PANWARFIN

Clinical safety rating: caution

Comprehensive clinical and safety monograph for PANWARFIN (PANWARFIN).

How it works

Anticoagulant that inhibits vitamin K epoxide reductase, thereby decreasing hepatic synthesis of vitamin K-dependent coagulation factors II, VII, IX, and X.

What the body does with it

Metabolism	Hepatic via CYP450 isoenzymes: S-enantiomer primarily by CYP2C9; R-enantiomer primarily by CYP1A2 and CYP3A4.
Excretion	Primarily renal as inactive metabolites; 60-92% of a dose is excreted in urine, with about 50% as the 7-hydroxywarfarin metabolite and the remainder as other metabolites. Biliary/fecal elimination accounts for approximately 10-20%.
Half-life	Terminal elimination half-life is 20-60 hours (mean ~40 hours). Clinically, the longer half-life allows for once-daily dosing and steady-state is achieved in 5-7 days; anticoagulant effect may persist for 2-5 days after discontinuation due to depletion of vitamin K-dependent clotting factors.
Protein binding	Highly bound to plasma proteins, mainly albumin, at 99% (bound fraction). Only the free (unbound) fraction is pharmacologically active; hypoalbuminemia may increase free drug and effect.
Volume of Distribution	Apparent volume of distribution is 0.1-0.2 L/kg (mean 0.14 L/kg). This low Vd reflects high protein binding and limited extravascular distribution; warfarin is primarily confined to the vascular space.
Bioavailability	Oral: 100% (completely absorbed). Intravenous: 100% (bioequivalent to oral). No other routes are clinically used.
Onset of Action	Oral: Anticoagulant effect (INR increase) begins 24-72 hours after a single dose; full therapeutic effect (INR in range) may require 5-7 days. Intravenous: Similar to oral; onset is determined by pharmacokinetics and clotting factor synthesis inhibition.
Duration of Action	Duration of anticoagulant effect is 2-5 days after cessation, corresponding to the half-lives of clotting factors (II, VII, IX, X). The effect is prolonged in liver disease or vitamin K deficiency.

Classification & Brands

Dosing & administration

5 mg orally once daily, adjusted to maintain INR 2-3.

Dosage form	TABLET
Renal impairment	No dosage adjustment required for any GFR; monitor INR closely.
Liver impairment	Child-Pugh A: no adjustment; Child-Pugh B: reduce dose by 50%; Child-Pugh C: contraindicated.
Pediatric use	0.1-0.2 mg/kg orally once daily, adjust based on INR.
Geriatric use	Initiate at 2.5 mg orally once daily; monitor INR frequently due to increased sensitivity.

Use during pregnancy

1st trimester	Consult provider
2nd trimester	Consult provider
3rd trimester	Consult provider

Clinical note

Comprehensive clinical and safety monograph for PANWARFIN (PANWARFIN).

Breastfeeding

Excreted into breast milk in small amounts; M/P ratio approximately 0.3. No adverse effects reported in breastfed infants when maternal INR is within therapeutic range. Considered compatible with breastfeeding, but monitor infant for bruising or bleeding. Caution if maternal INR supratherapeutic.

Teratogenic Risk

First trimester: High risk of warfarin embryopathy (nasal hypoplasia, stippled epiphyses) with exposure between 6-12 weeks gestation. Second and third trimesters: Risk of central nervous system abnormalities, optic atrophy, microcephaly, and fetal hemorrhage. Fetal bleeding risk increases near term; warfarin crosses the placenta and can cause fetal intracranial hemorrhage. Contraindicated throughout pregnancy unless mechanical heart valve necessitates use.

Warnings & precautions

■ FDA Black Box Warning

Warfarin can cause major or fatal bleeding. Risk factors include high dose, elderly, multiple comorbidities, and certain genetic variations. Regular monitoring of INR is required.

