Description of status quo
There are currently several possible mechanisms for placing a substance used as veterinary drug on the agenda of JECFA. However, in the past the typical mechanism included prioritisation by CCRVDF on the basis of a firm commitment of a private sponsor to provide the data necessary to perform a risk assessment and to elaborate proposed MRL for residues veterinary drugs. As a result, only a relatively small fraction of the existing substances currently used in veterinary medicine and would require international MRLs have been evaluated by the Committee. There is currently no backlog in JECFA for veterinary drug review.
For the majority of substances evaluated by JECFA the data had been generated in order to primarily support major uses in developed countries. Only in a very few cases was it possible to obtain the data to evaluate substances which were of special interest to certain specific regions. Examples are diminazene and of isometamidium which are both veterinary drugs with a long history of use for the treatment of animal trypanosomiasis in tropical countries, and in the case of oxytetracycline for use in shrimp culture where the government of Thailand generated the data.
In order to facilitate the evaluation of substances with a long history of use JECFA has adopted an approach implying that for the assessment of such substances and on a case by case basis certain studies not meeting modern criteria could be used in the light of other equivalent information, presented for example, in the form of literature reviews conducted by sponsors and/or evaluation reports drafted by experts in the field, provided that the safety of these products can be assured to an extent equivalent to that achieved for newer products supported by a contemporary data base.
Analysis of gaps and identification of problems
The consequences of the above described mechanisms are that many substances with the potential to leave residues in foods and to create problems in international trade have no ADI and no international MRLs, or their MRLs do not cover species and uses which were considered minor by the sponsors of the data. Some countries have a "minor use" policy that allows the extrapolation of data from approved uses in a "major use" species to use in "minor use" species. In those countries, minor use is typically defined as species not significantly consumed for food or species for which there is a very small market for pharmaceutical development. In these circumstances, the toxicological ADI is applied to the "minor use" species. The metabolism and residue evaluation data, up to and including the MRL, are extrapolated to the "minor use" species as is scientifically appropriate. This approach may be useful in increasing the number of species treated with the veterinary drug for which an MRL may be developed and may be particularly useful in aquaculture. The resulting problem for animal health, food safety and trade in food can be significant if minor uses in some regions represent major uses in other regions or if certain methods of production of animal-derived foods, for example aquaculture, grow rapidly in some parts of the world and only insufficient numbers of drugs with established specific good practices and international MRLs are available.
Inventories of substances currently needed in different regions of the world and the indications for which they are being used do not exist. Therefore it is currently not possible to develop concepts on how assessments by JECFA could be enabled. CCRVDF and JECFA have, up to now, not yet finalised the discussion of the risk assessment policy aspects and of the scientific criteria for extrapolating kinetic and residue data from species to species.
It is well known that for a significant number of substances state of the art risk assessments have been conducted by national authorities or international bodies. However, there is presently no mechanism to make the underlying data available to the JECFA/Codex system with the objective to promote the elaboration of international standards. In other cases at least parts of the data required for a JECFA evaluation are in the hands of national institutions, e.g. information on national good practices in the use of veterinary drugs and residue data.
