アセトアミノフェン (パラセタモール)
アセトアミノフェンは、軽度から中等度の痛みや発熱を抑えるために使用される中枢性鎮痛解熱薬です。従来のNSAIDsと比較して抗炎症作用は弱いですが、胃腸への副作用が少ないと考えられており、胃潰瘍のある患者にとって有用な代替薬となります。注射用アセトアミノフェンは、犬の周術期における補助的な鎮痛にも使用されます。 > **重大な警告：** 猫は本薬を安全に代謝するための酵素を欠いており、致命的な中毒を引き起こすため、猫への投与は**絶対に禁忌**です。 **臨床のポイント：** 認可された獣医用経口製剤（Pardale-V）にはコデインが含まれていますが、犬ではオピオイドの初回通過効果が高いため、コデイン成分のバイオアベイラビリティは低く、鎮痛にはほとんど寄与しません。
作用機序: The exact mechanism of action remains partially unclear. It is proposed that its antipyretic and analgesic actions are due to: - Decreased **prostaglandin synthesis** specifically within the central nervous system (CNS). - Possible indirect actions on the **cannabinoid system**. Unlike traditional NSAIDs, it has minimal peripheral cyclooxygenase (COX) inhibition, which explains its lack of significant anti-inflammatory activity and reduced gastrointestinal toxicity.
動物種別の用量
- Mild to moderate pain / Antipyretic · 10-20 mg/kg · PO/IV · q8h · 5-7 days (for acute pain) · For acute pain management, doses at the top of the range (20 mg/kg) can be used for up to 5-7 days.
- Mild to moderate pain (Pardale-V preparation) · 1 tablet per 12 kg body weight (equivalent to 33 mg/kg) · PO · q8h · Max 7 days before titrating down · Authorized dose for Pardale-V. After 7 days, titrate down to the lowest effective dose. Codeine component is not bioavailable.
- All indications · Do not use · PO/IV · N/A · N/A · Absolute contraindication. Fatal toxicosis due to methaemoglobinaemia.
用量は獣医療従事者向けの臨床リファレンスです。必ず最新の添付文書と個々の患者で確認してください。
投与経路
禁忌
- Cats (absolute contraindication due to fatal toxicosis)
- Patients with pre-existing severe hepatic impairment
有害事象
- Hepatotoxicity (dose-dependent)
- Methaemoglobinaemia (especially in cats)
- Facial edema
- Cyanosis
薬物相互作用
- Metoclopramide · Enhances the absorption of paracetamol, thereby enhancing its clinical and potentially toxic effects. · moderate
- Cytochrome P450 Inducers (e.g., Phenobarbital, certain NSAIDs) · May increase the production of toxic metabolites (NAPQI), enhancing the risk of hepatotoxicity. · major
モニタリング
- Liver enzyme panel (ALT, AST, ALP, Bilirubin) if prolonged use or overdose is suspected
- Clinical signs of toxicity (jaundice, vomiting, lethargy)
- Mucous membrane color (monitoring for cyanosis/brown blood indicative of methaemoglobinaemia)
過量投与
Overdose of paracetamol causes severe liver damage. Metabolism produces the toxic intermediate **N-acetyl-p-aminobenzoquinonimine (NAPQI)**, which depletes hepatic glutathione, leading to hepatocyte cell death and centrilobular hepatic necrosis. In cats, it causes fatal methaemoglobinaemia. **Treatment:** - Decontamination (emesis/activated charcoal) if ingestion is recent. - **Antidote:** Oral **methionine** or IV **acetylcysteine (N-acetylcysteine)**. These are directed at replenishing hepatic glutathione stores to neutralize NAPQI, though clinical data in veterinary species is limited. - Supportive care (IV fluids, oxygen therapy, blood transfusions if severe methaemoglobinaemia occurs).
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。