フィトナジオン (ビタミンK1)
Phytonadione (Vitamin K1)
Phylloquinone (2-methyl-3-phytyl-1,4-naphthoquinone)
別名: K-Caps · Veda-K1 · Veta-K1 · K-Chews · K-Ject · Vita-Jec · Aqua-Mephyton · Konakion · Vitamine K1 Laboratoire TVM · Vitamin K1 · K-1 · methylphytylnaphthochinonum · phylloquinone · phytomenadionum · phytomenadione · Phytonadione · Methylphytylnaphthoquinone
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 therapy of acute liver failure | 1-5 mg/kg PO or SC q24h | PO, SC | q24h | — | 🌎 NA |
| Anticoagulant rodenticide toxicity (exposed but non-bleeding) | 1.25-2.5 mg/kg PO twice daily with a fatty meal | PO | q12h | 2-4 weeks | 🌎 NA |
| Anticoagulant rodenticide toxicity (bleeding patient) | 2.5 mg/kg PO twice daily with a fatty meal | PO | q12h | minimum of 4 weeks | 🌎 NA |
| Anticoagulant rodenticide toxicity (symptomatic) | Loading dose of 2.5-5 mg/kg PO, then 3-5 mg/kg PO divided twice daily | PO | q12h | 14 days (1st gen) or at least 30 days (2nd gen/unknown) | 🌎 NA |
| Known 1st generation coumarin toxicity or vitamin K1 deficiency | initially 2.5 mg/kg s.c. in several sites, then 1-2.5 mg/kg in divided doses p.o. | SC/PO | q8-12h | 5-7 days | 🌍 EU |
| Known 2nd generation coumarin (brodifacoum) toxicity | initially 5 mg/kg s.c. in several sites, then 2.5 mg/kg p.o. | SC/PO | q12h | 3 weeks | 🌍 EU |
| Known inandione (diphacinone) or unknown anticoagulant toxicity | initially 2.5-5 mg/kg s.c. over several sites. Then 2.5 mg/kg p.o. divided | SC/PO | q8-12h | 3-4 weeks | 🌍 EU |
| Liver disease (pre-biopsy) | 0.5-1.0 mg/kg | SC | q12h | 1-2 days | 🌍 EU |
- Anticoagulant rodenticide toxicity (exposed but non-bleeding): Only give SC with starting dose if patient is vomiting or activated charcoal was administered.
- Anticoagulant rodenticide toxicity (bleeding patient): Plasma/blood transfusions are a necessity. Re-examine clotting times 2-3 days following cessation of therapy.
- Anticoagulant rodenticide toxicity (symptomatic): Check PT or PIVKA 48 hours after stopping therapy; if prolonged, continue for another week.
- Known 1st generation coumarin toxicity or vitamin K1 deficiency: Administer SC initially, followed by oral maintenance.
- Known 2nd generation coumarin (brodifacoum) toxicity: Restrict activity for 1 week post-treatment. Re-evaluate coagulation status 3 weeks after cessation of treatment.
- Known inandione (diphacinone) or unknown anticoagulant toxicity: Re-evaluate coagulation status 2 days after stopping therapy. If PT is elevated, continue therapy for 2 additional weeks. If normal, rest for 1 week.
- Liver disease (pre-biopsy): Re-evaluate coagulation time before biopsy. If minimal improvement, fresh frozen plasma may be required.
