Heparin: mechanism of action, pharmacokinetics, dosing considerations, monitoring, efficacy, and safety

Clinical guidance for unfractionated heparin dosing and monitoring in critically ill patients

INTRODUCTION

Unfractionated heparin is a widely used anticoagulant in critically ill patients. It has a well-established safety profile and remains an attractive option for clinicians due to its short half-life and reversibility. Heparin has a unique pharmacokinetic profile, which contributes to significant inter-patient and intra-patient variability in effect. The variability in anticoagulant effect combined with heparin's short half-life mean close monitoring is required for clinical efficacy and preventing adverse effects. To optimize heparin use in critically ill patients effective monitoring assays and dose adjustment strategies are needed.

AREAS COVERED

This paper explores the use of heparin as an anticoagulant and optimal approaches to monitoring in critically ill patients.

EXPERT OPINION

Conventional monitoring assays for heparin dosing have significant limitations. Emerging data appears to favor using anti-Xa assay monitoring for heparin anticoagulation which many centers have successfully adopted as the standard. The anti-Xa assay appears have important benefits relative to the aPTT for heparin monitoring in critically ill patients, and should be considered for broader use.

2021 ELSO Adult and Pediatric Anticoagulation Guidelines

DISCLAIMER

These guidelines for adult and pediatric anticoagulation for extracorporeal membrane oxygenation are intended for educational use to build the knowledge of physicians and other health professionals in assessing the conditions and managing the treatment of patients undergoing ECLS / ECMO and describe what are believed to be useful and safe practice for extracorporeal life support (ECLS, ECMO) but these are not necessarily consensus recommendations. The aim of clinical guidelines are to help clinicians to make informed decisions about their patients. However, adherence to a guideline does not guarantee a successful outcome. Ultimately, healthcare professionals must make their own treatment decisions about care on a case-by-case basis, after consultation with their patients, using their clinical judgment, knowledge and expertise. These guidelines do not take the place of physicians' and other health professionals' judgment in diagnosing and treatment of particular patients. These guidelines are not intended to and should not be interpreted as setting a standard of care or be deemed inclusive of all proper methods of care nor exclusive of other methods of care reasonably directed to obtaining the same results. The ultimate judgment must be made by the physician and other health professionals and the patient in light of all the circumstances presented by the individual patient, and the known variability and biological behavior of the clinical condition. These guidelines reflect the data at the time the guidelines were prepared; the results of subsequent studies or other information may cause revisions to the recommendations in these guidelines to be prudent to reflect new data, but ELSO is under no obligation to provide updates. In no event will ELSO be liable for any decision made or action taken in reliance upon the information provided through these guidelines.

Evaluation of effect of scheduled fresh frozen plasma on ECMO circuit life: A randomized pilot trial

BACKGROUND

Factor consumption is common during ECMO complicating the balance of pro and anticoagulation factors. This study sought to determine whether transfusion of coagulation factors using fresh frozen plasma (FFP) increased ECMO circuit life and decreased blood product transfusion. Secondly, it analyzed the association between FFP transfusion and hemorrhagic and thrombotic complications.

STUDY DESIGN AND METHODS

Thirty-one pediatric ECMO patients between October 2013 and January 2016 at a quaternary care institution were included. Patients were randomized to FFP every 48 hours or usual care. The primary outcome was ECMO circuit change. Secondary outcomes included blood product transfusion, survival to decannulation, hemorrhagic and thrombotic complications, and ECMO costs.

RESULTS

Median (interquartile range [IQR]) number of circuit changes was 0 (0, 1). No difference was seen in percent days without a circuit change between intervention and control group, P = .53. Intervention group patients received median platelets of 15.5 mL/kg/d IQR (3.7, 26.8) vs 24.8 mL/kg/d (12.2, 30.8) for the control group (P = .16), and median packed red blood cells (pRBC) of 7.7 mL/kg/d (3.3, 16.3) vs 5.9 mL/kg/d (3.4, 18.7) for the control group, P = .60. FFP transfusions were similar with 10.2 mL/kg/d (5.0, 13.9) in the intervention group vs 8.8 (2.5, 17.7) for the control group, P = .98.

CONCLUSION

In this pilot randomized study, scheduled FFP did not increase circuit life. There was no difference in blood product transfusion of platelets, pRBCs, and FFP between groups. Further studies are needed to examine the association of scheduled FFP with blood product transfusion.

Antifungal and Cytotoxic Evaluation of Photochemically Synthesized Heparin-Coated Gold and Silver Nanoparticles

Heparin-based silver nanoparticles (AgHep-NPs) and gold nanoparticles (AuHep-NPs) were produced by a photochemical method using silver nitrate and chloroauric acid as metal precursors and UV light at 254 nm. UV-Vis spectroscopy graphs showed absorption for AgHep-NPs and AuHep-NPs at 420 nm and 530 nm, respectively. TEM revealed a pseudospherical morphology and a small size, corresponding to 10-25 nm for AgHep-NPs and 1.5-7.5 nm for AuHep-NPs. Their antifungal activity against Candida albicans, Issatchenkia orientalis (Candida krusei), and Candida parapsilosis was assessed by the microdilution method. We show that AgHep-NPs were effective in decreasing fungus density, whereas AuHep-NPs were not. Additionally, the viability of human gingival fibroblasts was preserved by both nanoparticle types at a level above 80%, indicating a slight cytotoxicity. These results are potentially useful for applications of the described NPs mainly in dentistry and, to a lesser extent, in other biomedical areas.

