Following these guidelines will help to maximize therapeutic success of antibacterial agents whilst at the same time minimizing the development of antibacterial resistance, thereby safeguarding antimicrobials for future veterinary and human use. These guidelines should be read in conjunction with the updated BSAVA Guide to the Use of Veterinary Medicines, the PROTECT ME guidance and individual drug monographs (www.bsavalibrary.com). It is important that the veterinary profession uses antibacterials prudently in order to: minimize the selection of resistant veterinary pathogens (and therefore safeguard animal health); minimize possible resistance transfer to human pathogens; and retain the right to prescribe certain antibacterials.

It is important to remember that antibacterials do not make organisms resistant, but they do create selective pressure on populations of organisms. Resistance may be inherent, evolved (by chromosomal DNA changes) or acquired (by plasmid transfer). Resistance is reduced by the following:

1. Reducing the expectation of antibacterial prescriptions. Educate clients not to expect antibacterials when they are not appropriate; e.g. viral infections.
2. Minimizing and ideally avoiding prophylactic use.
   • Prophylactic antibacterial use may be appropriate in certain medical situations; for example, when an animal is considered to be at increased risk due to concurrent disease or immunosuppressant therapy and is in contact with other infected animals.
   • Prophylactic antibacterial use may be appropriate in the perioperative period, although it should not be a substitute for good asepsis. Examples of appropriate criteria for perioperative antibacterial use include:
     • Prolonged surgical procedures (>1.5 hours)
     • Introduction of an implant into the body
     • Procedures where introduction of infection would be catastrophic (e.g. CNS surgery)
     • Where there is an obvious identified break in asepsis
     • Bowel surgery with a risk of leakage
     • Dentistry with associated periodontal disease
     • Contaminated wounds.
   • In exotic pets, the choice of an appropriate antibiotic will be highly dependent on the species or group of species and the likely spectrum of bacterial involvement, and great care must be taken to avoid any known adverse effects (e.g. on gut microflora in rabbits and rodents).
3. Culturing appropriate material for sensitivity testing.
   • The results from culture and sensitivity tests considerably assist the choice of which antibacterial to use.
   • Culture is not required in every case, but when prolonged courses of antibacterials are likely to be needed (e.g. pyodermas, otitis externa, deep or surgical wound infections) then culture will improve the animal’s treatment.
4. Knowing the features of antibacterials. There are three key areas that veterinary surgeons must have a working knowledge of.
   • Spectrum of activity. Many of the antibacterials in routine veterinary use are broad-spectrum; however, to minimize resistance the narrowest spectrum agent should be chosen. Some specific examples of spectra covered are:
     • Anaerobes – metronidazole, clindamycin, many of the penicillins (especially the narrow spectrum penicillins such as Penicillin G) and cephalosporins
     • Gram-positive bacteria – penicillins, cephalosporins, lincosamides and macrolides
     • Gram-negative bacteria – aminoglycosides and fluoroquinolones.
   • Distribution. Many of the antibacterial classes are well distributed around the body, and it is important to be aware of some of the specifics of distribution. Key examples (in mammals) include:
     • Aminoglycosides are poorly distributed. They are not absorbed from the GI tract and even if given systemically distribution can be quite restricted. Conversely, it means that they are very appropriate for local delivery
     • Beta-lactams attain high concentrations in the urinary tract due to filtration and secretion into the renal tubule. Levels attained may be many times higher than plasma concentrations. Fluoroquinolones also attain extremely high levels in the urinary tract
     • Lipid-soluble basic antibacterials such as the macrolides and lincosamides become ion-trapped (concentrate) in sites such as the prostate gland and the mammary gland.
   • Adverse effects/toxicity. These must be considered in the context of the individual animal and in relation to concurrent treatment or pre-existing conditions.
5. Use the antibacterial you have chosen appropriately.
   • Consider the practicalities and owner compliance.
   • Give the appropriate dose, for the appropriate frequency and the appropriate duration. Too little or too much antibacterial will contribute to resistance and inappropriate use will lead to treatment failure.
   • Is the antibacterial time- or concentration-dependent? (Refer to the BSAVA Guide to the Use of Veterinary Medicines (www.bsavalibrary.com) for an explanation of these terms.)
6. Assess the response. Part of this may be carrying out repeated culture and sensitivity testing, where appropriate, and amending treatment if indicated from the results. If you are using an antibacterial which your clinical experience, or the results of culture and sensitivity, suggests should be effective in a particular situation and treatment fails, then this should be reported through the Suspected Adverse Reaction Surveillance Scheme (SARSS) organized by the Veterinary Medicines Directorate (VMD), as this is important in monitoring resistance development.
7. Certain antibacterials should be used judiciously. This means that their use as first line agents should be avoided, and they should only be used when other agents are ineffective (ideally determined by culture and sensitivity testing). These include:
   
   
   • Fluoroquinolones
   • Third and fourth generation cephalosporins
   • Amikacin.
   The VMD has published guidelines for responsible antibiotic use under the cascade which state that ‘it is justified, on a case-by-case basis, to prescribe an antibiotic on the cascade in the interests of minimizing the development of resistance’. Consequently, use of an alternative antibiotic may be justified, rather than first-line use of a licensed fluoroquinolone in an exotic animal, if the veterinary surgeon feels that this is appropriate for the individual case.
8. Certain antibacterials should probably NOT be used in veterinary species. These are agents of last resort in human patients and include:
   • Vancomycin
   • Carbapenams such as imipenam.

In addition to written guidelines on which antibacterials should be used and the appropriate dosing regimens, there should be a practice policy in terms of appropriate criteria warranting antibacterials. For example, it is feasible to work out appropriate first option antibacterials for uncomplicated urinary tract infections and surgical prophylaxis, which should then be used by all practice members.

Antibacterials in small mammals

Antibacterial therapy in several small mammal species poses a greater risk when compared with other species due to the suppression of normal bacterial flora, resulting in overgrowth of other species, notably Clostridium, resulting in enterotoxaemia and death. Mice, rats, ferrets and usually gerbils are fairly resistant, whereas hamsters, guinea pigs, chinchillas, degus and rabbits are more susceptible. The risk of enterotoxaemia is related to several factors, including the drug selected, the dose, the route of administration and the animal’s nutritional status and general health. Antibiotics that have been associated with this problem when given orally include penicillins, lincosamides, aminoglycosides (possibly), cephalosporins and erythromycin. Some species appear more sensitive to certain drugs than others, while some medications actually appear well-tolerated by alternative routes (for example, injectable benzylpenicillin in rabbits). See individual monographs for more details.