Clinical pharmacokinetics and pharmacodynamics of the oral direct thrombin inhibitor dabigatran etexilate

Pharmacology, pharmacokinetics, and pharmacodynamics of dabigatran etexilate, an oral direct thrombin inhibitor

Dabigatran etexilate is a novel, oral reversible direct thrombin inhibitor that is rapidly absorbed and converted to its active form, dabigatran. Dabigatran has been shown to be a potent, competitive, and reversible inhibitor of thrombin, inhibiting both thrombin activity and generation. Studies in healthy volunteers and in patients undergoing orthopedic surgery indicate that dabigatran has a predictable pharmacokinetic profile, allowing for a fixed-dose regimen without the need for coagulation monitoring. In healthy volunteers, peak plasma concentrations of dabigatran are reached approximately 2 hours after oral administration. The elimination half-life is 12 to 14 hours, with clearance predominantly occurring via renal excretion of unchanged drug. Dabigatran is not metabolized by cytochrome P450 isoenzymes, has no interactions with food, and also has a low potential for drug-drug interactions. The pharmacokinetic profile of dabigatran is consistent across a broad range of different patient populations and is unaffected by gender, body weight, ethnic origin, obesity, and mild-to-moderate hepatic impairment. Small differences in dabigatran pharmacokinetics associated with age are attributable to variation in renal function. Dabigatran etexilate produces a predictable pharmacodynamic effect and requires no coagulation monitoring. It has been approved in the European Union (EU) and Canada for prophylaxis of thromboembolism in patients undergoing total knee or hip arthroplasty. Ongoing clinical trials are investigating its use in the treatment of venous thromboembolism, prevention of stroke in patients with nonvalvular atrial fibrillation, and treatment of thromboembolic complications, following acute coronary syndromes.

Dabigatran etexilate for the prophylaxis of venous thromboembolism after hip or knee replacement rationale for dose regimen

Dabigatran etexilate is an oral reversible direct thrombin inhibitor that offers potential practical advantages over existing anticoagulants for the prevention of venous thromboembolism after major joint replacement surgery. These include oral administration, rapid onset of action, and a predictable anticoagulant effect that obviates the need for laboratory monitoring. Evidence from 3 phase II dose-finding trials showed that dabigatran etexilate, 100 to 300 mg daily, had similar efficacy, risk of bleeding, and tolerability compared with enoxaparin. Using pharmacokinetic modeling and taking into account efficacy/safety considerations, dabigatran etexilate 150 mg and 220 mg once daily, with a half-dose on the day of surgery, were selected for further evaluation in phase III trials. These doses were selected to ensure that the risk of bleeding did not exceed that of enoxaparin. This review discusses the rationale for selection of these dose regimens based on results from phase II trials.

Favorable therapeutic index of the direct factor Xa inhibitors, apixaban and rivaroxaban, compared with the thrombin inhibitor dabigatran in rabbits

BACKGROUND

Apixaban is an oral, direct factor Xa (FXa) inhibitor in late-stage clinical development. This study assessed effects of the direct FXa inhibitors, apixaban and rivaroxaban, vs. the direct thrombin inhibitor, dabigatran, on venous thrombosis (VT), bleeding time (BT) and clotting times in rabbits.

METHODS

We induced the formation of non-occlusive thrombus in VT models by placing threads in the vena cava, and induced bleeding by the incision of cuticles in anesthetized rabbits. Apixaban, rivaroxaban and dabigatran were infused IV to achieve a stable plasma level. Clotting times, including the activated partial thromboplastin time (aPTT), prothrombin time (PT), modified PT (mPT) and thrombin time (TT), were measured.

RESULTS

Apixaban, rivaroxaban and dabigatran exhibited dose-related efficacy in preventing VT with EC(50) of 65, 33 and 194 nm, respectively. At doses for 80% reduction of control thrombus, apixaban, rivaroxaban and dabigatran prolonged BT by 1.13 +/- 0.02-, 1.9 +/- 0.1-* and 4.4 +/- 0.4-fold*, respectively (*P < 0.05, vs. apixaban). In the treatment model, these inhibitors equally prevented growth of a preformed thrombus. Antithrombotic doses of apixaban and rivaroxaban prolonged aPTT and PT by <3-fold with no effect on TT. Dabigatran was > or = 50-fold more potent in prolonging TT than aPTT and PT. Of the clotting assays studied, apixaban, rivaroxaban and dabigatran responded the best to mPT.