Derivation and Validation of Age- and Body Mass Index-Adjusted Weight-Based Unfractionated Heparin Dosing

Unfractionated heparin dosing is unpredictable and subject to numerous pharmacokinetic changes including distribution and metabolic changes associated with obesity and age. Weight-based dosing is commonly used to better predict the dose for a patient when targeting a therapeutic range. A dosing equation that adjusts weight-based doses for age and body mass index may improve therapeutic dose prediction. We conducted a 2-phase observational study with a derivation and validation period to develop an equation to adjust weight-based unfractionated heparin for age and body mass index to target a therapeutic activated partial thromboplastin time of 60 to 80 seconds. The first phase retrospectively identified patients who acheived therapeutic anticoagulation and utilized linear regression to determine a predictive equation for weight-based dosing that adjusts for age and body mass index. The second phase prospectively identified patients in an observational manner and compared the dose of unfractionated heparin on which they became therapeutic against both the weight-based dose and the predicted dose adjusted for age and body mass index. The correlation between predictive age and body mass index adjusted dose and actual therapeutic dose was 0.703 compared to the correlation between the empiric weight-based dose and actual therapeutic dose which was 0.532 (P = .05). Age and body mass index adjusted weight-based dosing significantly improved therapeutic dose prediction for unfractionated heparin. Further study in a prospective, randomized trial is warranted for validation of this approach in a real world setting.

Reversible fluorescence modulation of BSA stabilised copper nanoclusters for the selective detection of protamine and heparin

Depicting fluorescence sensing of protamine and heparin based on aggregation and disaggregation of copper nanoclusters.

Heparin mimetics with anticoagulant activity

Heparin, a sulfated polysaccharide belonging to the glycosaminoglycan family, has been widely used as an anticoagulant drug for decades and remains the most commonly used parenteral anticoagulant in adults and children. However, heparin has important clinical limitations and is derived from animal sources which pose significant safety and supply problems. The ever growing shortage of the raw material for heparin manufacturing may become a very significant issue in the future. These global limitations have prompted much research, especially following the recent well-publicized contamination scandal, into the development of alternative anticoagulants derived from non-animal and/or totally synthetic sources that mimic the structural features and properties of heparin. Such compounds, termed heparin mimetics, are also needed as anticoagulant materials for use in biomedical applications (e.g., stents, grafts, implants etc.). This review encompasses the development of heparin mimetics of various structural classes, including synthetic polymers and non-carbohydrate small molecules as well as sulfated oligo- and polysaccharides, and fondaparinux derivatives and conjugates, with a focus on developments in the past 10 years.

Description and Evaluation of the Implementation of a Weight-Based, Nurse-Driven Heparin Nomogram in a Tertiary Academic Medical Center

Weight-based, nurse-driven heparin nomograms are reported in the medical literature to improve the time it takes to reach a minimum threshold for anticoagulation without compromising patient safety in specific indications or patient populations. This is the first report in the literature of an institution-wide protocol implementation and evaluation of effectiveness with simultaneous transition to an electronic health record. The purpose of implementing this practice change at our institution was to standardize practice, improve time to reach therapeutic anticoagulation, and improve patient safety. We conducted a retrospective analysis utilizing a pre/postimplementation design to compare outcomes. The primary end point evaluated was the time to reach minimum threshold value for therapeutic anticoagulation. Additionally, we assessed the percentage of patients who reached minimum threshold therapeutic anticoagulation within 24 hours, the percentage of patients with a critically supratherapeutic activated partial thromboplastin time (aPTT) value (≥120 seconds) during therapy, and a description of heparin titration for the first 4 aPTT results with nomogram use. Overall time to therapeutic anticoagulation decreased from a mean 18.7 to 11.7 hours (hazard ratio [HR] 1.59; 95% confidence interval 1.22-2.08; P < .0005). Percentage of patients receiving therapeutic anticoagulation within 24 hours increased from 74.4 to 88.5 (odds ratio [OR 2.97, P = .002) and the percentage of patients with an aPTT ≥120 seconds remained constant at 49.9 versus 46.8 (OR 0.92, P = .73). This practice change reduced time to therapeutic anticoagulation without an increase in the proportion of patients with a critically supratherapeutic aPTT at our institution.

Phytonadione Education Program in a Community Hospital

Purpose

Pharmacists and physicians were educated regarding updated guidelines on phytonadione indications, dosing, and routes of administration. Study objectives were to evaluate the use of phytonadione in a community hospital, educate pharmacists and physicians about phytonadione use, and assess the value of education in terms of patient outcomes.

