Levels of antibiotics

Table 1. Benefits of Subtherapeutic Level of Antibiotic in Food-Producing Animals, % Improvement...

The level of antibiotic resistance of the gut flora of pigs has been found to be influenced by factors other than the inclusion of antibiotics in the diet " " such factors include the herd environment, history and the opportunity for cross-contamination. 

One of the most popular orally active penicillins in present clinical use is amoxicillin (12). Its oral effectiveness and broad spectrum of activity against common pathogens as well as its better absorption than its closest precedent competitor, ampicillin (14), largely accounts for this. Higher blood and tissue levels of antibiotics is another means of dealing with resistance. In an attempt to achieve yet further improvements in oral bioavailability and hence blood and ti.ssue levels of amoxicillin, the prodmg fumoxicillin (13) is prepared from amoxicillin (12) by treatment with furfural [3]. The imine moiety is less basic than the primary amine so that the isoelectric point of fumoxicillin is more on the acid side than is that of amoxicillin. 

The practice of incorporating low levels of antibiotics in livestock feeds to promote growth has been particularly controversial. It is feared that this practice will result in development of resistant bacteria in animals, which will in turn be passed on to humans, thus diminishing the effectiveness of antibiotics in treatment of human disease. A petition from the Natural Resources Defense Council to ban such uses of penicillin and tetracyclines recently was denied by the Secretary of Health and Human Services. The controversy therefore is likely to continue. Opinion on the subject is quite polarized, and several points of view are presented in this book. 

There has been great concern that the feeding of low levels of antibiotics that are also used in human medicine could lead to serious human health problems. There is no question that bacteria develop resistance to these antibiotics, and that they can transfer their resistance to other bacteria, even to other species. There is also no question that antibiotic resistance has become a serious problem in human medicine. However, the extent to which the feeding of antibiotics to animals has contributed to the human health problem is still unclear and a source of great controversy. 

Table 1. Response of Pigs to Subtherapeutic Levels of Antibiotics...

Exposure of animals to therapeutic levels of antibiotics will markedly raise the level of resistance and a long period of time is required for the resistance levels to return to the pre-treatment level In an experiment replicated five times (Lang lo is et al ifi.) we found that exposure of animals to subtherapeutic levels of gram-positive spectrum antibiotics also resulted in increased levels of tetracycline resistance During the course of our study we have sampled pigs on two separate occasions (1974 and 1985) from another research herd in which antibiotics have never been used as feed additives but only for therapeutic purposes Of the 100 pigs sampled in 1974 only one had been... 

NRDC contended that the suspension of these subtherapeutlc uses of penicillin and the tetracyclines In animal feeds poses no human health problem. No potential human health problem has been Identified In the literature. Any risk of eating meat from an animal that becomes 111, because penicillin and the tetracyclines were not available, could be alleviated by using substitute antibiotics and better farming practices to prevent or reduce the Incidence of disease. Moreover, there would be an Increased probability of effectively treating the diseases with therapeutic levels of antibiotics If they were not used at subtherapeutlc levels. 

Low levels of antibiotics increase growth in healthy animals on nutritionally complete diets. 

The growth response to antibiotics depends on the "disease level," because various subacute diseases in farm animals are controlled by feeding antibiotics. Under these conditions, the growth response is increased, because growth is depressed by such diseases. As a result, subtherapeutic levels of antibiotics are... 

A level of antibiotic in edible tissues which is judged... 

There are three main arguments or theories against the use of low levels of antibiotics in livestock feeds. The first theory says... 

The Food Safety and Inspection Service (FSIS) of the United States Department of Agriculture (USDA) is responsible for providing meat and poultry products to the consumer that are safe, wholesome, and unadulterated. Before marketing, meat animals and poultry must be properly withdrawn from antibiotics to ensure that the levels of antibiotics in edible tissues at slaughter are at or below the tolerances established by the Food and Drug Administration (FDA), FDA is responsible for the approval and regulation of animal drugs used in animal husbandry in the USA,... 

Table I. Detection and Measurement Levels of Antibiotic Residues in Products of Animal Origin Using Diffusion Assays...

The aforementioned procedures (techniques) have significant potential and as assay problems are worked out could provide rapid, sensitive, specific and precise methods for the analysis of low levels of antibiotics in food and feed products. 

Subconjunctival injection-75 mg/0.25 ml injected subconjunctivally results in ocular fluid levels of antibiotic (lasting for 5 hours or more) with MICs sufficient for most susceptible pathogens. 

NOTE When high and rapid blood and urine levels of antibiotic are indicated, alternative parenteral therapy should be used... 

In some instances additional specialized studies may be required to assess drug-specific toxicological concerns. For example, hypersensitivity tests may be required for the -lactam antibiotics FDA has recently been concerned with how this standard human food safety assessment process accurately determines the safe concentration of antibiotic residues based on the traditional toxicological end-points. Of particular concern was the impact of low levels of antibiotics on the intestinal microflora. 

Antiporter or ion exchange transporters are also common. For example, E. coli uses a metal ion-tetracycline / H+ transporter to carry the antibiotic tetracycline out of cells. This protein, when present, provides a high level of antibiotic resistance to the bacteria.444... 

Antibiotics Therapeutic antibiotics are used for the treatment of sick or injured animals. Subtherapeutic antibiotics are lower levels of antibiotics than would be used to treat an infection and are used as growth promoters for livestock. 

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