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Dose‐effect relationship for several coagulation markers during administration of the direct thrombin inhibitor S 18326 in healthy subjects
Author(s) -
Gaussem P.,
Dubar M.,
le Bonniec B.,
RichardLordereau I.,
Jochemsen R.,
Aiach M.
Publication year - 2002
Publication title -
british journal of clinical pharmacology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.216
H-Index - 146
eISSN - 1365-2125
pISSN - 0306-5251
DOI - 10.1046/j.0306-5251.2001.01534.x
Subject(s) - partial thromboplastin time , pharmacokinetics , prothrombin time , pharmacology , thrombin , thromboplastin , clotting time , coagulation , pharmacodynamics , thrombin time , medicine , bolus (digestion) , placebo , population , in vivo , discovery and development of direct thrombin inhibitors , activated clotting time , chemistry , anticoagulant , platelet , biology , pathology , alternative medicine , microbiology and biotechnology , environmental health
Aims We conducted a phase I placebo‐controlled trial with two i.v. doses (0.5 mg h −1 and 3 mg h −1 ) of S 18326, a selective thrombin inhibitor that interacts with the catalytic site of thrombin, with the aim to study the relationships between increasing plasma levels of S 18326 and changes in coagulation tests and thrombin generation markers. Methods Thirty‐six healthy male volunteers were divided into three groups. In each group, 10 volunteers were randomly assigned to receive S 18326 and two to receive a placebo. Following a bolus of 4.5 mg, doses were 0.5 mg h −1 in the first group and 3 mg h −1 in the two other groups, administered as an i.v. infusion for 24 h. Blood was drawn repeatedly up to 36 h after the bolus, and tested for the activated clotting time (ACT) and activated partial thromboplastin time (APTT). The APTT reagent was chosen among five commercial reagents to yield a linear increase in the clotting time among possible therapeutic S 18326 concentrations in vitro . To accurately measure the thrombin‐inhibiting effects of low doses of S 18326 (< 0.5 µ m ), we developed a specific chromogenic assay. We also measured F1 + 2 prothrombin fragment levels to assess the effect of S 18326 on thrombin generation in vivo . Results A two‐compartment pharmacokinetic model was fitted to the S 18326 plasma concentration vs time data by using population pharmacokinetic methods. Results of the pharmacodynamic‐pharmacokinetic relationships showed that both the ACT and APTT methods yielded a linear increase according to the S 18326 concentration measured using a highly sensitive analytical method. At the end of infusion, ACT was prolonged 1.20 and 1.95‐fold in the 0.5 mg h −1 and the 3 mg h −1 groups, respectively, and APTT was prolonged 1.27 and 2.75‐fold. Thrombin inhibition plateaued above 0.5 µ m of S 18326 according to an Emax model, confirming that the test was highly sensitive. F1 + 2 levels fell significantly after the 24 h S 18326 infusion (0.83 n m to 0.6 n m and 0.80 n m to 0.44 n m in the 0.5 mg h −1 and the 3 mg h −1 groups, respectively), but remained stable after the placebo infusion. Conclusions Our results support specific monitoring of the thrombin inhibitor S 18326 with ACT and APTT to establish the safety range of the drug in further studies. Moreover, the fall in F1 + 2 prothrombin fragments suggests that S 18326 effectively reduces the retroactivation of factors V and VIII by thrombin.