Effect of cooking on veterinary drug residues in food. Part 9. Nitroimidazoles.

Most food containing drug residues is consumed after cooking or processing, yet surveillance for these residues is almost always conducted on raw tissue. This investigation was to establish the effect of cooking on residues of the nitroimidazole drugs dimetridazole and ronidazole in chicken muscle and egg, to enable dietary intake calculations based on surveillance results. In model aqueous and lipid solutions, dimetridazole and its 2-hydroxy metabolite, which is usually found when residues are present, were relatively stable for times and temperatures normally encountered during standard cooking methods. Ronidazole in hot aqueous solutions, except at acidic pH, was converted into the 2-hydroxy metabolite. Chicken meat and eggs from birds treated with dimetridazole or ronidazole were used to investigate the effects of cooking on food containing these residues. It was apparent that these residues were not destroyed by cooking chicken meat although some of the residue leached from the sample with juices which exuded as it cooked. Residue concentration in egg reduced during cooking by between 14% and 32% of the original concentration.