Agriculture Business Week

In 1996 the Department of Agriculture, through the now defunct Sub-committee on Veterinary Drugs(SCVD), banned the use of lower doses of antibiotics for growth promotion in livestock and poultry. Novartis Animal Health was one of the first veterinary drug companies to heed this government directive by revising the label information of its various antibiotic products and deleting the doses specific for growth promotion.

Before the ban on antibiotic growth promotants, it was customary for locally marketed antibiotic products for veterinary use to have three doses – one for treatment, another for prevention, and third for growth promotion. In a short time after the official ban on antibiotic growth promotants, Novartis launched a nationwide campaign on rational and judicious use of antibiotics in food animals through technical seminars and roundtable discussions with swine and poultry producers.

In 1998, on the occasion of the 15th International Pig Veterinary Society (IPVS) Congress in Birmingham, England, Novartis sponsored a lecture on the responsible use of antibiotics in pig medicine, with renowned microbiologist and author of Pig Diseases Dr. David J. Taylor as speaker. This was followed by similar seminars and lectures held in various local and other international forums. Since then, Novartis has always been active in promoting judicious use of antibiotics in food animals.

THE NATURE OF THE ANTIBIOTIC PROBLEM
Beginning in 1962, after more than a decade of widespread use of antibiotics in animals, and up to the present time, there have been formal inquiries in regard to the safety of antibiotic feed-additives for animals. Several reports of various international committees and organizations have been published. Of these reports, the Swann Committee (UK) Report has been seminal in the growing movement toward restriction of antibiotic use in animal agriculture. The Swann Committee was convened following a prolonged outbreak of antibiotic-resistant Salmonella infections in people of the United Kingdom in the 1960s.

In the years that followed, more and more human health problems with antibiotics surfaced, and in most of these cases the wide and “indiscriminate” uses of antibiotics in livestock and poultry are blamed. Volumes of popular and scientific literatures about these problems have been published, making the general public aware of the problems, real or imagined, of antibiotic resistance in both human and animal pathogens.

Some of the current controversial health problems related to use of antibiotics include (a) vancomycin-resistant enterococci (VRE), (b) methicillin-resistant Staphylococcus aureus (MRSA), and human foodborne pathogens that also show antibiotic resistant, such as Salmonella DT 104, Campylobacter, E. Coli O 157:H7 and Listeria. Many human deaths have been directly or indirectly related to these infections, which were also complicated that the usual antibiotics to treat these infections have proved ineffective. Vancomycin for example has been reserved as the last-resort antibiotic against pathogenic enterococcus, but is now considered almost useless in most cases of enterococcus infections. Methicillin, which was originally developed specifically against penicillin-resistant S. staphylococcus, has also become ineffective for this very same bacterial organism!

Although certain antibiotics such as avoparcin and virginiamycin have been used in Europe exclusively in animals, and have never been used in humans, they have been found to confer resistance to human infections that used to be responsive to vancomycin treatment. Being members of the glycopeptide or streptogramin group of antibiotics, these drugs have caused cross-resistance with vancomycin. Paradoxically, VREs have emerged as significant problems in human hospital not in Europe but rather in the United States. The basis of this paradox may relate to the high level of vancomycin use in human hospital in the United States relative to use in Europe. This observation shows that the problem of antibiotic resistance may as well be caused by antibiotic use in human medicine.

As a way of reducing the incidence of antibiotic resistance in people, the European Union (EU) has banned all growth-promoting antibiotics by the year 2000. Many other countries including the Philippines followed the initiatives of the EU.

A “NEW” CLASSIFICATION OF ANTIBIOTICS
With very few exceptions, all antibiotics or their derivatives used in humans are also used in animals – e.g. penicillins, tetracyclines, macrolides, and aminoglycosides. It is generally accepted that cross-resistance among antibiotics is most likely when they are used in both humans and animals, as shown by the interaction of avoparcin or virginiamycin (both are animal drugs) to vancomycin (an important human antibiotic).

Although the implementation of rules on use of antibiotics in animals has not been as rigid in the USA as in Europe, the US Food and Drug Administration proposed a classification of antibiotics with the goal of putting a limit to the choice of antibiotics for use in food animals. If approved, this proposal will limit tremendously the number of antibiotics that can be used in animals.

Included in Category I are antibiotics that are essential for treatment of life-threatening human infections, and where resistance to alternative antibiotics (Category II) may limit therapeutic options. Examples are fluoroquinolones, vancomycin, dalfopristin/quinupristin (Synercid) and the 3rd generation cephalosporins). These are to be used exclusively in human patients.

Those in Category II are drugs that do not meet the criteria for category I, and are drug of choice or important in treating potentially serious human diseases. These may be used in animals following a good medication practice. Examples are amoxicillin, trimethoprim-sulfas, erythromycin and other macrolides, and cephalosporins not in Category I.

The drugs in Category III are those that have little or no use in human medicine and are not drugs of choice or significant alternatives for treating human infections. Included here are the ionophores antibiotics (salinomycin, narasin, monensin, etc.), polymyxins (e.g. colistin), and the pleuromutilins like tiamulin (Dynamutilin) and valnemulin (Econor).

WAY OF CONTROLLING ANTIBIOTIC RESISTANCE
The most practical way to mitigate or minimize the development of bacterial resistance to antibiotics is not to ban antibiotic use in animals, as some social groups suggest, but to promote the practice-of prudent or judicious use of antibiotics. Prudent use is defined as use that maximizes therapeutic effects while minimizing the development of resistance.

There are three levels of guideline for judicious use of antibiotics: global (World Veterinary Association or WVA), national (national veterinary association in various countries), and species-oriented (associations of veterinarians dealing with specific animals; e.g. poultry, pigs, cattle, etc.). The WVA has come up with a general guideline for judicious use of antibiotics in animals, which may serve as `the basis for various national and species-oriented veterinary associations. As an important partner in animal industry locally and globally, Novartis Animal Health supports the promotion of prudent and judicious application of antibiotics in livestock and poultry.