Adults

For warfarin reversal: Typically 1-10 mg orally, depending on INR and clinical situation. For vitamin K deficiency: 2.5-25 mg orally, adjusted based on response.

Elderly

Similar to adults, but use with caution and monitor closely due to potential for increased sensitivity.

Renal_impairment

No specific dose adjustment is generally required in renal impairment, but clinical monitoring is advisable.

Onset

Oral: 6-10 hours to achieve significant effect on clotting factors (e.g., reduction in INR).

Excretion

Primarily excreted in bile and urine as glucuronide and sulfate conjugates.

Half life

Approximately 1.5-3 hours for the parent drug; the duration of action for clotting factor synthesis is longer.

Absorption

Readily absorbed from the gastrointestinal tract in the presence of bile salts; absorption may be impaired in patients with malabsorption syndromes.

Metabolism

Rapidly metabolized in the liver to more polar metabolites, primarily through reduction and glucuronidation.

Cholestyramine, Mineral oil, Orlistat

These can impair the absorption of orally administered vitamin K.

Warfarin and other coumarin anticoagulants

Phytomenadione directly antagonizes the anticoagulant effects of coumarin derivatives. Concurrent use requires careful monitoring and dosage adjustment.