No Pharmacokinetic or Pharmacodynamic Interaction Between Atorvastatin and the Oral Direct Thrombin Inhibitor Ximelagatran

Ximelagatran for stroke prevention in atrial fibrillation

Atrial fibrillation is the most common sustained cardiac arrhythmia and the most frequently encountered cause of embolic stroke. Vitamin K antagonists (such as warfarin) have represented the cornerstone of anticoagulation practice for the last 60 years. Although highly effective in preventing thromboembolic events among patients with atrial fibrillation, warfarin therapy is limited by a multitude of potential problems. Hence, warfarin is significantly underused in clinical practice, with only half of warfarin-treated patients actually achieving therapeutic anticoagulation in routine clinical practice. Consequently, there is an overwhelming need for an alternative oral anticoagulant for patients with atrial fibrillation that is safer, more practical and effective. Ximelagatran (Exanta, AstraZeneca) is a novel oral direct thrombin inhibitor that is rapidly converted to the active compound melagatran after oral absorption. It has a low potential for drug interactions, anticoagulation monitoring is not required, and it is administered at a fixed twice-daily dose. The Stroke Prevention using the ORal Thrombin Inhibitor in patients with nonvalvular atrial Fibrillation (SPORTIF) III and V trials have together demonstrated the noninferiority of ximelagatran relative to warfarin for the prevention of stroke and embolic events in atrial fibrillation. Unfortunately, initial optimism has been tempered by serious concerns over its safety data in view of its propensity to cause elevation in liver enzymes.

No Pharmacokinetic or Pharmacodynamic Interaction Between Digoxin and the Oral Direct Thrombin Inhibitor Ximelagatran in Healthy Volunteers

The interaction potential of digoxin and ximelagatran, an oral direct thrombin inhibitor being developed for the prevention and treatment of thromboembolic disease, was investigated in this randomized, double-blind, 2-way crossover study. On 2 separate occasions, healthy female and male volunteers (n = 16) received ximelagatran 36 mg or placebo twice daily for 8 days separated by a 4- to 14-day washout period. All volunteers received a single oral dose of digoxin 0.5 mg on day 4 of both study periods. No interaction between ximelagatran and digoxin was detected in the pharmaco-kinetic parameters (using a 90% confidence interval [CI] of least squares mean estimate ratios), including melagatran (the active form of ximelagatran) AUC(tau) and C(max) and digoxin AUC(t) and C(max). Digoxin did not alter the melagatran-induced prolongation of the activated partial thromboplastin time, and both drugs were well tolerated when administered in combination. In conclusion, no pharmacokinetic or pharmacodynamic interaction between digoxin and ximelagatran was observed in this study.

Absence of Clinically Relevant Interactions between Rivaroxaban - an Oral, Direct Factor Xa Inhibitor - and Digoxin or Atorvastatin in Healthy Subjects

Objective:

To investigate potential interactions between rivaroxaban, an oral direct Factor Xa inhibitor approved for the management of thromboembolic disorders, and digoxin or atorvastatin.

Methods:

Two randomized, phase 1 clinical trials were undertaken in healthy men to assess pharmacokinetic and pharmacodynamic interactions between rivaroxaban and digoxin or atorvastatin, and the safety of these drug combinations.

Results:

Steady-state rivaroxaban did not affect the pharmacokinetic profile of steady-state digoxin ( n = 17). Digoxin did not significantly influence the pharmacokinetic profile of single-dose rivaroxaban and had minimal effects on rivaroxaban-induced inhibition of Factor Xa activity and prolongation of clotting time. Similarly, steady-state atorvastatin did not affect the pharmacokinetic profile or the pharmacodynamics of rivaroxaban and vice versa ( n = 19). All drugs (alone or in combination) were well tolerated.

Conclusions:

There were no clinically relevant pharmacokinetic or pharmaco - dynamic interactions between rivaroxaban and digoxin, or between rivaroxaban and atorvastatin, suggesting that rivaroxaban can be coadministered with either drug. This study also confirmed that rivaroxaban does not interact with substrates for permeability (P)-glycoprotein alone (digoxin) or P-glycoprotein and cytochrome P450(CYP)3A4 (atorvastatin).

