Residue avoidance after topical application of veterinary drugs and parasiticides.

Deriving adequate withdrawal intervals for extralabel use of veterinary topical products is difficult because there are limited published data, and data for approved drugs and pesticides are usually proprietary. Where possible, approved products and doses labeled for the specific indication at hand should be used and label withdrawal times should be adhered to. When determining whether topical application of these chemicals may violate tolerance levels in meat and milk, the veterinarian often is limited to empirical data. In the decision-making process, factors, such as type of drug and pesticide formulations used, method of topical application, presence of hair or wool, environmental conditions, and animal species treated, should be considered. In many cases a conservative estimate for the slaughter withdrawal interval can be derived, despite the data gaps. Such recommendations should not be used for routine extralabel use, but are meant to apply to situations in which the drug or pesticide has been used, and human food safety concerns must be addressed.