Pharmacokinetics,pharmacodynamics and food effect of LB30870, a novel direct thrombin inhibitor,after single oral doses in healthy men

Abstract

1.?The safety, tolerability, pharmacokinetics, pharmacodynamics, and food effect of LB30870, a new selective thrombin inhibitor, were studied in 16 healthy men.

2.?A double-blind, placebo-controlled single ascending dose study was done at oral doses of 5, 15, 30, 60, 120, and 240?mg under fasting conditions. An open, randomized, balanced cross-over food effect study was done at 60?mg dose. Plasma and urinary concentrations were measured up to 48?h post-dose. Coagulation and thrombin activity markers were measured at selected time points.

3.?C_max of LB30870 was at 1.3–3.0?h post-dose with a mean apparent terminal half-life (t_1/2) of 2.8–4.1?h. AUC after doses above 15?mg appeared greater than dose-proportional. In fed state, AUC showed 80% reduction relative to fasting condition.

4.?At doses 60 and 120?mg, peak activated partial thromboplastin time (aPTT) increased by 1.5- and 2-fold, respectively, from baseline. The aPTT and international normalized ratio (INR) were concentration-dependent, with less within-individual variability than ecarin clotting time (ECT), prothrombin time (PT), or thrombin time (TT).

5.?Single oral doses of LB30870 up to 240?mg were well tolerated. The food effect must be overcome if LB30870 is to be used as an oral anti-coagulant.     

Safety, tolerability, pharmacodynamics, and pharmacokinetics of rivaroxaban--an oral, direct factor Xa inhibitor--are not affected by aspirin

Rivaroxaban (BAY 59-7939) is an oral, direct Factor Xa inhibitor in advanced clinical development for the prevention and treatment of thromboembolic disorders. This was a randomized, 2-way crossover study in healthy male subjects, with an aspirin run-in period, to examine whether aspirin influences the safety, tolerability, pharmacodynamics, and pharmacokinetics of rivaroxaban. All treatments were well tolerated; drug-related adverse events were mild and transient. Aspirin did not alter the effects of rivaroxaban on Factor Xa activity or clotting tests. Platelet aggregation and bleeding time were not affected by rivaroxaban, and rivaroxaban did not influence the effects of aspirin on these parameters to a clinically relevant extent. Aspirin did not affect the pharmacokinetics of rivaroxaban, including the fraction unbound. This study suggests that there is no clinically relevant interaction between rivaroxaban and aspirin and that the 2 drugs could be administered concomitantly at the doses used in this study.     

The pharmacokinetics of enoxaparin do not correlate with its pharmacodynamic effect in patients receiving dialysis therapies

The pharmacokinetics and pharmacodynamics of enoxaparin were studied in healthy volunteers and hemodialysis and peritoneal dialysis subjects. Antifactor Xa activity estimated the pharmacokinetics, whereas thrombin generation time (TGT) estimated the pharmacodynamics. Enoxaparin 1 mg/kg was given subcutaneously to all subjects. Antifactor Xa Amax and AUC(0-12) were similar between groups, but the TGTmax was significantly greater in the dialysis groups (P = .001). The thrombin generation time remained significantly more prolonged throughout the 12-hour study period, and there was a trend toward greater TGT AUEC(0-12) for both dialysis groups (P = .07). Patients receiving hemodialysis had greater sensitivity to enoxaparin compared to the other groups. These results suggest that in dialysis patients, there may be accumulation of active heparin metabolites that are undetected by the antifactor Xa assay. Therefore, these subjects exhibit greater thrombin generation time prolongation despite similar antifactor Xa exposure. Further large-scale studies are needed to corroborate the results of this exploratory pilot study.     