Side Effect Profile

Serious Effects

Absolute Contraindications

Active bleeding; hemorrhagic tendencies or blood dyscrasias; recent or contemplated surgery of the eye or central nervous system; major regional lumbar block anesthesia; malignant hypertension; pregnancy (except in women with mechanical heart valves); hypersensitivity to warfarin.

Clinical Precautions

Precautions

Hemorrhage risk; necrosis or gangrene of skin; systemic atheroemboli; calciphylaxis; need for regular INR monitoring; dose adjustments required with interacting drugs, diet, and disease states.

Clinical Tips & Counseling

Drug interactions

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PANWARFIN

Clinical safety rating: caution

Comprehensive clinical and safety monograph for PANWARFIN (PANWARFIN).

How it works

Anticoagulant that inhibits vitamin K epoxide reductase, thereby decreasing hepatic synthesis of vitamin K-dependent coagulation factors II, VII, IX, and X.

What the body does with it

Metabolism	Hepatic via CYP450 isoenzymes: S-enantiomer primarily by CYP2C9; R-enantiomer primarily by CYP1A2 and CYP3A4.
Excretion	Primarily renal as inactive metabolites; 60-92% of a dose is excreted in urine, with about 50% as the 7-hydroxywarfarin metabolite and the remainder as other metabolites. Biliary/fecal elimination accounts for approximately 10-20%.
Half-life	Terminal elimination half-life is 20-60 hours (mean ~40 hours). Clinically, the longer half-life allows for once-daily dosing and steady-state is achieved in 5-7 days; anticoagulant effect may persist for 2-5 days after discontinuation due to depletion of vitamin K-dependent clotting factors.
Protein binding	Highly bound to plasma proteins, mainly albumin, at 99% (bound fraction). Only the free (unbound) fraction is pharmacologically active; hypoalbuminemia may increase free drug and effect.
Volume of Distribution	Apparent volume of distribution is 0.1-0.2 L/kg (mean 0.14 L/kg). This low Vd reflects high protein binding and limited extravascular distribution; warfarin is primarily confined to the vascular space.
Bioavailability	Oral: 100% (completely absorbed). Intravenous: 100% (bioequivalent to oral). No other routes are clinically used.
Onset of Action	Oral: Anticoagulant effect (INR increase) begins 24-72 hours after a single dose; full therapeutic effect (INR in range) may require 5-7 days. Intravenous: Similar to oral; onset is determined by pharmacokinetics and clotting factor synthesis inhibition.
Duration of Action	Duration of anticoagulant effect is 2-5 days after cessation, corresponding to the half-lives of clotting factors (II, VII, IX, X). The effect is prolonged in liver disease or vitamin K deficiency.

Classification & Brands

Dosing & administration

5 mg orally once daily, adjusted to maintain INR 2-3.

Dosage form	TABLET
Renal impairment	No dosage adjustment required for any GFR; monitor INR closely.
Liver impairment	Child-Pugh A: no adjustment; Child-Pugh B: reduce dose by 50%; Child-Pugh C: contraindicated.
Pediatric use	0.1-0.2 mg/kg orally once daily, adjust based on INR.
Geriatric use	Initiate at 2.5 mg orally once daily; monitor INR frequently due to increased sensitivity.

Use during pregnancy

1st trimester	Consult provider
2nd trimester	Consult provider
3rd trimester	Consult provider

Clinical note

Comprehensive clinical and safety monograph for PANWARFIN (PANWARFIN).

Breastfeeding

Teratogenic Risk

Warnings & precautions

■ FDA Black Box Warning

Warfarin can cause major or fatal bleeding. Risk factors include high dose, elderly, multiple comorbidities, and certain genetic variations. Regular monitoring of INR is required.

Side Effect Profile

Serious Effects

Absolute Contraindications

Clinical Precautions

Precautions

Hemorrhage risk; necrosis or gangrene of skin; systemic atheroemboli; calciphylaxis; need for regular INR monitoring; dose adjustments required with interacting drugs, diet, and disease states.

Clinical Tips & Counseling

Drug interactions

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