Pharmacokinetics of ximelagatran and relationship to clinical response in acute deep vein thrombosis
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OBJECTIVE: Our objective was to characterize the pharmacokinetics of melagatran, the active form of the oral direct thrombin inhibitor ximelagatran, and the relationship between melagatran exposure and clinical outcome in patients with acute deep vein thrombosis. METHODS: A population pharmacokinetic analysis was performed on samples from patients with deep vein thrombosis participating in a randomized dose-finding study (THRombin Inhibitor in Venous thrombo-Embolism [THRIVE I]). Patients received fixed doses of oral ximelagatran (24, 36, 48, or 60 mg twice daily) for 12 to 16 days. Thrombus size was evaluated by venography before and after treatment. Exposure-response curves were characterized for the probability of regression, no change, and progression of the thrombus extension and of having a bleeding-related event, by use of logistic regression models. RESULTS: The pharmacokinetics of melagatran (1836 samples in 264 patients) was predictable, without significant time or dose dependencies. Clearance after oral administration (population mean, 27.3 L/h) was correlated with creatinine clearance (P < 10(-6)), and volume of distribution (population mean, 176 L) was correlated with body weight (P = 2 x 10(-5)). Gender, age, or smoking did not significantly influence melagatran pharmacokinetics after the influence of renal function and body weight was accounted for. Unexplained interpatient variability values in total plasma clearance and bioavailability were 19% and 21%, respectively. The median area under the plasma melagatran concentration versus time curve across all patients and dose levels was 3.22 h x micromol/L (5th-95th percentiles, 1.35-7.69). There was no significant relationship between area under the plasma concentration versus time curve and change in thrombus extension (P = .59) or bleeding-related events (P = .77), and the estimated exposure-response curves were relatively flat. CONCLUSIONS: The pharmacokinetics of melagatran in patients with acute deep vein thrombosis was predictable after oral ximelagatran administration. Shallow exposure-response curves for efficacy and bleeding indicate that there is no need for individualized dosing or therapeutic drug monitoring in the patient population studied.
