Recombinant hirudin: a specific thrombin inhibiting anticoagulant for hemodialysis

Anticoagulation for people receiving long-term haemodialysis

BACKGROUND

Haemodialysis (HD) requires safe and effective anticoagulation to prevent clot formation within the extracorporeal circuit during dialysis treatments to enable adequate dialysis and minimise adverse events, including major bleeding. Low molecular weight heparin (LMWH) may provide a more predictable dose, reliable anticoagulant effects and be simpler to administer than unfractionated heparin (UFH) for HD anticoagulation, but may accumulate in the kidneys and lead to bleeding.

OBJECTIVES

To assess the efficacy and safety of anticoagulation strategies (including both heparin and non-heparin drugs) for long-term HD in people with kidney failure. Any intervention preventing clotting within the extracorporeal circuit without establishing anticoagulation within the patient, such as regional citrate, citrate enriched dialysate, heparin-coated dialysers, pre-dilution haemodiafiltration (HDF), and saline flushes were also included.

SEARCH METHODS

We searched the Cochrane Kidney and Transplant Register of Studies up to November 2023 through contact with the Information Specialist using search terms relevant to this review. Studies in the Register are identified through searches of CENTRAL, MEDLINE, and EMBASE, conference proceedings, the International Clinical Trials Registry Platform (ICTRP) Search Portal and ClinicalTrials.gov.

SELECTION CRITERIA

Randomised controlled trials (RCTs) and quasi-randomised controlled studies (quasi-RCTs) evaluating anticoagulant agents administered during HD treatment in adults and children with kidney failure.

DATA COLLECTION AND ANALYSIS

Two authors independently assessed the risk of bias using the Cochrane tool and extracted data. Treatment effects were estimated using random effects meta-analysis and expressed as relative risk (RR) or mean difference (MD) with 95% confidence intervals (CI). Evidence certainty was assessed using the Grading of Recommendation, Assessment, Development and Evaluation approach (GRADE).

MAIN RESULTS

We included 113 studies randomising 4535 participants. The risk of bias in each study was adjudicated as high or unclear for most risk domains. Compared to UFH, LMWH had uncertain effects on extracorporeal circuit thrombosis (3 studies, 91 participants: RR 1.58, 95% CI 0.46 to 5.42; I2 = 8%; low certainty evidence), while major bleeding and minor bleeding were not adequately reported. Regional citrate anticoagulation may lower the risk of minor bleeding compared to UFH (2 studies, 82 participants: RR 0.34, 95% CI 0.14 to 0.85; I2 = 0%; low certainty evidence). No studies reported data comparing regional citrate to UFH on risks of extracorporeal circuit thrombosis and major bleeding. The effects of very LMWH, danaparoid, prostacyclin, direct thrombin inhibitors, factor XI inhibitors or heparin-grafted membranes were uncertain due to insufficient data. The effects of different LMWH, different doses of LMWH, and the administration of LMWH anticoagulants using inlet versus outlet bloodline or bolus versus infusion were uncertain. Evidence to compare citrate to another citrate or control was scant. The effects of UFH compared to no anticoagulant therapy or different doses of UFH were uncertain. Death, dialysis vascular access outcomes, blood transfusions, measures of anticoagulation effect, and costs of interventions were rarely reported. No studies evaluated the effects of treatment on non-fatal myocardial infarction, non-fatal stroke and hospital admissions. Adverse events were inconsistently and rarely reported.

AUTHORS' CONCLUSIONS

Anticoagulant strategies, including UFH and LMWH, have uncertain comparative risks on extracorporeal circuit thrombosis, while major bleeding and minor bleeding were not adequately reported. Regional citrate may decrease minor bleeding, but the effects on major bleeding and extracorporeal circuit thrombosis were not reported. Evidence supporting clinical decision-making for different forms of anticoagulant strategies for HD is of low and very low certainty, as available studies have not been designed to measure treatment effects on important clinical outcomes.

A phase I, single and continuous dose administration study on the safety, tolerability, and pharmacokinetics of neorudin, a novel recombinant anticoagulant protein, in healthy subjects

The aim of this study was to evaluate the tolerability, safety, and pharmacokinetics of single and continuous dose administration of recombinant neorudin (EPR-hirudin, EH) by intravenous administration in healthy subjects, and to provide a safe dosage range for phase II clinical research. Forty-four subjects received EH as a single dose of between 0.2 and 2.0 mg/kg by intravenous bolus and drip infusion. In addition, 18 healthy subjects were randomly divided into three dose groups (0.15, 0.30, and 0.45 mg/kg/h) with 6 subjects in each group for the continuous administration trial. Single or continuous doses of neorudin were generally well tolerated by healthy adult subjects. There were no serious adverse events (SAEs), and all adverse events (AEs) were mild to moderate. Moreover, no subjects withdrew from the trial because of AEs. There were no clinically relevant changes in physical examination results, clinical chemistry, urinalysis, or vital signs. The incidence of adverse events was not significantly related to drug dose or systemic exposure. After single-dose and continuous administration, the serum EH concentration reached its peak at 5 min, and the exposure increased with the increase in the administered dose. The mean half-life (T_1/2 ), clearance (Cl), and apparent volume of distribution (Vd) of EH ranged from 1.7 to 2.5 h, 123.9 to 179.7 ml/h/kg, and 402.7 to 615.2 ml/kg, respectively. The demonstrated safety, tolerability, and pharmacokinetic characteristics of EH can be used to guide rational drug dosing and choose therapeutic regimens in subsequent clinical studies. Clinical trial registration: Chinadrugtrials.org identifier: CTR20160444.