Differential effects of factor IIa inhibitors on the endogenous thrombin potential

Calibrated automated thrombin generation measurement in clotting plasma (endogenous thrombin potential, ETP) is being used increasingly to monitor the effects of anticoagulant drugs. Calibrated automated thrombography measures the concentration of thrombin in clotting plasma by monitoring the cleavage of a fluorogenic substrate (Z-Gly-Gly-Arg-7-amino-4-methylcoumarin) and comparing it with a constant known thrombin activity in a parallel nonclotting sample. This study compared the concentration-dependent effects of different factor IIa inhibitors on the ETP. In accordance with a theoretical prediction, the monovalent factor IIa inhibitors melagatran and argatroban reduced peak thrombin concentrations without a marked effect on the lag time of thrombin generation. However, both bivalent factor IIa inhibitors lepirudin and bivalirudin markedly prolonged the lag time of thrombin generation and thus behaved like "super" factor Xa inhibitors according to the theoretical model. These findings have important consequences for therapeutic drug monitoring using thrombin generation assays. For monitoring of hirudins, the lag time of thrombin generation seems to be a very sensitive parameter. In contrast, for monitoring of argatroban, the evaluation of the ETP seems to be useful.     

Pharmacodynamics and pharmacokinetics during the transition from warfarin to rivaroxaban: a randomized study in healthy subjects

Aims

This study investigated relevant pharmacodynamic and pharmacokinetic parameters during the transition from warfarin to rivaroxaban in healthy male subjects.

Methods

Ninety-six healthy men were randomized into the following three groups: warfarin [international normalized ratio (INR) 2.0–3.0] transitioned to rivaroxaban 20 mg once daily (od; group A); warfarin (INR 2.0–3.0) followed by placebo od (group B); and rivaroxaban alone 20 mg od (group C) for 4 days. Anti-factor Xa activity, inhibition of factor Xa activity, prothrombin time (PT), activated partial thromboplastin time, HepTest, prothrombinase-induced clotting time, factor VIIa activity, factor IIa activity, endogenous thrombin potential and pharmacokinetics were measured.

Results

An additive effect was observed on the PT and PT/INR during the initial transition period. The mean maximal prolongation of PT was 4.39-fold [coefficient of variation (CV) 18.03%; range 3.39–6.50] of the baseline value in group A, compared with 1.88-fold (CV 10.35%; range 1.53–2.21) in group B and 1.57-fold (CV 9.98%; range 1.37–2.09) in group C. Rivaroxaban had minimal influence on the PT/INR at trough levels. Inhibition of factor Xa activity, activated partial thromboplastin time and endogenous thrombin potential were also enhanced, but to a lesser extent. In contrast, the effects of rivaroxaban on anti-factor Xa activity, HepTest and prothrombinase-induced clotting time were not affected by pretreatment with warfarin.

Conclusions

Changes in pharmacodynamics during the transition from warfarin to rivaroxaban vary depending on the test used. A supra-additive effect on PT/INR is expected during the initial period of transition, but pretreatment with warfarin does not influence the effect of rivaroxaban on anti-factor Xa activity.     

Effect of the oral renin inhibitor aliskiren on the pharmacokinetics and pharmacodynamics of a single dose of warfarin in healthy subjects

AIMS: To investigate the effects of aliskiren, an oral renin inhibitor, on the pharmacokinetics and pharmacodynamics of warfarin. METHODS: In a single-blind, placebo-controlled, randomized, two-period crossover study, 15 healthy male and female subjects received a single oral dose of 25 mg racemic warfarin twice, once in the morning of the 8th day of treatment with 150 mg aliskiren and once at the same time point during treatment with placebo. Blood samples were collected for the measurement of prothrombin time (PT) and activated thromboplastin time (aPTT) and for determination of plasma concentrations of (R)- and (S)-warfarin. RESULTS: Aliskiren treatment had no effect on the blood coagulation parameters (PT, INR and aPTT). The ratios of least square means (90% CI) of pharmacokinetic parameters in the presence and absence of aliskiren for (R)- and (S)-warfarin were Cmax 0.89 (0.82, 0.96) and 0.88 (0.80, 0.97), AUC(0, infinity) 1.00 (0.94, 1.07) and 1.06 (0.96, 1.16) and t(1/2) 0.99 (0.92, 1.07) and 1.05 (0.96, 1.14). CONCLUSIONS: Multiple doses of aliskiren had no detectable effect on the pharmacokinetics or pharmacodynamics of a single dose of warfarin in healthy subjects.     

