Adverse Effects of Ivermectin in Dogs
Parasites in dogs are a concern that ranges from mild irritation to serious illness. These parasites may range from ectoparasites like fleas, ticks, mites to the endoparasites that include hookworms, ringworms, roundworms, whipworms and tapeworms. Management of these parasites is a mandatory part of the love of a pet owner to his pet, so as to ensure a better quality of life of the pet and maintain the obligatory safety of the owner himself. Management of dog parasites involves a periodic use of endoparacisitiside antihelminthics; praziquantal, albendazole and ectoparacisitisides namely amitraz, allethrin, indoxacarb and fipronil. Since dogs are simultaneously affected by both internal and external parasites, these agents are almost always used at same time.
Ivermectin is a endectocide that is effective against all external and internal parasites, except trematodes and cestodes. This semi-synthetic macrocyclic lactone obtained first from Streptomyces avermitilis mimics inhibitory neurotransmitter, γ-aminobutyric acid (GABA), which leads to ataxia, paralysis and death of the parasites. Due of its broad spectrum nematicidal, insecticidal, and acaricidal properties, it is a drug of choice that has been approved for prophylactic use against heartworm in dogs.
Ivermectin is relatively safe for mammals since the GABA mediated neurotransmission occurs in central nervous system which is protected by a highly stringent blood brain barrier that prevents ivermectin uptake into brain. However, poisonings have been reported due to over dosage of ivermectin in different animals including dogs. Young ones in general are more sensitive than adults because their blood brain barrier is more permeable to ivermectin. Certain dog breeds primarily, the Smooth Collie, the Shetland Sheepdog, and the Australian Shepherd are highly sensitive to exhibit signs of ivermectin toxicity due to mutation within the MDR1 gene coding for P-glycoprotein, an ivermectin effluxing transporter of blood brain barrier. Inadvertently improper use of formulations which are meant for cattle, sheep, horses, and swine can also produce toxicity in dogs. All these factors result in entry of higher levels of ivermectin in to the central nervous system producing neurotoxicity. In mammals, ivermectin exerts toxicity by blocking the post-synaptic transmission of nerve impulses by potentiating the release and binding of GABA. Some adverse may be due to GABA-mediated cholinergic effects manifested by raised serum pseudocholinesterase levels.
Clinical signs of toxicity
- Altered mentation (obtundation, stupor, coma),
- Blindness (characterized by absence of menace response),
- Respiratory depression
- Tremors/ seizures,
- Hypoglycemia may be present if tremors/seizures are prolonged,
Although ivermectin toxicosis typically does not induce algesia in animals, increased vocalization caused by anxiety or altered mentation may be difficult to discern from a pain response.
History of exposure.
Breed identification to confirm genetic predisposition to ivermectin toxicity.
Although, serum ivermectin concentration can confirm diagnosis, these results are not available immediately.
Ivermectin toxicity should be differentially diagnosed from exposure to other toxicants like ethylene glycol, methanol, hallucinogens, barbiturates, opioids, benzodiazepines as well as infectious, inflammatory, traumatic, or neoplastic intracranial diseases.
- There are no specific antidotes for ivermectin toxicosis. Ivermectin toxicity cannot be reversed.
- If the exposure is within the past 4 – 6 hours, vomiting may be induced.
- Oral administration of activated charcoal will help minimize the absorption of ivermectin from gastrointestinal tract.
- Intravenous fluids and nutritional support (possibly with a feeding tube) will correct dehydration nutrient balance.
- Placing dog on a ventilator incase of respiratory depression.
- Maintaining dog’s body temperature.
- Administering antiepileptics to control seizures.
Use of preparations intended for dogs rather than administering the preparations intended for use in other animals.
Recommended dose regulations for all medications should be followed strictly.
Ivermectin should be used with utmost caution in susceptible breeds and young animals.
Author: Adil Mehraj Khan
Assistant Professor-cum-Junior Scientist, Division of Veterinary Pharmacology and Toxicology, Sher-e-Kashmir University of Agricultural Sciences and Technology of Kashmir, Jammu and Kashmir, India