猫
| 適応 | 用量 | 経路 | 頻度 | 期間 | 地域 |
|---|---|---|---|---|---|
| Adjunctive therapy of acute liver failure | 1-5 mg/kg PO or SC q24h | PO, SC | q24h | — | 🌎 NA |
| Anticoagulant rodenticide toxicity (exposed but non-bleeding) | 1.25-2.5 mg/kg PO twice daily with a fatty meal | PO | q12h | 2-4 weeks | 🌎 NA |
| Anticoagulant rodenticide toxicity (bleeding patient) | 2.5 mg/kg PO twice daily with a fatty meal | PO | q12h | minimum of 4 weeks | 🌎 NA |
| Anticoagulant rodenticide toxicity (symptomatic) | Loading dose of 2.5-5 mg/kg PO, then 3-5 mg/kg PO divided twice daily | PO | q12h | 14 days (1st gen) or at least 30 days (2nd gen/unknown) | 🌎 NA |
| Known 1st generation coumarin toxicity or vitamin K1 deficiency | initially 2.5 mg/kg s.c. in several sites, then 1-2.5 mg/kg in divided doses p.o. | SC/PO | q8-12h | 5-7 days | 🌍 EU |
| Known 2nd generation coumarin (brodifacoum) toxicity | initially 5 mg/kg s.c. in several sites, then 2.5 mg/kg p.o. | SC/PO | q12h | 3 weeks | 🌍 EU |
| Known inandione (diphacinone) or unknown anticoagulant toxicity | initially 2.5-5 mg/kg s.c. over several sites. Then 2.5 mg/kg p.o. divided | SC/PO | q8-12h | 3-4 weeks | 🌍 EU |
| Liver disease (pre-biopsy) | 0.5-1.0 mg/kg | SC | q12h | 1-2 days | 🌍 EU |
- Known 1st generation coumarin toxicity or vitamin K1 deficiency: Administer SC initially, followed by oral maintenance.
- Known 2nd generation coumarin (brodifacoum) toxicity: Restrict activity for 1 week post-treatment. Re-evaluate coagulation status 3 weeks after cessation of treatment.
- Known inandione (diphacinone) or unknown anticoagulant toxicity: Re-evaluate coagulation status 2 days after stopping therapy. If PT is elevated, continue therapy for 2 additional weeks. If normal, rest for 1 week.
- Liver disease (pre-biopsy): Re-evaluate coagulation time before biopsy. If minimal improvement, fresh frozen plasma may be required.
小型哺乳類
| 適応 | 用量 | 経路 | 頻度 | 期間 | 地域 |
|---|---|---|---|---|---|
| Anticoagulant rodenticide toxicity | 5 mg/kg/day divided q8-12h | PO | q8-12h | — | 🌎 NA |
| Anticoagulant rodenticide toxicity (symptomatic) | Loading dose of 2.5-5 mg/kg PO, then 3-5 mg/kg PO divided twice daily | PO | q12h | 14-30 days | 🌎 NA |
- Anticoagulant rodenticide toxicity: Give with a fatty meal (e.g., peanut butter). Do not give IV; SC can cause anaphylaxis.
- Anticoagulant rodenticide toxicity (symptomatic): Treat pocket pets at the high end of this dosage range.
鳥
| 適応 | 用量 | 経路 | 頻度 | 期間 | 地域 |
|---|---|---|---|---|---|
| Hemorrhagic disorders | 0.25-0.5 mL/kg IM of the 10 mg/mL injectable product | IM | — | — | 🌎 NA |
| Hemorrhagic disorders | 0.2-2.5 mg/kg IM as needed | IM | as needed | usually only 1-2 injections required | 🌎 NA |
- Hemorrhagic disorders: Commonly used before surgery where hemorrhage is anticipated.
- Hemorrhagic disorders: May also be used prophylactically when amprolium and sulfas are administered.
馬
| 適応 | 用量 | 経路 | 頻度 | 期間 | 地域 |
|---|---|---|---|---|---|
| Warfarin (or related compounds) toxicity | 500 mg SC q4-6h | SC | q4-6h | Until OSPT returns to normal | 🌎 NA |
| Warfarin (or related compounds) toxicity | 0.5-2.5 mg/kg IM, if IV use is necessary dilute in saline or D5W/saline and give very slowly (not to exceed 5 mg/minute) | IM, IV | — | — | 🌎 NA |
- Warfarin (or related compounds) toxicity: Whole blood or fresh plasma may also be necessary early in treatment.