Apixaban,an oral,direct factor Xa inhibitor: single dose safety,pharmacokinetics, pharmacodynamics and food effect in healthy subjects

Aims

To evaluate apixaban single dose safety, tolerability, pharmacokinetics and pharmacodynamics and assess the effect of food on apixaban pharmacokinetics.

Methods

A double-blind, placebo-controlled, single ascending-dose, first-in-human study assessed apixaban safety, pharmacokinetics and pharmacodynamics in healthy subjects randomized to oral apixaban (n = 43; 0.5–2.5 mg as solution or 5–50 mg as tablets) or placebo (n = 14) under fasted conditions. An open label, randomized, two treatment crossover study investigated apixaban pharmacokinetics/pharmacodynamics in healthy subjects (n = 21) administered apixaban 10 mg in fasted and fed states. Both studies measured apixaban plasma concentration, international normalized ratio (INR), activated partial thromboplastin time (aPTT) and prothrombin time (PT) or a modified PT (mPT).

Results

In the single ascending-dose study increases in apixaban exposure appeared dose-proportional. Median t_max occurred 1.5–3.3 h following oral administration. Mean terminal half-life ranged between 3.6 and 6.8 h following administration of solution doses ≤2.5 mg and between 11.1 and 26.8 h for tablet doses ≥5 mg. Concentration-related changes in pharmacodynamic assessments were observed. After a 50 mg dose, peak aPTT, INR and mPT increased by 1.2-, 1.6- and 2.9-fold, respectively, from baseline. In the food effect study: 90% confidence intervals of geometric mean ratios of apixaban C_max and AUC in a fed vs. fasted state were within the predefined no effect (80–125%) range. Apixaban half-life was approximately 11.5 h. The effect of apixaban on INR, PT and aPTT was comparable following fed and fasted administration.

Conclusions

Single doses of apixaban were well tolerated with a predictable pharmacokinetic/pharmacodynamic profile and a half-life of approximately 12 h. Apixaban can be administered with or without food.     

In vitro and in vivo antithrombotic activity of PD-198961, a novel synthetic factor Xa inhibitor

PD-198961, 3-(4-5-[(2R,6S)-2,6-dimethyltetrahydro-1(2H)-pyridinyl]pentyl-3-oxo-3,4-dihydro-2-quinoxalinyl)-4-hydroxybenzenecarboximidamide, is a novel, synthetic factor Xa inhibitor with a Ki of 2.7 nM against human factor Xa. The aim of the present study was to evaluate the pharmacokinetic profile and antithrombotic efficacy of PD-198961 in rabbits. When tested in vitro, PD-198961 doubled prothrombin time (PT) and activated partial thromboplastin time (aPTT) at concentrations of 0.13 and 0.32 microM in human plasma, 0.2 and 0.09 microM in rabbit plasma, 0.3 and 0.4 microM in dog plasma, respectively. Intravenous administration of PD-198961 at 1 mg/kg over 30 minutes resulted in a maximal prolongation in PT and aPTT of 4.9 +/- 0.4 and 4.1 +/- 0.9-fold of baseline, respectively. The peak plasma concentration of PD-198961 was 977 +/- 96 ng/ml. The anticoagulant effect of PD-198961 was readily reversible; coagulation parameters and plasma concentration returned to near baseline 15 minutes after cessation of infusion. There was a good correlation between PT prolongation and plasma concentration of PD-198961 (r = 0.93). In an FeCl3-induced model of arterial thrombosis in rabbits, the antithrombotic effects of PD-198961 were compared with that of LB-30057, a direct thrombin inhibitor, and enoxaparin, a low molecular weight heparin (LMWH). PD-198961 dose dependently increased the time to occlusion (TTO), reduced thrombus weight (TW), and decreased the incidence of occlusion. When administered at 3.0 microg/kg/min IV, PD-198961 prolonged TTO from 28 +/- 5 minutes (control) to 120 +/- 0 minutes (P < 0.001) and reduced TW from 9.9 +/- 1.5 mg (control) to 2.8 +/- 0.9 mg (P < 0.01). PD-198961 also dose dependently inhibited ex vivo plasma FXa activity. At the highest dose tested, PD-198961 increased aPTT to 1.4 +/- 0.1-fold of baseline (compared with 1.5 +/- 0.1 and 2.8 +/- 0.3-fold of baseline for LB-30057 [CI-1028] and enoxaparin, respectively), and had modest effects on bleeding time (< or = 2-fold). These results indicate that PD-198961 is a potent FXa inhibitor and an effective antithrombotic agent at doses that produce only modest changes in normal hemostasis.     

