Anticoagulation therapy

Randomised controlled trial on vitreoretinal surgery with and without oral anticoagulants: surgical complications, visual results and perioperative thromboembolic events

BACKGROUND

Vitreoretinal surgery in anticoagulated patients is a challenging situation for vitreoretinal surgeons, who have to choose between being faced with the systemic thromboembolic risks that the interruption of anticoagulation involves, or the intra- and postoperative haemorrhagic risks associated with maintenance of this therapy. So far, no trial has compared, in a prospective and randomized manner, perioperative complications and the visual results associated with continuation or interruption of oral anticoagulant therapy before pars plana vitrectomy (PPV) under retrobulbar anaesthesia. The main objective of this trial is to compare haemostasis-related perioperative complications of PPV in patients maintaining anticoagulant therapy before surgery compared to patients with an interruption in this therapy before surgery.

METHODS

Ninety-six patients will be randomly assigned to either the control group, in whom oral anticoagulant therapy will be interrupted and substituted with subcutaneous heparin according to local clinical practice, or the intervention group in whom oral anticoagulant therapy will not be interrupted before surgery. Patients will be stratified according to the oral anticoagulant they were taking (direct or indirect anticoagulation). They will be followed up for 12 weeks, and the primary outcome, and haemorrhagic complications until 15 days after surgery, will be evaluated.

DISCUSSION

This trial will provide novel information on the possibility of continuing anticoagulant therapy during PPV. The benefits expected from the change in the current surgical management paradigm for anticoagulated patients would be a decreased risk in the incidence of perioperative thromboembolic events and the possibility of performing surgery without delay and without the need for patients to change their usual anticoagulation protocol to the more complex and less safe substitutive therapy.

TRIAL REGISTRATION

Clinical Trials Register EudraCT, 2018-000753-45. Registered on 11 November 2018.

Inherited thrombophilia and reproductive disorders

Apart from its established role in the pathogenesis of venous thromboembolism (VTE), inherited thrombophilia has been proposed as a possible cause of pregnancy loss and vascular gestational complications. There is a lot of controversy in the literature on the relationship between inherited prothrombotic defects and these obstetric complications. This is a review of the literature on inherited thrombophilia and reproductive disorders. Factor V Leiden, prothrombin G20210A mutation, and protein S deficiency seem to be associated with late and recurrent early pregnancy loss, while their impact on other pregnancy complications is conflicting. No definite association has been established between protein C and antithrombin deficiency and adverse pregnancy outcome, primarily due to their low prevalence. Screening is suggested only for women with early recurrent loss or late pregnancy loss. Anticoagulant treatment during pregnancy should be considered for women with complications who were tested positive for thrombophilia.

Assessment of bleeding during minor oral surgical procedures and extraction in patients on anticoagulant therapy

Introduction:

The risk of postoperative hemorrhage from oral surgical procedures has been a concern in the treatment of patients who are receiving long-term anticoagulation therapy. A study undertaken in our institution to address questions about the amount and severity of bleeding associated with minor outpatient oral surgery procedures by assessing bleeding in patients who did not alter their anticoagulant regimen.

Subjects and Methods:

Eighty-three patients receiving long-term anticoagulant therapy visited Department of Oral and Maxillofacial Surgery from May 2010 to October 2011 for extractions and minor oral surgical procedures. Each patient was required to undergo preoperative assessment of prothrombin time (PT) and measurement of the international normalized ratio. Fifty-six patients with preoperative PT values within the therapeutic range 3–4 were included in the study. The patients’ age ranged between 30 and 75 years. Application of surgispon was done following the procedure. Extraction of teeth performed with minimal trauma to the surrounding tissues, the socket margins sutured, and sutures removed after 5 days.

Results:

There was no significant incidence of prolonged or excessive hemorrhage and wound infection and the healing process was normal.

The detection of thrombin using a mixture of a fluorescent conjugated polyelectrolyte and fibrinogen and implementation of a logic gate

A highly sensitive and selective detection of thrombin is accomplished using an emission color-tunable conjugated polyelectrolyte. An implementation of a combined logic gate was realized upon emission modulation of the system including the polymer, fibrinogen, thrombin, and heparin.

