Antimicrobial use in exotics (Proceedings)
Objectives of the Presentation
• How to use different antimicrobial drugs safely and effectively in the exotic animal patient.
Key Points• there are many antimicrobials available for use in exotic species
• only a few are contraindicated in specific species
• it is important to understand the key physiological features which impact drug choice in certain species
• a good formulary for exotics will help clarify these species specific differences
In order to use antimicrobial drugs in exotic patients effectively, one has to understand both the basic pharmacokinetics of these drugs, as well as certain key physiological features of the species being treated (e.g. a poikilotherm animal vs. a homeotherm). One mayor problem in the use of antimicrobial drugs approved for dogs and cats in exotic species, is the fact that there is little clinical data available on the use of these drugs in exotic patients. While more and more pharmacological data is becoming available regarding the use of antimicrobials in exotics (mainly birds and reptiles), for the majority of the drugs used in the clinical setting in the different species, no exact figures have been published.
A specific diagnosis should be the foundation for the treatment choice in order to achieve the best results from the antimicrobial treatment. Drug choice based on a reliable culture and sensitivity helps avoid dispensing ineffective drugs and thus losing valuable treatment time. It is also important to remember that in many cases a systemic infection in the exotic patient is the result of a prolonged period of stress, and resulting immune suppression, and it is therefore of utmost importance not only to treat the infection but also to identify the underlying problem causing the stress. In poikilothermic pets (reptiles, amphibians, and fish) the underlying stressor is most likely an environmental problem such as inappropriate temperature or humidity. Chronic malnutrition is often also part of the problem. Once the underlying problem has been identified and corrected, treatment of the infection should be started. Often, and especially in severe cases, the animals will also need additional supportive care in order to maximize the success of the antimicrobial treatment.
The choice of an antimicrobial drug should be based both on the results of the culture and sensitivity, and on other pharmacological parameters. Some of the factors to consider in the choice of the appropriate antimicrobial drug are:
• The ability of the drug to reach therapeutic concentrations in specific tissues (e.g. CNS, bone, eye)
Oral administration is the preferred route of drugs in most exotic patients since it can often be easily managed at home, and it is also the least invasive route of drug delivery.
If the drug must to be given via the parenteral route, subcutaneous delivery is best. Often drugs can be added if fluids are being given subcutaneously to correct hydration deficits.
In birds the intramuscular route works well and drugs are commonly administered into the (generally) large pectoral muscle mass. Reptiles also usually have large muscle groups that can be used for intramuscular injections. In small mammals however, this route is less optimal, due to the lack of large muscle masses. When necessary hind leg musculature can be used.
The intravenous and intraosseus routes are possible in the hospitalized patient and are the preferred way to administer drugs quickly and accurately. In both birds and reptiles, intraosseus catheters can easily be placed and the fluid absorption through these catheters is equal to that obtained with intravenous access.
Topical application of antimicrobials can be used as an adjunct to systemic antibiotic treatments, but in most cases should not be the sole route of antibiotic delivery. In most cases a systemic infection is present, even when the clinical signs appear to be limited to one region (e.g. ear, eye).
"Pulse therapy" is a relatively new protocol for antibiotic treatment that has been described. In this protocol a single high dose of the antibiotic is given once a day rather than administering multiple smaller doses over the day. The idea utilizes the 'post antibiotic effect" of certain antibiotics. These drugs retain their efficacy even as the concentrations decreases. Not all drugs appear to be suitable for this use and currently only the fluroquinolones and amikacin are recommended as 'pulsing' agents. This form of drug delivery could obviously prove to be very useful in highly stress-prone animals where multiple handlings per day could be contraindicated.