Pharmacokinetics and pharmacodynamics of the oral direct thrombin inhibitor ximelagatran co-administered with different classes of antibiotics in healthy volunteers

OBJECTIVE

To study the effects of amoxicillin, doxycycline, ciprofloxacin, azithromycin, and cefuroxime on the pharmacokinetics and pharmacodynamics of melagatran, the active form of the oral direct thrombin inhibitor ximelagatran, which is a substrate for the P-glycoprotein pump (P-gp) transporter but is not metabolized by the cytochrome P450 (CYP450) enzyme system.

METHODS

Five parallel groups of 16 healthy volunteers received two sequential treatments. The first treatment was a single 36-mg dose of ximelagatran. During the second treatment period, one of the above antibiotics was given on days 1-5 after a washout of at least 2 days. A single 36-mg oral dose of ximelagatran was given on the mornings of days 1 and 5 of the second treatment period.

RESULTS

No pharmacokinetic interactions were detected between ximelagatran and amoxicillin, doxycycline, or ciprofloxacin as the least-squares geometric mean treatment ratio of ximelagatran with-to-without antibiotic fell within the intervals of 0.80-1.25 for the area under the curve (AUC) and 0.7-1.43 for C(max). After co-administration with azithromycin, the least square mean ratio with-to-without antibiotic for AUC of melagatran was 1.60 (90% CI, 1.40-1.82) on day 1 and 1.41 (90% CI, 1.24-1.61) on day 5. For melagatran C(max), the corresponding ratios were 1.63 (90% CI, 1.38-1.92) and 1.40 (90% CI, 1.18-1.66). After co-administration with cefuroxime, the ratios were 1.23 (90% CI, 1.07-1.42) and 1.16 (90% CI, 0.972-1.38) for AUC and 1.33 (90% CI, 1.07-1.66) and 1.19 (90%CI, 0.888-1.58) for C(max) of melagatran. Co-administration with the antibiotics did not change mean time to C(max), half-life, or renal clearance of melagatran. The melagatran plasma concentration-response relationship for activated partial thromboplastin time (APTT) prolongation was not altered by any of the studied antibiotics, but the increased plasma concentrations of melagatran after co-administration of ximelagatran with azithromycin resulted in a minor increase in the mean maximum APTT of about 15%.

CONCLUSION

The pharmacokinetics of ximelagatran were not affected by amoxicillin, doxycycline, or ciprofloxacin. Melagatran exposure was increased when ximelagatran was co-administered with azithromycin and, to a lesser extent, with cefuroxime. APTT was not significantly altered by any of the antibiotics.

INFLUENCE OF ERYTHROMYCIN ON THE PHARMACOKINETICS OF XIMELAGATRAN MAY INVOLVE INHIBITION OF P-GLYCOPROTEIN-MEDIATED EXCRETION

A pharmacokinetic interaction between erythromycin and ximelagatran, an oral direct thrombin inhibitor, was demonstrated in this study in healthy volunteers. To investigate possible interaction mechanisms, the effects of erythromycin on active transport mediated by P-glycoprotein (P-gp) in vitro in Caco-2 and P-gp-over-expressing Madin-Darby canine kidney-human multidrug resistance-1 cell preparations and on biliary excretion of melagatran in rats were studied. In healthy volunteers (seven males and nine females; mean age 24 years) receiving a single dose of ximelagatran 36 mg on day 1, erythromycin 500 mg t.i.d. on days 2 to 5, and a single dose of ximelagatran 36 mg plus erythromycin 500 mg on day 6, the least-squares mean estimates (90% confidence intervals) for the ratio of ximelagatran with erythromycin to ximelagatran given alone were 1.82 (1.64-2.01) for the area under the concentration-time curve and 1.74 (1.52-2.00) for the maximum plasma concentration of melagatran, the active form of ximelagatran. Neither the slope nor the intercept of the melagatran plasma concentration-effect relationship for activated partial thromboplastin time statistically significantly differed as a function of whether or not erythromycin was administered with ximelagatran. Ximelagatran was well tolerated regardless of whether it was administered with erythromycin. Erythromycin inhibited P-gp-mediated transport of both ximelagatran and melagatran in vitro and decreased the biliary excretion of melagatran in the rat. These results indicate that the mechanism of the pharmacokinetic interaction between oral ximelagatran and erythromycin may involve inhibition of transport proteins, possibly P-gp, resulting in decreased melagatran biliary excretion and increased bioavailability of melagatran.

