Ivermectin toxicity in German shepherd cross breed dog, A case study

Ivermectin toxicity in German shepherd cross breed dog,   A case study

Ganesh Ranabhat (AFU, 8^th sem)

Overview

It is a prototypic avermectin drug used in a variety of species as antiparasiticide. It is a mixture of 80% or more of an analog of avermectin B1a and 20% or less of an analog of avermectin B1b. Avermectin have no antibacterial or antifungal activity. These compound are produced by the actinomycete Streptomyces avermitis. In dog and cat ivermectin is approved only for use as a control for heartworm. It has also been used as a microfilaricide, ectoparasite and endoparasite.

Ivermectin can interact with other medication, vitamin or herbs. This can be harmful or prevent the drugs from working well. Toxicity can occur if dog is given an excessive dose of the medication( 10-20 times) the recommended dose. Additionally certain dogs are genetically hypersensitive to the medication. In these dogs ivermectin can pass directly to the brain and be the toxic or even lethal.

A genetic sensitivity to the ivermectin be seen in several breed most commonly Collie, Australian shepherd, German shepherd etc. The median lethal dose (LD50) of ivermectin for beagle dogs has been reported to be about 80mg/kg and the highest single oral dose without and adverse clinical effect was 2mg/kg.

History and clinical observation

A German shepherd cross male dog 14 month old weighing 14.5 kg was taken to the district livestock office Tanahun in 2077-2-29. Shyam sundar paudel came for the treatment with the complaint of vomiting, lethargy, ataxia, disorientation, tremors, seizure, dilation of pupils. The dog was treated for tick infestation.

The dog was injected 4 ml of Ivermectin IM 18 hours before to treat ectoparasite. After a certain hour animal became restless and exhibit clinical sign like hypothermia, mydriasis, incordination, grinding the teeth, circling movement, seizures. Blood chemistry parameter were normal ( table1). On the basis of  anamnesis and clinical observation  the case was diagnosed as a ivermectin toxicity.

Treatment and discussion

Toxicity cannot be reversed with the medication. There is no specific antidote for ivermectin toxicity. The treatment protocal for it is only managemental care, nursing, supportive therapy and symptomatic treatment. The dog was treated with neostigmine@0.05mg/kg BW S/C repeated 6 hourly , dexamethasone@0.25-0.5mg/kg BW IM BID and optineuron@1 ml total dose with infusion of 200ml dextrose(5%) IV and atropine sulphate@0.02-0.04mg/kg BW IV. The dog recovered after 2 days of regular treatment.

  Collie breed of dog are must susceptible to ivermectin. It may exhibit a  shock like reaction. Neurotoxicity possible mostly in collie( those with gene defict ; deletion mutation of motor 1 gene). Ivermectin is actively transported by the p-glycoprotein pump. Due to autosomal recessive trait (MDR-1) gene that cause a defict in p-glycoprotein leads to increase the permeability of blood brain barrier to the drug and this allow passage of ivermectin to the brain at low dosage thus causing toxicity. In our case, the animal was young and the blood brain barrier might not have been fully developed leading to toxicity. If we had not treat it timely it may collapse. Unfortunately, ivermectin toxicity cannot be reversed therefore, it is wise to treat the symptom to the best as we can.

Table1. showing normal blood chemistry profile of dog affected with ivermectin toxicity.

Parameter	Day 0	Reference value
RBC(×1O3/µL)	5.6	5.5-8.5
WBC(×103/µL)	6	6-17
PCV(%)	39	37-55
Haemoglobin(g/dl)	12.8	12-18
Monocyte(%)	5	3-10
Neutrophil(%)	75	60-76
Basophil (%)	3	0-11
Eosinophill(%)	2	2-10
Lymphocyte(%)	28	12-36
Albumin(g/dl)	2.8	2.6-4
Globulin(g/dl)	2.6	2.6-3.6
Creatinine(mg/dl)	0.6	0.5-1.5
BUN(mg/dl)	26	18.5-55.4

      

Phyostigmine is an anticholinesterase drug can be used for the improvement of clinical sign. Management can be overcome by kept in mind about the drug interaction to it. Ivermectin is photolabile so should be ptotect from light so store ivermectin product at room temperature.