(S)-warfarin is P4502C9-catalyzed to its major and biologically inactive metabolite S-7-hydroxywarfarin. S-7-hydroxywarfarin can be used to determine S-warfarin hydroxylation. S-warfarin is predominantly metabolized to S-7-hydroxywarfarin, catalyzed by CYP2C9, in humans but not mice.

Phenprocoumon is the dominant anticoagulant in clinical use in several continental European countries. It used for the prevention and treatment of thromboembolic disease including venous thrombosis, thromboembolism, and pulmonary embolism as well as for the prevention of ischemic stroke in patients with atrial fibrillation. Phenprocoumon inhibits vitamin K reductase, resulting in depletion of the reduced form of vitamin K (vitamin KH2). Bleedings are the most important side -effects of oral anticoagulants. The gastrointestinal and the urinary tract are often affected; the most dangerous are intracerebral hemorrhages. A great number of drugs increase the risk of bleeding of oral anticoagulants. Enzyme inhibitors (e.g. allopurinol, androgens, cimetidine, ciprofloxacin, co-trimoxazole, certain anti-inflammatory agents, fibrates, imidazoles, macrolide antibiotics, etc.) reinforce, and enzyme inducers (e.g. barbiturates, rifampicin) and oral contraceptives reduce, the anticoagulant action.

Warfarin, (S)- is an oral anticoagulant, S-enantiomer of warfarin, that having a greater pharmacologic potency than the R-enantiomer. Clinically available warfarin is a racemic mixture of (R)- and (S)-warfarin, and the (S)-enantiomer has 3 to 5 times greater anticoagulation potency than its optical congener. Both enantiomers are eliminated extensively via hepatic metabolism with low clearance relative to hepatic blood flow. The scientific debate on the contribution of the R- Warfarin -to-S- Warfarin effect is a long and conflictual story. It has shown that the pharmacodynamic response to (R/S)-Warfarin 25 mg (a mixture of equal amounts of S-Warfarin and R- Warfarin) was nearly twice that of S-Warfarin 12.5 mg given alone, thus indicating the substantial contribution of R-Warfarin to the (R/S)-Warfarin effect. (R/S)-Warfarin is indicated for the prophylaxis and/or treatment of venous thrombosis and its extension, and pulmonary embolism. It is also indicated for the prophylaxis and/or treatment of the thromboembolic complications associated with atrial fibrillation and/or cardiac valve replacement. Warfarin is thought to interfere with clotting factor synthesis by inhibition of the C1 subunit of the vitamin K epoxide reductase (VKORC1) enzyme complex, thereby reducing the regeneration of vitamin K1 epoxide.

Warfarin, (R)- is R-enantiomer of warfarin, an oral anticoagulant, with relatively low potency compared to S-enantiomer. Clinically available warfarin is a racemic mixture of (R)- and (S)-warfarin, and the (S)-enantiomer has 3 to 5 times greater anticoagulation potency than its optical congener. Both enantiomers are eliminated extensively via hepatic metabolism with low clearance relative to hepatic blood flow. The scientific debate on the contribution of the R- Warfarin -to-S- Warfarin effect is a long and conflictual story. It has shown that the pharmacodynamic response to (R/S)-Warfarin 25 mg (a mixture of equal amounts of S-Warfarin and R- Warfarin) was nearly twice that of S-Warfarin 12.5 mg given alone, thus indicating the substantial contribution of R-Warfarin to the (R/S)-Warfarin effect. (R/S)-Warfarin is indicated for the prophylaxis and/or treatment of venous thrombosis and its extension, and pulmonary embolism. It is also indicated for the prophylaxis and/or treatment of the thromboembolic complications associated with atrial fibrillation and/or cardiac valve replacement. Warfarin is thought to interfere with clotting factor synthesis by inhibition of the C1 subunit of the vitamin K epoxide reductase (VKORC1) enzyme complex, thereby reducing the regeneration of vitamin K1 epoxide.

Phylloquinone is often called vitamin K1 or phytonadione. It is a fat-soluble vitamin that is stable to air and moisture but decomposes in sunlight. It is found naturally in a wide variety of green plants. Phylloquinone is also an antidote for coumatetralyl. Vitamin K is needed for the posttranslational modification of certain proteins, mostly required for blood coagulation. MEPHYTON (Phytonadione tablets) are indicated in the following coagulation disorders which are due to faulty formation of factors II, VII, IX and X when caused by vitamin K deficiency or interference with vitamin K activity: anticoagulant-induced prothrombin deficiency caused by coumarin or indanedione derivatives; hypoprothrombinemia secondary to antibacterial therapy; hypoprothrombinemia secondary to administration of salicylates; hypoprothrombinemia secondary to obstructive jaundice or biliary fistulas but only if bile salts are administered concurrently, since otherwise the oral vitamin K will not be absorbed. MEPHYTON tablets possess the same type and degree of activity as does naturally-occurring vitamin K, which is necessary for the production via the liver of active prothrombin (factor II), proconvertin (factor VII), plasma thromboplastin component (factor IX), and Stuart factor (factor X). The prothrombin test is sensitive to the levels of three of these four factors II, VII, and X. Vitamin K is an essential cofactor for the gamma-carboxylase enzymes, which catalyze the posttranslational gamma-carboxylation of glutamic acid residues in inactive hepatic precursors of coagulation factors II (prothrombin), VII, IX, and X. Gamma-carboxylation converts these inactive precursors into active coagulation factors, which are secreted by hepatocytes into the blood. Supplementing with Phylloquinone results in a relief of vitamin K deficiency symptoms, which include easy bruisability, epistaxis, gastrointestinal bleeding, menorrhagia and hematuria. Oral phytonadione is adequately absorbed from the gastrointestinal tract only if bile salts are present. After absorption, phytonadione is initially concentrated in the liver, but the concentration declines rapidly. Very little vitamin K accumulates in tissues. Little is known about the metabolic fate of vitamin K. Almost no free unmetabolized vitamin K appears in bile or urine. In normal animals and humans, phytonadione is virtually devoid of pharmacodynamic activity. However, in animals and humans deficient in vitamin K, the pharmacological action of vitamin K is related to its normal physiological function; that is, to promote the hepatic biosynthesis of vitamin K-dependent clotting factors. MEPHYTON tablets generally exert their effect within 6 to 10 hours.