Population Pharmacokinetics of Melagatran, the Active Form of the Oral Direct Thrombin Inhibitor Ximelagatran, in Atrial Fibrillation Patients Receiving Long-Term Anticoagulation Therapy

BACKGROUND

Ximelagatran is an oral direct thrombin inhibitor for the prevention of thromboembolic disease. After oral administration, ximelagatran is rapidly absorbed and bioconverted to its active form, melagatran.

OBJECTIVE

To characterise the pharmacokinetics of melagatran in patients with nonvalvular atrial fibrillation (NVAF) receiving long-term treatment for prevention of stroke and systemic embolic events.

METHODS

A population pharmacokinetic model was developed based on data from three phase II studies (1177 plasma concentration observations in 167 patients, treated for up to 18 months) and confirmed by including data from two phase III studies (8702 plasma concentration observations in 3188 patients, treated for up to 24 months). The impact of individualised dosing on pharmacokinetic variability was evaluated by simulations of melagatran concentrations based on the pharmacokinetic model.

RESULTS

Melagatran pharmacokinetics were consistent across the studied doses and duration of treatment, and were described by a one-compartment model with first-order absorption and elimination. Clearance of melagatran was correlated to creatinine clearance, which was the most important predictor of melagatran exposure (explained 54% of interpatient variance in clearance). Total variability (coefficient of variation) in exposure was 45%; intraindividual variability in exposure was 23%. Concomitant medication with the most common long-term used drugs in the study population had no relevant influence on melagatran pharmacokinetics. Simulations suggested that dose adjustment based on renal function or trough plasma concentration had a minor effect on overall pharmacokinetic variability and the number of patients with high melagatran exposure.

CONCLUSION

The pharmacokinetics of melagatran in NVAF patients were predictable, and consistent with results from previously studied patient populations. Dose individualisation was predicted to have a low impact on pharmacokinetic variability, supporting the use of a fixed-dose regimen of ximelagatran for long-term anticoagulant therapy in the majority of NVAF patients.

Ximelagatran: a clinical perspective

Ximelagatran is a novel oral anticoagulant belonging to a class of drugs known as direct thrombin inhibitors. Numerous recent large-scale, randomised controlled clinical trials have given the drug a large clinical platform. These include data on the thromboprophylaxis of venous thromboembolism following major orthopaedic surgery and knee arthroscopy, as well as in the treatment of deep vein thrombosis and prevention of stroke with nonvalvular atrial fibrillation. One phase II study has also shown the efficacy and safety of ximelagatran in secondary prevention post-myocardial infarction. Unfortunately, approximately 6% of patients develop usually self-limiting derangement of liver dysfunction, and frequent monitoring of liver function is likely to be recommended for the first 6 months of treatment. Unlike the vitamin K antagonists, ximelagatran has a wide therapeutic interval with few food, alcohol or drug interactions, and it does not require anticoagulant monitoring. The aim of this overview is to review the clinical trials pertaining to this new drug, which is the first new oral anticoagulant for over 60 years, and one that is likely to influence our management of thrombosis-related disorders.

No effect of encapsulation on the pharmacokinetics of warfarin

BACKGROUND

In double-blind comparator studies with the oral direct thrombin inhibitor (oral DTI) ximelagatran, warfarin (Coumadin) was administered in encapsulated form in order to maintain patient and investigator blinding. This open, randomized, two-way crossover study was conducted to determine whether the encapsulated warfarin tablets (Coumadin) used in the ximelagatran studies are bioequivalent to nonencapsulated, commercially available warfarin (Coumadin) tablets.