Highly efficient control of thrombin activity by multivalent nanoparticles

We have demonstrated that the incorporation of sulfated galactose acid (sulf-Gal) into thrombin-binding-aptamer (TBA)-conjugated gold nanoparticles (TBA-AuNPs) enables highly effective inhibition of thrombin activity toward fibrinogen. AuNP bioconjugates (TBA(15)/TBA(29)/sulf-Gal-AuNPs) were prepared from 13 nm AuNPs, 15-mer thrombin-binding aptamer (TBA(15)), 29-mer thrombin-binding aptamer (TBA(29)), and sulf-Gal. The numbers of TBA and sulf-Gal molecules per AuNP proved to have a strong impact on inhibitory potency. The best results were observed for 15-TBA(15)/TBA(29)/sulf-Gal-AuNPs (with 15 TBA(15) and 15 TBA(29) molecules per AuNP), which, because of their particularly flexible conformation and multivalency, exhibited ultrahigh binding affinity toward thrombin (K(d)=3.4×10(-12) M) and thus extremely high anticoagulant (inhibitory) potency. Compared to the case without inhibitors (the "normal" value), their measured thrombin clotting time (TCT) was 91 times longer, whereas for TBA(15) alone it was only 7.2 times longer. Their anticoagulant activity was suppressed by TBA-complementary-sequence (cTBA)-modified AuNPs (cTBA(15)/cTBA(29)-AuNPs) at a rate that was 20 times faster than that of free cTBA(15)/cTBA(29). Thus, easily prepared, low-cost, multivalent AuNPs show great potential for biomedical control of blood clotting.

Enoxaparin, effective dosage for intensive care patients: double-blinded, randomised clinical trial

Introduction

Intensive care unit (ICU) patients are predisposed to thromboembolism. Routine prophylactic anticoagulation is widely recommended. Low-molecular-weight heparins, such as enoxaparin, are increasingly used because of predictable pharmacokinetics. This study aims to determine the subcutaneous (SC) dose of enoxaparin that would give the best anti-factor Xa levels in ICU patients.

Methods

The 72 patients admitted to a mixed ICU at Odense University Hospital (OUH) in Denmark were randomised into four groups to receive 40, 50, 60, or 70 mg SC enoxaparin for a period of 24 hours. Anti-factor Xa activity (aFXa) was measured before, and at 4, 12, and 24 hours after administration. An AFXa level between 0.1 to 0.3 IU/ml was considered evidence of effective antithrombotic activity.

Results

Median peak (4 hours after administration), aFXa levels increased significantly with an increase in enoxaparin dose, from 0.13 IU/ml at 40 mg, to 0.14 IU/ml at 50 mg, 0.27 IU/ml at 60 mg, and 0.29 IU/ml at 70 mg (P = 0.002). At 12 hours after administration, median aFXa levels were still within therapeutic range for those patients who received 60 mg (P = 0.02).

Conclusions

Our study confirmed that a standard dose of 40 mg enoxaparin yielded subtherapeutic levels of aFXa in critically ill patients. Higher doses resulted in better peak aFXa levels, with a ceiling effect observed at 60 mg. The present study seems to suggest inadequate dosage as one of the possible mechanisms for the higher failure rate of enoxaparin in ICU patients.

Trial Registration

ISRCTN03037804

ANTICOAGULATION WITH WARFARIN IN VITREORETINAL SURGERY

PURPOSE

To describe the clinical course of patients undergoing vitreoretinal procedures while receiving systemic anticoagulation with warfarin.

METHODS

We reviewed patient demographics, ocular findings, and clinical courses for 25 patients receiving systemic anticoagulation with warfarin who subsequently underwent vitreoretinal surgery.

RESULTS

Patient ages ranged from 49 years to 81 years (median, 69 years). Indications for anticoagulation included atrial fibrillation, cerebrovascular disease, deep vein thrombosis, prosthetic heart valves, and hypercoagulable state. Follow-up ranged from 4 months to 36 months (median, 19.5 months). The international normalized ratio ranged from 1.5 to 3.1 (median, 2.0). Final vision after surgery ranged from 20/20 to 20/400 (median, 20/100). One patient who underwent scleral buckling and external drainage of subretinal fluid had an intraoperative subretinal hemorrhage associated with the drainage procedure. In all other patients, no intraoperative complications occurred.

