<prompt> All about warfarin are true EXCEPT:Half-life is 36 hoursCrosses placentaContraindicated in hepatic failureInhibits all vitamin K dependent clotting factors  <response>: Contraindicated in hepatic failure REF: Goodman and Gillmans 11th edition, page 955-956 Warfarin: Therapeutic doses of warfarin decrease by 30-50 the total amount of each vitamin K-dependent coagulation factor made by the liver The usual adult dose of warfarin COUMADIN is 5 mgday for 2-4 days, followed by 2-10 mgday as indicated by measurements of the INR The bioavailability of warfarin is nearly complete when the drug is administered orally, intravenously, or rectally. Warfarin is almost completely 99 bound to plasma proteins, principally albumin, and the drug distributes rapidly into a volume equivalent to the albumin space The t12 ranges from 25 to 60 hours means 40 hours; the duration of action of warfarin is 2-5 days. Bleeding is the major toxicity of oral anticoagulant drugs. Crosses placenta and causes fetal malformations and aboion if given during pregnancy see APPENDIX-32 