Antibacterial prescribing is a common part of practice therefore it can be helpful to develop guidelines about when antimicrobials should (or should not) be prescribed and the appropriate dosing regimens. The practice policy should include information on which antibacterials can be used empirically, which should be used judiciously, i.e. when other agents are ineffective (ideally determined by culture and sensitivity testing), e.g. fluoroquinolones and third and fourth generation cephalosporins. Certain antibacterials should probably NOT be used in veterinary species. These are agents of last resort in human patients and include the carbapenems, such as imipenem, and vancomycin.

Prophylactic antibacterial use is the administration of antibacterials in the absence of infection, with the aim of preventing infection. Antibacterials should not be used for prophylaxis, unless the risk of infection is very high and the consequences of infection are severe. The use of ‘prophylactic antibacterials’ at other times is neither necessary nor desirable, and will contribute to the development of antimicrobial resistance in small animal practice. In the unlikely event of infections developing then they can be cultured and treated appropriately.

The most common reason for the prophylactic use of antibacterials in small animal veterinary practice is in the perioperative period, but their use may also be appropriate in certain medical situations; for example, when an animal is considered to be at increased risk due to concurrent disease or immunosuppressive therapy and is in contact with other infected animals.

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.

To be effective, prophylactic antibacterials must be present in tissues at the surgical site at the appropriate concentrations and at the time of contamination to prevent bacterial growth and subsequent infection. The following protocol is suggested:

• Administer the first dose 1 hour before the incision
• Re-administer during surgery if the procedure is ongoing after two half-lives of the antibacterial have passed
• Restrict treatment to the duration of the surgery or less than 24 hours, except where therapeutic doses are required (e.g. gross contamination, pre-existing infection)
• Avoid the use of newer broad-spectrum antibacterials.

Not all animals with bacterial infections require antibacterial treatment. In healthy individuals, reducing the bacterial load may be sufficient to enable recovery. Other options to reduce antibacterial use include:

• The use of antiseptic washes and ear cleaners, which may reduce the need for antibacterials in pyoderma and otitis externa, respectively
  • ▪  Effective lavage and debridement of infected material may reduce the need for antibacterials. Antiseptics and antibacterial wound dressings may also reduce the need for systemic antibacterials
  • ▪  The use of topical prescriptions reduces selection pressure on intestinal flora.
• The use of symptomatic relief (e.g. analgesia, cough suppressants) in uncomplicated viral infections or self-limiting disease)
  • ▪  Rectifying the underlying cause of disease may reduce the need for antibacterial treatment.

It is also important to educate clients not to expect antibacterials when they are not appropriate, e.g. uncomplicated viral infections.

Having a good knowledge of the types of bacteria likely to be involved in a particular infection, as well as of the properties of the antibacterials available to treat them, enables rational choices to be made which give the best chance of effective treatment and the lowest risk of selecting resistant bacteria.

There are three key areas where knowledge will help veterinary surgeons in the appropriate selection of antibacterials.

1. Spectrum of activity: many of the antibacterials in routine veterinary use are broad-spectrum; however, to minimize resistance, narrow-spectrum agents should be chosen whenever possible. Some 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.
2. Distribution: it is important to be aware of some of the specifics of distribution. Key examples 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.
3. Adverse effects/toxicity: these must be considered in the context of the individual animal and in relation to concurrent treatment or pre-existing conditions.

Cytology and culture can be used to diagnose bacterial infection correctly. 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.

Treat for long enough and at a sufficient dose to kill the bacteria, and then stop. Avoid under-dosing and consider how the drug will penetrate the target area. Repeat culture after long courses of antibacterials. Make sure owners know they should complete the course, even if their pet is better, and provide them with a Client Information Leaflets.

• Use the antibacterial you have chosen appropriately.
  1. Consider the practicalities and owner compliance.
  2. 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.
  3. Think about whether the antibacterial is time- or concentration-dependent? (Refer to the BSAVA Guide to the Use of Veterinary Medicines (www.bsava.com/Resources/Veterinary-resources/Medicines-Guide) for an explanation of these terms.)
  4. 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.