A reversible aptamer improves outcome and safety in murine models of stroke and hemorrhage

Treatment of acute ischemic stroke with intravenous tissue-type plasminogen activator is underutilized partly due to the risk of life-threatening hemorrhage. In response to the clinical need for safer stroke therapy, we explored using an aptamer-based therapeutic strategy to promote cerebral reperfusion in a murine model of ischemic stroke. Aptamers are nucleic acid ligands that bind to their targets with high affinity and specificity, and can be rapidly reversed with an antidote. Here we show that a Factor IXa aptamer administered intravenously after 60 minutes of cerebral ischemia and reperfusion improved neurological function and was associated with reduced thrombin generation and decreased inflammation. Moreover, when the aptamer was administered in the setting of intracranial hemorrhage, treatment with its specific antidote reduced hematoma volume and improved survival. The ability to rapidly reverse a pharmacologic agent that improves neurological function after ischemic stroke should intracranial hemorrhage arise indicates that aptamer-antidote pairs may represent a novel, safer approach to treatment of stroke.

Clinical experience with the use of clotting factor concentrates in oral anticoagulation reversal

We report the clinical experience of a large Haemophilia Centre and Haemostasis Unit in reversing oral anticoagulation (OAC) using clotting factor concentrates. This is a retrospective study extending over 2 years (January 1996-December 1997). Reversal was performed using a combination of factor IX and factor VII concentrates administered by intravenous infusion. in a dose varying between 12 i.u./kg and 50 i.u./kg. We identified 20 episodes of OAC reversal in 18 patients, with a prevalence of 10 reversal episodes/1000 OAC patients/year. The median age was 77 years old (range 53-92 years). Indications for OAC reversal were divided into major bleeds (muscle haematoma [9], haematuria [3], subarachnoid haemorrhage [1], oesophageal bleeding [1], haemoptysis [1], haemarthrosis [1]); minor bleeds (extensive bruising [9], epistaxis [3], oral cavity bleeding [1]); and emergency invasive investigation (2). Pre-reversal, the international normalized ration (INR) was greater than 6.0 in 15/18 patients. Post-infusion. there was an immediate reduction in the INR towards normal (mean 1.3; range 1.1-2.3). There were no thrombotic complications or other adverse effects. The median use of factor 9 A concentrate was 2300 units/patient (range 570-4195), at a cost of 645 Pounds/patient and for factor VII concentrate 2200 units/patient (range 815-3630), at a cost of 664 Pounds/patient. Clotting factor concentrates provide a safe, rapid and effective means for OAC reversal and although expensive it is the treatment of choice in the over anticoagulated, bleeding patient.

High purity factor IX and prothrombin complex concentrate (PCC): pharmacokinetics and evidence that factor IXa is the thrombogenic trigger in PCC

Recent studies using assays for surrogate markers of thrombogenicity in man have demonstrated that activation of the coagulation system occurs following infusion of clinical doses of prothrombin complex concentrates (PCC) but not after the same doses of high-purity factor IX concentrates (HP-FIX) in patients with haemophilia B. Here we have investigated the mechanism of such thrombogenesis by applying assays that detect early-through to late-events in coagulation system activation in a pharmacokinetic cross-over study of 50 IU/kg PCC and a new HP-FIX product in haemophilia B patients. Satisfactory recoveries and half-lives were observed for both concentrates. HP-FIX caused no increases in thrombin-antithrombin III complex (TAT), prothrombin activation peptide fragment F1+2 (F1+2), factor X activation peptide (FXAP) or factor VIIa (FVIIa). In contrast the same dose of factor IX in the form of PCC was followed by significant increases over pre-infusion levels of TAT, F1+2 and FXAP, but not FVIIa. Elevations of FIXAP occurred after both HP-FIX and PCC but did not reach normal levels and were attributed to normalisation of the FIX concentration in those patients whose levels of FIXAP were initially low. We conclude that the thrombogenic trigger associated with PCC infusion occurs at the level of factor X activation. In the absence of any increase in FVIIa, we would attribute this to the likely presence of FIXa in the PCC.

The problem of therapeutic equivalence with paired qualitative data: an example from a clinical trial using haemophiliacs with an inhibitor to factor VIII

The problem of demonstrating the equivalence of two treatments or drugs occurs fairly frequently in medicine, but is quite often misformulated. The common error is to assume equivalence is demonstrated if the usual null hypothesis of no difference is not rejected, which ignores the potential of a substantial beta-error. We describe here two procedures for testing equivalence when the data are paired and dichotomous, and provide sample size formulas. We give an example based on a clinical trial of haemophiliacs with inhibitor to Factor VIII.