Doses - WARFARIN SODIUM

Dogs:

For adjunctive therapy of thromboemboli:
a) For pulmonary thromboemboli: 0.1 mg/kg PO once daily. Monitor PT (begin 3-4 daysafter starting therapy) and aim for an increase to 1.5 - 2 times baseline value. (Bauer1988)
b) For pulmonary thromboembolism: 0.2 mg/kg PO once daily then 0.05 - 0.1 mg/kg POonce daily. Adjust dosage to increase PT to 1.5 - 2.5 times baseline. Heparin may bestopped once appropriate warfarin dosage is established. If PT exceeds 2.5 timesbaseline, reduce dose. If bleeding develops, stop dose and institute blood or phytonadione therapy as appropriate. (Roudebush 1985)

Cats:

For adjunctive therapy of thromboembolism:
a) For feline aortic thromboembolism: 0.06 - 0.1 mg/kg once daily PO. Evaluate using PT,
APTT, or preferably PIVKA (proteins induced by vitamin K antagonists) daily duringinitial titration (3 days), then every other day (2 times) and weekly thereafter until stable.
New steady state may require one week after dosage adjustments. Long-term therapyshould be monitored at least one monthly. (Pion and Kittleson 1989)
b) For chronic management/prevention of recurrence: 0.1 - 0.2 mg/kg PO once daily.
Adjust dosage to prolong PT to 2 - 2.5 times normal. Collect blood sample 8 hours afterdosing. Requires 48-72 hours to achieve effective anticoagulation. Monitor PT weeklyfor 1 month, then at monthly intervals. Also determine hematocrit with each PT.(Harpster 1988)
c) For pulmonary thromboembolism: 0.2 mg/kg PO once daily then 0.05 - 0.1 mg/kg POonce daily. Adjust dosage to increase PT to 1.5 - 2.5 times baseline. Heparin may bestopped once appropriate warfarin dosage is established. If PT exceeds 2.5 timesbaseline, reduce dose. If bleeding develops, stop dose and institute blood or phytonadione therapy as appropriate. (Roudebush 1985)

Horses:

As an anticoagulant:
a) 30 - 75 mg/450 kg body weight PO. (Robinson 1987)
b) Initially, 0.018 mg/kg PO once daily and increase dose by 20% every day until baseline
PT is doubled. Final dose rates may be from 0.012 mg/kg to 0.57 mg/kg daily. (Vrins,
Carlson, and Feldman 1983)
Monitoring Parameters - Note: The frequency of monitoring is controversial, and is dependenton several factors including dose, patient's condition, concomitant problems, etc. See the Dosagesection above for more information.

1) While Prothrombin Times (PT) are most commonly used to monitor warfarin, PIVKA(proteins induced by vitamin K antagonists) has been suggested as being more sensitive.

2) Platelet counts and hematocrit (PCV) should be done periodically

3) Occult blood in stool and urine; other observations for bleeding

4) Clinical efficacy
Client Information - Clients must be counseled on both the importance of administering the drugas directed and also to immediately report any signs or symptoms of hemorrhage.
Dosage Forms/Preparations/FDA Approval Status/Withholding Times - Veterinary-Approved Products: None.

Human-Approved Products:

Warfarin Sodium Tablets (scored) 1 mg, 2 mg, 2.5 mg, 3 mg, 4 mg, 5 mg, 6 mg, 7.5 mg, 10 mg;
Coumadin® (DuPont), (Rx)
Warfarin Sodium Powder for Injection lyophilized 2 mg in 5 mg vials; Coumadin® (DuPont);(Rx)
A method of suspending warfarin tablets in an oral suspension has been described (Enos 1989).
To make 30 ml of a 0.25 mg/ml suspension: Crush three 2.5 mg tablets in a mortar and pestle. Add10 ml glycerin to form a paste. Then 10 ml of water; and q.s. to 30 ml with dark corn syrup(Karo®). Warm gently. Shake well and use within 30 days.