Page 257 - ONLINE PROCEEDING BOOK WSAVA 2017
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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  uoroquinolones.
Potential toxicity
Ticarcillin, polymyxin B, neomycin, tobramycin and amikacin are potentially ototoxic. Neomycin can cause contact reactions. Enro oxacin, marbo oxacin, ceftazidime, silver sulfadiazine and soluble gentamicin appear to be safe in the middle ear.
Treatment of bio lms and mucus
Bio lms can be physically broken up and removed
by thorough  ushing and aspiration. TrizEDTA and
2% n-acetylcysteine can disrupt bio ms. Systemic n-acetylcysteine (NAC; 600mg q12h) can help dissolve bio lms in the middle ear and other mucous surfaces. NAC and bromhexine can help drainage of mucus in PSOM and feline in ammatory otitis media.
Triz-EDTA
TrizEDTA damages bacterial cell walls and increases antibiotic ef cacy. 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  uoroquinlones. Solutions of 0.6% enro oxacin, 0.2% marbo oxacin, 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-in ammatory 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 in ammatory 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  ushed 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. enro oxacin, marbo oxacin or gentamicin), using large volumes of topical therapy, or combining systemic and topical therapy.
Compliance and adherence
Poor compliance or adherence will compromise ef cacy 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
Cipro oxacin*
0.2% sol. 0.15-0.3 ml/ear q24h
Enro oxacin
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
Marbo oxacin
5-10/kg PO q24h; 1% injectable sol. diluted 1:4 with saline topically q24h; 20mg/ml sol. 0.15-0.3ml/ear q24h
O oxacin
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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