7. Protecting Future Effectiveness

Pharmacovigilance is the process whereby concerns in relation to safety or effectiveness of medicines are reported to the national authorities. Where a concern arises, the farmer should consult the veterinarian and a report of the incident should be submitted to the authorities if the veterinarian suspects that a safety or efficacy problem has arisen.

This system is very beneficial in allowing the ongoing monitoring of products in use under actual field conditions.


Monitoring sensitivity by the animal health industry

Resistance is a phenomenon in which certain bacteria stop responding to treatment by a specific antibiotic. Therefore, it is of great importance to monitor the sensitivity of bacteria to antimicrobials on an ongoing basis. The monitoring of sensitivity is a complex operation which includes collection of representative samples and consistent evaluation of results.

The animal health industry is engaged in this type of activity, sometimes concurrently with the regulatory authorities or government agencies. The communication of information on levels of resistance will allow veterinarians to make informed decisions on which antimicrobials they should use for the best chance of success. Moreover, monitoring antimicrobial resistance in animal production is also relevant to public health.


The development of resistance

Antimicrobials have activity against particular bacterial species or groups of species. Clinical trials will prove the effectiveness of a particular product against a particular bacterium. At the outset, very effective results should be achieved.
However, any particular population of bacteria may be made up of different individuals with slightly different genetic properties. A few bacteria, making up a tiny fraction of the overall population, may the natural ability to survive treatment with the antimicrobial. The result may be that the resistant bacteria survive and become an increasingly dominant part of the population over time and in response to selective pressure imposed by the use of the antimicrobial.
As time progresses, treatment may become less effective eventually leading to the situation where the product no longer effectively controls the disease. At this point, we have clinical resistance. As may be appreciated, this is usually a gradual process with samples showing increasing levels of resistance over time, although in some cases antimicrobials may remain efficacious over many decades.
As an alternative, bacteria may adapt or acquire genetic material from other bacteria and develop the ability to survive treatment. in this case, the switch from susceptibility to resistance may be relatively rapid if the resistant bacteria multiply and spread rapidly. Most resistance emerges through this latter process.
Having developed resistance to one type of antimicrobial, the bacteria may be resistant to related antimicrobials in the same class of antimicrobials. In some cases, bacteria may develop resistance to a number of separate classes and so become multi-drug resistant.