Pharmacotherapeutic Group: Endectocide
ATC Vet Code: QP54 AA01
Pharmacodynamic Properties
Ivermectin is a 22, 23-dihydro derivative of an avermectin (which is a fermentation product produced by Streptomyces avermitilis) and consists of 2 homologues: B1a and B1b. It is a parasiticide with nematocidal, insecticidal and acaricidal activity documented in a wide range of domesticated animals.
Ivermectin is a member of the macrocyclic lactone class of endectocides which have a unique mode of action. Compounds of this 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 the hyper-polarisation 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 (GABP).
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 lactone have a low affinity for other mammalian ligand-gated chloride channels and they do not readily cross the blood-brain barrier.
Pharmacokinetic Properties
Cattle:
At a dose level of 0.2 mg ivermectin per kg, a maximum plasma concentration of 35-50 ng/ml is reached in +/- 2 days and the half-life in plasma is of 2.8 days. It is also established that ivermectin is carried mainly in the plasma (80%). The distribution between plasma and blood cells remains relatively constant.
Sheep:
At a dose level of 0.2 mg ivermectin per kg an average peak of 16 ng/ml is reached one day after injection.
Pigs:
During trials carried out at a dose rate of 0.3 mg/kg ivermectin, a plasma concentration of 10-20 ng/ml was reached in +/- 2 days and the half-life in plasma was 0.5 day.