Extracorporeal Model for Study of Factors Affecting Thrombus Formation

Factors determining thrombus formation on a foreign surface were studied with the use of plastic flow chambers introduced into extracorporeal shunts. Silicone rubber shunts, joining the carotid artery and jugular vein, were implanted in dogs and remained patent for several weeks. The flow chamber geometry consisted of a 4.8 mm diameter straight tube having a 3.2 × 3.2 mm circumferential cavity in the wall. Chambers were introduced sequentially into the shunts for exposure times of 10 to 30 minutes and regulated blood flow rates of 100 to 400 ml/min. The dry weight of thrombus accumulated in the chamber (5 to 50 mg) was found to increase with exposure time up to 20 minutes and to decrease with increasing flow rate. Various components of the process of thrombus formation were altered by the administration of acetylsalicylic acid, heparin and lysozyme, used alone and in pairs. Heparin was found to be the most effective antithrombotic agent, dry weights of accumulated thrombus being on the order of 50 percent lower when compared to control values. The efficacy of heparin was found to be unaffected by the presence of aspirin and lysozyme, which themselves were not effective antithrombotic agents under the conditions of these experiments. The technique described here may provide a useful animal model for studying the influence of blood flow and different biomaterials on thrombus formation.

Prophylactic Use of Factor VIII: an Economic Evaluation

Background: Since the introduction of exogenous factor VIII therapy, several studies have explored the clinical benefits of prophylactic use of factor VIII. Little research, though, has focused on the economic aspects of this regimen. We conducted a cost analysis using data from the Orthopedic Outcomes Study, a prospective, cross-national study of the clinical outcomes associated with different patterns of factor VIII utilization to examine the health care costs incurred and expenditures averted in patients receiving on-demand versus prophylactic use of factor VIII in hemophilia. Methods and Analysis: 831 patients with severe hemophilia aged 1 to 31 years, from 19 centers around the world were included in the cost analysis. Patients were categorized into three groups according to the number of weeks during the study years in which they received prophylactic regimens of factor VIII. For each subject, we estimated the costs of hospitalization, surgery, days lost from school or work, and factor VIII utilization. Costs were then stratified by age and by joint score to assess confounding, and a multivariate model developed to determine the relationship between use of factor VIII prophylaxis and total costs, while controlling for potential confounders.

Results: Patients who received factor VIII episodically incurred substantially greater disability-related costs (days lost from school or work, days hospitalized due to hemophilia, surgery) than patients who received factor VIII prophylactically for some or all of the study period. For all treatment regimens, most disability-related costs were accounted for by hospitalization for hemophilia-related conditions. The cost of factor VIII itself was substantial in all treatment categories but was highest among patients who received year-round prophylaxis, exceeding the savings resulting from reduced disability and other health care expenditures.

Conclusions: Reductions in non-factor health care costs and disability associated with prophylactic use of factor VIII in hemophilia were substantial and helped somewhat to offset the much higher costs of this regimen. For certain subgroups, frequent episodic treatment may be more expensive than full-time prophylaxis. However, because of the very high cost of year-round prophylactic use of factor VIII, total health care expenditures were highest among patients receiving this therapeutic regimen. However, because prophylaxis clearly offers important clinical benefits, this approach may be warranted on medical rather than economic grounds.

The evolution of comprehensive haemophilia care in the United States: perspectives from the frontline

The establishment of dedicated comprehensive treatment centres more than a half century ago transformed the management of haemophilia in the United States. Formerly, a disease associated with crippling disability and premature death, today, persons with haemophilia who are treated appropriately from infancy and do not develop inhibitors can expect a normal life expectancy and relatively few bleeding episodes. The evolution of the comprehensive haemophilia care, while chastened by the viral epidemics of the 1980s, has been marked by ongoing advances, including prophylaxis, immune tolerance induction, new drugs and gene therapy research. Current challenges include sustaining the comprehensive care model despite decreased funding and expanding the delivery and affordability of comprehensive haemophilia care.