The effects of a hirudin/liposome complex on a diabetic nephropathy rat model

BACKGROUND

Hirudin, an extract from Hirudo spp., is an anticoagulant used to treat a variety of renal diseases, including diabetic nephropathy (DN). Currently, hirudin has to be used at high dosages to treat DN because it poorly targets the kidneys, although at high dosages it can have severe side effects. Developing a targeted drug delivery system for hirudin, then, could boost its positive therapeutic effects while lowering the risk of side effects. Liposomes have been demonstrated to have significant renal targeting potential, but here we show that a hirudin-loaded liposome is an effective delivery method for patients with DN.

METHOD

In this study, we prepared a hirudin/liposome complex and tested its efficacy by injecting it into a rat model. We then compared the renal accumulation of hirudin between complex-injected rat models and rat models that received injections of hirudin alone. We also investigated the mechanisms behind the complex's effects.

RESULT

The hirudin/liposome complex increased the accumulation of hirudin in kidney tissues and relieved the renal injury in DN rat models. Moreover, the hirudin/liposome complex down-regulated the expression of TGF-β1 and VEGF in the kidneys.

CONCLUSION

We demonstrated that a hirudin/liposome complex can have a significant positive effect on DN. The mechanism may be that the complex inhibits the expression of VEGF and TGF-β1.

Lepirudin for anticoagulation in patients with heparin-induced thrombocytopenia treated with continuous renal replacement therapy

Lepirudin is a potent, direct thrombin inhibitor used for anticoagulation in patients with heparin-induced thrombocytopenia type II (HIT). The half-life of lepirudin is prolonged in patients with renal insufficiency. Preliminary studies suggest that it is safe to use lepirudin in patients being treated with intermittent hemodialysis but information regarding its use with continuous renal replacement therapy (CRRT) is scarce. CRRT is used in acute care settings to remove fluid and uremic toxins in patients with renal failure with hemodynamic instability. Patients with HIT, renal failure, and hemodynamic instability pose a complex situation for clinical management. These patients require anticoagulation with nonheparin agents with simultaneous CRRT. There are no guidelines in the literature regarding the management of this patient group. We report our experience with lepirudin at managing four such patients with HIT, being treated with CRRT.

Heparin-induced thrombocytopenia (an overview)

Heparin induced thrombocytopenia is a serious side effect of a drug that is widely used in clinical practice. All patients exposed to heparin, administered by any route or at any dose, are at varying risk of developing HIT and its potentially devastating thrombotic complications. There are two clinical forms of HIT, type I and type II. Type I HIT, is a non-immunologic response, while type II HIT is an immunologic response to heparin therapy. Type I HIT is not associated with an increased risk of thrombosis and is characterized by reversible thrombocytopenia. Type II HIT occurs in approximately 1 to 3% of patients receiving unfractionated heparin. Type II HIT is more severe because of the increased risk of thrombotic events. Venous and arterial thromboembolic complications may lead to amputation, stroke, myocardial infarction, and death.

HEMATOLOGY: ISSUES IN THE DIALYSIS PATIENT: When Heparin Causes Thrombosis: Significance, Recognition, and Management of Heparin-Induced Thrombocytopenia in Dialysis Patients

Heparin-induced thrombocytopenia (HIT) is characterized by thrombocytopenia and paradoxical hypercoagulability. HIT occurs when an antibody ("HIT antibody") produced against the complex of heparin and platelet factor 4 (PF4) causes systemic platelet consumption and activation. Nephrologists encounter HIT in the care of end-stage renal disease (ESRD) patients because heparin is a routine anticoagulant in hemodialysis. The incidence of HIT in ESRD appears to be lower than in other clinical settings. However, HIT is equally life threatening in ESRD patients and therefore demands the same prompt recognition and aggressive treatment. Diagnosing HIT requires the detection of HIT antibodies. A functional assay (e.g., [(14)C] serotonin release assay) relies on the patient's HIT antibodies to activate donor platelets at pharmacologic heparin concentrations. The more common antigen assay (e.g., enzyme-linked immunosorbent assay [ELISA]) detects the binding of the patient's HIT antibodies to antigens (e.g., heparin-PF4 complex) in a microtiter well and does not involve platelets. The moment HIT is suspected, heparin should be stopped and an alternative anticoagulant initiated immediately, even before the result of a serologic test becomes available. The advent of several new anticoagulants in the last decade, especially argatroban and bivalirudin, has expanded treatment options for HIT in dialysis patients. This review discusses the epidemiology, pathogenesis, clinical features, diagnosis, and treatment of HIT, with special emphasis on concepts relevant to the care of dialysis patients.

Regional Citrate Anticoagulation during Hemodialysis

BACKGROUND

Regional citrate anticoagulation during hemodialysis is promising, but its clinical implementation is routinely cumbersome because a continuous adjustment of calcium infusion at the dialyzer outlet is needed. Duocart biofiltration (DCB) is a new hemodialysis method using a calcium and magnesium-free dialysate containing only sodium chloride and bicarbonate combined with the infusion into the venous line of a solution containing the ionic complement (K, Ca, Mg) and glucose. Since the dialysate is calcium- and magnesium-free and infusion rate of the solution containing calcium is automatically determined by the dialysis delivery system according to the on-line measured value of ionic dialysance, DCB seems a technique especially suitable for citrate anticoagulation procedure.