Antiplatelet,anticoagulant, and profibrinolytic activities of cudratricusxanthone A

Cudratricusxanthone A (CTXA), a natural bioactive compound extracted from the roots of Cudrania tricuspidata Bureau, is known to possess hepatoprotective, antiproliferative and anti-inflammatory activities. However, antiplatelet, anticoagulant, and profibrinolytic properties have not been studied. The anticoagulant activities of CTXA were measured by monitoring activated partial thromboplastin-time (aPTT), prothrombin time (PT), and the activities of cell-based thrombin and activated factor X (FXa). The effects of CTXA on the expressions of plasminogen activator inhibitor type 1 (PAI-1) and tissue-type plasminogen activator (t-PA) were also tested in tumor necrosis factor-α (TNF-α) activated human umbilical vein endothelial cells. Our data showed that CTXA inhibited thrombin-catalyzed fibrin polymerization and platelet aggregation, prolonged aPTT and PT significantly and inhibited the activities and production of thrombin and FXa. CTXA prolonged in vivo bleeding time and inhibited TNF-α induced PAI-1 production. Furthermore, PAI-1/t-PA ratio was significantly decreased by CTXA. Collectively, these results indicate that CTXA possesses antithrombotic activities and suggest that the current study could provide bases for the development of new anticoagulant agents.     

Pharmacokinetics and pharmacodynamics of melagatran,the active form of the oral direct thrombin inhibitor ximelagatran,are not influenced by acetylsalicylic acid

OBJECTIVE: The aim of this study was to evaluate the effect of acetylsalicylic acid (ASA or aspirin) on the pharmacokinetics (PK) and pharmacodynamics (PD) of melagatran in healthy volunteers. Melagatran is the active form of the oral direct thrombin inhibitor, ximelagatran. METHODS: This was a double-blind, randomised, two-way, crossover study consisting of two treatment periods separated by a washout period of at least 2 weeks. Twelve subjects received, in a randomised order, either melagatran plus ASA in the first treatment period and melagatran plus placebo in the second treatment period or vice versa. Two single doses of ASA were given, first 450 mg on the day before (day 1) and then 150 mg just before administration of melagatran on day 2. Melagatran 4.12 mg was administered as an intravenous (i.v.) infusion over 4 h on day 2 of both treatment periods. Serial blood samples were collected over the course of the study for the determination of melagatran plasma concentration and coagulation analyses [activated partial thromboplastin time (APTT) and activated clotting time (ACT)]. Capillary bleeding time was measured before ASA/placebo on day 1 and before and after the start of the melagatran infusion on day 2. RESULTS: The plasma concentration of melagatran during the i.v. infusion was maintained at about 0.2 micro mol/l, and ASA did not influence the PK parameters of melagatran. APTT and ACT increased with increasing melagatran plasma concentration, and the observed increases were similar whether melagatran was administered on top of ASA or placebo. Administration of ASA significantly prolonged the capillary bleeding time (by 41% relative to placebo). Melagatran also prolonged the bleeding time significantly (by 25% relative to placebo alone), but this prolongation was not significantly different from the observed prolongation when melagatran was administered on top of ASA (by 17% relative to ASA alone). CONCLUSION: In young healthy volunteers, ASA had no effect on the PK or PD properties of melagatran at the studied dose. That the combination of ximelagatran with ASA may be used with acceptable safety must be verified in the relevant patient populations.     