Restoring hemostasis: fibrinogen concentrate versus cryoprecipitate

Fibrinogen plays a key role in the coagulation process, and therefore maintaining adequate quantities of fibrinogen is an essential step in achieving satisfactory hemostasis in patients with acquired hypofibrinogenemia. Potential options for treating acquired hypofibrinogenemia in patients with uncontrolled bleeding include the use of cryoprecipitate or fibrinogen replacement therapy. This review provides a brief overview of the hemostatic process and the methods for assessing coagulopathy and discusses the efficacy and safety of cryoprecipitate and fibrinogen concentrate in restoring fibrinogen levels, achieving hemostasis and reducing transfusion requirements in different patient populations requiring rapid hemostasis. Other issues relevant to the clinical use of these agents in restoring hemostasis, including variations in product composition, preparation time and cost, are also examined.

Efficacy and safety of intravenous anti-D immunoglobulin (Rhophylac®) in chronic immune thrombocytopenic purpura

OBJECTIVES

This Phase III study examined the efficacy and safety of Rhophylac (CSL Behring AG, Bern, Switzerland), a highly pure, liquid-stable anti-D preparation, in chronic immune thrombocytopenic purpura (ITP).

MATERIALS AND METHODS

Ninety-eight patients (96 adults, two adolescents) with chronic ITP and platelet counts < 30 x 10(9)/l received a single intravenous injection of 50 microg/kg bodyweight Rhophylac.

RESULTS

A response (defined as an increase in platelet count by >or= 20 x 10(9)/l to >or= 30 x 10(9)/l in the first 15 days after treatment) was seen in 66% of patients. Mean time to response was 3.1 +/- 3.0 days, and mean duration of response was 19.2 +/- 1.1 days for responders. The most frequent drug-related adverse events were chills, pyrexia, an increase in bilirubin, and headache; events were mainly mild or moderate. there was no severe hemolysis or renal failure.

CONCLUSION

rhophylac is well tolerated and efficacious in chronic itp.

Another role for the VW molecule

My comments on the implication of the vW molecule in down-regulating the immunogenicity of factor VIII.

Can B-domain deletion alter the immunogenicity of recombinant factor VIII? A meta-analysis of prospective clinical studies

BACKGROUND

As a result of the infrequency of inhibitors in previously treated patients (PTPs) with hemophilia A and the small size of available clinical studies, the immunogenicity of factor (F)VIII products has been difficult to assess.

OBJECTIVES

A meta-analysis of prospective clinical studies was conducted to test the hypothesis that de novo inhibitor incidence differs between PTPs receiving full-length recombinant FVIII (FL-rFVIII) and B-domain deleted recombinant FVIII (BDD-rFVIII).

METHODS

Prospective studies with data on inhibitors in PTPs receiving FL-rFVIII or BDD-rFVIII were sought using systematic methods including bibliographic database searches. Data were secured from published study reports and inquiries to investigators. Between-group differences in inhibitor incidence rates were evaluated using mixed effects Cox regression.

RESULTS

Twenty-nine studies with 3012 total PTPs were included. Patients were at risk of de novo inhibitor development for a median of 79 exposure days. A total of 35 de novo inhibitors were observed. The cumulative hazard for all de novo inhibitors was 1.25% with a 95% confidence interval (CI) of 0.63-1.88%. The corresponding rate for high-titer de novo inhibitors [> 5 Bethesda units (BU)] was 0.29% (CI, 0.01-0.57%). Exposure to BDD-rFVIII was associated with an increased risk of all de novo inhibitors (hazard ratio, 7.26; CI, 2.12-24.9; P = 0.0016) and of high-titer de novo inhibitors (hazard ratio, 10.8; CI, 2.17-53.7; P = 0.0037), compared with FL-rFVIII.

CONCLUSIONS

This meta-analysis of prospective clinical studies suggests that recombinant FVIII products may differ in immunogenicity.

