Ivermectin was injected subcutaneously into five pigs at the usual dose rate of 300 micrograms/kg and found to distribute well to all tissues and body fluids which were sampled 24 h post-injection.
Ivermectin was detected in the contents and mucus at all levels of the gastrointestinal tract. The
drug was excreted in bile, with high concentrations of the
drug in the intestines and faeces. High concentrations of
ivermectin were measured in skin, ears and ear wax, suggesting that the
drug should be effective in the treatment of
ectoparasitic infestations, particularly ear mites. The high
lipid solubility of the
drug may explain the high concentrations found in ear wax and skin.
Ivermectin was also detected in the body fluids and tissues of an untreated pig penned with the treated animals. Direct contact appeared to be necessary for transfer of
ivermectin from the treated to the untreated pig but coprophagia or urine drinking is a possible explanation. The pharmacokinetics of
ivermectin administered subcutaneously at a dose rate of 300 micrograms/kg to six pigs were studied. There was marked individual variation in the pharmacokinetics of
ivermectin. In one pig the area under the plasma concentration-time curve was particularly high. This may reflect individual variation in uptake and excretion of the
drug. The mean elimination half-life of the
drug was 35.2 h, suggesting that the
drug is cleared slowly from pigs with
drug detectable in plasma for 6-10 days. This persistence should allow a short period of protection before
re-infection with parasites.