Residues of spinosad in the tissues of sheep after aerosol treatment of blowfly myiasis.
OBJECTIVE
To measure the residues of spinosad and chlorhexidine in the tissues of sheep after treatment of blowfly strike.


METHODS
Fourteen sheep with natural myiasis and 12 with artificial infestations of Lucilia cuprina larvae had the wool removed over their infestations and were treated with an aerosol wound dressing containing spinosad and chlorhexidine. Sheep were killed up to 14 days after treatment and residues of the chemicals measured in tissues.


RESULTS
Chlorhexidine was not detected in any tissue. Residues of spinosad were highest in fat, lowest in muscle and intermediate in liver and kidney. The highest residue detected was 0.2 mg/kg spinosad in perirenal fat 7 days after generous treatment of a sheep with a large fly strike. Residues of spinosad in fat peaked 3 to 7 days after treatment and 1 to 3 days after treatment in liver and kidney.


CONCLUSIONS
These studies present a realistic worst-case in struck sheep and at the highest dose studied, equivalent to 5.8 mg spinosad per kg body weight, the maximum residue detected of 0.2 mg/kg in peri-renal fat was 20% of the Australian maximum residue limit. Muscle, liver and kidney residues of spinosad were also below the Australian maximum residue limits at all times.
Rothwell
J T
JT
Elanco Animal Health, Level 5, 123 Epping Rd, Macquarie Park, New South Wales 2113 6140, USA.
Carson
J
J
Sherwood
N
N
Shields
R
R
Hacket
K
K
Burnett
T
T
D000273:Adipose Tissue / Q000378:metabolism; D000336:Aerosols; D000818:Animals; D000891:Anti-Infective Agents, Local / Q000493:pharmacokinetics / Q000627:therapeutic use; D002710:Chlorhexidine / Q000493:pharmacokinetics / Q000627:therapeutic use; D003257:Consumer Product Safety; D004338:Drug Combinations; D005506:Food Contamination; D007306:Insecticides / Q000493:pharmacokinetics* / Q000627:therapeutic use; D007668:Kidney / Q000378:metabolism; D008099:Liver / Q000378:metabolism; D018942:Macrolides / Q000493:pharmacokinetics* / Q000627:therapeutic use; D008460:Meat / Q000592:standards; D009198:Myiasis / Q000188:drug therapy / Q000662:veterinary; D010573:Pesticide Residues / Q000032:analysis*; D012756:Sheep / Q000378:metabolism*; D012757:Sheep Diseases / Q000188:drug therapy; D012869:Skin Absorption; D014018:Tissue Distribution
D000336:Aerosols; D000891:Anti-Infective Agents, Local; D004338:Drug Combinations; D007306:Insecticides; D018942:Macrolides; D010573:Pesticide Residues; D002710:Chlorhexidine; C415329:spinosad