Monitoring of recombinant hirudin: assessment of a plasma-based ecarin clotting time assay.
Assay conditions of a plasma-based ecarin clotting time (ECT) were evaluated and the precision of the ECT in monitoring plasma levels of r-hirudin assessed. The snake venom enzyme ecarin converts prothrombin to meizothrombin possessing only weak coagulant but strong esterase activity. In r-hirudin containing plasma samples, meizo thrombin is rapidly neutralized by r-hirudin resulting in a dose-dependent prolongation of the clotting times. Among the different assay conditions tested, addition of 50 microliters of ecarin (4 U/ml) to 100 microliters of undiluted citrate-anticoagulated plasma gave optimal results with respect to precision and reproducibility. The measuring range of the ECT performed in this way is about 0.02-5.0 micrograms/ml r-hirudin. In vitro studies performed on r-hirudin-spiked plasma samples of 50 healthy individuals demonstrate remarkably low interindividual differences in r-hirudin responsiveness as indicated by CV-values below 5% and 7% at r-hirudin concentrations between 0-3 micrograms/ml and 4-5 micrograms/ml, respectively. The specificity for r-hirudin of the ECT is further demonstrated by the strong correlation (r = 0.94) between the results of a chromogenic assay and the ECT-measured r-hirudin concentrations obtained on 67 ex vivo blood samples. Depending on the concentration of r-hirudin the ECT is sensitive to plasma levels of prothrombin. In the absence of r-hirudin the critical prothrombin concentration was found to be 20% but increasing to 60% in the presence of 2.0 micrograms/ml r-hirudin. A fibrinogen concentration of 50 mg/dl was found to be the minimal concentration independent of the r-hirudin concentration. The precision of the ECT in measuring plasma levels of r-hirudin is not influenced by treatment with heparin, aprotinin or oral anticoagulants. The data demonstrate that the ECT is a rapid and easily perfor mable clotting assay which allows accurate measurement of r-hirudin plasma levels. ECT-monitored hirudin treatment will help to establish optimal dose regimens that are more efficacious but still as safe as heparin.
Pötzsch
B
B
Kerckhoff-Klinik, Max-Planck-Institut für Physiologische und Klinische Forschung, Bad Nauheim, Germany.
Hund
S
S
Madlener
K
K
Unkrig
C
C
Müller-Berghaus
G
G
D000284:Administration, Oral; D000925:Anticoagulants / Q000008:administration & dosage; D000991:Antithrombins / Q000008:administration & dosage / Q000009:adverse effects / Q000378:metabolism*; D001780:Blood Coagulation Tests / Q000379:methods / Q000706:statistics & numerical data; D010450:Endopeptidases; D005340:Fibrinogen / Q000378:metabolism; D006629:Hirudins / Q000008:administration & dosage / Q000009:adverse effects / Q000097:blood*; D006801:Humans; D066298:In Vitro Techniques; D010314:Partial Thromboplastin Time; D011516:Prothrombin / Q000378:metabolism; D011994:Recombinant Proteins / Q000008:administration & dosage / Q000009:adverse effects / Q000097:blood; D012016:Reference Values; D015203:Reproducibility of Results; D012449:Safety
D000925:Anticoagulants; D000991:Antithrombins; D006629:Hirudins; D011994:Recombinant Proteins; D011516:Prothrombin; D005340:Fibrinogen; D010450:Endopeptidases; C020097:ecarin