Harmonization of clinical trial guidelines for assessing the risk of inhibitor development in hemophilia A treatment

At the present time, the most significant complication of hemophilia therapy is the development of neutralizing antibodies (inhibitors) to factor (F) VIII, which adds greatly to the difficulty and expense of preventing and treating bleeding episodes. Both patient-related and therapy-related variables contribute to the development of inhibitors. The multifactorial nature of inhibitor development and the relatively small numbers of patients that participate in clinical trials make it difficult to accurately assess the risk of inhibitor development. Adding to that challenge is the lack of a uniform standard of design for conducting clinical trials to evaluate the safety of FVIII products. This hinders the comparison of products and is an obstacle to the meta-analysis necessary to make statistically valid assessments of inhibitor risk. This article reviews similarities and differences in clinical trial guidelines of European and US regulatory agencies and discusses the need for their harmonization to facilitate the assessment of FVIII products.

Screening coagulation testing using the APTT: which reagent to choose?

APTT testing is integral to hemostasis testing. A prolonged result, however, can be difficult to interpret, depending on the APTT reagent's sensitivity to the lupus anticoagulant. This often generates additional laboratory testing for both factor deficiencies and the presence of a lupus anticoagulant, and in so doing, delays patient management. We have found it useful to provide APTT testing with both a lupus anticoagulant sensitive and insensitive reagent, to facilitate the rapid exclusion of significant factor deficiencies. The following case report illustrates the utility of this approach and provides a backdrop for necessary discussions between laboratories and clinicians regarding which APTT reagent best meets their clinical need for screening hemostasis testing.

Evaluation of bleeding and thrombotic events during long-term use of romiplostim in patients with chronic immune thrombocytopenia (ITP)

BACKGROUND

Romiplostim is a peptibody protein that raises platelet counts during long-term treatment of patients with chronic immune thrombocytopenia (ITP). Clinical outcomes related to increased platelet counts include a reduced risk of bleeding and a potential risk of thrombosis.

OBJECTIVE

To evaluate bleeding and thrombotic events occurring in chronic ITP patients during two phase 3, randomized, placebo-controlled, 24-week studies of romiplostim and during subsequent treatment in an open-label extension study.

PATIENTS/METHODS

In the phase 3 trials, 125 patients were randomized to romiplostim or placebo; romiplostim dose was adjusted to maintain platelet counts of 50-200 x 10(9) L(-1). Patients who completed the phase 3 trials could enroll in the extension study in which all patients received romiplostim.

RESULTS

In the phase 3 trials, a significantly greater percentage of patients treated with placebo (34%) had bleeding adverse events of moderate or greater severity than did patients treated with romiplostim (15%, P = 0.018). In the extension study, the incidence of bleeding adverse events of moderate or greater severity decreased from 23% of patients in the first 24 weeks to 12% after 24-48 weeks, remaining < or = 6% thereafter. The exposure-adjusted incidence of thrombotic events was 0.1 per 100 patient-weeks in the phase 3 studies, and 0.08 per 100 patient-weeks in the extension study where patients received romiplostim for up to 144 additional weeks.

CONCLUSIONS

The incidence and severity of bleeding was decreased in chronic ITP patients treated with romiplostim compared with placebo, and the incidence of thrombotic events was not different between the two groups.

Factor IX and thrombosis

Fractionation technology has made Factor IX concentrates available. In addition to a very high incidence of hepatitis, thrombosis is being recognized as a consequence of their use. Contradictory reports exist in the literature as to the incidence of thrombotic events. A recent study of thrombohemorrhagic phenomena after infusion with Factor IX concentrates in patients with congenital Factor IX deficiency (hemophilia B) or liver disease, revealed an incidence of twenty episodes in 188 cases (11%). It is imperative to delineate the thrombogenic factors and find methods for their removal to insure the safety of Factor IX products.

Recurrent orthostatic global amnesia in a patient with postoperative hyperfibrinogenemia

Transient global amnesia (TGA) is characterized by sudden, temporary dysfunction of antegrade and recent retrograde memory without other neurologic deficits. Although there is sometimes a precipitating event, the origin of TGA remains controversial. We encountered a patient who developed recurrent TGA when upright, in whom the symptom promptly and regularly resolved when supine. Symptoms began about a week after cardiac surgery concurrent with marked hyperfibrinogenemia and acceleration of the erythrocyte sedimentation rate, and abated without recurrence when these laboratory abnormalities were ameliorated by anticoagulant and corticosteroid therapy. Diagnostic studies, including temporal artery biopsy and cerebral angiography, disclosed no anatomic vascular pathology. This is the first report of TGA associated with postoperative inflammation in which amnesia was provoked by orthostatic positioning. In conclusion, these observations implicate ischemia caused by hemodynamic vascular insufficiency as a possible cause of TGA.