Antithrombotic effects of low molecular weight heparin (FR-860) in rabbits

Effects of low molecular weight heparin (FR-860) were investigated on the arterio-venous (A-V) shunt model and on the in vitro blood coagulation system compared to conventional unfractionated heparin (UF-heparin) in rabbits. In the A-V shunt model, FR-860 (12.5-50 U/kg, i.v.) and UF-heparin (25 and 50 U/kg, i.v.) dose-related inhibited thrombotic formation in the tube of the A-V shunt at 30 min after starting blood circulation. Both FR-860 and UF-heparin dose-relatedly increased the anti-F.Xa activity at 5 min after starting blood circulation. However, FR-860 showed weaker effects in a prolongation of the aPTT, PT and thrombin time than UF-heparin in the A-V shunt model. Neither FR-860 nor UF-heparin had any influence on platelet aggregation. FR-860 also had a weaker effect in the prolongation of the plasma recalcification time, aPTT and PT than UF-heparin in vitro. FR-860 showed equipotent efficacy on the anti-F.Xa activity and had weak anti-thrombin activity compared to that of UF-heparin in vitro. These results suggest that the antithrombotic effect of FR-860 mainly depends on its anti-F.Xa activity but not on the antithrombin activity. Therefore, FR-860 is more efficient and lower in bleeding risk than UF-heparin in hemodialysis and thrombotic disorders.     

Anticoagulant activities of persicarin and isorhamnetin

Persicarin and isorhamnetin were isolated from Oenanthe javanica and their anticoagulant activities were examined by monitoring activated partial thromboplastin time (aPTT), prothrombin time (PT), and the activities of cell-based thrombin and activated factor X (FXa). In addition, the effects of persicarin and isorhamnetin on the expressions of plasminogen activator inhibitor type 1 (PAI-1) and tissue-type plasminogen activator (t-PA) were tested in tumor necrosis factor-α (TNF-α) activated human umbilical vein endothelial cells (HUVECs). The data obtained showed that persicarin and isorhamnetin both prolonged aPTT and PT significantly and inhibited the activities of thrombin and FXa. In addition, they both inhibited the generations of thrombin and FXa in HUVECs. In accordance with these anticoagulant activities, persicarin and isorhamnetin prolonged in vivo bleeding time and inhibited TNF-α induced PAI-1 production. Furthermore, PAI-1/t-PA ratio was significantly decreased by persicarin. Interestingly, the anticoagulant and profibrinolytic effects of persicarin were greater than those of isorhamnetin, which suggest that the sulfonate group of persicarin positively regulates its anticoagulatory function. Accordingly, our results suggest that persicarin and isorhamnetin possess antithrombotic activities and that they could provide bases for the development of new anticoagulant agents.     

No differences in the pharmacodynamics and pharmacokinetics of the thrombin receptor antagonist vorapaxar between healthy Japanese and Caucasian subjects

Background

Vorapaxar, a novel antiplatelet agent in advanced clinical development for the prevention and treatment of atherothrombotic disease, is a potent, orally bioavailable thrombin receptor antagonist selective for the protease-activated receptor 1 (PAR-1).

Methods

Since race/ethnicity may affect the safety, efficacy and dosage of drugs, this study was conducted to evaluate potential differences in the pharmacodynamics, pharmacokinetics and safety of vorapaxar after single (5, 10, 20, or 40?mg) or multiple (0.5, 1, or 2.5?mg once daily) doses in healthy Japanese and matched (gender, age, height, and weight) Caucasian volunteers.

Results

Vorapaxar was well tolerated in both Japanese and Caucasian subjects. Pharmacodynamic and pharmacokinetic profiles of vorapaxar in the two racial/ethnic groups were similar. In both racial groups, complete inhibition of platelet aggregation was achieved most rapidly with vorapaxar 40?mg and was consistently achieved and maintained with a 2.5?mg daily maintenance dose.

Conclusion

There were no substantial differences in the safety, pharmacokinetics or pharmacodynamics of vorapaxar between Japanese and Caucasian subjects.     