METHODS

Thirty DCB sessions were performed in 10 patients with increased risk of bleeding. A commercially available mixture of trisodium citrate, citric acid and glucose was infused into the arterial line at a rate equal to 3% of dialyzer blood flow. The ionic complement (K: 48 mM, Ca: 42 mM, Mg: 14 mM, glucose: 110 mM) was infused at a rate equal to 1/24 ionic dialysance value automatically determined each 15 min by the dialysis monitor. DCB sessions were compared to 21 conventional bicarbonate hemodialysis (BHD) sessions with low-molecular-weight heparin anticoagulation.

RESULTS

Whole blood activated clotting time (WBACT) measured in the venous line (before infusion of ionic complement) was 200% of the WBACT value in the arterial line. Clotting and citrate-related adverse events were not observed. Postdialysis compression time of the arteriovenous access is significantly (p<0.001) shorter after DCB sessions (3.9+/-1.1 min) compared with BHD sessions (8.7+/-4.6 min).

CONCLUSION

Citrate anticoagulation during Duocart biofiltration is effective, safe and suitable for routine use because calcium infusion rate is automatically adjusted without the need of monitoring degree of anticoagulation and level of ionized calcium.

Intermittent hirudin versus continuous heparin for anticoagulation in continuous renal replacement therapy

BACKGROUND

Besides possible bleeding complications a further problem in anticoagulation during continuous renal replacement therapy (CRRT) is the development of heparin-induced thrombocytopenia type II (HIT II) where further anticoagulation with heparin is contraindicated. The application of continuous hirudin as alternative for heparin caused bleeding complications by comparable filter efficacy. Aim of this prospective-controlled pilot study was to compare the efficacy and safety of intermittent hirudin and continuous heparin for anticoagulation during CRRT in critically ill patients.

METHODS

26 patients receiving CRRT were randomly allocated to two groups: Heparin group (14 patients): continuous administration of 250 IU/h heparin, dose was adjusted in 125 IU/h steps with a targeted activated clotting time (ACT) of 180-210 s. Hirudin group (12 patients): initial bolus application of 2-2-5 microg/kg hirudin, dose was adjusted in 2 microg/kg bolus steps with a targeted ecarin clotting time (ECT) >80 s. Observation time was 96 hours.

RESULTS

Measured filter run time was virtually longer for heparin. No bleeding complications were observed in the hirudin group, two bleeding complications in the heparin group.

CONCLUSIONS

Intermittent hirudin can be used safely for anticoagulation in CRRT. However, the in tendency better filter survival for heparin elucidates the need for further investigations to find the right dosage equilibrium between filter clotting and bleeding complications.

Diagnosis and management of heparin-induced thrombocytopenia

Heparin use is ubiquitous, wherein 1 to 5% of patients exposed to standard unfractionated heparin develop thrombocytopenia due to antibodies to a complex of heparin and platelet factor 4. Classic features include onset of thrombocytopenia after 5 to 10 days of ongoing heparin exposure, a 50% fall in the platelet count from baseline, resolution of the thrombocytopenia 5 to 10 days after cessation of heparin and a high risk of thrombosis noted in 30 to 75% of patients with heparin-induced thrombocytopenia (HIT) in terms of every-other-day platelet-count monitoring in patients on standard unfractionated heparin. And those patients developing thrombocytopenia necessitate an accurate, readily accessible diagnostic test for HIT. Diagnosis has been recently facilitated by the development of an enzyme-linked immunosorbent assay (ELISA) test for the heparin-P4 antibody complex, although this test carries a relatively low specificity. Widespread use of the ELISA demonstrates a relatively high prevalence of the antibody in patients exposed to heparin in certain settings, such as cardiopulmonary bypass, wherein a quarter of patients have a positive ELISA of unclear significance. Once HIT is diagnosed, the high risk of thrombosis necessitates empiric anticoagulation with an antithrombin such as argatroban or lepirudin, or the heparinoid danaparoid. Additional agents under further study include the antithrombin bivalirudin and the pentasaccharide fondaparinux. Future issues in HIT include increasing awareness for HIT, improving the specificity of HIT testing and the development of new anticoagulants for HIT that will enable out-patient management.

Anticoagulant efficacy of PEG-Hirudin in patients on maintenance hemodialysis

BACKGROUND

Heparins are currently the anticoagulants of choice in long-term hemodialysis (HD). Because of their shortcomings, including the increasing incidence of heparin-induced thrombocytopenia (HIT II), alternative anticoagulation is necessary. The study objectives were to provide safe and effective HD by investigating an appropriate PEG (polyethylene glycol)-Hirudin dosage regimen in patients on HD, as well as to compare the safety, tolerability, and efficacy of PEG-Hirudin with that of unfractionated heparin (UFH).