Methods

Baseline and follow-up data on phytonadione indications, dosages, and routes of administration were collected. Pretests and post-tests were administered before and after an education session. A Pharmacy and Therapeutics newsletter article highlighting the appropriate use of phytonadione was published.

Results

The baseline and follow-up medication use evaluations (MUEs) revealed that 53% and 62% of patients had an appropriate indication for phytonadione, respectively (P = 0.181). Among patients with an appropriate indication, 44% were administered an appropriate dose in the baseline group and 46% in the follow-up (P = 0.876). The baseline MUE revealed that 20% of phytonadione routes of administration were appropriate; 18% were considered appropriate in the follow-up (P = 0.842). Pharmacists' knowledge showed improvement after education efforts, with the mean score improving from 57% to 93.4% from pretest to post-test (P < 0.05) and the median score changing from 50% to 100%.

Conclusion

Improving pharmacists' knowledge is beneficial and necessary; however, it was not enough to change practice in this study. Additional steps must be taken to encourage routine application of the knowledge.

State-of-the-Art Review : Activated Partial Thromboplastin Time in Heparinized Plasma: Influence of Reagent, Acute-Phase Reaction, and Interval Between Sampling and Testing

Plasma samples from 10 healthy persons and 10 patients with acute-phase reaction were heparinized in vitro to obtain up to 0.70 U/ml. Activated partial throm boplastin time (APTT) was then determined using an op tical method (Automated Coagulation Laboratory or ACL Machine) and four different reagents (Actin, Ceph otest, Platelin, and Thrombosil). Heparin sensitivity var ied between individuals, and it was lower in acute-phase plasma than in healthy plasma. There was also a marked difference in heparin sensitivity among the different re agents; Actin was the least sensitive reagent, while Plate lin was the most sensitive reagent in healthy plasma and Thrombosil the most sensitive reagent in acute-phase plasma. Delay in testing prolonged the APTT values both in acute-phase and healthy heparinized plasma. With Ac tin and Cephotest, a delay of 90 min at 22°C resulted in 30-50% prolongation of APTT. A delay of 150 min caused a prolongation of 75-110% with Actin. Cephotest, Plate lin, and Thrombosil were less prolonged. Ex vivo samples from heparinized plasma showed similar degrees of pro longation. Storage at 4°C resulted in less prolongation. Assuming a therapeutic range of 0.35-0.70 U/ml of hep arin, the therapeutic APTT ratios in heparinized acute- phase plasma were 1.5-3.0 for Actin and 2.5-4.5 for Cephotest, Platelin, and Thrombosil. These results un derscore certain limitations in monitoring heparin therapy with the APTT system. Unless the assay is performed within 30 min after sampling, unduly prolonged APTT values will be recorded, which may lead to giving the patient an inappropriately small dose of heparin.

Outcome Analysis for Treatment in 100 Patients with Deep Vein Thrombosis

The treatment of acute deep vein thrombosis has been the subject of much research aimed at delineat ing the safest and most effective approach to diagnosis and treatment. Studies regarding long-term treatment have been limited by the narrow scope of laboratory and clinical analyses of many patients. In this study of 100 patients with a history of deep vein thrombosis, treated on an outpatient basis by a diverse group of clinicians, follow-up data were retrieved in order to determine the outcomes of various approaches to acute and long-term care. Among individuals followed for > 1 year, in only two patients (2%) was death attributable to a thrombotic event related to the etiology of the first episode of deep vein thrombosis. Most deceased patients succumbed to unrelated causes (11%). Among the 77 survivors, most (52%) received long-term antiplatelet therapy. All individ uals with a plasma coagulation defect, whether inherited or acquired, received anticoagulation with either heparin or warfarin. Since the long-term clinical outcome of most patients with deep vein thrombosis is dependent upon the underlying factor predisposing to thrombosis, the most important treatment decision is to select the therapy most likely to provide benefit without causing hemorrhage. An tiplatelet therapy, heparin, or warfarin may be chosen as appropriate for the individual patient.

Citric Acid Enhances the Antithrombotic Effect of Aspirin in Many Aspirin-Resistant Subjects

