As these things sometimes do, it often surprises me that I now spend a lot of time thinking about the best medicines to treat sick koalas.
The koala is an Australian iconic animal. What does this mean? When you think of Australia’s amazing diversity of marsupials; it is the koala that is one of the best known. When celebrities and dignitaries come to Australia they want to touch one of these beautiful animals and be photographed doing so. Consequently the koala is very important to attract tourists.
For such an iconic species, it is interesting that prior to 2010 that were no published studies on what happens to conventional veterinary medicines when administered to koalas. For example, if a medicine is administered by mouth, how much is absorbed via the gastro-intestinal tract? If the medicine gets into the circulation how much binds to proteins in the plasma? How quickly is the medicine broken down (i.e. metabolised) by the liver and how fast is it eliminated by the kidney and or faeces? It is important to know these things because this determines the dose rate of medicine required to be therapeutic. Koalas had been dosed traditionally at the same dosage for dogs and cats.
The beginning of this research started when Dr Joanna Griffith was undertaking her PhD into treatments for koala chlamydiosis. Chlamydiosis is the most serious bacterial disease affecting wild koala populations in northern NSW and south-eastern Queensland.
She was interested in documenting how affective the current medicines were for reducing the signs of ‘wet-bottom’ in koalas. Wet bottom is the colloquial term for chlamydial infection in the urinary and genital tracts. It is painful and the animals leak urine onto the fur that results in the fur discolouration. Joanna administered the medicine enrofloxacin (has the trade names of Baytril or Enotril) at the traditional dose recommended for koalas i.e. 5 mg/kg and she found very little found its way into the koala’s circulation. She carefully increased the dose by four times to 20 mg/kg and it was only at this concentration could this medicine be detected in the koala’s blood. This was the first sign that may be the dog/cat dosage is not applicable to koalas for this medicine. Joanna published her findings in the Journal of Veterinary Pharmacology & Therapeutics http://onlinelibrary.wiley.com/doi/10.1111/j.1365-2885.2010.01169.x/full. The information gleaned from this research suggested that a medicine’s pharmacokinetic profile in the koala may not be the same as for the dog and cat and thus the dosage often needs to be specifically modified for koalas. My research group has been studying the pharmacokinetics of medicines for koalas since. We have learnt many things about these amazing and unique animals and will be sharing our insights here.