- Warfarin (or related compounds) toxicity: Avoid IV if possible.
牛
| 適応 | 用量 | 経路 | 頻度 | 期間 | 地域 |
|---|---|---|---|---|---|
| Anticoagulant rodenticide toxicity | Initially 0.5-2.5 mg/kg IV in D5W at a rate of 10 mg/minute. Subsequent doses may be given IM or SC. | IV, IM, SC | — | 3-4 weeks for second generation agents | 🌎 NA |
| Anticoagulant rodenticide toxicity | 0.5-2.5 mg/kg IM, if IV use is necessary dilute in saline or D5W/saline and give very slowly (not to exceed 5 mg/minute) | IM, IV | — | — | 🌎 NA |
| Acute hypoprothrombinemia with hemorrhage | 0.5-2.5 mg/kg IV, not to exceed 10 mg/minute in mature animals and 5 mg/minute in newborn and very young animals | IV | — | — | 🌎 NA |
| Non-acute hypoprothrombinemia | 0.5-2.5 mg/kg IM or SC | IM, SC | — | — | 🌎 NA |
| Sweet clover or lespedeza toxicity | 1-1.5 mg/kg SC for several days | SC | q24h | several days | 🌎 NA |
- Anticoagulant rodenticide toxicity: Avoid IV if possible.
- Sweet clover or lespedeza toxicity: Remove from source, avoid stress/injury.
豚
| 適応 | 用量 | 経路 | 頻度 | 期間 | 地域 |
|---|---|---|---|---|---|
| Warfarin (or related compounds) toxicity | 0.5-2.5 mg/kg IM, if IV use is necessary dilute in saline or D5W/saline and give very slowly (not to exceed 5 mg/minute) | IM, IV | — | — | 🌎 NA |
- Warfarin (or related compounds) toxicity: Avoid IV if possible.
羊
| 適応 | 用量 | 経路 | 頻度 | 期間 | 地域 |
|---|---|---|---|---|---|
| Warfarin (or related compounds) toxicity | 0.5-2.5 mg/kg IM, if IV use is necessary dilute in saline or D5W/saline and give very slowly (not to exceed 5 mg/minute) | IM, IV | — | — | 🌎 NA |
- Warfarin (or related compounds) toxicity: Avoid IV if possible.
ヤギ
| 適応 | 用量 | 経路 | 頻度 | 期間 | 地域 |
|---|---|---|---|---|---|
| Warfarin (or related compounds) toxicity | 0.5-2.5 mg/kg IM, if IV use is necessary dilute in saline or D5W/saline and give very slowly (not to exceed 5 mg/minute) | IM, IV | — | — | 🌎 NA |
- Warfarin (or related compounds) toxicity: Avoid IV if possible.
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
フィトナジオン（ビタミンK1）は、天然のビタミンK1と同一の合成脂溶性ビタミンです。獣医療において重要な解毒剤であり、主に抗凝固性殺鼠剤（ワルファリン、ブロディファクム、ブロマジオロンなど）の摂取による血液凝固障害を回復させるために使用されます。
主な臨床応用：
- 抗凝固性殺鼠剤中毒： 治療の要。第2世代の殺鼠剤は半減期が非常に長いため、多くの場合3〜4週間の継続的なビタミンK1の補充が必要です。
- スイートクローバー中毒： 反芻動物において、カビの生えたスイートクローバーによるジクマロール中毒の治療に使用されます。
- 肝疾患： ビタミンKの吸収や利用が障害される急性肝不全や胆道閉塞の補助療法として使用されます。
- スルファキノキサリン中毒： この抗コクシジウム薬に関連する出血性疾患を回復させます。
臨床のポイント： ビタミンK1（フィトナジオン）はこれらの中毒に有効ですが、ビタミンK3（メナジオン）は無効であり、毒性のリスクが高くなります。フィトナジオンが新しい凝固因子を合成するには6〜12時間かかります。したがって、活動性出血のある患者には、活性凝固因子を提供するために直ちに血漿または全血の輸血が必要です。
作用機序
Phytonadione is essential for the hepatic synthesis of Vitamin K-dependent coagulation factors (Factors II, VII, IX, and X).
