Unlike traditional anticoagulants, the more recently developed agents rivaroxaban, dabigatran and apixaban target\r\nspecific factors in the coagulation cascade to attenuate thrombosis. Rivaroxaban and apixaban directly inhibit Factor\r\nXa, whereas dabigatran directly inhibits thrombin. All three drugs exhibit predictable pharmacokinetic and\r\npharmacodynamic characteristics that allow for fixed oral doses in a variety of settings. The population\r\npharmacokinetics of rivaroxaban, and also dabigatran, have been evaluated in a series of models using patient data\r\nfrom phase II and III clinical studies. These models point towards a consistent pharmacokinetic and\r\npharmacodynamic profile, even when extreme demographic factors are taken into account, meaning that doses\r\nrarely need to be adjusted. The exception is in certain patients with renal impairment, for whom pharmacokinetic\r\nmodelling provided the rationale for reduced doses as part of some regimens. Although not routinely required, the\r\nability to measure plasma concentrations of these agents could be advantageous in emergency situations, such as\r\noverdose. Specific pharmacokinetic and pharmacodynamic characteristics must be taken into account when\r\nselecting an appropriate assay for monitoring. The anti-Factor Xa chromogenic assays now available are likely to\r\nprovide the most appropriate means of determining plasma concentrations of rivaroxaban and apixaban, and\r\nspecific assays for dabigatran are in development.
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