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Published byPearl Ferguson Modified over 8 years ago
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Veterinary Specialists of South Florida Presents:
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Outline Clinical Case Summary Definition Etiology and Pathophysiology Epidemiology Clinical Presentation Diagnosis Treatment/Prognosis
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Chook 4 yo FS Australian Shepherd 8 AM Owner dewormed horses with 2% Ivermectin Paste 10 AM Chook was normal when owner left the house 12 PM Daughter found Chook wobbly and stumbling around
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Chook - Presentation Alert and hyper-responsive MM – pink & moist, CRT < 2 seconds Temp = 102.4 F HR = 200, RR = pant Absent menace and PLR’s bilaterally Mydriasis
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Chook - Diagnosis Ivermectin Toxicity ○ History of exposure ○ Breed susceptibility ○ Physical exam findings
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Chook - Treatment IV catheter placed IV fluids started Owner decline further treatment
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Ivermectin Toxicity - Definition Ivermectin toxicity A clinical syndrome that is used to describe an exposure to the macrocyclic lactone antiparasitic drug ivermectin Other drugs Milbemycin, moxidectin, selamectin, doramectin, eprinomectin, abamectin
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Etiology & Pathophysiology Enhance the release of GABA (inhibitory neurotransmitter) Parasites GABA mediated neurons present throughout PNS -> enhanced GABA release -> paralysis Mammals GABA mediated neurons restricted to CNS & BBB excludes the drug at therapeutic dosages Overdose With overdosages, or animals with a defect in the BBB, drug enters the CNS and causes an inhibitory effect -> CNS depression
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Epidemiology Young animals More likely in dogs, but cats can show clinical signs as well Genetics and Breed predispositions Risk Factors LA formulations for SA CNS disease or BBB disruption
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Genetics & Breed Predispositions MDR-1 gene mutation Autosomal recessive trait Defect in the P- glycoprotein multidrug transporter in the BBB Defect allows Ivermectin to pass into the CNS at even low doses, causing toxicosis
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Breeds Affected www.vetmed.wsu.edu/depts-vcpl/breeds.aspx
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Ivermectin Dosages Heartworm prevention 0.006 mg/kg PO q 30 days Off-label use Dosage range from 0.05-0.3 mg/kg PO/SQ Most dogs tolerate up to 2.5 mg/kg PO LD 50 in Beagles = 80 mg/kg In MDR-1 gene mutation dogs Up to 0.1 mg/kg (16X label dose)
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Clinical Presentation History Exposure to ivermectin containing compounds Presenting Complaint Depression, disorientation, vocalization, stupor, ataxia, tremors, vomiting, anorexia, recumbency, blindness, coma, seizure, death
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Clinical Presentation Physical Exam Findings Mydriasis +/- blindness CNS depression Ataxia Disorientation Hypersalivation Tremors +/- bradycardia, vomiting, seizures Hypothermia or hyperthermia
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Differential Diagnosis Other intoxications Brain neoplasia Encephalitis Hepatic encephalopathy Blue-green algae Hypoglycemia Hypocalcemia Phenobarbital toxicity
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Initial Database Neurological examination No specific clinical pathologic alterations expected Baseline CBC/Chem/UA Bile acids +/- thoracic/abdominal imaging
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Advanced Testing Physostigmine 1 mg/40 lbs or 0.06 mg/kg IV Supports diagnosis -> not confirmatory Not generally recommended Ivermectin sensitivity testing Tests for the presence of the MDR-1 gene mutation WSU Other Liver, adipose tissue, brain or serum levels
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Treatment - Goals Manage life-threatening situations Supportive care Decrease absorption/enhance elimination Nursing care – comatose patients
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Treatment - Immediate Induce emesis Recent ingestion No signs of respiratory distress, comatose state Gastric lavage Control airway and respiration Activated charcoal Orogastric/nasogastric intubation
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Treatment – Supportive Care Manage seizures Continue activated charcoal administration Fluid therapy/Electrolyte balance Manage comatose patients Supportive care is the mainstay of treatment
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Prognosis Largely dependent on Dose Relative individual sensitivity Provision of supportive care May require supportive care for one day, several days, or even several weeks Even those in a coma, or a seemingly hopeless case, can have a full recovery
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References Cote, Etienne. Interceptor toxicity. Cote Clinical Veterinary Advisor pp 610-611, Copyright © 2009 Elsevier Inc. Dowling P. Pharmacogenetics: It’s not just about ivermectin in collies. Clinical Pharmacology Update; 47: 1165-1169, 2006. Edwards G. Ivermectin: does P-glycoprotein play a role in neurotoxicity? Filaria Journal, 2:58, 2003. Hopper K, Aldrich J, Haskins SC. Ivermectin Toxicity in 17 Collies. J Vet Intern Med; 16:89-94, 2002. Mealey KL, Northrup NC, Bentjen SA. Increased toxicity of P-glycoprotein- substrate chemotherapeutic agents in a dog with MDR1 deletion mutation associated with ivermectin sensitivity. J Am Vet Med; 223(10):1453-5, 1434, 2003.. Merola V, Khan S, Gwaltney-Brant S. Ivermectin Toxicosis in Dogs: A Retrospective Study. J Am Anim Hosp Assoc. 45:106-111, 2009. Paul AJ, Tranquilli WJ. Ivermectin. Kirk RW, editor: Current veterinary therapy X, Philadelphia, 1989, WB Saunders. Peterson, Michael E.; Talcott, Patricia A. Small Animal Toxicology, 2 nd Edition. Elsevier, Missouri, 2006, pp 785-93. Plumb, Donald C. Plumb’s Veterinary Drug Handbook, 5 th Edition. Blackwell Publishing, 2005, pp 763-4. Shell, L. Ivermectin. VIN database, 2006. Veterinary Clinical Pharmacology Laboratory. Affected Breeds. Washington State University. 2010.
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Thank you for your continued support and referrals.
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