Parasitin-Vet

Horses:

Large strongyles (adult) (Strongylus vulgaris, S. edentatus, S. equinus, Triodontophorus spp.), small strongyles, pinworms (adults and 4th stage larva), ascarids (adults),
hairworms (adults), large-mouth stomach worms (adults), neck threadworms (microfilaria), bots (oral and gastric stages), lungworms (adults and 4th stage larva), intestinal threadworms (adults), and summer sores (cutaneous 3rd stage larva) secondary to Hebronema or Draschia Spp.

Cattle/sheep/goat:
treatment and control of GI nematodes (adults and fourth-stage larvae) (Haemonchus placei, Ostertagia ostertagi) (including inhibited larvae), Ostertagia lyrata, T. axei, T. colubriformis, Cooperia oncophora, Cooperia punctata, Cooperia pectinata, Oesophagostomum radiatum, Nematodirus helvetianus (adults only), Nematodirus spathiger (adults only), Bunostomum phlebotomum; 

Stephenophileria, paraphileria

lungworms (adults and fourth-stage larvae) (Dictyocaulus viviparus); grubs (parasitic stages) (Hypoderma bovis, H. lineatum); 

sucking lice (Linognathus vituli, Haematopinus eurysternus, Solenopotes capillatus); and mites (scabies) (Psoroptes ovis [syn. P. communis var. bovis], Sarcoptes scabiei var. bovis).

Swine:

treatment and control of GI roundworms (adults and fourth-stage larvae) large roundworm, Ascaris suum; red stomach worm, Hyostrongylus rubidus; nodular worm, Oesophagostomum species; threadworm, Strongyloides ransomi (adults only); somatic roundworm larvae (threadworm, S. ransomi [somatic larvae]); lungworms (Metastrongylus spp. [adults only]); lice (H. suis); and mites (Sarcoptes scabiei var. suis).

In dogs and cats, it is used as a heartworm preventative (low dose) or to treat external parasites (mites) and intestinal parasites at higher doses. The benefit for heartworm prophylaxis in animals is the ability to kill young larvae, older larvae, and immature or young adults and adult filariae. Ivermectin is an effective microfilaricide after adulticide therapy. It has been recommended by the American Heartworm Society to treat heartworm-positive
dogs for 2–3 months prior to adulticide therapy. This allows immature worms to reach full maturity that are more susceptible to melarsomine, as well as preventing new infection. Ivermectin can also reduce numbers of adult heartworms when administered long term at preventive
doses. For optimal heartworm adulticide effect, it is often administered with oral doxycycline (10 mg/kg per day for 28 days). Treatment of Demodex infections is effective but requires higher doses than for any other indication.

Ectoparasites: Hypoderma, Crysomia flies. Lice, Mange, Mites, Tick, Nasal bot fly,  

Horses:

not be used in foals less than 4 months old, as safety of the drug in animals this young has not been firmly established. However, foals less than 30 days of age have tolerated doses as high as 1 mg/kg without signs of toxicity.

Dog:
Ivermectin is not recommended for use in puppies less than 6 weeks old.
After receiving heartworm prophylaxis doses, the manufacturer recommends observing Collie-type breeds for at least 8 hours after administration. Most clinicians feel that ivermectin should not be used in breeds susceptible (Collies, Shelties, Australian shepherds, etc.)
Ivermectin is reportedly contraindicated in chelonians, Indigo snakes and skinks. Milbemycin has reportedly been given safely to chelonians.

Mode of Action:

Ivermectin enhances the release of gamma amino butyric acid (GABA) at presynaptic neurons. GABA acts as an inhibitory neurotransmitter and blocks the post-synaptic stimulation of the adjacent neuron in nematodes or the muscle fiber in arthropods. By stimulating the release of GABA, ivermectin causes paralysis of the parasite and eventual death. 

As liver flukes and tapeworms do not use GABA as a peripheral nerve transmitter, ivermectin is ineffective against these parasites.

Pharmacokinetics:

In simple-stomached animals, ivermectin is up to 95% absorbed after oral administration. Ruminants only absorb ¼–⅓ of a dose due to inactivation of the drug in the rumen. While there is greater bioavailability after SC administration, absorption after oral dosing is more rapid than SC. It has been reported that ivermectin’s bioavailability is lower in cats than in dogs, necessitating a higher dosage for prophylaxis of heartworm in this species.
Ivermectin is well distributed to most tissues, but does not readily penetrate into the CSF, thereby minimizing its toxicity. Collie-breed dogs with a specific gene defect allow more ivermectin into the CNS than other breeds/species.
Ivermectin has a long terminal half-life in most species (see below). It is metabolized in the liver via oxidative pathways and is primarily excreted in the feces. Less than 5% of the drug (as parent compound or metabolites) is excreted in the urine.
Pharmacokinetic parameters of ivermectin have been reported for various species:
Cattle: Volume of distribution = 0.45–2.4 L/kg; elimination half-life = 2–3 days; total body clearance = 0.79 L/kg/day.
Dogs: Bioavailability = 0.95; volume of distribution = 2.4 L/kg; elimination half-life = 2 days.
Swine: Volume of distribution = 4 L/kg; elimination half-life = 0.5 days.
Sheep: Bioavailability = 1 (intra-abomasal), 0.25 (intra-ruminal); volume of distribution = 4.6 L/kg; elimination half-life = 2–7 days.

Horses: Swelling & pruritus at the ventral mid-line can be seen approximately 24 hours after ivermectin administration due to a hypersensitivity reaction to dead Onchocerca spp. microfilaria. 

Dogs: May exhibit a shock-like reaction when ivermectin is used as a microfilaricide, presumably due to a reaction associated
with the dying microfilaria. 

Cattle: Ivermectin can induce serious adverse effects by killing the larva when they are in vital areas; may also cause discomfort or transient swelling at the injection site. 

Mice & rats: May cause neurologic toxicity at doses slightly more than usually prescribed. 

Birds: Death, lethargy, or anorexia may be seen. Orange-cheeked Waxbill Finches & budgerigars may be more
sensitive to ivermectin than other species

In horses, doses of 1.8 mg/kg (9x recommended dose) PO did not produce signs of toxicity, but doses of 2 mg/kg caused signs of visual impairment, depression and ataxia. 

In cattle, toxic effects generally do not appear until dosages of 30x those recommended are injected. At 8 mg/kg, cattle showed signs of ataxia, listlessness, and occasionally, death.
Sheep have shown signs of ataxia and depression at ivermectin doses of 4 mg/kg.

Reproductive studies performed in dogs, horses, cattle and swine have not demonstrated adverse effects to fetuses.