CONCLUSION

Cessation of therapy with warfarin may not be necessary in patients receiving anticoagulation who are undergoing vitreoretinal procedures. Successful visual and anatomical results may be achieved after vitreoretinal surgery for patients receiving anticoagulation with warfarin. The management of anticoagulation should occur in conjunction with the patient's internist to allow a clear understanding of the potential systemic risks of cessation of warfarin treatment preoperatively.

The potential of aptamers as anticoagulants

Useful additional options for anticoagulant therapy have been introduced over the last 15 years, including low-molecular-weight heparins and direct thrombin inhibitors. Despite these impressive advances, a need for safer effective anticoagulants remains. Aptamers represent a therapeutic modality that has the potential to address this unmet need. Aptamers are small nucleic acid molecules that function as direct protein inhibitors, much like monoclonal antibodies. Aptamers are delivered by parenteral administration, can be formulated to possess a very short or sustained half-life, and are purported to be nonimmunogenic. Perhaps most relevant to the development of safer anticoagulant therapies, recent studies have shown that antidotes can be rationally designed to control the pharmacologic effects of aptamers in vivo, paving the way for a new class of antidote-controlled therapeutics. This review discusses the limitations of current anticoagulant therapies, the properties of aptamers and how these properties can be exploited to address the unmet needs within this therapeutic class, and the progress to date in developing new aptamer-based anticoagulant therapies.

[What kind of treatment are available in deep vein thrombosis prevention?]

In order to propose new recommendations concerning deep vein thrombosis prevention in surgery and obstetrics, we identified all the available tools. We performed a Medline search for ten years to review all the studies published in this field. This preliminary stage is mandatory in assessing guidelines able to work out strategies considering each patient in each particular surgical situation. There are no formal guidelines and we outlined a practical approach for the prevention of deep vein thrombosis. Data concerning all available treatment were not classified in an evidence-based strategy.

Aptamers: an emerging class of therapeutics

Numerous nucleic acid ligands, also termed decoys or aptamers, have been developed during the past 15 years that can inhibit the activity of many pathogenic proteins. Two of them, Macugen and E2F decoy, are in phase III clinical trials. Several properties of aptamers make them an attractive class of therapeutic compounds. Their affinity and specificity for a given protein make it possible to isolate a ligand to virtually any target, and adjusting their bioavailability expands their clinical utility. The ability to develop aptamers that retain activity in multiple organisms facilitates preclinical development. Antidote control of aptamer activity enables safe, tightly controlled therapeutics. Aptamers may prove useful in the treatment of a wide variety of human maladies, including infectious diseases, cancer, and cardiovascular disease. We review the observations that facilitated the development of this emerging class of therapeutics, summarize progress to date, and speculate on the eventual utility of such agents in the clinic.

Prevention of thrombosis with warfarin, aspirin, and mechanical methods

Venous thromboembolism (VTE) is a serious disorder and a major cause of morbidity and mortality among acutely ill medical patients. However, despite the growing number of patients with acute medical illnesses who have an associated risk of VTE, the widespread use of VTE prophylaxis does not yet occur for both surgical and nonsurgical patients. Although individuals at greatest risk for VTE include patients undergoing major orthopedic surgery and those with medical conditions that require prolonged immobilization, all patients who have acute medical illnesses should be considered for VTE prophylaxis. Several strategies, including various mechanical and pharmacologic approaches, are currently used for VTE prophylaxis. Increased awareness about the full range of options for VTE prophylaxis can help health care providers select the appropriate course of action to help reduce the incidence of VTE among patients with acute medical illnesses.

Administration of a small molecule tissue factor/factor VIIa inhibitor in a non-human primate thrombosis model of venous thrombosis: effects on thrombus formation and bleeding time

INTRODUCTION

Pharmacological treatment of deep vein thrombosis (DVT) in the future may target inhibitors of specific procoagulant proteins. This study used a non-human primate model to test the effect of PHA-798, a specific inhibitor of the tissue factor/Factor VIIa complex (TF/VIIa), on venous thrombus formation.