This study had three objectives: (1) to determine the frequency of high platelet aggregators in a consecutive series of 268 apparently healthy volunteers who presented to our Center; (2) to assess the inhibitory effect of aspirin (ASA) on these high aggregators; (3) to determine, in a double-blind trial, whether or not the addition of citric acid (CTA) to ASA would increase its inhibitory effect in subjects who had a suboptimal response to aspirin alone. A platelet aggregation-scoring methodology developed for turbidimetric platelet aggregometry was used to quantify baseline aggregation and medicinal effects. We define a high aggregator as one whose unmedicated PA score is ≥30. We define the response of a high aggregator to ASA as poor if the medicated PA score stays at ≥30. We found that 58 of 268 apparently healthy unmedicated volunteers (22%) had PA scores ≥30. and that 27 of these (47%) had a poor response to 325 mg ASA, with an average drop in their PA scores from 49.5 ± 13.1 to 41.1 ± 8.6 (16%). Twenty-five of these 27 people were enrolled in the double-Mind study comparing the effect of ASA and ASA + CTA on platelet aggregability. Of these high aggregators who had a poor response to ASA, 12 of 25 (50%) had a good response to 162.5 mg of ASA plus 162.5 mg of CTA, with an average drop of their PA scores from 46.7 ± 13.2 to 22.0 ± 5.2 (53%). CTA alone had no effect on the PA score, which was similar to the control placebo. Our data suggest that a 1:1 combination of ASA and CTA may offer significantly greater protection agairtst arterial thrombotic events than ASA alone in subjects who respond poorly to ASA. Key Words: Platelet aggregation—Antithrombotic medication—Thrombosis.

A Review of Common Approaches to Heparin Dosing

The use of heparin has remained steady for the last 20 years. Significant advances have been made in the understanding of the pathogenesis of clotting disorders and their prevention. Despite these gains, our understanding of the most safe and effective approach to optimizing the dosing of heparin has lagged. With new insight into improvements in outcome related to rapid achievement of the therapeutic range, it has become apparent that the standard approach to heparin dosing is out of date. Individualized heparin dosing based on weight and computer-assisted dosing methods is superior for bringing patients into the desired therapeutic range more quickly, with less cost and better short- and long-term outcomes. Copyright © 1995 by W.B. Saunders Company

Low-Dose Warfarin in Patients with Carbomedics Heart Valve Prostheses

All patients who received a Carbomedics heart valve prosthesis were assessed retrospectively by interview regarding thromboembolic, hemorrhagic, or other valve-related events. In cases of such events, the patient's practitioner or cardiologist was interviewed. Hospital records were reviewed in cases of hospital admission. Included in the study were patients who had isolated replacement of the aortic or mitral valve in whom it was possible to collect all International Normalized Ratio values from discharge through follow-up. There were 148 patients with isolated aortic valve replacement and 56 with isolated mitral valve replacement. Bleeding events were 3 times more frequent than thromboembolic events. Based on our results we will apply an International Normalized Ratio between 2 and 2.5 for patients with a Carbomedics heart valve prosthesis in aortic position and ratios between 2.5 and 3 for those with a mitral valve prosthesis.

Controlled continuous systemic heparinization increases success rate of artery-only anastomosis replantation in single distal digit amputation: A retrospective cohort study

Replantation is a prime indication for distal digital amputation, as it helps restore hand aesthetics and functions; however, venous anastomosis is often not feasible. Previous studies used systemic anticoagulation in distal digital artery only anastomosis replantation surgery to improve replantation success rate, however, which yielded limited level of clinical evidence. This study aimed to compare controlled continuous heparinization (CCH) and intermittent bolus heparinization (IBH) for surgical outcome and clinical variables after single distal digital artery only anastomosis replantation surgery.A single-institution, retrospective cohort study was performed. Out of 324 patients who underwent digital replantation surgery, we focused the study for the Zone I and II single distal digital amputation patients excluding confounding factors. Sixty-one patients were included in this study and underwent artery-only anastomosis replantation surgery with postoperative CCH (34 patients) or IBH (27 patients) protocols. The CCH group targeted activated partial thromboplastin time (aPTT) at 51 to 70 seconds, monitoring aPTT levels every eight hours and administering 100 mg of aspirin per day. The IBH group received 300 mg of aspirin per day and underwent IBH (12,500 U). Both groups received intravenous prostaglandin E1 drips (10 μg). To verify the factors affecting the success rate of the heparin protocol, patient factors, clinical factors, and operative factors were extracted from the medical records. Statistical analysis with inverse probability of treatment weights propensity score methods compared treatment outcomes and clinical variables.The CCH group's replantation success rate was higher (91.17% vs 59.25%), and the transfusion rate was increased (P = 0.032). However, the significant decrease in hemoglobin levels (>15%) did not differ between the groups (P = 0.108). Multivariable logistic regression analysis with potent univariate variables (P < .10) revealed that CCH was a statistically significant variable in replantation success rate (P = 0.004). Neither the major bleeding complications nor the significant decrease in patients' platelet levels were observed in both groups.Our study suggests that CCH after artery-only anastomosis replantation surgery in Zone I and II distal digital replantation is a safe method to improve the replantation success rate and may provide a guideline for use of the anticoagulation method following artery-only anastomosis distal digital replantation surgery.

Hemodynamic and Hematologic Effects of Histotripsy of Free-Flowing Blood: Implications for Ultrasound-Mediated Thrombolysis

PURPOSE

To investigate the extent and consequences of histotripsy-induced hemolysis in vivo.

