ワルファリンナトリウム
Warfarin Sodium
別名: Coumadin · Jantoven · Panwarfin · sodium warfarin · warfarinum natricum
VetSheet 獣医チームが監修更新日 2026年4月5日エビデンスに基づく獣医学リファレンス
用量は獣医専門家向けの臨床参考資料です。必ず最新の医薬品情報および個別症例に基づいて確認してください。
動物種別用量
🌎 NA — North America🌍 EU — Europe
犬
| 適応 | 用量 | 経路 | 頻度 | 期間 | 地域 |
|---|---|---|---|---|---|
| Adjunctive maintenance therapy for venous thrombosis with or without pulmonary thromboembolism (PTE) | 0.22 mg/kg | PO | q12h | — | 🌎 NA |
| Adjunctive therapy of thromboemboli | 0.22 mg/kg | PO | q12h | — | 🌎 NA |
| Prophylactic use in patients with glomerular disease and severe proteinuria | 0.22 mg/kg | PO | once daily | — | 🌎 NA |
- Adjunctive maintenance therapy for venous thrombosis with or without pulmonary thromboembolism (PTE): Initially, then adjusted to achieve a PT prolongation of 1.25 to 1.5 times the pretreatment value.
- Adjunctive therapy of thromboemboli: Target dosage to prolong PT by 1.25-1.5 times the pretreatment value.
- Prophylactic use in patients with glomerular disease and severe proteinuria: Initially. Monitor PT and adjust dose so that PT is maintained at 1.5 times normal.
猫
| 適応 | 用量 | 経路 | 頻度 | 期間 | 地域 |
|---|---|---|---|---|---|
| Adjunctive maintenance therapy for venous thrombosis with or without pulmonary thromboembolism (PTE) | 0.5 mg (total dose per cat) | PO | once daily | — | 🌎 NA |
| Maintenance therapy for feline arterial thromboembolism | 0.06 to 0.09 mg/kg/day | PO | once daily | — | 🌎 NA |
| Long-term thromboprophylaxis | 0.06-0.09 mg/kg per day | PO | once daily | — | 🌎 NA |
| Adjunctive therapy of thromboembolism | 0.25-0.5 mg (total dose) per cat | PO | once daily | — | 🌎 NA |
| Cardiogenic arterial thromboembolism | 0.25-0.5 mg total dose per cat | PO | q24h | — | 🌎 NA |
- Adjunctive maintenance therapy for venous thrombosis with or without pulmonary thromboembolism (PTE): Initially, then adjusted to achieve a PT prolongation of 1.25 to 1.5 times the pretreatment value.
- Maintenance therapy for feline arterial thromboembolism: Heparinization is recommended during the first 5 to 7 days that warfarin is administered.
- Long-term thromboprophylaxis: Initially. Tablets should be crushed and mixed well due to unequal drug distribution. Overlap heparin and warfarin therapy by at least 4-5 days.
- Adjunctive therapy of thromboembolism: Initially. Adjust dosage to prolong PT to twice normal value, or INR to be between 2-3. Overlap therapy with heparin.
- Cardiogenic arterial thromboembolism: Heparin (150-250 Units/kg SC q8h) should be administered concurrently during the first 4-6 days. Target PT range is 1.3-1.6 times baseline, or INR 2.0-3.0.
馬
| 適応 | 用量 | 経路 | 頻度 | 期間 | 地域 |
|---|---|---|---|---|---|
| Adjunctive treatment of laminitis | 0.0198 mg/kg | PO | once daily | — | 🌎 NA |
| Anticoagulant | 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. | PO | once daily | — | 🌎 NA |
- Adjunctive treatment of laminitis: Monitor OSPT (one-step prothrombin time) until prolonged 2-4 seconds beyond baseline.
- Anticoagulant: ARCI UCGFS Class 5 Drug.
用量は獣医専門家向けの臨床参考資料です。必ず最新の医薬品情報および個別症例に基づいて確認してください。
概要
ワルファリンはクマリン系抗凝固薬であり、主に猫、犬、馬における血栓性疾患の長期治療または予防に使用されます。治療域が狭く、致命的な出血のリスクがあること、また頻繁で高価な凝固モニタリングが必要なため、獣医療での使用には議論があり、他の抗凝固薬が使用できない特定のケースに限られることが多くなっています。
作用機序
Warfarin acts as an indirect anticoagulant by antagonizing Vitamin K.
- It competitively inhibits the enzyme Vitamin K epoxide reductase (VKORC1).
- This inhibition prevents the conversion of inactive Vitamin K epoxide back into its active form (Vitamin K hydroquinone).
- Active Vitamin K is an essential cofactor for the γ-carboxylation (activation) of coagulation factors II, VII, IX, and X, as well as the endogenous anticoagulant proteins C and S.
- Pathway: VKORC1 inhibition → Depletion of active Vitamin K → Production of inactive, undercarboxylated clotting factors (PIVKA) → Prolonged clotting times and anticoagulation.
