ATCvet code: QP54AB02
Pharmacodynamics
Moxidectin is a parasiticide active against a wide range of internal and external parasites and is a second-generation macrocyclic lactone of the milbemycin family. Moxidectin interacts with GABA and glutamate gated chloride channels. The net effect is to open the chloride channels on the postsynaptic junction to allow the inflow of chloride ions and induce an irreversible resting state. This results in flaccid paralysis and eventual death of parasites exposed to the drug.
The veterinary medicinal product is effective against benzimidazole resistant strains of cyathostomes.
Pharmacokinetics
Moxidectin is absorbed following oral administration with maximum blood concentrations being achieved 8 hours post application.
Bioavailability by the oral route is 40%. The drug is distributed throughout the body tissues but due to its lipophilicity it is selectively concentrated in the fat.
The elimination half-life is 28 days.
Moxidectin undergoes partial biotransformation by hydroxylation in the body and the only significant route of excretion is the faeces.
Environmental properties
Moxidectin fulfils the criteria for a (very) persistent, bioaccumulative and toxic (PBT) substance. In particular, in acute and chronic toxicity studies with algae, crustaceans and fish, moxidectin showed toxicity to these organisms, yielding the following endpoints:
Organism | EC50 | NOEC |
Algae | S. capricornutum | >86.9 μg/l | 86.9 μg/l |
Crustaceans (Water fleas) | Daphnia magna (acute) | 0.0302 μg/l | 0.011 μg/l |
Daphnia magna (reproduction) | 0.0031 μg/l | 0.010 μg/l |
Fish | O. mykiss | 0.160 μg/l | Not determined |
L. macrochirus | 0.620 μg/l | 0.52 μg/l |
P. promelas (early life stages) | Not applicable | 0.0032 μg/l |
| Cyprinus carpio | 0.11 μg/l | Not determined |
EC50: the concentration which results in 50% of the test species individuals being adversely affected, i.e. both mortality and sub-lethal effects.
NOEC: the concentration in the study at which no effects are observed.
This implies that when allowing moxidectin to enter water bodies, this may have a severe and lasting impact on aquatic life. To mitigate this risk, all precautions for use and disposal must be adhered to.