author: roxana angelats m.
dvm, research and experimental design chief of agrovet market animal health
bovine mastitis is a disease with a high incidence in the dairy industry worldwide and is considered the major cause of economic loss in that sector not only for the decrease in the amount of milk production, the cost of treatment, veterinary services and the wear of the animal (bradley, 2002; oviedo et al., taverna et al., 2007) but mainly for the decrease of the milk quality because of antibiotic residues, resulting in penalty or milk rejection from the dairy industry.
it is important to indicate that mastitis remains as the leading cause of antibacterial use, and the use of milk containing these agents is the main problem of residues in food production (sumano and ocampo, 1997). the presence of antibiotics in milk is a major concern for public health (lewis, 1967) and the dairy industry (jones and seymour, 1988). this is due to the generation of multi-resistant bacteria (sawant et al., 2007) and allergic processes caused to the consumer (lewis, 1967); as well as by the interruption of milk fermentation treatment (nascimento et al., 2001; schiffmann, 1992; cogan, 1972). for this reason, dairy companies permanently track the presence of these residues in milk and the results are considered in their payment policies (idf, 2002); even, in some countries, government regulations prohibit the presence of antibiotic residues in milk for human consumption (ruegg and tabone, 2000).
international organizations such as the food and drug administration (fda), the united states department of agriculture (usda), the codex alimentarius commission (fao/oms), and the european union among others, have established maximum residue levels (mrl) for veterinary drugs, which established the maximum permitted concentration of residues of these drugs in food intended for human consumption. the antibiotic residues in milk can be determined by analytical techniques, which give us the exact concentration of the antibiotic, this way it can be compared easily with the respective mrl. however, there are also qualitative techniques that determine the “absence” or “presence” of antimicrobial residues, considering “presence” when the test detect antibiotic’s concentrations above the detection limit of the test and “absence” when they are below this limit. these qualitative techniques establish its detection limits below the established mrl to assure the milk safety. antibiotic residue studies in milk and the knowledge of the mrl allow establishing the needed withdrawal time after the administration of antimicrobials on the target species. we have to mention that the used terms such as “zero residues in milk” or “without withdrawal in milk” indicates that the antibiotic is present in milk but at a concentration lower than the respective mrl.
in this context, the veterinary pharmaceutical industry is required to investigate and inform about the withdrawal times of the antibiotic formulations that develops, based on studies of antibiotic residues that respect the established mrl on its jurisdiction. for instance, among the recommended antibiotics for the mastitis treatment there is a commercial intrammamary infusion based on cephalexin, gentamycin, dexamethasone and vitamin a. the attributes of such pharmaceutical combination are not just based on the spectrum wideness, the anti-inflammatory and the epithelial regeneration effects, the good efficacy of the cephalexin due to its good diffusion capacity on the mammary tissue, or by the specific activity of the gentamycin over escherichia coli, one of the main mastitis agents (sumano and ocampo, 1997), but also by its short withdrawal time being possible to use the milk for human consumption since 72 hours post treatment. thus, during the development of new molecules or combinations, one of the main objectives of the veterinary pharmaceutical industry must be to get a short withdrawal time, in benefit of the producer.
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