detect and quantify the residues of these compounds. A separate issue relates to
limitations of the conventional NOEL-safety factor approach to the toxicological
evaluation of very potent compounds that exert their effects through receptors (for a
review, see Greenlees and Hooberman 2004 ). Reports in the literature describe
modifications to the conventional approaches to toxicological evaluations (Crump
1984 ) and the development of new approaches that are able to provide quantitative
estimates of toxicological risk of low levels of veterinary drug residues (Kroes and
Kozianowski 2002 ). Data analysis and interpretation with these new approaches to
safety assessment will be challenging. It requires risk assessors and risk managers
to interact closely. Advances in toxicology also need to be incorporated into the risk
analysis framework. Toxicogenomics, which combines our ever-increasing know-
ledge of the genome and its processes with conventional toxicology, is a case in
point.
Refinement of the exposure assessment of residues of veterinary drugs was
addressed by the JECFA at its 66th meeting (WHO 2006 ). The new procedure
yields more realistic estimates of chronic dietary intake of residues. A procedure for
estimating the acute dietary exposure to residues of veterinary drugs needs to be
developed to address acute exposure scenarios, which are of particular interest for
pharmacologically active substances.
In developing countries, the demand for animal protein is rapidly increasing as is
the desire of some of these countries to participate in international trade in animal-
derived food commodities. However, many developing countries do not have the
capacity required to produce food that complies with the standard required for local
and international markets (Cannavan 2004 ). Frequently, national legislative frame-
works for regulating veterinary drugs are inadequate or non-existent and residue
control laboratories lack the required capability. The situation is confounded by the
needs of animal production systems in developing countries, which frequently rely
on the use of veterinary drugs not approved in developed countries. As a con-
sequence, Codex MRLs have not been established for many veterinary drugs that
are essential in developing countries. Examples include parvaquone and buparva-
quone, which are used for treating tick-transmitted Theileria parva infection (East
Coast fever) of cattle in east and central Africa, and homidium which is used for
treating tsetse-transmitted trypanosomiasis (sleeping sickness) of food animals in
some regions of Africa. Dossiers for all three substances were unsuccessfully
sought at the twelfth session of the CCRVDF (CCRVDF 2000 ). The delegation
of the USA has offered to assist developing countries in identifying data gaps and
seeking commitments from sponsors to provide dossiers for evaluation by the
JECFA (CCRVDF 2009 ). As a result of this collaboration, the number of MRLs
for veterinary drugs required for animal production in developing countries might
increase.
Finally, a series of safety guidelines have been developed and published by the
VICH and other guidelines are in development (VICH websitehttp://www.vichsec.
org/). In addition to harmonising the technical requirements for veterinary medici-
nal product registration globally and reducing the costs associated with product
development, the guidelines minimise the use of test animals.
288 P.T. Reeves