METHODS

Twenty patients (12 males, 8 females, mean age 57.8 years) with end-stage renal disease (ESRD) took part in the study. Dialysis sessions lasting a mean of 4.3 hours (QB 250 to 300 mL/min, QD 500 mL/min) were performed 3 times a week with a Gambro GFS plus 16 dialyzer. Ten patients (group I) received UFH at 3 regular dialysis sessions (HD1-3) followed by 5 dialysis sessions using PEG-Hirudin (HD4-8). Another 10 patients (group II) received UFH at 3 regular dialysis sessions (HD1-3) followed by 10 sessions on PEG-Hirudin (HD4-13). The starting dose of PEG-Hirudin was a single bolus injection of 80 microg/kg BW (HD4), except for the first patient, who received 50 microg/kg BW followed by a 12 microg/kg bolus. Before each of the following sessions (HD5-13), an individualized PEG-Hirudin dose of between 26 to 65 microg/kg body weight (BW) (mean dose 41 microg/kg BW) was injected. PEG-Hirudin plasma and blood concentrations derived from anti-Iia activity and ecarin clotting time (ECT), respectively, activated partial thromboplastin time (aPTT), bleeding time, and arteriovenous (AV) fistula compression time were investigated to calculate the pharmacokinetic parameters or to assess anticoagulant efficacy.

RESULTS

Mean predialysis PEG-Hirudin plasma concentrations increased up to a maximum of 488 ng/mL in group I (HD8) and up to 536 ng/mL in group II (HD8). Mean plasma concentrations measured at 5 minutes after the 1st (HD4), 5th (HD8), and 10th (HD13) PEG-Hirudin injection ranged from 1076 to 1298 ng/mL. Mean post-dialysis plasma levels ranged from 818 to 995 ng/mL. Mean predialysis aPTT was not affected by UFH, but was prolonged by 46 to 56 seconds by PEG-Hirudin. Five minutes after injecting PEG-Hirudin or UFH, mean aPTT was prolonged to a maximum of 85 and 188 seconds, respectively. Mean post-dialysis aPTT values ranged from 60 to 68 seconds after PEG-Hirudin and 34 to 46 seconds after UFH. PEG-Hirudin was well tolerated; no serious adverse events or bleeding complications were observed. Safety assessments yielded no significant difference between the two anticoagulants.

CONCLUSION

This pilot study confirmed the usefulness and tolerability of a PEG-Hirudin dose regimen consisting of a single, fixed bolus dose of 80 microg/kg BW injected before starting the first dialysis session (HD4) and followed by a dose titration period over at least 4 sessions (HD5-8), which again was followed by a fixed maintenance dose period (HD9-13). On the basis of PEG-Hirudin data from patients with various degrees of renal insufficiency but not undergoing hemodialysis and prior recombinant-hirudin (r-hirudin) experience, patients were titrated into an EC-controlled dose range that proved to be efficacious enough to prevent clotting and safe enough to prevent bleeding. Due to the favorable pharmacokinetic properties of PEG-Hirudin, a residual anticoagulant effect is maintained in the intervals between dialysis sessions, and this permanent state of anticoagulation may prevent vascular access complications as well as other vascular events.

Drugs for the prevention and treatment of thrombosis in patients with heparin-induced thrombocytopenia

Most patients with heparin-induced thrombocytopenia (HIT), a serious adverse effect of heparin mediated by platelet-activating heparin-dependent antibodies, require alternative anticoagulation. This is because HIT is highly prothrombotic and is characterized by markedly increased thrombin generation. Unfractionated heparins seem to induce HIT more often than low molecular weight heparins. There are three anticoagulants for which there is an emerging consensus for their efficacy in management of HIT, and which are currently approved for treatment of HIT in several countries: the recombinant hirudin, lepirudin, a direct thrombin inhibitor; the synthetic direct thrombin inhibitor, argatroban; and the heparinoid, danaparoid sodium, mainly exhibiting antifactor-Xa activity. Recommendations for optimal use of these drugs in HIT are given in this review stressing the need for immediate treatment of patients with HIT without awaiting laboratory diagnosis. Hirudin, the drug for which most data from prospective trials exists, can be safely and effectively used in patients with HIT, its dramatically increased elimination half-life in patients with renal failure being the most important drawback. Argatroban, which is mainly eliminated by the liver, could be used preferentially in such patients with renal impairment. Interference with the international normalized ratio makes oral anticoagulation, which is necessary in many patients with HIT, problematic. Activated partial thromboplastin time is sufficient to monitor lepirudin and argatroban treatment in most cases. Danaparoid sodium, with an antifactor-X activity half-life of about 24 hours seems to be best suited for thrombosis prophylaxis in patients with HIT. In some patients monitoring by determining antifactor-Xa activity is necessary. No antidote is available for any of the drugs discussed, and bleeding complications are the most important adverse effects. In situations such as hemodialysis or cardiopulmonary bypass, not only the characteristics of the drug in use itself, but also availability of monitoring methods play an important role. Adjunctive treatments have not been systematically evaluated and should be used cautiously. Recent data suggest that re-exposure of patients with a history of HIT with heparin, for example during cardiopulmonary bypass, can be well tolerated provided no circulating HIT antibodies are detectable at the time of re-exposure, and heparin is strictly avoided pre- and postoperatively.

