Vitamin K antagonists have a narrow therapeutic
window, and patients require frequent laboratory monitoring
to ensure that they are neither excessively anticoagulated,
which increases the risk for a bleeding event,
or underanticoagulated, which increases the risk for
thromboembolism. Recent trials have shown that direct
thrombin inhibitors, which do not require intensive
monitoring, may be as efficacious as vitamin K antagonists
(3, 4), and in October 2010, the U.S. Food and
Drug Administration approved the first of these agents
(dabigatran) for prevention of stroke in atrial fibrillation.
Nevertheless, given the high cost of these new
agents and the absence of long-term safety data, it is
likely that vitamin K antagonists will continue to be
used widely for the foreseeable future.
Because management of long-term oral anticoagulant