METHODS AND RESULTS

Eighteen healthy men received two 2.5 mg tablets of encapsulated warfarin and two 2.5 mg tablets of nonencapsulated warfarin as single oral doses, 14 days apart. The 90% confidence intervals for the mean treatment ratio (encapsulated tablet/nonencapsulated tablet) fell within the limits considered to reflect bioequivalence (0.80, 1.25) for total area under the plasma concentration-versus-time curve (AUC(infinity)), AUC to the last evaluable concentration (AUC(t)), and maximum plasma concentration (C(max)) for both R-warfarin (AUC(infinity) [0.93, 1.03], AUC(t) [0.95, 1.03], C(max) [0.90, 1.04]) and S-warfarin (AUC(infinity) [0.93, 1.03], AUC(t) [0.94, 1.03], C(max) [0.90, 1.06]).

CONCLUSIONS

The encapsulated form of warfarin (Coumadin) used in comparator studies with the oral DTI ximelagatran is bioequivalent to the nonencapsulated, commercially available form of warfarin (Coumadin). Thus, the results of ximelagatran clinical trials with encapsulated warfarin can be generalized to the commercially available form.

No Influence of Food on the Pharmacokinetics, Pharmacodynamics or Tolerability of the 24mg and 36mg Oral Tablet Formulations of Ximelagatran

OBJECTIVE

To assess the potential effects of food on the pharmacokinetics and tolerability/safety of ximelagatran, an oral direct thrombin inhibitor developed for the prevention and treatment of thromboembolic disease that is rapidly bioconverted to its active form, melagatran.

DESIGN AND STUDY PARTICIPANTS

In two open-label, randomised, crossover studies, healthy male and female volunteers received oral ximelagatran as a single 24mg tablet (study 1, n = 30) or a single 36mg tablet (study 2, n = 50). Potential effects of food on the pharmacodynamics (activated partial thromboplastin time; APTT) of the 36mg tablet were also investigated in study 2.

RESULTS

For the 24mg tablet, the 90% confidence intervals (CIs) and least-squares mean estimates for the ratio of the tablet with food to the tablet without food fell within the predefined bounds demonstrating no effect on area under the melagatran concentration-time curve (AUC ratio = 0.94 [90% CI 0.90, 0.99]) or maximum plasma concentration (C(max) ratio = 0.88 [90% CI 0.82, 0.95]). The same result was observed for the 36mg tablet (AUC ratio = 1.07 [90% CI 1.03, 1.12]; C(max) ratio = 1.05 [90% CI 0.98, 1.12]). Melagatran AUC normalised for differences in bodyweight was comparable between women and men administered the 24mg or 36mg tablet without food. In addition, food did not clinically significantly alter the melagatran-induced prolongation of the APTT of the 36mg tablet. Ximelagatran was well tolerated with or without food.

CONCLUSION

The pharmacokinetics (AUC, C(max)), pharmacodynamics (APTT) and tolerability of melagatran after administration of oral ximelagatran tablets were not affected by food.

Comparative Pharmacokinetics of Vitamin K Antagonists

Vitamin K antagonists belong to the group of most frequently used drugs worldwide. They are used for long-term anticoagulation therapy, and exhibit their anticoagulant effect by inhibition of vitamin K epoxide reductase. Each drug exists in two different enantiomeric forms and is administered orally as a racemate. The use of vitamin K antagonists is complicated by a narrow therapeutic index and an unpredictable dose-response relationship, giving rise to frequent bleeding complications or insufficient anticoagulation. These large dose response variations are markedly influenced by pharmacokinetic aspects that are determined by genetic, environmental and possibly other yet unknown factors. Previous knowledge in this regard principally referred to warfarin. Cytochrome P450 (CYP) 2C9 has clearly been established as the predominant catalyst responsible for the metabolism of its more potent S-enantiomer. More recently, CYP2C9 has also been reported to catalyse the hydroxylation of phenprocoumon and acenocoumarol. However, the relative importance of CYP2C9 for the clearance of each anticoagulant substantially differs. Overall, the CYP2C9 isoenzyme appears to be most important for the clearance of warfarin, followed by acenocoumarol and, lastly, phenprocoumon. The less important role of CYP2C9 for the clearance of phenprocoumon is due to the involvement of CYP3A4 as an additional catalyst of phenprocoumon hydroxylation and significant excretion of unchanged drug in bile and urine, while the elimination of warfarin and acenocoumarol is almost completely by metabolism. Consequently, the effects of CYP2C9 polymorphisms on the pharmacokinetics and anticoagulant response are also least pronounced in the case of phenprocoumon; this drug seems preferable for therapeutic anticoagulation in poor metabolisers of CYP2C9. In addition to these vitamin K antagonists, oral thrombin inhibitors are currently under clinical development for the prevention and treatment of thromboembolism. Of these, ximelagatran has recently gained marketing authorisation in Europe. These novel drugs all feature some major advantages over traditional anticoagulants, including a wide therapeutic interval, the lack of anticoagulant effect monitoring and a low drug-drug interaction potential. However, they are also characterised by some pitfalls. Amendments of traditional anticoagulant therapy, including self-monitoring of international normalised ratio values or prospective genotyping for individual dose-tailoring may contribute to the continuous use of warfarin, phenprocoumon and acenocoumarol in the future.

