Some observations on the pharmacological properties of ivermectin during treatment of a mite infestation in mice.

Ivermectin has become one of the most widely used drugs for the treatment of parasitic infections in laboratory rodents. Despite its wide popularity, little has been published regarding its pharmacokinetic properties in mice. We made use of a routine mite control treatment in a conventional animal unit to gain some knowledge of these properties. Numerous inbred, outbred, and transgenic lines of mice were being treated with ivermectin in the drinking water (32 mg/L) for a chronic Myocoptes infestation. A sample of mice from different cages and rooms was culled at various time intervals to check levels of ivermectin in blood. In addition, cellophane tape impressions of fur were obtained from mice undergoing treatment to monitor the effectiveness of ivermectin in controlling the mite infestation. Results showed that ivermectin levels rose sharply in the serum of treated mice and gradually fell once treatment was discontinued. Maximum levels detected at the end of a 10-day period of treatment were 90 ng/ml. Once treatment was discontinued, serum levels of the drug were undetectable after 7 days. In addition, treatment with ivermectin proved very effective in reducing parasite burdens in the colony. Results were in line with known pharmacological properties of ivermectin in other species. Nevertheless, it was worth noting that serum levels can vary markedly depending on various factors, something to be taken into account when considering treatment of mice, especially transgenics.