Effects of low molecular weight heparin (FR-860) on coagulative and fibrinolytic activities

We studied the effects of FR-860 on coagulative and fibrinolytic activities in human plasma compared to conventional unfractionated heparin (UF-heparin). Both FR-860 and UF-heparin dose-dependently prolonged the recalcification time, activated partial thromboplastin time, prothrombin time, factor Xa (F.Xa) clotting time and thrombin time. These effects of FR-860 were weaker than that of UF-heparin. FR-860 showed equipotent efficacy on the anti-F.Xa activity, and weak antithrombin activity compared to UF-heparin. FR-860 had no effects on the activity of ATIII and fibrinolytic activity. UF-heparin shortened the urokinase-activated euglobulin lysis time and showed antiplasmin activity, but did not influence the activities of ATIII, plasminogen and alpha 2-plasmin inhibitor. UF-heparin decreased the fibrinogen level at higher doses. These efficacies of FR-860 were weaker than that of UF-heparin. These results suggest that FR-860 is more efficient and lower in bleeding risk than UF-heparin in clinical use.     

Antiplatelet,anticoagulant, and profibrinolytic activities of withaferin A

Withaferin A (WFA), an active compound from Withania somnifera, is widely researched for its anti-inflammatory, cardioactive and central nervous system effects. However, antiplatelet, anticoagulant, and profibrinolytic properties of WFA have not been studied. In this study, the anticoagulant activities of WFA were measured by monitoring activated partial thromboplastin-time (aPTT), prothrombin time (PT), fibrin polymerization, platelet aggregation, thrombus formation, and the activities of cell-based thrombin and activated factor X (FXa). The effects of WFA on the expressions of plasminogen activator inhibitor type 1 (PAI-1) and tissue-type plasminogen activator (t-PA) were also tested in tumor necrosis factor-α (TNF-α) activated human umbilical vein endothelial cells (HUVECs). Our data showed that WFA inhibited thrombin-catalyzed fibrin polymerization and platelet aggregation, FeCl3-induced thrombus formation, prolonged aPTT and PT significantly and inhibited the activities and production of thrombin and FXa. WFA prolonged in vivo and ex vivo bleeding time and inhibited TNF-α induced PAI-1 production. Furthermore, PAI-1/t-PA ratio was significantly decreased by WFA. Collectively, these results indicate that WFA possesses antithrombotic activities and suggest that the current study could provide bases for the development of new anticoagulant agents.     

Clinical pharmacokinetics,pharmacodynamics, safety and tolerability of darexaban,an oral direct factor Xa inhibitor,in healthy Caucasian and Japanese subjects

Background. Darexaban (YM150) is a potent direct factor Xa (FXa) inhibitor developed for the prophylaxis of venous and arterial thromboembolic disease. This drug is rapidly and extensively metabolized to darexaban glucuronide (YM‐222714), which is a pharmacologically active metabolite. The objective of the present study was to evaluate the clinical pharmacokinetics (PK), pharmacodynamics (PD), safety and tolerability of ascending multiple oral doses of darexaban in healthy non‐elderly Caucasian and Japanese subjects. Methods. A randomized, double‐blind, placebo‐controlled, single and multiple dose‐escalating study of healthy Caucasian and Japanese male and female subjects was performed. The tested doses were 20, 60, 120 and 240 mg of darexaban. Results. Plasma concentrations of darexaban glucuronide increased with dose, and C_max and AUC increased dose‐dependently after both single and repeated doses in both Caucasians and Japanese. C_max was about 17%–19% lower in Caucasians than in Japanese, although AUC appeared to be similar. The time‐profiles of prothrombin time reported as the international normalized ratio (PT‐INR), activated partial thromboplastin time (aPTT) and FXa activity closely followed the time–concentration profile of darexaban glucuronide, and no clear differences were observed in ethnicity. Overall, 38 of the 82 enrolled subjects reported a total of 57 treatment‐emergent adverse events (TEAEs). Fifty‐five TEAEs were of mild intensity and two were of moderate intensity. Conclusion. It is concluded that single and multiple doses of darexaban are safe and well tolerated up to 240 mg with predictable PK and PD profiles in both Caucasians and Japanese, and that ethnicity does not affect its PK, PD or tolerability. Copyright © 2013 John Wiley & Sons, Ltd.     

