Suspected melarsomine myositis highlights heartworm treatment risks

Melarsomine, the standard adulticide used in canine heartworm treatment, remains the recommended therapy because it clears adult worms quickly, but a new Today’s Veterinary Nurse case report highlights how severe local complications can be when post-injection inflammation extends beyond the expected soreness and swelling. FDA labeling for melarsomine notes that about 30% of treated dogs have some kind of injection-site reaction, including pain, swelling, tenderness, and reluctance to move, while the American Heartworm Society says proper deep injection into the epaxial muscles is critical because placement in the wrong tissue plane can lead to significant lameness, sterile abscess formation, or worse. Published literature has also described rare but serious sequelae, including extensive epaxial myositis, epidural steatitis, neurologic injury, and other severe post-treatment complications. (dailymed.nlm.nih.gov)

Why it matters: For veterinary professionals, this case is a reminder that melarsomine’s benefits still usually outweigh its risks, but injection technique, pain assessment, and follow-up monitoring matter. Today’s Veterinary Nurse has previously emphasized that veterinary nurses are often the first to detect adverse reactions after melarsomine, including respiratory changes, vomiting, diarrhea, and injection-site problems, and that they play a central role in documenting changes, escalating concerns, and coaching pet parents on strict exercise restriction and warning signs after treatment. (todaysveterinarynurse.com)

What to watch: Expect continued attention on injection technique, post-treatment monitoring, and whether more practices adopt added safeguards, such as closer follow-up or imaging-guided approaches in select cases, to reduce rare but severe melarsomine complications. (journals.sagepub.com)