アマンタジン塩酸塩
**アマンタジン**は、もともとA型インフルエンザの予防および治療のための抗ウイルス薬として開発されましたが、現代の獣医学では主に**NMDA（N-メチル-D-アスパラギン酸）受容体拮抗薬**としての特性が利用されています。 主な臨床応用は以下の通りです： * **補助的鎮痛**：主に犬や猫において、慢性疼痛、神経障害性疼痛、またはオピオイド耐性疼痛（重度の変形性関節症、骨肉腫など）の治療に使用されます。単独の鎮痛薬として有効であることは稀ですが、NSAIDs、オピオイド、またはガバペンチンと併用することで、中枢性感作（セントラルセンシタイゼーション）に対抗する優れた効果を発揮します。 * **馬インフルエンザ**：馬-2型インフルエンザウイルスに対して研究されていますが、高価であること、経口吸収のばらつき、静脈内投与による発作のリスクがあるため、臨床での使用は限られています。 > **臨床のポイント**：アマンタジンは、神経系が痛みのシグナルに対して過敏になる「ワインドアップ（wind-up）痛」（アロディニアや痛覚過敏）を治療するための重要なツールです。
作用機序: Amantadine has distinct mechanisms depending on the therapeutic target: * **Analgesia (NMDA Antagonism)**: Chronic pain causes excessive release of excitatory neurotransmitters (glutamate and aspartate). These bind to the **NMDA receptor** on postsynaptic neurons in the dorsal horn of the spinal cord. Amantadine acts as a non-competitive antagonist, blocking the open ion channel of the **NMDA receptor** → prevents calcium (Ca2+) influx → reduces central sensitization and "wind-up" pain. * **Antiviral**: Interferes with the **influenza A virus M2 transmembrane protein** → blocks the uncoating of the virus particle and prevents viral replication. * **Antiparkinsonian (Human)**: Potentiates dopaminergic neurotransmission in the CNS and exhibits mild anticholinergic activity.
動物種別の用量
- Osteoarthritis pain when NSAIDs alone are not effective · 3-5 mg/kg PO once daily in addition to an NSAID · PO · q24h · Meloxicam at approved doses was used for this study.
- Adjunctive therapy for chronic pain · 3-5 mg/kg PO once daily · PO · q24h
- To decrease wind-up · 3-5 mg/kg PO once daily for one week · PO · q24h · 1 week
- Analgesia (adjunct for chronic pain) · 3-5 mg/kg · PO · sid to bid · Chronic · Potentiates the effects of other analgesics. Often combined with NSAIDs.
- Adjunctive therapy for chronic pain · 3 mg/kg PO once daily · PO · q24h · May be useful addition to NSAIDs; has not been evaluated for toxicity. May need to be compounded.
- Adjunctive therapy for chronic pain · 3-5 mg/kg PO once daily · PO · q24h
- Adjunctive therapy for chronic pain · 3 mg/kg PO once daily · PO · q24h
- Analgesia (adjunct for chronic pain) · 3-5 mg/kg · PO · sid · Chronic · Liquid formulations may be bitter and difficult to administer.
- Acute treatment of equine-2 influenza · 5 mg/kg IV q4h · IV · q4h · Not commonly used due to expense, PK variability, and seizure risk.
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
- Known hypersensitivity to amantadine or rimantadine
- Untreated angle-closure glaucoma
- Extra-label use in chickens, turkeys, and ducks (Prohibited by FDA)
有害事象
- Agitation or restlessness (especially early in therapy)
- Loose stools, flatulence, or diarrhea
- Narrow safety margin in cats (potential for neurotoxicity)
- Seizures (reported in horses given IV)
薬物相互作用
- Anticholinergic drugs · May enhance the anticholinergic effects of amantadine.
- CNS Stimulants (e.g., selegiline) · Concomitant use may increase the CNS stimulatory effects of amantadine.
- Trimethoprim/sulfa, quinidine, quinine, thiazide diuretics, triamterene · May decrease the renal excretion of amantadine, yielding higher and potentially toxic blood levels.
- Urinary acidifiers (e.g., methionine, ammonium chloride, ascorbic acid) · May increase the renal excretion of amantadine, potentially decreasing its efficacy.
- Trimethoprim/Sulfamethoxazole · Decreased renal clearance of amantadine, potentially leading to toxicity · moderate
- Anticholinergics · Increased anticholinergic side effects (e.g., dry mouth, urine retention) · minor
- CNS stimulants · Increased risk of agitation, restlessness, or seizures · moderate
モニタリング
- Adverse effects (especially GI upset and agitation/behavioral changes)
- Clinical efficacy (reduction in pain scores, improved mobility)
過量投与
Overdoses are potentially very serious due to a fairly narrow therapeutic index. * **Cats**: Toxic dose reported is 30 mg/kg. Behavioral effects may be noted at 15 mg/kg. * **Dogs**: Behavioral effects noted at 15 mg/kg. * **Humans**: Overdoses as low as 2 grams have been fatal. Signs include cardiac dysfunction (arrhythmias, hypertension, tachycardia), pulmonary edema, CNS toxicity (tremors, seizures, psychosis, agitation, coma), hyperthermia, and renal dysfunction. **Treatment**: No specific antidote. Empty the gut if possible. Provide intensive monitoring and supportive therapy. Forced urine acidifying diuresis may increase renal excretion. Physostigmine has been suggested for cautious use in treating CNS effects.
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。