The pharmacokinetics, pharmacodynamics and tolerability of dabigatran etexilate, a new oral direct thrombin inhibitor, in healthy male subjects

AIMS: The novel direct thrombin inhibitor (DTI), dabigatran etexilate (Boehringer Ingelheim Pharma GmbH & Co. KG), shows potential as an oral antithrombotic agent. Two double-blind, randomized trials were undertaken to investigate the pharmacokinetics (PK), pharmacodynamics (PD) and tolerability of orally administered dabigatran etexilate in healthy male subjects. METHODS: Dabigatran etexilate or placebo was administered orally at single doses of 10-400 mg (n = 40) or at multiple doses of 50-400 mg three times daily for 6 days (n = 40). Plasma and urine samples were collected over time to determine the PK profile of dabigatran. PD activity was assessed by its effects on blood coagulation parameters: activated partial thromboplastin time (aPTT), prothrombin time (PT), reported as international normalized ratio (INR), thrombin time (TT), and ecarin clotting time (ECT). All adverse events were recorded. RESULTS: Dabigatran etexilate was rapidly absorbed with peak plasma concentrations of dabigatran reached within 2 h of administration. This was followed by a rapid distribution/elimination phase and a terminal phase, with associated estimated half-lives of 8-10 h and 14-17 h with single and multiple dose administrations, respectively. Dabigatran exhibited linear PK characteristics with dose-proportional increases observed in maximum plasma concentration and area under the curve. Steady-state conditions were reached within 3 days with multiple dosing. The mean apparent volume of distribution during the terminal phase (V(z)/F) of 1860 l (range 1430-2400 l) and the apparent total clearance after oral administration (CL(tot)/F) of 2031 ml min(-1) (range 1480-2430), were dose independent. Time curves for aPTT, INR, TT and ECT paralleled plasma concentration-time curves with values increasing rapidly and in a dose-dependent manner. At the highest dose of 400 mg administered three times daily, maximum prolongations over baseline of 3.1 (aPTT), 3.5 (INR), 29 (TT) and 9.5-fold (ECT) were observed. Dabigatran underwent conjugation with glucuronic acid to form pharmacologically active conjugates that accounted for approximately 20% of total dabigatran in plasma. Overall, variability in PK parameters was low to moderate, with an average interindividual coefficient of variation (CV) of approximately 30% and variability in PD parameters was low, with CV < 10%. Of the four assays, TT and ECT exhibited the greatest sensitivity and precision within the anticipated therapeutic dose range. Bleeding events were few and were mild-to-moderate in intensity, occurring only in the higher, multiple dose groups. CONCLUSIONS: These data suggest that dabigatran etexilate is a promising novel oral DTI with predictable PK and PD characteristics and good tolerability. Further investigation of dabigatran etexilate for the treatment and prophylaxis of patients with arterial and venous thromboembolic disorders, acute coronary syndromes and other medical conditions is warranted.     

Anticoagulant activity of captopril

The antihypertensive drug, captopril, exerted an anticoagulant effect upon clotting time as followed by prothrombin time (PT) and activated partial thromboplastin time (APTT), with prolongation of clotting observed at 4.25 x 10(-3) M and 4 x 10(-3) M captopril for PT and APTT, respectively, using commercial level I plasma. Utilizing level III plasmas, PT and APTT values were both prolonged by 4.25 x 10(-3) M captopril. Captopril (6 x 10(-3) M) also directly prolonged the clotting of thrombin in a thrombin-factor II-deficient plasma assay, whereas 5 x 10(-3) M captopril inhibited FIIDP in a thrombin-FIIDP assay. In thrombin-fibrinogen assays, pre-incubation of 2.5 x 10(-3) M captopril with fibrinogen also prolonged clotting time, whereas 3 x 10(-3) M captopril prolonged thrombin activity. These data suggest that thiol-disulfide exchange permits reduction of disulfide groups in thrombin and fibrinogen, altering their tertiary structure and physiological function. Lisinopril at a pharmacological 10(-2) M also prolonged APTT, although it lacks a thiol group. Polylysine (1k-4k) affected a prolongation of APTT at 6.7 x 10(-6) M, suggesting inhibition of clotting by a different mechanism.     

