To date there have been very few pharmacokinetic studies published in reptiles, and with only only limited numbers of antibiotics.
So far, all of the studies have been done in snakes, turtles and crocodilians. There have been no pharmacokinetic studies
done in lizards.
There are a number of factors that must be considered when choosing an antibiotic. The results of microbiological culture
and sensitivity testing, the species being treated, physical condition of the patient, frequency of administration, cost of
the therapy, owner compliance, and a host of other factors are all important.
The veterinary clinician must have a thorough understanding of reptile physiology and biology prior to administering medications.
Since all reptiles are ectotherms, and their metabolism is temperature dependent, they will often react unpredictably to the
same drug in different settings. A good working knowledge of the more common species of reptiles, their life histories and
their peculiarities will help prevent potential disasters during therapy.
Before treatment is initiated the patient should be given a thorough exam including a CBC and serum profile, with a uric acid,
to assess hydration status. Dehydrated or hyperuricemic patients should be properly rehydrated prior to initiating therapy.
It is the rare case that cannot wait one to two days to assure appropriate hydration prior to treatment. However, if for some
reason treatment must be instigated immediately, it would behoove the practitioner to choose a non-nephrotoxic drug.
Another important consideration is the ambient temperature of the reptile's environment. Pharmacokinetic studies have shown
that an increase in ambient temperature tends to increase both the volume of distribution and body clearance of the drug.
A decrease in ambient temperature with a resultant decrease in body clearance could potentially allow a build up in concentration
of the drug to a point where it might reach toxic levels if dosing is not decreased accordingly.
When reptile pathogens are treated at higher temperatures the Mean Inhibitory Concentration (MIC) needed to achieve effective
treatment significantly decreases. This allows for a lower dose of antibiotic to be given, another positive factor when dealing
with potentially nephrotoxic drugs.
Most researchers feel that it is best to treat sick reptiles near the higher end of their preferred optimum temperature zone.
Not only is it beneficial for reasons already mentioned, but elevated ambient temperatures have been shown to stimulate the
host's immune system and aid in fighting disease in other ways already discussed.
When selecting the appropriate antibiotic it is important to consider the status of the host's immune system. In critically
ill or immuno-compromised reptiles, bactericidal, rather than bacteriostatic antibiotics are preferable. In cases of gram negative sepsis, especially with Pseudomonas infections, the reptile patient is often severely immunocompromised.
In many cases the animals are infirmed because they have been immunocompromised due to improper husbandry conditions. The
most common cause is from being maintained at suboptimal environmental temperatures.
Methods of administration
There are very few instances where oral antibiotic therapy is required. Enteric infections often warrant oral administration
of appropriate drugs. There are two common methods for administering oral antibiotics. If the patient is still feeding, the
antibiotic can be mixed with the food or injected into the dead prey and fed to the animal. Gavaging, or stomach tubing, is
a second technique which can be used to administer oral medications.