Rapid and sensitive detection of moxidectin and fluralaner in wombat skin

Sarcoptic mange in wombats is caused by the scabies mite (Sarcoptes scabiei) and is treated with antiparatsitic pour-ons used in cattle and companion animals, such as moxidectin and fluralaner. These treatments are applied topically by pouring the chemical along the back of infected animals, allowing the active ingredient to be absorbed by the skin and then entering the blood stream. While blood is most commonly analysed to investigate absorption and metabolism of these pesticides, analysis of skin is essential to understanding their potential bioaccumulation. Wombat skin is used as a defence mechanism and is much thicker than most animals. No method appears to be available that describes how to disrupt and extract wombat skin for analysis of moxidectin and fluralaner. A 5 mm biopsy punch was used to sample skin harvested from a deceased roadkill wombat. Several approaches were tested to disrupt skin tissue to allow the simultaneous extraction and analysis of moxidectin and fluralaner. The optimal approach was to pulp and extract skin in acetone using an Ultra-Turrax. This approach effectively overcame the mechanical strength of the thick skin, and efficiently extracted both chemicals due to their high acetone solubilities. As the two processes occurred simultaneously in the same vessel, the likelihood of sample loss and cross contamination was dramatically reduced. Moxidectin and fluralaner recoveries from wombat skin were 101 ± 3.7% and 120 ± 2.8%, respectively, over the range of 1-80 ng/g when using their respective internal standard. The limit of quantitation for each chemical was 1 ng/g using a 50 mg skin sample, but the moxidectin limit of quantitation is likely to be lower, but was limited in the current study by a low moxidectin background in the harvested skin used for spike recoveries. The extraction and analysis approach reported in this study is rapid and efficient, and is only limited by having to analyse moxidectin and fluralaner separately due to the need for different optimal MS conditions for each analyte. The method resulted in the simultaneous recovery of both moxidectin and fluralaner in the same extraction process, making screening of a large number of samples highly efficient.