Efficacy of romiplostim in patients with chronic immune thrombocytopenic purpura: a double-blind randomised controlled trial

BACKGROUND

Chronic immune thrombocytopenic purpura (ITP) is characterised by accelerated platelet destruction and decreased platelet production. Short-term administration of the thrombopoiesis-stimulating protein, romiplostim, has been shown to increase platelet counts in most patients with chronic ITP. We assessed the long-term administration of romiplostim in splenectomised and non-splenectomised patients with ITP.

METHODS

In two parallel trials, 63 splenectomised and 62 non-splenectomised patients with ITP and a mean of three platelet counts 30x10(9)/L or less were randomly assigned 2:1 to subcutaneous injections of romiplostim (n=42 in splenectomised study and n=41 in non-splenectomised study) or placebo (n=21 in both studies) every week for 24 weeks. Doses of study drug were adjusted to maintain platelet counts of 50x10(9)/L to 200x10(9)/L. The primary objectives were to assess the efficacy of romiplostim as measured by a durable platelet response (platelet count > or =50x10(9)/L during 6 or more of the last 8 weeks of treatment) and treatment safety. Analysis was per protocol. These studies are registered with ClinicalTrials.gov, numbers NCT00102323 and NCT00102336.

FINDINGS

A durable platelet response was achieved by 16 of 42 splenectomised patients given romplostim versus none of 21 given placebo (difference in proportion of patients responding 38% [95% CI 23.4-52.8], p=0.0013), and by 25 of 41 non-splenectomised patients given romplostim versus one of 21 given placebo (56% [38.7-73.7], p<0.0001). The overall platelet response rate (either durable or transient platelet response) was noted in 88% (36/41) of non-splenectomised and 79% (33/42) of splenectomised patients given romiplostim compared with 14% (three of 21) of non-splenectomised and no splenectomised patients given placebo (p<0.0001). Patients given romiplostim achieved platelet counts of 50x10(9)/L or more on a mean of 13.8 (SE 0.9) weeks (mean 12.3 [1.2] weeks in splenectomised group vs 15.2 [1.2] weeks in non-splenectomised group) compared with 0.8 (0.4) weeks for those given placebo (0.2 [0.1] weeks vs 1.3 [0.8] weeks). 87% (20/23) of patients given romiplostim (12/12 splenectomised and eight of 11 non-splenectomised patients) reduced or discontinued concurrent therapy compared with 38% (six of 16) of those given placebo (one of six splenectomised and five of ten non-splenectomised patients). Adverse events were much the same in patients given romiplostim and placebo. No antibodies against romiplostim or thrombopoietin were detected.

INTERPRETATION

Romiplostim was well tolerated, and increased and maintained platelet counts in splenectomised and non-splenectomised patients with ITP. Many patients were able to reduce or discontinue other ITP medications. Stimulation of platelet production by romiplostim may provide a new therapeutic option for patients with ITP.

Factor VIII inhibitor bypassing activity (FEIBA) - addressing safety issues

Bypassing therapy is usually necessary to control or prevent bleeding episodes in patients with haemophilia A or B and high-titre inhibitors. Factor VIII inhibitor bypassing activity (FEIBA) has a long history of successful use in the acute, surgical and prophylactic treatment settings, but safety concerns have made some reluctant to administer this bypassing agent. A review of the literature and clinical trial data show that FEIBA has a low prevalence of thrombosis, a low prevalence of anamnesis that does not impact haemostatic efficacy and an excellent record of pathogen safety and clinical tolerability.

The 5, 10 methylenetetrahydrofolate reductase C677T mutation and risk of fetal loss: a case series and review of the literature

BACKGROUND

The true relationship between methylenetetrahydrofolate reductase C677T homozygosity and risk of recurrent spontaneous abortion is unknown, and it is unclear if women with these mutations should be anticoagulated during pregnancy.

