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1
Kaushik V, Malik T, Saeed SR. Interventions for acute otitis externa. Cochrane Database of Systematic Reviews 2010,
Issue1. Art. No.:CD004740. DOI: 10.1002/14651858.CD004740.pub2. RATIONALE: The best evidence we have to date. Includes 19 low quality RCT‟s only two of which are from primary care, and therefore probably included more severe or chronic cases. One big downside for primary care is that over half of the trials involved ear cleaning. The meta-analysis demonstrates topical treatments alone are adequate for treating most cases of AOE. Acetic acid was as effective and comparable to antibiotic/steroid for the first 7 days, but inferior after this point. It is important to instruct patients to use drops for at least one week, and to continue for up to 14 days if symptoms persist.

2
Thorp MA, Krunger J, Oliver S et al. The antibacterial activity of acetic acid and Burow's solution as topical otological preparations. Journal of laryngology and Otology, Vol 112/10 (925-8). Oct 1998. RATIONALE: There is little evidence to support the use of one agent over the other. Both have shown a similar efficacy compared to other topical treatments such as antibiotics and corticosteroids, although caution should be taken due to the lack of quality in these studies. Based on the fact that acetic acid is recommended as 1st line treatment for mild otitis externa whilst aluminium is for more resistant cases or extensive swelling, acetic acid's availability compared to aluminium acetate and that an ear wick requires specialist referral for insertion, acetic acid would seem to be a better first-line option. Although there are no trials of acetic acid versus placebo there are trials comparing its use to a topical antibiotic-corticosteroid combination they show equivalence. Only one study was found from a literature search which compared the efficacy between acetic acid and aluminium acetate (also known as Burow's solution). This was a small (n=20) in vitro study which compared activity of one, two and three percent acetic acid with Burow's solution (aluminium acetate 13%) on an agar plate with the following organisms; Pseudomonas aeruginosa, Staphylococcus aureus, Proteus mirabilis and Streptococcus pyogenes. The activity of each agent was ascertained by the size of the zone of inhibition of bacterial growth. Burow's solution showed significantly larger average zones of inhibition than acetic acid (p <0.001). Both the two and three percent acetic acid as well as the Burow's solution were active against all organisms tested.

3
CKS (2007) Acute otitis externa. Clinical Knowledge Summaries. http://cks.nice.org.uk/otitis-media-acute#azTab Accessed 24.09.14. RATIONALE: For acetic acid CKS states that: ''Acetic acid alone has not been compared with placebo for treating otitis externa in randomized controlled trials (RCTs). One double blind RCT found no statistically significant difference in efficacy between topical acetic acid and a topical antibiotic-corticosteroid combination at day 7. However, an antibiotic-corticosteroid combination was more effective after 14 and 21 days of treatment. A single blind RCT found that a topical acetic acid-antibiotic-corticosteroid combination was more effective than topical acetic acid alone after 14 days. The evidence comparing topical acetic acid-antibiotic-corticosteroid combinations with topical antibiotic-corticosteroid combinations is not of sufficient quality to determine which is more effective.''
Whilst for aluminium acetate it states: ''Aluminium acetate has not been compared with placebo for the treatment of otitis externa. Two randomized controlled trials (RCTs) found no clinically important difference between topical aluminium acetate and topical antibiotics with or without corticosteroid. However, these results should be interpreted with caution because of the very low methodological quality of the studies.''

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Rosenfeld RM, Brown L, Cannon R, Dolor RJ, Ganiats TG, Hannley M, Kokemueller P, Marcy M, Roland PS, Shiffman RN, Stinnett SS, Witsell DL, Singer M, Wasserman JM. Clinical Practice Guideline: Acute Otitis Externa. OtolaryngologyHead and Neck Surgery 2006;134(Suppl 4): S4-S23 RATIONALE: Up to 40% of patients with AOE receive oral antibiotics unnecessarily. The oral antibiotics in the trails were often inactive against P aeruginosa (incidence 36%) and S aureus (incidence 21%). Topical antibiotics such as neomycin have a broader spectrum of activity. When using topical antibiotics in this situation bacterial resistance is far less of a concern as the high concentration of the drug in the ear canal will generally eradicate all susceptible organisms, plus those with marginal resistance. Malignant Otitis Externa is an aggressive infection that affects the immunocompromised and elderly that requires prompt admission. Facial Nerve paralysis may be an early sign. GPs should refer severe cases, characterised by unremitting pain, cranial nerve deficits, perforated tympanic membrane or history of previous ear surgery.

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Abelardo E, Pope L, Rajkumar K, Greenwood R, Nunez DA. A double-blind randomised clinical trial of the treatment of otitis externa using topical steroid alone versus topical steroid-antibiotic therapy. European Archives of Oto-rhino-laryngology: 2009;266(1):41-5 RATIONALE: A hospital outpatient RCT showing superiority of topical steroid-antibiotic therapy. The Cochrane Review 2010 also stated that „the evidence for steroid-only drops is very limited and as yet not robust enough to allow us to reach a conclusion or provide recommendations.‟

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NEOMYCIN SULPHATE with CORTICOSTEROID is suggested as topical antibiotic + steroid as it contains an antibiotic that is not used orally, Neomycin is active against Pseudomonas and Staphylococci the most common bacterial causes, plus there is the choice of four agents: Betnesol-N; Otomize; Otosporin and Predsol-N.

The POCAST project is funded by the National Institute for Health Research Health Protection Research Unit (NIHR HPRU) in Healthcare Associated Infections and Antimicrobial Resistance at Imperial College London and by the Imperial College Healthcare Charity (Grant Ref No:7006/P36U).