The Role of Recombinant Hirudins in the Management of Thrombotic Disorders

Native hirudin is the most potent natural direct thrombin inhibitor currently known; it is capable of inhibiting not only fluid phase, but also clot-bound thrombin. Recombinant technology now allows production of recombinant hirudins (r-hirudins), which are available in sufficient purity and quantity with essentially unaltered thrombin-inhibitory potency. As thrombin is known to play a key role in a number of thrombotic disorders, numerous studies focused on the impact of r-hirudins on the clinical course in these diseases. R-hirudins provided significantly more stable anticoagulation than standard heparin, but demonstrated a relatively narrow therapeutic range with relevant bleeding risk even at clinically effective doses. In doses that are not associated with an increased bleeding risk, r-hirudins often failed to demonstrate significant superiority to heparin. To date, r-hirudins have a definite role in the treatment of heparin-induced thrombocytopenia, where they markedly reduce the high risk of thrombosis. For prophylaxis of deep vein thrombosis, r-hirudins have been shown to be superior to both unfractionated and low molecular weight heparin, but are not extensively used in this indication. In acute coronary syndromes, a definite role of r-hirudins has not yet been firmly established. When applied in an appropriate dose as adjunct to thrombolysis in patients with acute myocardial infarction, randomized, controlled trials did not show a consistent benefit of r-hirudins, especially in the long-term. In patients undergoing coronary balloon angioplasty for acute coronary syndromes, promising effects in the early postprocedural phase did not translate to an improved outcome after 6 months. In patients with unstable angina pectoris, efficacy and safety of r-hirudins as primary antithrombotic therapy are still under debate. In the future, r-hirudins are to be compared with alternative or additional potent antithrombotic agents or treatment strategies. This comparison will ultimately lead to their final placement in the management of thrombotic disorders.

Long-term citrate anticoagulation for high-flux haemodialysis in a patient with heparin-induced thrombocytopenia type II

For the first time, long-term use of regional citrate anticoagulation for high-flux haemodialysis is reported in a patient with heparin-induced thrombocytopenia type II. A simple, flow-independent, citrate infusion protocol allowed efficient anticoagulation. Excellent solute removal, indicated by KT/V values of 1.52 to 1.98, was achieved. Electrolyte and acid-base balance as well as calcium homeostasis were well controlled over a period of 9 months.

Drug-induced and drug-dependent immune thrombocytopenias

Thrombocytopenia is a frequent comorbid condition in many in hospital patients. In some patients, drugs are the cause of low platelet counts. While cytotoxic effects of anti-tumor therapy are the most frequent cause, immune mechanisms should also be considered. This review addresses thrombocytopenias in four groups. Heparin-dependent thrombocytopenia (HIT), by far the most frequent drug-induced immune-mediated type of thrombocytopenia, has a unique pathogenesis and clinical consequences. HIT is a clinicopathological syndrome in which antibodies mostly directed against a multimolecular complex of platelet factor 4 and heparin cause paradoxical thromboembolic complications. The mechanisms through which heparin can enhance thrombin generation are discussed and treatment alternatives for affected patients are presented in detail. It is of primary importance to recognize these patients as early as possible and to substitute heparin with a compatible anticoagulatory drug, such as hirudin, danaparoid or argatroban. Patients seem to benefit from therapeutic doses of alternative treatment rather than from low-dose prophylactic doses. With the increasing use of glycoprotein (GP) IIb/IIIa inhibitors in patients with acute coronary syndromes, thrombocytopenias are increasingly recognized as an adverse effect of these drugs. Up to 4% of treated patients are affected. Most important, pseudothrombocytopenia, a laboratory artefact, is as frequent as real drug-induced thrombocytopenia and must be excluded before changes in treatment are considered. The pathogenesis of these thrombocytopenias is still debated; an immune mechanism involving preformed antibodies is likely. However, since these antibodies are also detectable in a high percentage of normal controls and of patients not developing thrombocytopenia, their impact is still unclear. Patients with real thrombocytopenia are at an increased risk of bleeding; treatment consists of cessation of the GP IIb/IIIa inhibitor and platelet transfusions in cases of severe hemorrhage. Classic immune thrombocytopenia can be induced by some drugs, e.g. gold, which trigger anti-platelet antibodies indistinguishable from platelet autoantibodies found in autoimmune thrombocytopenia. Drug-induced and drug-dependent immune thrombocytopenia is induced by antibodies recognizing an epitope on platelet GP formed after binding of a drug to a platelet glycoprotein. Still unresolved is whether antibody binding is the consequence of a conformational change of the antigen, the antibody, or both. These antibodies typically react with monomorphic epitopes on platelet GP, but only in the presence of the drug or a metabolite. Although several platelet GP have been identified as antibody target (GPIb/IX, GPV, GP IIb/IIIa), antibodies in an individual patient are highly specific for a single GP. Clinically, these patients present with very low platelet counts and acute, sometimes severe, hemorrhage. Treatment is restricted to withdrawal of the drug and symptomatic treatment of bleeding.

Anticoagulation with hirudin for continuous veno-venous hemodialysis in liver transplantation

Postoperative encephalopathy after orthotopic liver transplantation can be difficult to diagnose. We report a case of heparin-induced thrombocytopenia in a liver transplant patient who had seizures. Due to poor liver function the patient developed hepatorenal syndrome requiring continuous veno-venous hemodialysis (CVVHD). Initially we used heparin as the anticoagulant. After the diagnosis of heparin-induced thrombocytopenia (HIT) was made, we switched to r-hirudin. No serious side effects, e.g. bleeding or immune sensitization, were seen.