- Mechanism: In the liver, inactive precursors of these factors require γ-carboxylation of their glutamic acid residues to become functional. This carboxylation is catalyzed by the enzyme γ-glutamyl carboxylase, which requires the reduced form of Vitamin K (Vitamin K hydroquinone) as a cofactor.
- The Vitamin K Cycle: During carboxylation, Vitamin K is oxidized to Vitamin K epoxide. The enzyme Vitamin K epoxide reductase (VKOR) recycles the epoxide back to the active hydroquinone form.
- Anticoagulant Rodenticides → inhibit VKOR, depleting active Vitamin K and halting the production of functional clotting factors. Exogenous phytonadione bypasses this blockade, providing the necessary substrate to resume factor synthesis.
安全性・警告
禁忌
- Known hypersensitivity to phytonadione or its components
- Hypoprothrombinemia due to hepatocellular damage (Vitamin K cannot correct this if the liver cannot synthesize the protein precursors)
- Intravenous administration (relative contraindication due to anaphylaxis risk)
- Known hypersensitivity to phytomenadione
- Intramuscular administration in severely coagulopathic patients (risk of severe hematoma)
有害事象
- Anaphylactoid reactions (especially following IV administration)
- Acute bleeding from the injection site (IM administration during early stages of treatment)
- Slow or poor absorption from SC or PO routes in hypovolemic patients
- Anaphylactic reactions (following IV administration)
- Haemolytic anaemia (in cats when overdosed)
- Anaphylaxis (primarily with IV administration)
- Injection site reactions (pain, swelling)
- Hematoma formation at injection sites (due to underlying coagulopathy)
注意事項
Intravenous Administration Warning: The FDA-CVM warns against administering phytonadione IV due to a significant risk of severe anaphylactoid reactions. If IV use is absolutely necessary (e.g., severe bleeding with very high INR in large animals), it must be diluted and given extremely slowly.
Injection Site Bleeding: IM injections can cause acute bleeding at the site in coagulopathic patients. Use small-gauge needles for SC or IM injections.
Delayed Onset: It takes 6-12 hours for new clotting factors to be synthesized. Emergency needs for clotting factors in actively bleeding patients MUST be met with blood products (fresh frozen plasma or whole blood).
Absorption: SC or PO doses may be poorly absorbed in hypovolemic animals. Oral absorption requires bile salts and is significantly enhanced (4-5x) by administering with a fatty meal.
医薬品相互作用
May decrease the numbers of Vitamin K-producing bacteria in the gut, though chronic therapy usually has no significant effect on phytonadione absorption.
Concomitant oral administration may reduce the GI absorption of oral Vitamin K.
Phytonadione directly antagonizes the anticoagulant effects of these drugs.
May prolong or enhance the effects of anticoagulants, thereby antagonizing some of the therapeutic effects of phytonadione.
Antagonizes the effects of vitamin K
Antagonizes the effects of vitamin K
Antagonizes the effects of vitamin K
Antagonizes the effects of vitamin K
Antagonizes the effects of vitamin K
Antagonizes the effects of vitamin K
Antagonizes the effects of vitamin K
Antagonizes the effects of vitamin K
Antagonizes the effects of vitamin K
Antagonizes the effects of vitamin K
Antagonizes the effects of vitamin K
May decrease gut flora production of vitamin K, though clinically minor when exogenous K1 is supplemented
May exacerbate bleeding tendencies through platelet inhibition
監視
- Clinical efficacy (resolution or lack of hemorrhage, pale mucous membranes, weakness)
- One-stage prothrombin time (OSPT / PT)
- Proteins Induced by Vitamin K Absence (PIVKA)
- International Normalized Ratio (INR)
- Prothrombin time (PT) is the best method of monitoring therapy
- Prothrombin Time (PT) - typically normalizes within 12-24 hours of starting therapy
- Activated Partial Thromboplastin Time (aPTT)
- PIVKA (Proteins Induced by Vitamin K Absence or Antagonism)
- Clinical signs of bleeding (mucous membranes, heart rate, respiratory rate)
薬物動態
半減期
吸収
Absorbed from the GI tract via intestinal lymphatics, requiring bile salts. Oral absorption is significantly enhanced (4-5 times in dogs) when administered with fatty foods. SC or PO doses may be poorly absorbed in hypovolemic animals.