OBJECTIVES

We report a series of 8 patients with this issue and review the current literature.

METHODS

8 patients (3 of whom were actively pregnant) were referred with histories of spontaneous fetal loss; hypercoaguability work-ups revealed each were homozygous for the MTHFR C677T mutation without other thrombophilias.

RESULTS

In the 3 women who have conceived, treatment with LMW heparin during pregnancy led to two full-term births and one additional pregnancy without complication. For the 5 who have not, we recommended treatment with LMW heparin upon conception.

CONCLUSION

We provide evidence to support the relationship between MTHFR C677T mutations and recurrent fetal loss, and to suggest that anticoagulation of these patients during pregnancy can lead to a successful pregnancy outcome.

Surgical interventions in a cohort of patients with haemophilia A and inhibitors: an experiential retrospective chart review

Strategies for the management of perioperative bleeding in patients with haemophilia and inhibitors have evolved rapidly as a result of the development of the bypassing agents Factor Eight Inhibitor Bypassing Activity, Anti-inhibitor Coagulant Complex (FEIBA) and activated recombinant factor VII (rFVIIa). However, there are currently no established guidelines for perioperative use of bypassing agents, and few controlled clinical studies have been carried out. Thus, case reports, such as those presented here, provide useful anecdotal evidence to guide the treatment of inhibitor patients. The purpose of this report was to describe experiences in the use of bypassing agents in a small cohort of patients with haemophilia A and inhibitors undergoing surgical procedures. Cases from five treatment centres were reviewed. Twenty-two procedures using FEIBA, rFVIIa or a combination of both agents were compiled from seven inhibitor patients (six with an alloantibody inhibitor and one with an acquired autoantibody inhibitor). Eleven procedures used FEIBA monotherapy, two employed rFVIIa monotherapy and nine were performed using combination therapy. Supplemental therapies were required to manage bleeding in some cases. Haemostatic control was achieved in all cases, and treatment regimens were generally well tolerated. One thrombotic adverse event was reported: evidence of disseminated intravascular coagulation (DIC) was found after rFVIIa use in one case, although the direct cause of DIC was unknown. The experiences in this case review demonstrate that both major and minor surgical procedures can be safely performed in patients with haemophilia and high-titre inhibitors under the cover of bypassing agents, with a high expectation of success.

Reconstruction of the hepatitis C virus epidemic in the US hemophilia population, 1940-1990

Hepatitis C virus (HCV) is a blood-borne infection readily transmitted by transfusion. Persons with hemophilia were at very high risk of acquiring HCV, but the chronology and correlates of HCV incidence in the US hemophilia population remain unknown. The authors used multiple data sources and new statistical methods to reconstruct HCV incidence in White males with hemophilia A from 1940 through 1990. HCV incidence was approximately 1%/year until 1950 but 2-3%/year by 1955. With mild hemophilia, HCV incidence increased in the 1960s, reaching a plateau of approximately 8%/year from 1969 to 1980. With moderate and severe hemophilia, HCV incidence increased steeply to peaks of 11.7%/year in 1970 and 17.2%/year in 1968, respectively. Overall, HCV incidence declined after 1970, steeply after 1984, to nearly zero by 1990. With improving and increasing use of plasma derivatives, the size of the hemophilia population increased 86% during these 50 years. Study results imply that these life-saving treatments also carried an increasing risk of HCV, particularly before clotting factor concentrates were licensed in the 1970s. They also suggest that multiple synergistic interventions since 1970, particularly donor deferral, screening for hepatitis B and human immunodeficiency virus, and viral inactivation of clotting factor concentrates, were needed to reduce transfusion of HCV prior to its discovery.

AMG 531, a thrombopoiesis-stimulating protein, for chronic ITP

BACKGROUND

Most current treatments for chronic immune thrombocytopenic purpura (ITP) act by decreasing platelet destruction. In a phase 1-2 study, we administered a thrombopoiesis-stimulating protein, AMG 531, to patients with ITP.

