Vitamin k antagonists

Coumarin is a naturally occurring plant substance whose devirates are used in anticoagulation.

The half-life of coumarin marcoumar is six to seven days, and 33-45 hours for warfarin.

Coumarin acts by inhibiting the synthesis of the vitamin K-dependent coagulation factors Factor II, Factor VII, Factor IX and Factor X as well as the proteins Z, Protein C and Protein S.

Coumarins prevent the gamma-carboxylglutamic acid residues, which are important for binding calcium ions to the lipid surfaces.

In addition, coumarins inhibit vitamin K epoxide reductase. This prevents the cofactor vitamin-K-hydroquinone from being formed, which prevents carboxylation.

Resistance to coumarins is based on a defect in vitamin K epoxide reductase.

Coumarins are almost completely resorbed enteral. The plasma protein binding is over 90%.

During a coumar therapy the Quick value is lowered, the aPTT is normal. A clinically effective coumarisation is present when the Quick value is between 20-30% and the INR value is between 2.4 and 4.5.

In the event of an extreme drop in coagulation, e.g. due to a coumarin overdose or other disorders, PPSB must be substituted with the prothrombin complex. This contains the factors II, VII, IX and X. One E/kg body weight increases the Quick value by 1%.

1. HA Neumann (2014) The coagulation system. ABW-Scientific Publisher GmbH Berlin