MATERIALS AND METHODS

Porcine femoral venous blood was treated with histotripsy in 11 animals with systemic heparinization and 11 without heparin. Serum and hemodynamic measurements were obtained at 0, 2, 5, 10, 15, and 30 minutes and 48-72 hours after the procedure. Fisher exact test was used to determine differences in mortality between heparinized and nonheparinized groups. A linear mixed effects model was used to test for differences in blood analytes and hemodynamic variables over time.

RESULTS

Of 11 animals in the nonheparinized group, 5 died during or immediately after histotripsy (45% nonheparin mortality vs 0% heparin mortality, P = .035). Serum hematocrit, free hemoglobin, lactate dehydrogenase (LDH), and right ventricular systolic pressure changed significantly (P < .001) over the treatment time. Serum hematocrit decreased slightly (from 32.5% ± 3.6% to 29.4% ± 4.2%), whereas increases were seen in free hemoglobin (from 6.2 mg/dL ± 4.6 to 348 mg/dL ± 100), LDH (from 365 U/L ± 67.8 ± to 722 U/L ± 84.7), and right ventricular systolic pressure (from 23.2 mm Hg ± 7.2 to 39.7 mm Hg ± 12.3). After 48-72 hours, hematocrit remained slightly decreased (P = .005), whereas LDH and free hemoglobin remained slightly increased compared with baseline (both P < .001).

CONCLUSIONS

Intravascular histotripsy applied to free-flowing venous blood is safe with systemic heparinization, causing only transient hemodynamic and metabolic disturbances, supporting its use as a future noninvasive thrombolytic therapy modality.

Evaluating Unfractionated Heparin Fixed Dosing Protocol and Establishing an Institutional Therapeutic Range for UFH in Hospital Setting in Jordan

This study was conducted to evaluate current unfractionated heparin (UFH) dosing regimen and establish an institutional therapeutic range for UFH in a public hospital in Jordan. In the first part, medical records of 241 patients who received UFH were reviewed retrospectively. In the second part, blood samples were withdrawn from 60 patients on UFH, and activated partial thromboplastin time and anti-Xa assay were measured. Most activated partial thromboplastin time readings were not therapeutic (91.4%) and recurrence of thrombosis was reported in 35.3% of patients. In the second part, therapeutic activated partial thromboplastin time range corresponding to the UFH concentration of 0.3 to 0.7 anti-factor Xa unit/mL was 56 to 95 seconds, which corresponds to an activated partial thromboplastin time range of 1.5 of 2.8 times the mean control value. The traditional activated partial thromboplastin time range ratio of 1.5 to 2.5 times the control value can result in subtherapeutic UFH levels.

A review of the role of anticoagulation in the treatment of peripheral arterial disease

Peripheral arterial disease (PAD) is a major medical/surgical problem associated with high risk for coronary heart disease (CHD). Anticoagulation plays a significant role in the management of the PAD patient. However, evidence-based medicine supports only select anticoagulants, mainly antiplatelet agents. The available anticoagulant classes, their individual medications, and the mechanisms of action are described. Dextran 40, platelet glycoprotein (GP) IIb/IIIa receptor antagonists, direct thrombin (factor IIa, FIIa) inhibitors, and factor Xa (FXa) inhibitors do not, at this juncture, appear to have a significant role to play in the PAD patient. Aspirin has been used in PAD patients for a few decades, as has warfarin, but the role of warfarin is very limited. An attempt has been made to place each medication and its function in context all the way to the present with oral direct thrombin (FIIa) and FXa inhibitors described. These inhibitors may ultimately play an, as yet, undefined role in PAD. Specific use of anticoagulants in PAD patients is described and aspirin still stands out as a fundamental therapy. The thienopyridines, especially clopidogrel, have their established place and there is some evidence for benefit from the use of clopidogrel in dual therapy with aspirin. Dipyridamole, especially with aspirin as dual therapy, and cilostazol also have their evidence-based niches. The main role played by warfarin is for the patient with a vein graft in the arterial circulation. Heparin retains significant procedural importance. For now, Class I, Level of Evidence A center around aspirin for the PAD patient with clopidogrel, an alternative agent.

A novel fluorescent nanosensor for detection of heparin and heparinase based on CuInS2 quantum dots

In this work, a novel fluorescence "turn off-on" nanosensor for the determination of heparin and heparinase based on CuInS2 quantum dots (QDs) was established. CuInS2 QDs (modified by l-cysteine) featuring amino groups were directly prepared in aqueous solution via a hydrothermal synthesis method. The amino groups on the surface of CuInS2 QDs can interact with sulfate and carboxylate groups in heparin via electrostatic interactions and hydrogen bonding, which led the fluorescence of CuInS2 QDs to "turn-off". However, the heparin could be hydrolyzed into small fragments in the presence of heparinase, which resulted in the fluorescence of CuInS2 QDs being recovered. Therefore, the addition of heparinase to the heparin/CuInS2 QDs system activated the fluorescence of CuInS2 QDs to "turn-on" state. Thus, the determination of heparin and heparinase could be achieved by monitoring the fluorescence "turn off-on". Under the optimum conditions, there was a good linear relationship between I/I0 (I and I0 were the fluorescence intensity of CuInS2 QDs in the presence and absence of heparin, respectively) and heparin concentration in the range of 0.05-15 μmol L(-1) with the detection limit of 12.46 nmol L(-1). The linear detection for heparinase was in the range of 0.2-5 μg mL(-1) with the detection limit of 0.07 μg mL(-1). The proposed nanosensor was employed for the detection of heparin in fetal bovine serum samples with satisfactory results.

