ダントロレンナトリウム
ダントロレンナトリウムは、ユニークな直接作用型の**骨格筋弛緩薬**です。中枢性筋弛緩薬（メトカルバモールやジアゼパムなど）とは異なり、末梢の筋線維に直接作用します。 獣医療における主な適応症は以下の通りです： * **悪性高熱症（MH）：** 特に豚や犬における悪性高熱症および豚ストレス症候群の救命薬。 * **馬の筋疾患：** 馬の**労作性横紋筋融解症**（タイイングアップ）や**麻酔後筋炎（PAM）**の予防および治療に広く使用されます。 * **小動物の泌尿器科：** 犬や猫の外尿道括約筋の緊張を低下させることによる**機能性尿道閉塞**の管理に頻繁に利用されます。 * **毒素咬傷：** 大量のセチルコリン放出と重度の筋肉の痙攣を引き起こす**クロゴケグモ咬傷**の補助治療として推奨されます。 **臨床のポイント：** 注射剤は非常に高価であり、溶解後の使用期限が短いため、通常は重度で急性の危機（MHなど）に限定して使用され、経口剤は慢性的な管理や予防に使用されます。
作用機序: Dantrolene acts intracellularly to uncouple the excitation-contraction process in skeletal muscle. * It binds specifically to the **ryanodine receptor (RyR1)** located on the **sarcoplasmic reticulum (SR)**. * This binding **blocks the release of calcium (Ca²⁺)** from the SR into the myoplasm. * Decreased intracellular calcium → prevents the interaction of actin and myosin → produces **skeletal muscle relaxation**. Because it specifically targets the RyR1 isoform (found primarily in skeletal muscle) rather than RyR2 (cardiac muscle), it has minimal direct effects on cardiac or smooth muscle at standard therapeutic doses. The exact mechanism for its mild CNS effects (drowsiness, dizziness) remains poorly understood.
動物種別の用量
- Treatment of functional urethral obstruction due to increased external urethral tone · 0.5-2 mg/kg PO q12h OR 0.5-1 mg/kg IV · PO/IV · q12h · IV product very expensive.
- Treatment of functional urethral obstruction due to increased external urethral tone · 0.5-2 mg/kg PO three times daily · PO · TID
- Treatment of functional urethral obstruction due to increased external urethral tone · 2-10 mg (total dose) PO three times daily · PO · TID · Given with either prazosin (0.5 mg/cat once to twice daily) or phenoxybenzamine (2.5-7.5 mg/cat once to twice daily).
- Treatment of functional urethral obstruction due to increased external urethral tone · 0.5-1 mg/kg PO q12h · PO · q12h
- Treatment of acute rhabdomyolysis · 15-25 mg/kg slow IV four times daily · IV · QID
- Treatment of acute rhabdomyolysis · 2-4 mg/kg PO via nasogastric tube once daily · PO · SID
- Prevention of recurrent exertional rhabdomyolysis in Thoroughbreds · 4 mg/kg PO in horses fasted (12-hour fast in study) prior to administration. · PO · Once
- Prevention of rhabdomyolysis · 2 mg/kg PO once daily for 3-5 days and then every 3rd day for a month · PO · SID then q3d · 1 month · Drug is diluted in normal saline and given via stomach tube. Monitor hepatic function.
- Prevention of rhabdomyolysis · 300 mg (total dose) PO once daily · PO · SID · May be preferable because the drug is hepatotoxic.
投与経路
禁忌
- Preexisting liver disease (use with extreme caution)
- Severe cardiac dysfunction (use with caution)
- Pulmonary disease (use with caution)
有害事象
- Weakness
- Sedation
- Dizziness
- Headache
- Nausea
- Vomiting
- Constipation
- Increased urinary frequency
- Hypotension
- Hepatotoxicity (especially with chronic use)
薬物相互作用
- Benzodiazepines & other CNS depressants · Increased sedation may be seen if tranquilizing agents are used concomitantly.
- Calcium-Channel Blockers · Rare reports of cardiovascular collapse in humans; concomitant use during malignant hyperthermia crises is not recommended. · major
- Estrogens · Increased risks of hepatotoxicity have been seen in women >35 years of age; veterinary significance is unknown.
- Warfarin · Dantrolene may be displaced from plasma proteins by warfarin, resulting in increased effects or adverse reactions.
モニタリング
- Baseline and periodic liver function tests (ALT, AST, Alk Phos, etc.) if projecting to be used chronically or using high dosages
- Body temperature (especially for malignant hyperthermia)
- Urine volume, frequency, continence
過量投与
There is no specific antidotal therapy for dantrolene overdoses. * **Decontamination:** Remove the drug from the gut if possible (e.g., emesis induction, activated charcoal) if exposure was recent and oral. * **Supportive Care:** Treat supportively, monitoring respiratory, cardiovascular, and hepatic function.
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。