Melarsomine
Melarsomine is an organic arsenical chemotherapeutic agent used exclusively as an adulticide for canine heartworm disease (*Dirofilaria immitis*). It is highly effective against mature adult worms and immature (4-month-old, stage L5) larvae. **Clinical Pearl**: While melarsomine is the only approved adulticide, current American Heartworm Society (AHS) guidelines strongly recommend a multimodal approach. Pre-treatment with a macrocyclic lactone (e.g., ivermectin) and **doxycycline** for 1-2 months prior to melarsomine administration is advised. Doxycycline eliminates *Wolbachia* (a symbiotic bacterium essential to the heartworm's survival and reproduction), which weakens the worms, reduces worm biomass, and significantly decreases the inflammatory response and risk of severe pulmonary thromboembolism when the worms die. Melarsomine is significantly safer and more efficacious than its predecessor, thiacetarsamide, but still carries a narrow margin of safety and requires precise dosing and administration techniques.
Mecanismo: 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).
Dosificación por especie
- 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.
Las dosis son una referencia clínica para veterinarios colegiados. Confirme siempre con la ficha técnica vigente y el paciente individual.
Vías de administración
Contraindicaciones
- Class IV (very severe) heartworm disease / Caval syndrome
- Cats (reportedly very toxic)
- Intravenous (IV) administration
- Subcutaneous (SC) administration
Efectos adversos
- 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)
Interacciones farmacológicas
- 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.
Monitorización
- Clinical efficacy
- Adverse effects (observe dogs for 24 hours after the last injection)
- Signs of pulmonary thromboembolism (coughing, hemoptysis, tachypnea, dyspnea)
- Injection site reactions
Sobredosis
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.
La referencia de fármacos de VetSheet está destinada a veterinarios colegiados como apoyo a la decisión clínica, no sustituye el juicio profesional ni la ficha técnica vigente del fabricante.