Pharmacodynamics and pharmacokinetics of polyethylene glycol-hirudin in patients with chronic renal failure

BACKGROUND

Hirudin selectively inhibits thrombin without cofactors and is eliminated via the kidneys. Recombinant hirudin (r-hi) has a terminal elimination half-life (t1/2) of about 50 to 100 minutes. Coupling of polyethylene glycol (PEG) to r-hi, giving PEG-hirudin (PEG-Hi), prolongs its t1/2 while enhancing efficacy. We looked at the pharmacodynamic and pharmacokinetic behavior of PEG-Hi in patients with impaired renal function.

METHODS

Anticoagulant activity and the pharmacokinetic parameters of a single intravenous bolus injection of 0.05 mg/kg body weight PEG-Hi were studied in 38 subjects. They were assigned to five groups: group IA, creatinine clearance (CCr) >/= 80 mL/min, 8 healthy volunteers; group IB, CCr >/= 80 mL/min, 8 patients with normal renal function); group II, CCr 79 to 50 mL/min, 7 patients with mild chronic renal failure (CRF); group III, CCr 49 to 20 mL/min, 10 patients with moderate CRF; and group IV, CCr </= 19 mL/min, 5 patients with severe CRF. Plasma and urine samples were collected from patients for up to 120 hours after dosing and from healthy volunteers for up to 24 hours.

RESULTS

PEG-Hi was well tolerated in all groups. No serious adverse events were noted. Cmax values were similar in all groups; area under the curve (AUC) increased in patients from 2.9 +/- 1.0 microg. h/mL (IB) to 21.3 +/- 5.0 microg h/mL (IV). According to the severity of renal function, t1/2 was prolonged from 2 hours (IB) to 38.4 hours (IV), while total body clearance (CTB), renal clearance (CRenal), and recovery of PEG-Hi in the urine (FEo-t) decreased as follows: CTB from 23.3 +/- 6.6 (IB) to 2.9 +/- 0.6 mL/min (IV), CRenal from 7.8 +/- 5.0 (IB) to 0.8 +/- 0.5 mL/min (IV), and FEo-t from 40.2 +/- 18. 9% (IB) to 12.6 +/- 13.0% (IV). Total plasma clearance of PEG-Hi was well correlated with CCr. Anti-IIa activity of PEG-Hi showed a closer linear relationship to ecarin clotting time than to activated partial thromboplastin time.

CONCLUSION

Hence, PEG-Hi is considered safe in patients with CRF, but dosing and/or dose intervals should be adjusted according to the severity of renal impairment. Ecarin clotting time is well suited for safe and reliable monitoring of PEG-Hi.

Lepirudin dosing in dialysis-dependent renal failure

Lepirudin is a direct thrombin inhibitor indicated for parenteral anticoagulation in patients with heparin-induced thrombocytopenia. In patients with normal renal function, a bolus dose of 0.4 mg/kg is injected over 15-20 seconds, followed by a continuous infusion of 0.15 mg/kg/hour adjusted to prolong the activated partial thromboplastin time (aPTT) to 1.5-2.5 times the patient's baseline. Because renal function directly influences lepirudin elimination, patients with renal impairment require significant adjustments in the initial infusion rate. Current recommendations suggest that patients with dialysis-dependent renal failure should receive an initial bolus of 0.2 mg/kg, followed by 0.1 mg/kg every other day if the aPTT falls below the lower limit of the therapeutic range; however, this dosing may result in significant and prolonged overanticoagulation. A review of available literature regarding pharmacokinetics of lepirudin in renal failure suggests considerable variability in patient response over a narrow creatinine clearance range. Because there is no antidote for lepirudin if significant bleeding occurs, lower and less frequent dosing, guided by aPTT results, is recommended.

In vitro study of r-hirudin permeability through membranes of different haemodialysers

BACKGROUND

After introducing the specific thrombin inhibitor recombinant hirudin (r-hirudin) into clinical practice in cases of heparin-induced thrombocytopenia (HIT, type II) the possibility of its use as an anticoagulant during haemodialysis treatment in HIT II patients is being discussed more frequently. On the one hand, the efficient, safe and routine use of r-hirudin during haemodialyses, including the maintenance of a therapeutic blood level, presupposes that no r-hirudin will leave the circulation by passing through the dialyser membrane. On the other hand, it is important to have dialysers whose permeability to r-hirudin allows its efficient removal from the human body because, to date, no antidote is commercially available in cases of dangerously high blood concentrations of r-hirudin.

METHODS

An in vitro circulation model was used to study the r-hirudin permeability of some low- and high-flux dialysers. As r-hirudin-containing vehicles, both albumin-containing saline solution and bovine blood were circulated in the blood space of the system for 2 h. Transmembrane r-hirudin passage was tested by measuring r-hirudin concentration both in the blood and dialysate space fluids using the ecarin clotting time (ECT).

RESULTS

Low-flux dialysers with membranes made from polysulfone or regenerated cellulose proved to be almost impermeable to r-hirudin. In contrast, other low-flux membranes were partly permeable to r-hirudin (e.g. Hemophan) or even almost completely permeable (e.g. cellulose acetate). All high-flux dialysers tested were permeable to r-hirudin.

CONCLUSIONS

Only low-flux dialysers with polysulfone or regenerated cellulose membranes proved to be suitable for r-hirudin use in routine haemodialysis therapy. Other low-flux, and all high-flux, capillaries are permeable to r-hirudin and offer the possibility of lowering toxic r-hirudin concentrations after overdosing.