CONCLUSION

Comparable antithrombotic efficacy was observed between apixaban, rivaroxaban and dabigatran in the prevention and treatment of VT in rabbits. Apixaban and rivaroxaban exhibited lower BT compared with dabigatran at equivalent antithrombotic doses. The clinical significance of these findings remains to be determined.

Economic evaluation of dabigatran etexilate for the prevention of venous thromboembolism after total knee and hip replacement surgery

OBJECTIVE

This was an evaluation of the cost-effectiveness of oral dabigatran etexilate compared with subcutaneous low-molecular-weight heparin (enoxaparin) for the prevention of venous thromboembolism (VTE) after total knee replacement (TKR) and total hip replacement (THR) surgery from the perspective of the UK National Health Service.

METHODS

Dabigatran etexilate (220 mg once daily) was compared with enoxaparin (40 mg once daily) in patients undergoing TKR (duration of prophylaxis, 6-10 days) and THR (duration of prophylaxis, 28-35 days). The 10-week acute postsurgical phase was modeled using a decision tree. A Markov process (1-year cycle length) was used to model long-term events (recurrent VTE, postthrombotic syndrome, and consequences of intracranial hemorrhage) for patients' remaining lifetimes. Relative risks for VTE and bleeding events were derived from 2 Phase III studies that compared dabigatran etexilate with enoxaparin 40 mg once daily. The probabilities of long-term events were estimated using data from published longitudinal studies.

RESULTS

Rates of VTE and bleeding events did not differ significantly between dabigatran etexilate and enoxaparin. Dabigatran etexilate was less costly than enoxaparin in TKR and substantially less costly in THR, primarily due to differences in administration costs. The cost of prophylaxis for THR patients, including drugs and administration costs, was estimated at pound 137 for dabigatran etexilate and pound 237 for enoxaparin ( pound 7 for nursing time during the hospital stay, pound 91 for nurse home visits for administration after hospital discharge, and an additional pound 2 in drug costs). At a willingness-to-pay threshold of pound 20,000 per quality-adjusted life-year, the probability of cost-effectiveness for dabigatran etexilate was 75% in TKR and 97% in THR. These results were robust across a range of sensitivity analyses.

CONCLUSION

From the perspective of the UK National Health Service, thromboprophylaxis with dabigatran etexilate was cost-saving compared with enoxaparin 40 mg once daily, with comparable efficacy and safety profiles.

[New oral anticoagulants: molecular characteristics, mechanisms of action, pharmacokinetics and pharmacodynamics]

The search for the ideal anticoagulant has been one of the most active research fields in medicine in the past few years. Anti-vitamin K replacement, particularly in the long term treatment of venous thromboembolism is a difficult objective to achieve due to the wide experience gathered in normal practice and low costs. But to improve the weak points of these drugs is an attractive challenge and would have a great health and social impact. It can be seen that the low molecular weight heparins, or even pentasaccharide, drugs that are already available on the market, although the have very predictable pharmacokinetics, their parenteral use, or their long half life, they are far from being ideal anticoagulants. Ximelagatran, a promising drug, a direct inhibitor of thrombin seemed to be a step forward, but the appearance of undesirable side effects led to its withdrawal. However, this line of investigation has remained open, as such that we now have data from clinical trials that back it up: the direct inhibition of thrombin and activated factor X. These two different mechanisms of action are showing promising results, in that the direct inhibitors of thrombin (dabigatran, hirudins...) are showing not to be inferior in efficacy and safety to enoxaparin in the primary prophylaxis of venous thromboembolism. Similarly, the activated factor X inhibitors (Rivaroxaban, Apixaban ) are also showing the same and in some cases, superior in its prevention. This review looks at the mechanisms of action of both pharmacological groups, their effects on haemostasis, and how they are reflected in coagulation times, their pharmacokinetics and pharmacodynamics. These new anticoagulants are nearer to the ideal anticoagulant and may, in the near future, change the panorama of anticoagulation, not only at health level, but also by achieving improved levels in the quality of life of the patients.