Comparable pharmacokinetics and pharmacodynamics of melagatran in Japanese and caucasian volunteers after oral administration of the direct thrombin inhibitor ximelagatran

OBJECTIVES: Two studies were conducted to elucidate the pharmacokinetics and pharmacodynamics of melagatran after administration of the oral direct thrombin inhibitor ximelagatran to Caucasian and Japanese volunteers. METHODS: In study 1, with a single-blind, parallel-group design, young Japanese and Caucasian male volunteers were randomised to receive four single escalating oral doses of ximelagatran (12, 24, 36 and 60mg on separate days; n = 27 per ethnic group) or placebo (n = 6 per ethnic group). In study 2, with an open-label design, elderly Japanese male volunteers (n = 12) received three single escalating oral doses of ximelagatran (12, 24 and 36mg on separate days). RESULTS: Regardless of the ethnicity or age of the volunteers, ximelagatran given in single oral doses was rapidly absorbed and bioconverted to melagatran, and the melagatran area under the plasma concentration-time curve (AUC) and peak plasma concentration (C(max)) increased in proportion with the ximelagatran dose, with only small deviations from absolute linearity. Higher melagatran AUC and C(max) were observed in young Japanese volunteers compared with young Caucasian volunteers, and in elderly Japanese volunteers compared with young Japanese volunteers. These results appear to be attributed to weight- and age-related decreases in renal elimination of melagatran rather than to absorption of ximelagatran and formation of melagatran. The pattern of metabolites in plasma and urine was comparable between young Japanese and Caucasian volunteers, and between young and elderly Japanese volunteers. The melagatran plasma concentration-activated partial thromboplastin time (aPTT, an ex vivo coagulation time measurement used to demonstrate inhibition of thrombin) relationship did not differ significantly between young Japanese and Caucasian volunteers or between young and elderly Japanese volunteers. CONCLUSIONS: Ethnicity does not affect the absorption of ximelagatran or the formation of melagatran or the melagatran plasma concentration-aPTT relationship. The elimination of melagatran is correlated with renal function.     

Antithrombotic effect of a novel protein from Fusarium sp. CPCC 480097 in a rat model of artery-vein bypass thrombosis

Context: The incidence and mortality of thrombotic disorders are rapidly increasing throughout the world. Therefore, attempts have been made to develop new anticoagulant and antithrombotic drugs. Our previous studies showed that a novel protein, named Fu-P, had fibrinogenolytic activity and much higher fibrinolytic activity on the fibrin plate than urokinase in vitro.

Objective: The antithrombotic activities of Fu-P in vivo are investigated here for the first time.

Materials and methods: Antithrombotic activity of Fu-P was studied in a rat model of artery-vein bypass thrombosis. The anticoagulant activity of Fu-P was measured by clotting assay of activated partial thrombinplastin time and prothrombin time (PT). The effects of Fu-P on the factor Xa and thrombin were assayed using the chromogenic substrate S-2765 and S-2238.

Results: Intravenous injection of Fu-P produced a 58.4% inhibition ratio of thrombus formation at 0.1?mg/kg body weight, while heparin produced 42.5% inhibition ratio of thrombus formation at 0.6?mg/kg body weight. Fu-P significantly prolonged fibrinogen clotting time, activated partial thrombinplastin time and thrombin time, which also prolonged PT. The inhibition assay of the coagulant factors using chromogenic substrates S-2238 and S-2765 showed that Fu-P was not the inhibitor of the thrombin and Xa.

Discussion and conclusion: These findings demonstrated that the novel fibrinolytic enzyme (Fu-P) might also be used as a natural agent for thrombolytic therapy or thrombosis prevention.