Laboratory monitoring of pentasaccharide in a dog model of hemodialysis

Varying dosages of pentasaccharide (400-800 nmol/kg) were compared to a 250-U/kg single bolus dosage of unfractionated heparin (UFH) in a dog model of hemodialysis. Several laboratory assays were used to monitor the effects of pentasaccharide and UFH. The pentasaccharide did not produce any anticoagulant effects as measured by the activated partial thromboplastin time. However, in the anti-Xa chromogenic assay and the Heptest assays, there was a dose-dependent prolongation after pentasaccharide administration. In the group of dogs administered 800 nmol/kg of pentasaccharide, there was a 50% decrease in the thrombin antithrombin (TAT) complex level after 60 minutes on dialysis. In the UFH-treated dogs, wide variations in assays were observed. There was a marked elevation in the activated partial thromboplastin time and Heptest assays up to 6 hours after UFH administration. Both anti-Xa and anti-IIa activity was measured up to 4 hours. In the TAT assay, UFH was found to have a stronger effect in suppressing the formation of TAT in comparison to the pentasaccharide. These results suggest that pentasaccharide can be used as a replacement for UFH in a dog model of hemodialysis to keep the dialysis circuit patent. In addition, the anti-Xa-based assays such as the Heptest and the chromogenic anti-Xa assays can be used to monitor the effects of pentasaccharide in this model.

Thrombin stimulates synthesis of type IV collagen and tissue inhibitor of metalloproteinases-1 by cultured human mesangial cells

Glomerular accumulation of extracellular matrix (ECM) is the common pathologic feature following glomerular injury, and the alteration in the synthesis and degradation of ECM may be involved in the glomerular accumulation of ECM. Glomerular fibrin formation occurs in various forms of human and experimental glomerulonephritis, and it may play an important role in progressive glomerular injury. Thrombin, a multifunctional serine proteinase that is generated at the site of vascular injury, has central functions in hemostasis and it also shows various biologic effects. In this study, it is hypothesized that thrombin may alter the production and the degradation of type IV collagen, which is an important component of ECM in the glomeruli. Human mesangial cells (HMC) were cultured, and the levels of type IV collagen, tissue inhibitor of metalloproteinase-1 (TIMP-1), and matrix metalloproteinase-2 (MMP-2) in the culture supernatants were measured by enzyme immunoassay using specific antibodies. MMP-2 activity was also evaluated by zymography using polyacrylamide/ sodium dodecyl sulfate gel-containing gelatin. Thrombin increased the production of type IV collagen and TIMP-1 in a dose-and time-dependent manner, but it did not increase MMP-2. Thrombin also stimulated the gene expressions of the type IV collagen and TIMP-1 in HMC in a dose- and time-dependent manner. Thrombin treated with diisopropylfluorophosphate, a serine proteinase inhibitor, did not show any of these effects. Hirudin, a natural thrombin inhibitor, and anti-transforming growth factor-beta-neutralizing antibody inhibited the stimulating effect of thrombin. These findings suggest that thrombin may contribute to the excessive accumulation of ECM and progression of glomerulosclerosis through an increase of type IV collagen production and a decreased matrix degradation presumably via a transforming growth factor-beta-dependent mechanism.

R-hirudin as anticoagulant in regular hemodialysis therapy: finding of therapeutic R-hirudin blood/plasma concentrations and respective dosages

Recently heparin-induced thrombocytopenia type II has been diagnosed more frequently and does not exclude hemodialysis patients. Up to now, recombinant hirudin is the only available anticoagulant showing no immunologic cross reactions with heparin. However, the use of r-hirudin in hemodialysis patients with different degrees of residual renal functions is impossible using standard dosages because elimination of r-hirudin varies depending on the degree of residual renal function. Therefore the first study was carried out using consecutive r-hirudin anticoagulated hemodialyses to determine the appropriate dose of r-hirudin. Ten hemodialysis patients with creatinine clearance values ranging between 0 and 13 mL/min/1.73m2 were anticoagulated with r-hirudin. An initial bolus of 0.1 mg/kg bwt before the first hemodialysis, resulted in an average r-hirudin blood concentration of 305 ng/mL at the end of treatment. The dose for each of the following four hemodialyses was adjusted individually to reach the minimum therapeutic r-hirudin blood concentration. At the end of these treatments the mean blood r-hirudin concentration was 422 ng/mL. The necessary mean doses ranged between 0.008 and 0.125 mg/kg bwt correlating to the creatinine clearance values of the patients. All hemodialyses of the study were effective and safe. Bleeding times determined during r-hirudin anticoagulation were significantly lower than control values measured 2 days after a heparin administration. The study proved that r-hirudin may be an efficient and safe heparin alternative as a hemodialysis anticoagulant when the individual's residual renal function is noted for dosage and dose adjustment and is controlled by drug monitoring using the ecarin clotting time.

Recombinant hirudin (lepirudin) provides safe and effective anticoagulation in patients with heparin-induced thrombocytopenia: a prospective study

BACKGROUND

The immunological type of heparin-induced thrombocytopenia (HIT) is the most frequent drug-induced thrombocytopenia. This study evaluated the efficacy of recombinant hirudin (r-hirudin or lepirudin), a potent thrombin inhibitor, for anticoagulation in patients with confirmed HIT.