Ximelagatran: Oral direct thrombin inhibition as anticoagulant therapy in atrial fibrillation

Atrial fibrillation (AF) causes 50,000 to 100,000 ischemic strokes annually in the U.S., most of which could be prevented by oral anticoagulant treatment of the highest-risk patients. The greatest barrier to such treatment is the narrow therapeutic index of the vitamin K antagonists ([VKAs]: warfarin and related coumarin derivatives), the only oral anticoagulant agents currently available. Safe and effective treatment with the VKAs requires careful monitoring, because they interact with many other drugs and foods, and their anticoagulant action is unpredictable. Besides vitamin K, candidate targets for anticoagulant therapy include thrombin, a key prothrombotic mediator. Ximelagatran, the oral direct thrombin inhibitor at the most advanced stage of clinical development, is rapidly absorbed and bioconverted to its active moiety, melagatran-a potent, competitive inhibitor of both free and clot-bound thrombin. Two large clinical trials have demonstrated that fixed-dose oral ximelagatran, 36 mg twice daily, administered without coagulation monitoring, prevents stroke and systemic embolic events in patients with nonvalvular AF as effectively as well-controlled, adjusted-dose warfarin (international normalized ratio 2.0 to 3.0). The overall risk of bleeding was lower with ximelagatran than warfarin, although differences in rates of major hemorrhage were not statistically significant. Elevation of serum alanine aminotransferase levels above 3x the upper limit of normal occurred in approximately 6% of ximelagatran-treated patients but typically returned toward pretreatment levels without associated symptoms. In terms of preventing thromboembolism without hemorrhage, ximelagatran may have a more favorable benefit:risk profile than warfarin for patients with AF.

Ximelagatran: an oral direct thrombin inhibitor

OBJECTIVE

To present the chemistry, pharmacology, and pharmacokinetics of ximelagatran, an oral direct thrombin inhibitor (DTI), and to review available comparative clinical trial data evaluating its efficacy and safety relative to other antithrombotic agents in the prevention and treatment of thromboembolism.

DATA SOURCES

A search of the PubMed and Cochrane databases (1995-August 2004), supplemented by a manual search of article bibliographies, conference abstracts, and data on file from the manufacturer, was conducted. Key search terms were ximelagatran, melagatran, H376/95, and direct thrombin inhibitors.

STUDY SELECTION AND DATA EXTRACTION

Pertinent information from available clinical trials, including study design, patient demographics, dosing regimens, anticoagulant comparators, methods for evaluating effectiveness, treatment outcomes, adverse events, and pharmacokinetic and pharmacodynamic evaluations, was extracted.

DATA SYNTHESIS

Ximelagatran is an orally administered DTI under development for use in the treatment of venous thromboembolism (VTE), long-term prevention of a second VTE event, stroke secondary to atrial fibrillation, prevention of VTE after orthopedic procedures, and recurrent ischemic events after acute myocardial infarction.

CONCLUSIONS

Ximelagatran, in twice-daily doses of 24 or 36 mg, is an alternative to low-molecular-weight heparins or warfarin in thromboprophylaxis following orthopedic knee replacement, atrial fibrillation, or initial treatment of VTE. Improved outcomes versus placebo were seen in the long-term prevention of VTE in patients who completed an initial 6 months of treatment. Liver-related effects need further clarification.