Management of anticoagulation in the critically ill patient

This article presents a review of the most commonly used anticoagulants in the intensive care unit setting. The difference between agents as well as the advantages and disadvantages are reviewed. For each agent, the mechanism of action, dosing, monitoring, adverse effects, and reversal strategies are discussed.

Oversulfated chondroitin sulfate inhibits the complement classical pathway by potentiating C1 inhibitor

Oversulfated chondroitin sulfate (OSCS) has become the subject of multidisciplinary investigation as a non-traditional contaminant in the heparin therapeutic preparations that were linked to severe adverse events. In this study, it was found that OSCS inhibited complement fixation on bacteria and bacterial lysis mediated by the complement classical pathway. The inhibition of complement by OSCS is not due to interference with antibody/antigen interaction or due to consumption of C3 associated with FXII-dependent contact system activation. However, OSCS complement inhibition is dependent on C1 inhibitor (C1inh) since the depletion of C1inh from either normal or FXII-deficient complement plasma prevents OSCS inhibition of complement activity. Surface plasmon resonance measurements revealed that immobilized C1inhibitor bound greater than 5-fold more C1s in the presence of OSCS than in presence of heparin. Although heparin can also inhibit complement, OSCS and OSCS contaminated heparin are more potent inhibitors of complement. Furthermore, polysulfated glycosaminoglycan (PSGAG), an anti-inflammatory veterinary medicine with a similar structure to OSCS, also inhibited complement in the plasma of dogs and farm animals. This study provides a new insight that in addition to the FXII-dependent activation of contact system, oversulfated and polysulfated chondroitin-sulfate can inhibit complement activity by potentiating the classical complement pathway regulator C1inh. This effect on C1inh may play a role in inhibiting inflammation as well as impacting bacterial clearance.

Bleeding incidence after oral surgery with continued oral anticoagulation

OBJECTIVES

The aim of this retrospective study was to assess the incidence of postoperative hemorrhage in patients treated with coumarins without interruption of the anticoagulant treatment undergoing oral surgical procedures, mostly osteotomies for tooth removal, when compared with patients who had never been anticoagulated.

MATERIAL AND METHODS

Six hundred thirty-seven patients underwent 934 oral surgical procedures on an outpatient basis. The INR was measured preoperatively being 2.44 in the mean SD 0.61. Local hemostasis was carried out routinely (80%) with collagen fleece, local flap, and acrylic splint.

RESULTS

Of these 637 patients, 47 presented with a postoperative hemorrhage (7.4%), 15 of these 47 cases had to be treated in hospital (2.4%). All patients showed up finally with a good wound healing, no administration of blood was necessary, and local measures revealed to be sufficient in all cases except for two patients, where the preoperative anticoagulant treatment had to be changed for 6 days. The bleeding incidence in 285 patients with comparable oral surgical procedures, who had never been anticoagulated, was 0.7%.

CONCLUSIONS

The results suggest that oral surgical procedures can be performed safely without alteration of the oral anticoagulant treatment. CINICAL RELEVANCE: Local hemostasis with collagen fleece, local flap, and acrylic splint seems to be sufficient to prevent postoperative bleeding.

The prevention and treatment of venous thromboembolism with LMWHs and new anticoagulants

As the risk factors for thrombosis are becoming better understood, so is the need for anticoagulation. The inherent difficulties with warfarin are such that a low-molecular-weight heparin (LMWH) is often the key therapeutic. However, there are several different species of LMWH available to the practitioner, which leads to the need for an objective guide. New agents are coming onto the marketplace, and these may supersede both warfarin and the heparins. The current report will review the biochemistry and pharmacology of different LWMHs and identify which are more suitable for the different presentations of venous thromboembolism. It will conclude with a brief synopsis of new agents which may supersede warfarin and heparin.

A cellular conformation-based screen for androgen receptor inhibitors

The androgen receptor (AR), a member of the steroid nuclear receptor family of transcription factors, regulates a wide range of physiological processes. Androgen signaling is also associated with numerous human diseases, including prostate cancer. All current antiandrogen therapies reduce ligand access to AR, whether by competitive antagonism or inhibition of androgen production, but are limited by acquired resistance and serious side-effects. Thus, novel antiandrogens that target events subsequent to ligand binding could have important therapeutic value. We developed a high throughput assay that exploits fluorescence resonance energy transfer (FRET) to measure ligand-induced conformation change in AR. We directly compared this assay to a transcription-based assay in a screen of FDA-approved compounds and natural products. The FRET-based screen identified compounds with previously unrecognized antiandrogen activities, with equivalent sensitivity and superior specificity compared to a reporter-based screen. This approach can thus improve the identification of small molecule AR inhibitors.