MATERIALS AND METHODS

PHA inhibits the TF/VIIa complex with an IC(50) of 13.5 nM (K(i) 9 nM) and is more than 2000-fold selective for the TF/VIIa complex with respect to IC(50)s for factor Xa and thrombin. In the model, a thrombogenic surface was introduced into the vena cava of a primate, and the amount of thrombus accumulated after 30 min was determined.

RESULTS

PHA-798 reduced thrombus formation on the thrombogenic surface in a dose-dependent manner (56+/-1.9% and 85+/-0.3% inhibition with 100 and 200 microg/kg/min PHA-798, respectively) indicating that the model is sensitive to TF/VIIa inhibition. Treatment with 1 mg/kg intravenous (IV) acetyl salicylic acid (ASA) resulted in only a slight (4-12%), non-significant inhibition of thrombus formation. However, the combination of 100 microg/kg/min PHA-798 and 1 mg/kg ASA resulted in an 89% inhibition of thrombus formation. Additionally, while ASA alone increased bleeding time (BT) from 3.3 min at baseline to 4.6 min following treatment, addition of PHA-798 (100 microg/kg/min) to ASA did not significantly increase the BT further (4.7 min).

CONCLUSIONS

The results of this study indicate that inhibition of TF/VIIa may be safe and effective for the prevention of the proprogation of venous thrombosis and that the combination of ASA and PHA may provide increased efficacy with little change in safety.

Diagnosis and treatment of heparin-induced thrombocytopenia

Heparin-induced thrombocytopenia (HIT) is a major side effect secondary to the administration of heparin. This syndrome is serious and potentially life threatening. This response is the result of antibodies formed against the platelet factor 4 (PF4)/heparin complex. The incidence of this immune-mediated syndrome has been estimated to be 1-3% of all patients receiving heparin therapy. The occurrence of HIT in patients requiring full anticoagulation for cardiopulmonary bypass (CPB), therefore, presents a serious challenge to the cardiac surgery team. The diagnosis of HIT should be based on both clinical and laboratory evidence. While functional assays, platelet aggregation tests, and the serotonin release assay can be used to support the diagnosis, the negative predictive value of these tests is generally less than 50%. In contrast, although non-functional antibody detection assays are more sensitive, they have a low specificity. HIT can be treated in several ways, including cessation of all heparin and giving an alternative thrombin inhibitor, platelet inhibition followed by heparin infusion, and the use of low molecular weight heparins. In this presentation, the pathology and current diagnostic tests, as well as the successful management of patients with HIT undergoing CPB at New York Presbyterian Hospital, are reviewed.

Low molecular weight heparins and heparinoids

Several low molecular weight (LMW) heparin preparations, including dalteparin, enoxaparin and nadroparin, as well as the heparinoid danaparoid sodium, are approved for use in Australia. LMW heparins are replacing unfractionated heparin for the prevention and treatment of venous thromboembolism and the treatment of non-ST-segment-elevation acute coronary syndromes. The advantages of LMW heparins over unfractionated heparin include a longer half-life (allowing once-daily or twice-daily subcutaneous dosing), high bioavailability and predictable anticoagulant response (avoiding the need for dose adjustment or laboratory monitoring in most patients), and a low risk of heparin-induced thrombocytopenia and osteoporosis. Laboratory monitoring of LMW heparin therapy should be considered in newborns and children, patients with renal impairment, those who are pregnant, and those at the extremes of bodyweight (eg, < 40 kg or > 100 kg). LMW heparins should: be avoided or used with caution in patients undergoing neuraxial anaesthesia, owing to the potential for epidural haematoma formation; not be used (ie, are contraindicated) in patients with immune heparin-induced thrombocytopenia, as they may cross-react with anti-heparin antibodies. Conventional unfractionated heparin retains a role in the management of patients at high risk of bleeding, undergoing invasive procedures, and patients with renal failure owing to its shorter half-life, reversibility with protamine sulfate, and extrarenal metabolism. The heparinoid danaparoid sodium is effective for the treatment of heparin-induced thrombocytopenia.