メラルソミン
メラルソミン（Melarsomine）は、犬糸状虫（*Dirofilaria immitis*）の成虫駆除に特化して使用される有機ヒ素系化学療法剤です。成熟した成虫および未成熟（生後4ヶ月、L5期）の幼虫に対して高い有効性を示します。 **臨床上のポイント**：メラルソミンは唯一承認されている成虫駆除薬ですが、現在の米国犬糸状虫学会（AHS）のガイドラインでは、マルチモーダルなアプローチが強く推奨されています。メラルソミン投与の1〜2ヶ月前から、マクロライド系薬剤（イベルメクチンなど）と**ドキシサイクリン**による前治療を行うことが推奨されます。ドキシサイクリンは、糸状虫の生存と繁殖に不可欠な共生細菌（*Wolbachia*）を排除し、糸状虫を弱体化させ、虫体のバイオマスを減少させることで、虫体死滅時の炎症反応や重篤な肺血栓塞栓症のリスクを大幅に低下させます。 メラルソミンは以前の薬剤であるチアセタルサミドよりも安全で有効ですが、依然として安全域が狭く、正確な用量計算と投与技術が必要です。
作用機序: While the exact mechanism of action is not definitively established, as an arsenical compound, melarsomine is believed to exert its parasiticidal effect by binding to **sulfhydryl (-SH) groups** of essential enzymes within the parasite. * **Enzyme Inhibition** → Disrupts cellular respiration and vital metabolic pathways in the parasite. * **Target** → Highly effective (90-99%) at killing adult and L5 larval stages of *D. immitis* in dogs. * **Clearance** → Dead worms degrade and are swept into the pulmonary vasculature, where they are eventually cleared by the host's immune system (macrophages).
動物種別の用量
- Heartworm disease (Class I & II) · 2.5 mg/kg deep IM as directed (lumbar epaxial muscles (L3-L5) twice 24 hours apart · IM · q24h for 2 doses · 2 days · Use alternating sides with each administration. In 4 months, the regimen may be repeated.
- Heartworm disease (Class III) · 2.5 mg/kg deep IM as directed (lumbar epaxial muscles (L3-L5). Strict rest and give all necessary systemic treatment. One month later, give 2.5 mg/kg deep IM as directed (lumbar epaxial muscles (L3-L5) twice 24 hours apart. · IM · Once, then q24h for 2 doses 1 month later · 1 month + 2 days · Requires strict rest.
- Heartworm disease (Alternative Protocol / AHS Treatment of Choice) · 2.5 mg/kg deep IM as directed (lumbar epaxial muscles; L3-L5). Strict rest and give all necessary systemic treatment. One month later, give 2.5 mg/kg deep IM as directed (lumbar epaxial muscles; L3-L5) twice 24 hours apart · IM · Once, then q24h for 2 doses 1 month later · 1 month + 2 days · Treatment of choice regardless of stage of disease due to increased safety and efficacy.
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
- Class IV (very severe) heartworm disease / Caval syndrome
- Cats (reportedly very toxic)
- Intravenous (IV) administration
- Subcutaneous (SC) administration
有害事象
- Injection site reactions (pain, swelling, tenderness, firm nodules)
- Coughing/gagging
- Depression/lethargy
- Anorexia/inappetence
- Excessive salivation
- Fever
- Lung congestion
- Vomiting
- Pulmonary thromboembolism (can be fatal)
- Paresis and paralysis (rare)
薬物相互作用
- Aspirin · Has been shown not to reduce adverse effects and may complicate therapy; use is not recommended.
- CNS Depressant Drugs · Drugs that have similar adverse effects (e.g., depression) may cause additive adverse effects or increase their incidence when used with melarsomine.
モニタリング
- Clinical efficacy
- Adverse effects (observe dogs for 24 hours after the last injection)
- Signs of pulmonary thromboembolism (coughing, hemoptysis, tachypnea, dyspnea)
- Injection site reactions
過量投与
There is a **low margin of safety** with melarsomine. * **3X dose (7.5 mg/kg)** in healthy dogs causes respiratory inflammation and distress, excessive salivation, restlessness, panting, vomiting, edema, tremors, lethargy, ataxia, cyanosis, stupor, and death. * **2X dose** in infected dogs has caused diarrhea, excessive salivation, restlessness, panting, vomiting, and fever. * **Treatment**: Dimercaprol (BAL in Oil) may be considered to treat melarsomine overdoses, though it may reduce the clinical efficacy of the melarsomine.
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。