Evaluation of self-dissolving needles containing low molecular weight heparin (LMWH) in rats

Feasibility study of self-dissolving needles containing polysaccharide was performed. Low molecular weight heparin (LMWH) was used as a representative polysaccharide. Using chondroitin, dextran and dextrin as the base, self-dissolving needles (SDN) were prepared. The obtained SDNs were evaluated in rat absorption experiment, where pharmacological availability (PA) was calculated by comparing the plasma anti-Xa activity vs. time curves between SDNs and i.v. solution. After the insertion of SDNs to rats skin where the doses of LMWH were 25, 50 and 100 IU/kg, plasma samples were collected for 6h and anti-Xa activity was measured as the pharmacological index of LMWH. The anti-Xa level was maintained above 0.2 IU/ml, the therapeutic level, for about 2h at a dose of 100 IU/kg. Almost the same PAs of LMWH were obtained with dextran and dextrin SDNs, 97.7% and 102.3%, though lower PA was obtained with chondroitin SDN, 81.5%. In vitro dissolution experiment showed that LMWH was released from dextran, dextrin and chondroitin SDNs within 10 min. The T(50%)s were 0.84+/-0.06 min for dextran SDN, 1.07+/-0.12 min for chondroitin SDN and 2.11+/-0.31 min for dextrin SDN, respectively. Plasma anti-Xa activity vs. time profiles showed good dose-dependency in the 25-100 IU/kg range and high PAs were obtained, 90.0% for 25 IU/kg, 95.4% for 50 IU/kg and 97.7% for 100 IU/kg from dextran SDNs. Stability experiment was performed with dextran SDNs for 3 months. Above 97% of LMWH were remained in SDNs under three different conditions, -80, 4 and 40 degrees C. These results suggest the usefulness of SDN to polysaccharide drug.

Warfarin and cytochrome P450 2C9 genotype: possible ethnic variation in warfarin sensitivity

INTRODUCTION

Warfarin is a widely prescribed, efficacious oral anticoagulant. S-warfarin, the more active form, is metabolized by the cytochrome P450 (CYP)2C9 enzyme. The aim was to evaluate the influence of two CYP2C9 functional polymorphisms (*2 and *3) on warfarin dose in African-Americans, an unstudied population and Caucasians, and also to assess the effect of these polymorphisms on anticoagulation response after accounting for nongenetic factors and genetic factors that might also impact the dose-response relationship of warfarin.

PATIENTS AND METHODS

A prospective cohort of 362 patients with a target international normalized ratio of between 2.0 and 3.0 were genotyped. Warfarin sensitivity stratified by genotype was investigated using univariate and multivariate analyses.

RESULTS

The maintenance dose of warfarin was significantly related to genotype (p < 0.01) (variant carriers: 31.25 mg/week; wild-type: 37.5 mg/week), even after adjustment for possible confounding factors (p = 0.046). However, the effect of genotype was restricted to Caucasians, in whom variant carriers had a significantly lower maintenance dose compared with wild-type homozygotes (unadjusted: p < 0.01; adjusted: p = 0.02). There was a greater risk of over-anticoagulation among Caucasian variant carriers, although this was only observed prior to reaching maintenance dose. For African-American variant carriers, there was no difference in warfarin response based on CYP2C9 genotype.

DISCUSSION

CYP2C9 *2 and *3 variants provide predictive information in anticoagulation response. However, these variants may not be useful in African-Americans or as a marker of long-term over-anticoagulation once a stable dose is reached.

A Fluorescent Polymeric Heparin Sensor

Linear copolymers have been developed which carry binding sites tailored for sulfated sugars. All binding monomers are based on the methacrylamide skeleton and ensure statistical radical copolymerization. They are decorated with o-aminomethylphenylboronates for covalent ester formation and/or alkylammonium ions for noncovalent Coulomb attraction. Alcohol sidechains maintain a high water solubility; a dansyl monomer was constructed as a fluorescence label. Statistical copolymerization of comonomer mixtures with optimized ratios was started by AIBN (AIBN=2,2'-azoisobutyronitrile) and furnished water-soluble comonomers with an exceptionally high affinity for glucosaminoglucans. Heparin can be quantitatively detected with an unprecedented 30 nM sensitivity, and a neutral polymer without any ammonium cation is still able to bind the target with almost micromolar affinity. From this unexpected result, we propose a new binding scheme between the boronate and a sulfated ethylene glycol or aminoethanol unit. Although the mechanism of heparin binding involves covalent boronate ester formation, it can be completely reversed by protamine addition, similar to heparin's complex formation with antithrombin III.

