Recurrent ear infection whilst on penicillin?

Question
Hi Dana

I have a 5 year old large domestic up eared rabbit who has had recurrent middle ear infections over the last 2-3 years. The first one resulted in severe tilt which we nursed him through and got his head back to just 10 degree residual tilt with acupuncture.

Each time he gets an infection we treat with injectible penicillin weekly, of varying durations. Usually minimum 6 weeks treatment. Our vet told us eventually he may require lifelong treatment to stave off infections. This is fine. I do the injections myself at home ad he tolerates it well so it ihas been an easily sustainable regime for us.

He gets 2 infections a year on average.  The last two times I feel strongly that the penicillin has JUST kept the infection at bay ie the day before it's due (5-6 days post the last injection) he starts dropping his ear again and is very quiet. It is obviously painful as he picks up each time with Metacam.

We are in the midst of treating him now- he has had 5 injections over five weeks and he is not 100% still. Do you think he needs more frequent injections than weekly, or would adding another antibiotic be your recommendation? My vet just said we may need to extend the duration from 6 weeks to 8-12 weeks but I wonder if it should have made more of an impact by now..

Thanks so much for your input

Natalie

Answer
Dear Natalie,

If the infections are becoming more frequent and serious, despite the penicillin injections, then it's possible you've been selecting resistant bacteria with your on-again/off-again Pen treatments.  One injection a week is allowing the therapeutic levels of penicillin in your bunny's tissues to dissipate, as even long-acting Benzathine lasts in the tissues for only about 48 hours.  So it's important to keep up injections at a constant, close-spaced rate to avoid conditions that favor the survival (and reproduction) of the more resistant individual bacteria in your bunny's population.

Evolution of resistant bacteria can happen even with constant treatment, too.  And you're kind of between a rock and a hard place:  do you keep up the medication and risk the evolution of resistant bacteria, or do you stop treament and let the bunny live in misery?  The choice is clear, if you love your bunny.

Fortunately, there is not only one antibiotic in the arsenal. I would suggest you ask the vet about doing a culture and sensitivity test:

http://www.bio.miami.edu/dana/culture.html

to determine the identity of the pathogens, as well as the array of antibiotics to which they are sensitive.  It might be time to try a different antibiotic, or combination of antibiotics, to keep this problem at bay.

Also consider that if you haven't had cultures done, the infection could be due to yeast, not bacteria. If this is the case, then antibiotics might do more harm than good:  they kill of the bacteria competing with the yeast, and give the yeast a competitive advantage that lets them reproduce wildly.

Hope some of this will help.

Dana