Friday, May 17, 2013

Three things I learned: fluoroquinolones

Microbiologists agree that love IS the best medicine...but the antimicrobial properties of fluoroquinolones are needed in some situations.

I've been sitting a little while on a webinar on the fluoroquinolone (FQ) class of antimicrobials (accessible on Bayer's Accelerate website).

Dr Darren Trott, senior lecturer in veterinary microbiology at the University of Adelaide, is an expert on antimicrobials and has spoken extensively about the issue of antimicrobial resistance. In fact, I've even stuck a swab up my nose in order to contribute to his research on MRSA carriage (my result returned negative, thank goodness).

The webinar was a nice review of FQ pharmacology, so in many ways it was a reminder of some important messages as much as anything else. I am sure others will take away different messages from the talk (so please watch it yourself - its 36 minutes).

So what did I learn?
1) If a pathogen becomes resistant to one FQ, it will typically be resistant to this whole class of drugs.
2) FQs are great because they are broad-spectrum, bactericidal, concentration dependent antimicrobials which allows their once a day dosing. But they do have some post-antibiotic activity which renders pathogens vulnerable to the host immune system even as the course is finished.
3) Prescribing veterinarians should opt for the higher end of the dose-range to minimise the risk of resistant pathogen emergence (in this regard pradofloxacin may be superior in that it has lower MICs (minimum inhibitory concentration) and lower MPCs (mutant prevention concentration) than other FQs.
I am going to cheat and add two more points as I think they are worth making. We all know that FQs at high doses are associated with retinal degeneration in cats. Risk factors include older patients, drug interactions, concurrent renal disease and possibly rapid intravenous injection so watch out for those.

Also, all FQs can inhibit cartilage growth which is why we avoid using them in young animals. 

It was a thought-provoking presentation as antimicrobial resistance is a major problem for the welfare of humans and animals. One barrier to prudent antimicrobial use, in real life, is the sheer cost of culturing every pathogen and determining sensitivity. At present, owners pay for this. But surely as a society we need to think about setting up systems where culture and sensitivity testing can be performed cheaply so that the appropriate antimicrobial could be used in every case.