New blood thinner offers first potential alternative in 50 years: ximelagatran

Novel oral anticoagulants

Oral anticoagulants have been used widely for the treatment of venous thromboembolism and stroke prevention. The vitamin K antagonists (VKAs), such as warfarin, have been around for the last 65 years and its efficacy as thromboprophylaxis remained largely unchallenged, at least until recently. Nonetheless, the VKAs have significant limitations with marked inter- and intra-individual variability, requiring regular monitoring and have important food and drug interactions. Thus, there is an unmet need, with the quest for alternative oral anticoagulants with stable pharmacokinetics and pharmacodynamics that do not need monitoring. The novel oral anticoagulants are in 2 broad drug classes - the oral direct thrombin inhibitors and oral factor Xa inihibitors. This review article provides an overview of the pharmacology and describes the most recent published data on clinical trials with the new oral anticoagulants, which are in the more advanced stages of clinical development.

Pharmacokinetics and pharmacodynamics of the direct oral thrombin inhibitor dabigatran in healthy elderly subjects

OBJECTIVES

To investigate the pharmacokinetic and pharmacodynamic profile of dabigatran in healthy elderly subjects; to assess the intra- and interindividual variability of dabigatran pharmacokinetics in order to assess possible gender differences; and to assess the effect of pantoprazole coadministration on the bioavailability of dabigatran.

STUDY DESIGN AND SETTING

Open-label, parallel-group, single-centre study, consisting of a baseline screening visit, 7-day treatment period and post-study examination visit.

SUBJECTS AND INTERVENTION

36 healthy elderly subjects (aged > or =65 years) with a body mass index of 18.5-29.9 kg/m(2). Subjects were randomized to receive dabigatran etexilate either with or without coadministration of pantoprazole. Dabigatran etexilate was administered as capsules at 150 mg twice daily over 6 days and once on the morning of day 7. Pantoprazole was administered at 40 mg twice daily, starting 2 days prior to dabigatran etexilate administration and ending on the morning of day 7.

MAIN OUTCOME MEASURES

The primary pharmacokinetic measurements included the area under the plasma concentration-time curve at steady state (AUC(ss)), maximum (C(max,ss)) and minimum (C(min,ss)) plasma concentrations at steady state, terminal half-life (t((1/2))), time to reach C(max,ss) and renal clearance of dabigatran. The secondary pharmacokinetic parameters included the mean residence time, total oral clearance and volume of distribution. The pharmacodynamic parameters measured were the blood coagulation parameters ecarin clotting time (ECT) and activated partial thromboplastin time (aPTT).

RESULTS

With twice-daily administration of dabigatran etexilate, plasma concentrations of dabigatran reached steady state within 2-3 days, which is consistent with a t((1/2)) of 12-14 hours. The mean (SD) peak plasma concentrations on day 4 of treatment in male and female elderly subjects were 256 ng/mL (21.8) and 255 ng/mL (84.0), respectively. The peak plasma concentrations were reached after a median of 3 hours (range 2.0-4.0 hours). Coadministration with pantoprazole decreased the average bioavailability of dabigatran (the AUC(ss)) by 24% (day 4; 90% CI 7.4, 37.8) and 20% (day 7; 90% CI 5.2, 33.3). Intra- and interindividual pharmacokinetic variability in the overall population was low (<30% coefficient of variation), indicating that dabigatran has a predictable pharmacokinetic profile. Prolongation of the ECT and aPTT correlated with, and paralleled, the plasma concentration-time profile of dabigatran, which demonstrates a rapid onset of action without a time delay, and also illustrates the direct mode of action of the drug on thrombin in plasma. The ECT increased in direct proportion to the plasma concentration, and the aPTT displayed a linear relationship with the square root of the plasma concentration. The mean AUC(ss) was 3-19% higher in female subjects than in male subjects, which was likely due to gender differences in creatinine clearance. The safety profile of dabigatran was good, with and without pantoprazole coadministration.

CONCLUSIONS

Dabigatran demonstrated reproducible and predictable pharmacokinetic and pharmacodynamic characteristics, together with a good safety profile, when administered to healthy elderly subjects. Minor gender differences were not considered clinically relevant. The effects of pantoprazole coadministration on the bioavailability of dabigatran were considered acceptable, and dose adjustment is not considered necessary.

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.

New Anticoagulant Agents: Direct Thrombin Inhibitors

Decades of research have been devoted to developing effective, safe, and convenient anticoagulant agents. In recent years, much emphasis has been placed on the development of direct thrombin inhibitors (DTIs) that offer benefits over agents like heparin and warfarin including the inhibition of both circulating and clot-bound thrombin; a more predictable anticoagulant response, because they do not bind to plasma proteins and are not neutralized by platelet factor 4; lack of required cofactors, such as antithrombin or heparin cofactor II; inhibiting thrombin-induced platelet aggregation; and absence of induction of immune-mediated thrombocytopenia. Various injectable DTIs are currently available and used for many indications. In addition, research is now focusing on oral DTIs that seem promising and offer various advantages, such as oral administration, predictable pharmacokinetics and pharmacodynamics, a broad therapeutic window, no routine monitoring, no significant drug interactions, and fixed-dose administration.