分布
Concentrates in the liver for a short period but is not appreciably stored in the liver or other tissues. Small amounts cross the placenta. Enters maternal milk.
代謝
Rapidly metabolized in the liver to polar metabolites.
消失
The exact elimination pathways of Vitamin K1 are not completely understood, but metabolites are excreted in bile and urine.
過剰投与
Phytonadione is relatively non-toxic. It is highly unlikely that toxic clinical signs would result after a single overdosage. However, inappropriate routes of administration (like rapid IV injection) can cause severe anaphylactoid reactions regardless of the dose.
製品
製剤
- Oral capsules
- Oral chewable tablets
- Aqueous colloidal solution for injection
- Emulsion for injection
- Injectable: 10 mg/ml
- Oral: 50 mg tablets
- Nutraceuticals (containing small amounts)
- Injectable solution (10 mg/ml)
- Oral tablets (10 mg, 25 mg, 50 mg)
動物用医薬品
- Phytonadione Oral Capsules: 25 mg, 50 mg (K-Caps, Veda-K1, Veta-K1, Vitamin K1 Double Strength)
- Phytonadione Oral Tablets, Chewable: 25 mg, 50 mg (Vitamin K1 Chewable, K-Chews)
- Phytonadione Aqueous Colloidal Solution for Injection: 10 mg/mL (K-Ject, Veda-K1, Vita-Jec)
- Vitamine K1 Laboratoire TVM
- Konakion
- Vitamin K1 Injection (10 mg/ml)
- Vitamin K1 Tablets (10 mg, 50 mg)
ヒト用医薬品
- Phytonadione Oral Tablets: 5 mg (Mephyton)
- Phytonadione Injection, Emulsion: 2 mg/mL & 10 mg/mL
- Konakion (Phytomenadione) injection (10 mg/ml)
- Konakion tablets (10 mg)
規制ステータス
Widely approved across EU member states for veterinary use.
Available as authorized veterinary medicines.
規制データなし: 🇺🇸 US · 🇭🇰 HK · 🇹🇼 TW · 🇯🇵 JP · 🇰🇷 KR · 🇦🇺 AU
保管・安定性
Phytonadione is highly sensitive to light and must be protected from light at all times. Store tablets and capsules in well-closed, light-resistant containers. If used as an IV infusion, the container and tubing should be wrapped with an opaque material.
飼主向け情報
- スケジュールの厳守： 現代の殺鼠剤（第2世代殺鼠剤）は体内に非常に長く留まるため、指示された全期間（多くの場合3〜4週間）この薬を投与し続けることが極めて重要です。早期に中止すると、突然の生命を脅かす内出血を引き起こす可能性があります。
- 食事と一緒に与える： 経口ビタミンK1は、脂肪分の多い食事（缶詰のペットフード、少量のチーズ、ピーナッツバターなど）と一緒に与えることで、血中への吸収量が大幅に増加します。
- 運動制限： 治療中はペットを安静にし、厳密に制限してください（リードでの散歩のみ、ジャンプや激しい遊びは禁止）。これは、軽い衝突による打撲や内出血のリスクを最小限に抑えるためです。
- フォローアップ検査： 獣医師は通常、毒素が体から完全に排出されたことを確認するため、ビタミンK1の最後の投与から約48時間後にペットの血液凝固時間を再検査する必要があります。
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