Response characteristics of a reversible electrochemical sensor for the polyion protamine

We describe here in detail the first reversible electrochemical sensors for the polyion protamine. Potentiometric sensors were proposed in recent years, mainly for the determination of the polyions heparin and protamine. Such potentiometric polyion sensors functioned on the nonequilibrium extraction of polyions into a hydrophobic membrane phase via ion pairing with lipophilic ion exchangers. This made it difficult to design sensors that operate in a truly reversible fashion. The reversible sensors described here utilize the same basic response mechanism as their potentiometric counterparts, but the processes of extraction and ion stripping are now fully controlled electrochemically. Spontaneous polyion extraction is avoided by using membranes containing highly lipophilic electrolytes that possess no ion-exchange properties. Reversible extraction of polyions is induced if a constant current pulse of fixed duration is applied across the membrane, followed by a baseline potential pulse. The key theoretical response principles of this new class of polyion sensors are discussed here and compared to those of its classical potentiometric counterpart. The electrochemical sensing system is characterized in terms of optimal working conditions, membrane composition, selectivity, and influence of sample stirring and organic-phase diffusion coefficient on the response characteristics. Excellent potential stability and reversibility of the sensors are observed, and measurements of heparin concentration in whole blood samples via protamine titration are demonstrated.

Preparation and evaluation of oral solid heparin using emulsifier and adsorbent for in vitro and in vivo studies

Oral anticoagulant therapy with heparin has been challenged by formulating heparin in oral solid preparation. As heparin, low molecular weight heparin (LMWH) was used. LMWH was dispersed with a surfactant used for the self-microemulsifying drug delivery system (SMEDDS), PEG-8 caprylic/capric glycerides (Labrasol), and the mixture was solidified with three kinds of adsorbents, microporous calcium silicate (Florite RE), magnesium alminometa silicate (Neusilin US(2)) and silicon dioxide (Sylysia 320). The in vitro release study showed that the T50%s were 3.2+/-0.1min for Sylysia 320, 4.6+/-0.2min for Florite RE, 13.7+/-0.1min for Neusilin US(2). The in vivo rat absorption study showed that Florite RE system had the highest C(max), 0.42+/-0.01IU/mL and AUC, 0.59+/-0.06IUh/mL, where plasma LMWH levels were measured as anti-Xa activity. Other preparations had the C(max) and AUC, 0.12+/-0.01IU/mL and 0.15+/-0.02IUh/mL for Neusilin US(2) and 0.25+/-0.02IU/mL and 0.40+/-0.03IUh/mL for Sylysia 320, respectively. The bioavailability (BA) of LMWH from the microporous calcium silicate preparation, Florite RE, was 18.8% in rats by comparing the AUC obtained after i.v. injection of LMWH, 40IU/kg to another group of rats. Florite RE system was evaluated in dogs after oral administration in an enteric capsule made of Eudragit S100 at the LMWH dose of 200IU/kg. High plasma anti-Xa activity levels were obtained, i.e., the C(max) was 0.48+/-0.11IU/mL and AUC was 1.64+/-0.32IUh/mL. These results suggest that adsorbent system is useful as an oral solid delivery system of poorly absorbable drugs such as LMWH.

Aspirin resistance: mechanisms and clinical implications

Acetylsalicylic acid (aspirin) has been shown to irreversibly interfere with platelet function, an effect that is associated with a reduction in morbid and mortal arterial thrombotic events in multiple clinical studies. This clinical benefit appears to be attenuated by resistance to the antiplatelet effects of aspirin in up to 35% of patients. The mechanisms for aspirin resistance are multifactorial and include noncompliance with aspirin therapy, diabetes mellitus, cell-cell and drug-drug interactions, genetic polymorphisms, and coronary artery disease. It has not been determined what the best laboratory procedure is to screen for aspirin resistance. Those individuals at high risk for aspirin resistance might best be treated with an additional oral antiplatelet drug (eg, clopidogrel) to achieve maximal protection against arterial thrombotic events.

Venous thromboembolic prophylaxis after elective total hip arthroplasty

Elective total hip arthroplasty is a common orthopaedic procedure that has been proven to relieve pain and reliably improves the quality of life of its patients. However, patients having a total hip arthroplasty are among those at greatest risk for venous thromboembolic disease. Therefore, most orthopaedic surgeons use routine prophylaxis. Although several agents have been shown to reduce the risk of thromboembolic disease, there is no clear preference for a particular agent in elective total hip arthroplasty. This evidence-based review focuses on the efficacy and safety of the agents that currently are used for prophylaxis against deep venous thrombosis. These agents include warfarin, low-molecular-weight heparin, fondaparinux, aspirin, and mechanical devices. Furthermore, the influence of shorter hospital stays on duration of prophylaxis and screening will be discussed. The most effective prophylactic agents for patients after total hip arthroplasty include low-molecular-weight heparin, warfarin, and fondaparinux. Pneumatic compression devices have been proven to reduce distal thromboembolic events but multi-center, randomized studies need to be done to determine the efficacy of mechanical prophylaxis with short hospital stays. The selection of a prophylaxis regimen is a balance between efficacy and safety, and individual patient factors can influence the prophylaxis regimen that is used.