Vitamin K (trade name Konakion) is used in neurosurgery to reverse the effects of vitamin K antagonists such as Marcoumar. The vitamin K–dependent coagulation factors (X, IX, VII, II) are produced again as a result, but with a latency period of 4-50 hours. Factor VII, with a synthesis time of approximately 4-6 hours, is synthesized first and has the strongest effect on the INR among the vitamin K–dependent coagulation factors. In the event of active bleeding, coagulation must therefore also be reversed by direct substitution of the coagulation factors.