moxidectin and Coma

Moxidectin is a macrolide endectocide available as a 2% equine oral gel in the US. This report presents clinical signs of moxidectin toxicosis and its treatment in equines as reported to the ASPCA Animal Poison Control Center (APCC) from January 1998 to December 2000. Nine cases of moxidectin overdose in equines occurred: 5 had signs of toxicosis such as coma, dyspnea, depression, ataxia, tremors, seizures, or weakness. The approximate dose of moxidectin at which these signs were observed ranged from 1.0 to 5.1 mg/kg. The 4 equines that ingested moxidectin between 0.9 mg/kg to 1.7 mg/kg did not show signs of toxicosis. Clinical signs were seen within 6-22 h and lasted for 36-168 h. Only 1/5 clinical equines was an adult, the others were < 4 month of age. This study supports earlier report that young foals are more susceptible to moxidectin toxicosis. All 4 equines with known outcomes recovered with treatment that included decontamination, seizure control, thermoregulation, fluid therapy, and supportive care.

Topics: Animals; Animals, Newborn; Anti-Bacterial Agents; Antinematodal Agents; Coma; Drug Overdose; Dyspnea; Female; Horse Diseases; Horses; Macrolides; Male; Retrospective Studies; Risk Factors; Seizures

Outcome and complications associated with administration of moxidectin gel to 3 foals < 4 months old are described. Two foals became comatose but survived following supportive treatment. One foal died following loss of consciousness associated with moxidectin administration. Risk of moxidectin overdose exists, because horse owners often fail to read or comprehend the package insert instructions pertaining to use of the syringe-locking mechanism. In addition, moxidectin should not be administered to foals < 4 months old, because it is likely that treated foals will become comatose.

Topics: Administration, Oral; Animals; Animals, Newborn; Anthelmintics; Anti-Bacterial Agents; Coma; Drug Overdose; Fatal Outcome; Female; Gels; Horse Diseases; Horses; Macrolides; Male; Nonprescription Drugs

A 2 day old foal was presented with central nervous depression (coma) after moxidectin overdose. Moxidectin belongs to the milbemycin anthelmintics which elicit their working mechanism through a GABA (gamma-aminobutyric acid)-stimulatory mode of action. The foal developed profound hypothermia, bradycardia and hypoventilation. Absence of urine voiding and mild abdominal distension suggested a ruptured bladder, which was confirmed by transabdominal ultrasound and clinical-pathologic parameters. Repeat auscultation of the ventral lung parts and the occurrence of gastric reflux were suggestive of an aspiration pneumonia. The foal underwent surgical bladder repair, however, did succumb due to mixed acidosis and early signs of sepsis postoperatively. The findings in this foal are suggestive for moxidectin overdosing. The GABAergic working mechanism of moxidectin does explain the development of profound central nervous depression and its sequels hypothermia, bradycardia, hypoventilation and paralytic ileus. Dyssynergia was unexpected, however, has to be related to a central nervous problem, rather than a peripheral nervous problem.

Topics: Animals; Animals, Newborn; Anthelmintics; Anti-Bacterial Agents; Coma; Drug Overdose; Fatal Outcome; Female; Horse Diseases; Horses; Macrolides