Mechanism of Action
Ivermectin is a member of the macrocyclic lactone class of endectocides which have a unique mode of action. Compounds of the class bind selectively and with high affinity to glutamate-gated chloride ion channels which occur in invertebrate nerve and muscle cells. This leads to an increase in the permeability of the cell membrane to chloride ions with hyperpolarization of the nerve or muscle cell, resulting in paralysis and death of the parasite. Compounds of this class may also interact with other ligand-gated chloride channels, such as those gated by the neurotransmitter gamma-aminobutyric acid (GABA). The margin of safety for compounds of this class is attributable to the fact that mammals do not have glutamate-gated chloride channels, the macrocyclic lactones have a low affinity for other mammalian ligand-gated chloride channels and they do not readily cross the blood-brain barrier.

Pharmacokinetic particulars
Maximum plasma concentration After topical administration of 0.5 mg ivermectin per kg bodyweight, the plasma samples averaged 1 ng/ml 8 hours post treatment and on days 1 through 7 post dose the average plasma residues were reasonably constant at approximately 3 ng/ml. After day 7 the ivermectin residues gradually decreased to an average of 2 ng/ml at 14 days and 1 ng/ml at 28 days. The concentrations mentioned relate to the main compound of ivermectin, 22,23-dihydroavermectin B1a. Excretion: length of time and route After topical administration of 0.5 mg ivermectin per kg bodyweight, liver, the target tissue, generally had the highest residues, averaging 48 ppb at 7 days post dose, 12 ppb at Day 28, and 0 at Day 56. Fat residues averaged 29 ppb at 7 days, 9 ppb at 28 days and 1 ppb on Day 56 after treatment. The dose site residues averaged 13 ppb at Day 7 and dropped to 5 ppb by Day 35. The excretion occurs mainly through faeces and, in a lesser proportion, via urine.

Environmental Properties
Ivermectin is moderately persistent in soil and may accumulate in sediments