METHODS AND RESULTS

Eighty-two patients in this prospective, multicenter study received 1 of 4 intravenous r-hirudin regimens: A1, HIT patients with thrombosis (n=51), 0.4-mg/kg bolus and then 0.15 mg. kg-1. h-1; A2, HIT patients with thrombosis receiving thrombolysis (n=5), 0. 2-mg/kg bolus and then 0.1 mg. kg-1. h-1; B, HIT patients without thrombosis (n=18), 0.1 mg. kg-1. h-1; and C, during cardiopulmonary bypass surgery (n=8), 0.25-mg/kg bolus and then 5-mg boluses as needed. Response criteria were increase in platelet count by >/=30% to >10(9)/L and activated partial thromboplastin time (aPTT) values 1.5 to 3.0 times baseline values achieved with a maximum of 2 dose increases. No placebo control was used for ethical reasons. Outcomes of a subset of r-hirudin-treated patients who met predefined inclusion criteria (n=71) were compared with those of a historical control group (n=120) for combined and individual incidences of death, amputations, new thromboembolic complications, and incidences of bleeding. Platelet counts increased rapidly in 88.7% of r-hirudin-treated patients with acute HIT. In regimens A1 and A2, the 25% and 75% quartiles of the aPTT were within the target range at all but 1 time point. The incidence of the combined end point (death, amputation, new thromboembolic complications) was significantly reduced in r-hirudin patients compared with historical control patients (P=0.014). During first selected treatment, the adjusted hazard ratio for r-hirudin patients versus historical control was 0.279 (95% CI, 0.112 to 0.699; P=0.003). Bleeding rates were similar in both groups.

CONCLUSIONS

r-Hirudin treatment is associated with a rapid and sustained recovery of platelet counts, sufficient aPTT prolongations, and true clinical benefits for patients with HIT.

Efficacy of pentasaccharide in a dog model of hemodialysis

A synthetic heparin pentasaccharide with sole anti-Xa actions has been evaluated for its antithrombotic efficacy in a dog model of hemodialysis. Various dosages of pentasaccharide, 400-800 nmol/kg, were compared with a single bolus dose of unfractionated heparin (250 U/kg). The primary endpoint in these studies was the duration of dialysis time. In addition, dialyzer filter content, venous trap protein, celite and saline ACT and hematocrit measurement. Pentasaccharide at dosages of 600 and 800 nmol/kg produced an extension of dialysis time (> 180 minutes) in contrast to unfractionated heparin at 250 U/kg which only produced antithrombotic effects for periods of up to 150 +/- 42 minutes (n = 5). At a lower dosage of 400 nmol/kg pentasaccharide produced weaker effects and the dialysis circuit was patent for periods of 122 +/- 14.8 (n = 5) minutes. The saline and celite ACT times were not extended at any dosage of pentasaccharide; however, at 250 U/kg, a strong effect was noted with unfractionated heparin (> 800 secs, 647 +/- 211 secs.), respectively. A dose dependent antithrombotic effect was also evident in the studies on the filter clots and venous trap protein content. No difference in the hematocrit was noted in any group. These results clearly suggest that despite the fact that pentasaccharide does not produce any prolongation of the coagulation times, it produces a dose dependent antithrombotic effect in this model of dog hemodialysis. Furthermore, these results also suggest that pentasaccharide at an appropriate dosage can be used as an alternate antithrombotic agent during hemodialysis.

The approach to anticoagulation in patients treated with extracorporeal therapy in the intensive care unit

No wholly satisfactory drug or system has yet been devised for preventing thrombosis in extracorporeal blood circuits needed for renal replacement treatments. Heparin is still regarded by some as a standard approach, but advances in many areas of intensive care unit (ICU) medicine have created the potential for saving the lives of many patients in whom heparin anticoagulation is no longer appropriate. Several nonheparin methods are now readily performed, and the great risk of bleeding that is imposed by the use of heparin demands that citrate or other nonheparin methods be made available in the ICUs of all major medical centers that deal with trauma or major surgical procedures. Details of the practicalities, difficulties, and advantages are compared for low-dose heparin, regional heparin, low-molecular-weight heparin, no-anticoagulant systems, citrate, and other anticoagulants for both intermittent and continuous modalities. The clinical features and complications in individual patients that impact on the selection of the best method of management are reviewed.

A comparison between the use of recombinant hirudin and heparin during hemodialysis

The purpose of this study was to determine the anticoagulant and antithrombotic potential of hirudin during hemodialysis by comparing the efficacy of dialysis with heparin to that of dialysis with recombinant hirudin (r-hirudin). Eleven patients with chronic renal failure and on maintenance hemodialysis were included in this open cross-over study. Conventional doses of heparin were administered during the first dialysis of the study. Two days later r-hirudin, at a dose of 0.15 mg/kg, was given as a bolus at the start of the second dialysis. The mean decreases in plasma levels of urea, uric acid and creatinine were approximately 50% after dialysis with both anticoagulants. Dialysis was therefore equally effective. However, effective dialysis with r-hirudin was achieved with a shorter activated partial thromboplastin time (APTT; range 65 to 103 seconds) compared to that with heparin (> 120 seconds), thereby decreasing the risk of bleeding. Markedly less 111In-labeled platelets accumulated at the inlet of the artificial kidney when r-hirudin was used, suggesting a smaller loss of hollow fiber volume. The results indicate that hirudin may be a suitable alternative anticoagulant for use during hemodialysis and it thus warrants further investigation.