安全性・警告
禁忌
- Preexistent hemorrhagic tendencies or diseases
- Patients undergoing or contemplating eye or CNS surgery
- Major regional lumbar block anesthesia
- Surgery of large, open surfaces
- Active bleeding from the GI, respiratory, or GU tract
- Aneurysm
- Acute nephritis
- Cerebrovascular hemorrhage
- Blood dyscrasias
- Uncontrolled or malignant hypertension
- Hepatic insufficiency
- Pericardial effusion
- Pregnancy (Teratogenic - FDA Category X / Papich Class D)
- Visceral carcinomas
有害事象
- Dose-related hemorrhage (primary adverse effect)
- Anemia
- Thrombocytopenia
- Weakness
- Hematomas and ecchymoses
- Epistaxis (nosebleeds)
- Hematemesis (vomiting blood)
- Hematuria (blood in urine)
- Melena (dark, tarry stools)
- Hematochezia (fresh blood in stools)
- Hemarthrosis (bleeding into joints)
- Hemothorax
- Intracranial hemorrhage
- Pericardial hemorrhage
- Death
注意事項
Strict Monitoring Required: Warfarin has a narrow therapeutic index. Frequent monitoring of coagulation status (PT/INR) is mandatory to prevent fatal hemorrhage.
- Teratogenicity: Warfarin is embryotoxic and causes congenital malformations. It is strictly contraindicated in pregnancy. Low-dose heparin is preferred if anticoagulation is required during pregnancy.
- Nursing: Use with caution in nursing patients; prolonged prothrombin times have been reported in some breast-fed human infants.
- Dietary Changes: Sudden changes in diet (especially foods high in Vitamin K) can alter the efficacy of warfarin.
- Laboratory Interference: May cause falsely decreased theophylline values if using the Schack and Waxler ultraviolet method.
医薬品相互作用
May increase anticoagulant response (via protein displacement or platelet inhibition); increases bleeding risk.
May increase anticoagulant response (often via inhibition of hepatic metabolism).
May increase anticoagulant response.
May increase anticoagulant response.
May increase anticoagulant response.
Increases anticoagulant response; often used concurrently during the initial overlap phase but requires careful monitoring.
May decrease anticoagulant response (via induction of hepatic metabolizing enzymes).
May decrease anticoagulant response.
Directly antagonizes warfarin, decreasing its anticoagulant response (used as an antidote for overdose).
監視
- Prothrombin Time (PT) - Target usually 1.25 to 1.5x (or up to 2x) normal depending on protocol
- International Normalized Ratio (INR) - Target usually 2.0 to 3.0 (Note: not fully validated for veterinary patients)
- PIVKA (Proteins Induced by Vitamin K Antagonists) - May be more sensitive than PT
- Platelet counts and hematocrit (PCV)
- Occult blood in stool and urine
- Physical observations for bleeding (mucous membranes, bruising, epistaxis)
- Clinical efficacy (resolution/prevention of thromboembolism)
薬物動態
半減期
吸収
Rapidly and completely absorbed after oral administration in humans and cats.
分布
Highly bound to plasma proteins (approximately 99% in humans, >96% in cats). Wide species variation exists; horses have a higher free (unbound) fraction than rats, sheep, or swine. Only the free fraction is active. Does not enter milk in humans.
代謝
Principally metabolized in the liver to inactive metabolites.
消失
Metabolites are excreted in urine and bile (then reabsorbed and excreted in the urine).
過剰投与
Acute overdosages of warfarin may result in life-threatening hemorrhage.
- Toxic Doses: In dogs and cats, single doses of 5-50 mg/kg have been associated with toxicity. Cumulative toxic doses are reported as 1-5 mg/kg for 5-15 days in dogs, and 1 mg/kg for 7 days in cats.
- Lag Time: A lag time of 2-5 days may occur before clinical signs of toxicity manifest. Animals must be monitored closely during this period.
- Treatment: If detected early, prevent absorption from the gut using standard decontamination protocols (emesis, activated charcoal). If clinical signs of bleeding are noted, treat with blood products (plasma/whole blood to replace active clotting factors) and Vitamin K1 (phytonadione).
製品
製剤
- Oral tablets
- Powder for injection (lyophilized)
動物用医薬品
- None (ARCI Class 5 substance for racing)
ヒト用医薬品
- Warfarin Sodium Oral Tablets (scored): 1 mg, 2 mg, 2.5 mg, 3 mg, 4 mg, 5 mg, 6 mg, 7.5 mg & 10 mg (Coumadin, Jantoven, generic)
- Warfarin Sodium Powder for Injection, lyophilized: 5.4 mg (2 mg/mL when reconstituted) preservative-free in 5 mg vials (Coumadin)
規制ステータス
規制データなし: 🇺🇸 US · 🇪🇺 EU · 🇬🇧 UK · 🇭🇰 HK · 🇹🇼 TW · 🇯🇵 JP · 🇰🇷 KR · 🇦🇺 AU
保管・安定性
Tablets should be stored in tight, light-resistant containers at temperatures less than 40°C, preferably at room temperature. Powder for injection should be protected from light and used immediately after reconstituting.
飼主向け情報
獣医師の指示通りに正確に投薬することが非常に重要です。自己判断で用量を変更しないでください。出血の兆候（歯茎の蒼白、異常な内出血、鼻血、血尿、黒色便や血便、突然の虚弱など）が見られた場合は、直ちに獣医師に連絡してください。外傷による重篤な出血を防ぐため、投薬中のペット（特に猫）は室内飼育とし、激しい運動は避けてください。獣医師の許可なく新しい薬やサプリメントを与えないでください。
VetSheet医薬品リファレンスは獣医専門家の臨床意思決定支援を目的としており、専門的判断または製造業者の最新医薬品情報の代替にはなりません。