Analysing for Residues of Veterinary Drugs in Depletion Studies
Methods of analysis for veterinary drug residues are required for the conduct of
depletion studies in food-producing animals and the monitoring of food. Method
validation provides assurance that a method is fit-for-purpose, and it produces
results that can be reliably used for making decisions. The process of method
validation involves a defined set of experiments to establish the performance
criteria that should be achieved by an analyst using the method. The type of method
and its intended use will determine the specific requirements of method validation
(MacNeil 2004 ). In the case of analytical methods used in residue depletion studies,
the performance characteristics that apply to the validation include linearity, accu-
racy, precision, limit of detection, limit of quantitation, specificity, stability of the
analyte during analysis under stipulated conditions, and robustness of the method.
Detailed information on the specific acceptance criteria relating to the performance
characteristics for validation purposes can be found on the websites of the regu-
latory authorities. Currently, a VICH guidance on the validation of analytical
methods used in residue depletion studies is under development.
In support of registration applications, sponsors typically submit to regulatory
authorities a description of, and validation data for, the method used to quantify the
marker residue in residue depletion studies. As data generated with this method are
the basis for assigning withdrawal periods, the method must be validated across a
range of marker residue concentrations, including one half and twice the MRL. The
method should also be available for the enforcement of the proposed MRLs and for
assisting laboratories in the development and validation of a multi-residue screen-
ing method or a confirmatory method or both.
Good Practice in the Use of Veterinary Drugs
Good practice in the use of veterinary drugs (GPVD) is defined as the official
recommended or authorised usage, including withdrawal periods, approved by
national authorities, of veterinary drugs under practical conditions (Codex Alimen-
tarius Commission Procedural Manual, 18th edition, 2008). In some jurisdictions,
veterinary surgeons may be subject to legislative sanction if found responsible
for causing illegal residues in food (for example,Veterinary Practice Act 1997
(Victoria, Australia)).
Residues of Veterinary Drugs at Injection Sites
Injection site residues pose unique challenges in terms of public health and the
international trade in animal-derived foods (Reeves 2007 ). The kinetic behaviour of
drugs at injection sites is notable for high initial concentrations, which reflect the
magnitude of the dose administered, followed (for some products) by slow and
often erratic depletion. While the current risk assessment methodologies minimise
278 P.T. Reeves