on the indirect effects. The possible indirect effects of veterinary medicines
should be identified. For example, concern has been raised over the possible
indirect effects of anthelmintics on higher trophic levels (such as bat or bird
species) that may result from the loss of dung invertebrates as a food source.
l There is increasing interest in the way in which mixtures of chemicals interact in
the landscape. Although this interest is not confined to veterinary medicines, the
detection of mixtures of agricultural pesticides, human and veterinary medicines
and industrial chemicals in aquatic systems has challenged the traditional con-
cept of substance-by-substance risk assessment. The high biological activity of
medicines, by design, has drawn particular attention to their role in mixture
toxicity within watersheds and the wider environment. Further research is
therefore required on the mixture toxicity of veterinary medicines (in combina-
tion with other medicines and non-medicinal substances) and the likely occur-
rence and effects of these on ecosystems in natural landscapes.
l Finally, there is a need to establish the potential for veterinary medicines to
bioaccumulate. It may be possible to perform these assessments using data on
target animals obtained in pharmacodynamic/pharmacokinetic studies per-
formed by manufacturers as part of the current regulatory process. In addition
to this, recent research on the extrapolation of mammalian toxicity data,
contained in regulatory submissions for human medicines, to predict effects on
ecological receptors such as fish has shown considerable promise. This may be a
cost-effective way of using existing data to predict at least some aspects of
environmental hazard or risk.
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