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* - not licensed for animals; # reconstituted sol. stable for up to 7 days at 4oC or 1 month frozen; ¶ silver sulfadiazine shows additive activity with gentamicin and fluoroquinolones.
Potential toxicity
Ticarcillin, polymyxin B, neomycin, tobramycin and amikacin are potentially ototoxic. Neomycin can cause contact reactions. Enrofloxacin, marbofloxacin, ceftazidime, silver sulfadiazine and soluble gentamicin appear to be safe in the middle ear.
Treatment of biofilms and mucus
Biofilms can be physically broken up and removed
by thorough flushing and aspiration. TrizEDTA and
2% n-acetylcysteine can disrupt biofims. Systemic n-acetylcysteine (NAC; 600mg q12h) can help dissolve biofilms in the middle ear and other mucous surfaces. NAC and bromhexine can help drainage of mucus in PSOM and feline inflammatory otitis media.
Triz-EDTA
TrizEDTA damages bacterial cell walls and increases antibiotic efficacy. It is best given 20-30 minutes before the antibiotic but can be co-administered. It is well tolerated and non-ototoxic. It shows additive activity with chlorhexidine, gentamicin and fluoroquinlones. Solutions of 0.6% enrofloxacin, 0.2% marbofloxacin, 0.3% gentamicin, 0.1% amikacin, 2.8% ticarcillin and 1.7% ceftazidime in trizEDTA are effective against many multi- drug resistant bacteria including Pseudomonas.
Anti-inflammatory treatment
Reducing pruritus, swelling, exudation and tissue proliferation is a key goal, and maintenance treatment is necessary in ongoing conditions (e.g. atopic dermatitis). Dexamethasone helps reverse the ototoxic effect of Pseudomonas. Systemic treatment is necessary in cases with severe ear canal stenosis, and/or generalized inflammatory skin disease.
Ear wicks
Polyvinyl acetate ear wicks can be cut to size and inserted into the ear canal under anaesthesia, soaked with an antibiotic, trizEDTA and/or steroid solution and left for 3-10 days, applying the ear solution once daily. The wicks absorb discharge and draw the antibiotic solution into the ear canals. Steroid soaked wicks can prevent stenosis following laser surgery to remove polyps etc. They may prevent drainage from the middle ear in discharging otitis media though.
Treating otitis media
Debris must be flushed out under general anaesthesia by passing a catheter into the middle ear. Otitis media may need 3-4 weeks (and possibly longer) systemic treatment, which is a problem if parenteral drugs are used. Pseudomonas infections, however, usually clear quickly once effective cleansing, antimicrobial treatment and control of the primary cause are established. Other options include instilling antimicrobials into the middle ear every 3-10 days (e.g. enrofloxacin, marbofloxacin or gentamicin), using large volumes of topical therapy, or combining systemic and topical therapy.
Compliance and adherence
Poor compliance or adherence will compromise efficacy and encourage resistance. This can be improved by:
• Using medication that the owner is able and wants to administer
• Giving written instructions
• Showing how to administer topical therapy and clean
the ears
• Using precise terminology – e.g. ‘every 12 hours’
instead of ‘twice daily’
• Follow up and communication
• Analgesia to facilitate cleaning and medication
An Urban Experience
 Antibiotics useful in resistant Pseudomonas otitis
     Ciprofloxacin*
   0.2% sol. 0.15-0.3 ml/ear q24h
   Enrofloxacin
 15-20mg/kg PO q24h; 2.5% injectable sol. diluted 1:4 with saline or Epiotic® topically q24h; 22.7mg/ml sol. 0.15-0.3 ml/ear q24h
 Marbofloxacin
  5-10/kg PO q24h; 1% injectable sol. diluted 1:4 with saline topically q24h; 20mg/ml sol. 0.15-0.3ml/ear q24h
 Ofloxacin
  0.3% 0.15-0.3 ml/ear q24h
 Carbenicillin*
   10-20mg/kg IV q8h
   Clavulanate-ticarcillin*#
 15-40 mg/kg IV q8h; reconstituted injectable sol. 0.15- 0.3 ml/ear q12h; 160mg/ml sol. 0.15- 0.3 ml/ear q12h
 Ceftazidime*#
  25-50mg/kg IV q8h; 100mg/ml 0.15–0.3 ml/ear q12h
 Silver sulfadiazine¶
  Dilute 0.1-0.5% in saline
 Amikacin*
  10-15mg/kg SC q24h; 50mg/ml 0.15-0.3ml/ear q24h
 Gentamicin
  5-10mg/kg SC q24h
 Tobramycin*
   Use eye drops or 8mg/ml injectable sol. 0.15-0.3ml/ear q24h
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