ヘパリン (未分画)
ヘパリンは獣医療において血栓塞栓症の予防および治療、静脈カテーテルの開存性維持に使用される未分画の注射用抗凝固薬です。その効果を発揮するためには、内因性のアンチトロンビンIII（AT III）の存在に依存します。 > **臨床上の警告：** ヘパリンは出血の重大なリスクを伴います。既存の血栓を溶解することはできませんが、その拡大を防ぎます。 **臨床のポイント：** ヘパリンが機能するためにはAT IIIが必要であるため、重度の蛋白漏出性腎症や腸症などでAT IIIが枯渇している患者では効果がない場合があります。
作用機序: Heparin exerts its effects primarily by enhancing the binding of **antithrombin III (AT III)** to **factors IIa, IXa, Xa, XIa and XlIa**. * **AT III/clotting factor complex** formation → subsequent removal by the liver. * Inactivates **thrombin** → blocks the conversion of **fibrinogen** to **fibrin**. * Inhibition of **Factor XII** activation → prevents the formation of stable fibrin clots. > **Note:** Heparin is only effective if adequate AT III is present. It does not significantly change the concentrations of clotting factors, nor does it lyse pre-existing clots.
投与経路
禁忌
- Active bleeding or severe bleeding disorders
- Severe thrombocytopenia
- Recent neurosurgery or ocular surgery
- Known hypersensitivity to heparin
有害事象
- Hemorrhage (most common)
- Heparin-induced thrombocytopenia (HIT)
- Injection site reactions (hematoma, pain)
- Hypersensitivity reactions
薬物相互作用
- Aspirin · Increased risk of bleeding due to platelet inhibition · major
- NSAIDs · Increased risk of gastrointestinal ulceration and bleeding · major
- Warfarin · Synergistic anticoagulant effect; increased bleeding risk · major
- Clopidogrel · Increased risk of bleeding · major
モニタリング
- aPTT (Activated Partial Thromboplastin Time) - typically target 1.5 to 2.5 times baseline
- Platelet count
- Packed Cell Volume (PCV) and Total Protein (TP)
- Clinical signs of bleeding (mucous membranes, feces, urine)
過量投与
The primary sign of overdosage is **hemorrhage** (e.g., epistaxis, hematuria, melena, petechiae). * **Mild to moderate overdose:** Discontinue heparin therapy; due to its short half-life, coagulation parameters often normalize quickly. * **Severe, life-threatening hemorrhage:** Administer **protamine sulfate** as a specific reversal agent (antidote). Administer slowly IV to avoid hypotension and anaphylactoid reactions.
VetSheet の薬剤リファレンスは、獣医療従事者向けの臨床意思決定支援を目的としており、専門的判断やメーカーの最新添付文書に代わるものではありません。