products, better injection techniques have resulted in less wastage of edible meat
tissue as a result of trimming blemishes. Veterinarians play an important role
in minimising drug residues by instructing livestock producers on good practices
in the use of approved veterinary drugs and by providing professional advice in
relation to off-label (extra-label) use of veterinary drugs. The incidence of injection
site residues entering the food chain is also reduced by trimming of the injection
site lesions at meat processing plants.
5 Perspectives and Future Challenges
The process of managing risk in relation to drug residues in animal-derived food-
stuffs is based on a risk analysis approach that is both science-based and rigorous.
The desired outcome of the process is nil violations of the relevant health standards.
This has been achieved, by and large, as demonstrated by the results of residue
monitoring programmes that indicate the incidence of illegal drug residues in food
is very low (Reeves 2005 ). The finding of these programmes points to effective
regulation of veterinary drugs. It also provides reassurance to the public that food
obtained from animals treated with veterinary drugs does not contain residues that
might constitute a health hazard for consumers.
Many veterinary drugs were in therapeutic use before the current human food
safety evaluation was developed and are referred to by the JECFA as “substances
with a long history of use”. Contemporary data packages for these compounds are
not available for establishing MRLs. However, the JECFA will consider proposing
MRLs for these substances if their safety can be assured to be equivalent to that for
newer products. The following example demonstrates this concept. Suppose a
decision is made to market an older generation parasiticide to fill a void caused
by the emergence of parasitic strains resistant to newer chemotherapeutic agents. In
this example, the generation of additional data to address deficiencies in the data
package and the assembly of existing information and data may permit the estab-
lishment of MRLs.
The requirement for a human food safety evaluation for a generic product
formulation that has been shown to be bioequivalent to a drug approved for use
in food-producing animals is a common source of confusion and debate. However,
drug formulations demonstrated to be bioequivalent on the basis of plasma drug
concentrations and derived variables such asCmaxand AUC may have very
different tissue residue profiles. This difference can be pronounced with formulations
that demonstrate “flip-flop” pharmacokinetics and has been described for a hypothe-
tical scenario involving bioequivalent injectable formulations (Reeves 2007 ).
A future challenge for the risk analysis of food safety relates to the increasing
complexity of the toxicological evaluation. To some extent, this is driven by certain
newer drugs that are very potent and exert their actions via receptor-mediated
mechanisms, or they are drugs derived from biotechnology. From a food safety
perspective, modern analytical instrumentation with low limits of sensitivity can
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