METHODS

In phase 1, 24 patients who had received at least one treatment for ITP were assigned to escalating-dose cohorts of 4 patients each and given two identical doses of AMG 531 (0.2 to 10 microg per kilogram of body weight). In phase 2, 21 patients were randomly assigned to receive six weekly subcutaneous injections of AMG 531 (1, 3, or 6 microg per kilogram) or placebo. The primary objective was to assess the safety of AMG 531; the secondary objective was to evaluate platelet counts during and after treatment.

RESULTS

No major adverse events that could be attributed directly to AMG 531 occurred during the treatment period; 4 of 41 patients had transient post-treatment worsening of thrombocytopenia. In phase 1, a platelet count that was within the targeted range (50,000 to 450,000 per cubic millimeter) and at least twice the baseline count was achieved in 4 of 12 patients given 3, 6, or 10 mug of AMG 531 per kilogram. Overall, a platelet count of at least 50,000 per cubic millimeter was achieved in 7 of 12 patients, including 3 with counts exceeding 450,000 per cubic millimeter. Increases in the platelet count were dose-dependent; mean peak counts were 163,000, 309,000, and 746,000 per cubic millimeter with 3, 6, and 10 microg of AMG 531 per kilogram [corrected], respectively. In phase 2, the targeted platelet range was achieved in 10 of 16 patients treated with 1 or 3 mug of AMG 531 per kilogram per week for 6 weeks. Mean peak counts were 135,000, 241,000, and 81,000 per cubic millimeter in the groups that received the 1-mug dose, the 3-mug dose, and placebo, respectively.

CONCLUSIONS

AMG 531 caused no major adverse events and increased platelet counts in patients with ITP. (ClinicalTrials.gov number, NCT00111475 [ClinicalTrials.gov].).

Echinocytosis--an unusual manifestation of hemangioma

The case of a 21 year-old female with echinocytosis and a littoral cell hemangioma is reported. The patient had no significant past medical history and presented with abdominal pain and splenomegaly. A large percentage of echinocytes were noted on her peripheral smear in the absence of any known causes. A CT-recognized splenic mass led to splenectomy and a benign hemangioma was found. Red blood cell abnormalities resolved immediately after the surgery. This is the first case reported in the literature of echinocytosis as a consequence of a hemangioma.

United States' factor XI-deficiency patients need a safer treatment

A replacement factor for Factor XI with is virally inactivated is not available in the U.S. Elsewhere an inactivated concentrate has been used. A review of the experience over 15 years suggests that this product is safe and effective and suggests its potential use in the U.S. The most serious complication of the factor was a slight increase in DIC and thrombotic events.

Therapeutic choices in the current millennium: hemophilia workshop highlights

Many issues affect hemophilia care providers when managing bleeding episodes in individuals with hemophilia. A diverse group of hemophilia providers from the United States met at two workshops to discuss the issues influencing treatment choices in the current millennium and to learn about current advances in treatment of hemophilia. This paper provides a summary of the discussions at these workshops. Despite the progress made in the management of patients with hemophilia, the workshop highlighted the fact that there were still many unanswered questions.

Thrombotic microangiopathy: differential diagnosis, pathophysiology and therapeutic strategies

Several disease states manifest as thrombotic microangiopathies (TMA), most prominently thrombotic thrombocytopenic purpura (TTP) and hemolytic uremic syndrome (HUS). The recent discovery of the von Willebrand factor cleaving protease ADAMTS-13 (a disintegrin and metalloprotease with thrombospondin type 1 motif), found to be deficient in TTP, has helped separate these entities. In contrast, HUS is caused by direct endothelial damage by bacterial toxins, while in familial cases inappropriate complement activation through deficient factor H appears to be a major pathogenetic mechanism. Although enormous progress has been made towards understanding these syndromes, the diagnostic tools and therapies used have hardly changed in the last 20 years, with the standard of care remaining plasma exchange in most cases. In this review, we will cover the multiple etiologic factors for TMAs, with the resultant differential diagnoses, as well as provide insight into the latest pathophysiologic findings and possible implications for treatment.