematic review. Discrepancies were independently adjudicated.

RESULTS

Of 153 drugs that were clinically implicated in thrombocytopenic reactions, 72 (47%) were associated with positive laboratory testing. Of those, 16 drugs met criteria for a definite laboratory diagnosis of DITP and thus had the highest probability of causing DITP. Definite drugs were: quinine, quinidine, trimethoprim/sulfamethoxazole, vancomycin, penicillin, rifampin, carbamazepine, ceftriaxone, ibuprofen, mirtazapine, oxaliplatin and suramin; the glycoprotein IIbIIIa inhibitors abciximab, tirofiban and eptifibatide; and heparin.

CONCLUSIONS

We identified drugs with the strongest evidence for an association with immune thrombocytopenia. This list may be helpful for ranking potential causes of thrombocytopenia in a given patient.