The Southern Medical Journal (SMJ) is the official, peer-reviewed journal of the Southern Medical Association. It has a multidisciplinary and inter-professional focus that covers a broad range of topics relevant to physicians and other healthcare specialists.

SMJ // Article

Original Article

Declining Susceptibility to Neomycin and Polymyxin B of Pathogens Recovered in Otitis Externa Clinical Trials

Authors: H. Furman Cantrell, PHD, Elyane E. Lombardy, MD, Frederick P. Duncanson, MD, Ephraim Katz, PHD, Joseph S. Barone, MD

Abstract

Background: Otitis externa is usually treated empirically with topical neomycin/polymyxin B/hydrocortisone. The predominant pathogens associated with this infection arePseudomonas aeruginosa and Staphylococcus aureus.


Methods: Two multicenter clinical trials (one in adults and adolescents, and one in children), conducted between 1995 and 1996, compared neomycin/polymyxin B/hydrocortisone with ofloxacin for the treatment of otitis externa; two similar trials were conducted between 1999 and 2000. Assessments included the minimum inhibitory concentrations (MICs) of each antimicrobial drug for the major pathogens, bacterial eradication, and clinical efficacy.


Results: The MICs of all bacterial isolates (including P aeruginosa) for neomycin and polymyxin B increased markedly in the 1999 to 2000 studies compared with the 1995 to 1996 studies. In the later studies, mean MICs for all major pathogens tested had increased above the breakpoint for polymyxin B (≥4 μg/ml). In contrast, MICs of all isolates for ofloxacin remained similar between the two study periods and were within the susceptible range for this drug.


Conclusions: Although the bacterial eradication rates for both treatments in each study were equivalent, the clinical cure rate for neomycin/polymyxin B/hydrocortisone was lower (87%) than for ofloxacin (93%). Therefore, the organisms most often causing otitis externa appear to be developing resistance to neomycin and polymyxin B but not to ofloxacin.

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References

1. Cassisi N, Cohn A, Davidson T, et al. Diffuse otitis externa: clinical and microbiologic findings in the course of a multicenter study on a new otic solution. Ann Otol Rhinol Laryngol Suppl 1977;86(3 Pt 3 Suppl 39):1–16.
 
2. Data on file at Daiichi Pharmaceutical Corp., Montvale, NJ, 2002.
 
3. National Committee for Clinical Laboratory Standards. Performance standards for antimicrobic disc susceptibility tests (Approved Standard M2-A2 S2). Wayne, PA, National Committee for Clinical Laboratory Standards, 1981.
 
4. Matsen JM, Barry AL. Susceptibility testing: Diffusion test procedures, in Lennette EH, Spaulding EH, Truant JP (eds):Manual of Clinical Microbiology. Washington, DC, American Society for Microbiology, 1974, ed 2, pp 418–427.
 
5. Gales AC, Reis AO, Jones RN. Contemporary assessment of antimicrobial susceptibility testing methods for polymyxin B and colistin: review of available interpretative criteria and quality control guidelines. J Clin Microbiol 2001;39:183–190.
 
6. Clayton MI, Osborne JE, Rutherford D, et al. A double-blind, randomized, prospective trial of a topical antiseptic versus a topical antibiotic in the treatment of otorrhoea. Clin Otolaryngol 1990;15:7–10.
 
7. Emgard P, Hellstrom S. A topical steroid without an antibiotic cures external otitis efficiently: a study in an animal model. Eur Arch Otorhinolaryngol 2001;258:287–291.
 
8. Dohar JE. Evolution of management approaches for otitis externa. Pediatr Infect Dis J 2003;22:299–308.
 
9. Dohar JE, Kenna MA, Wadowsky RM. Therapeutic implications in the treatment of auralPseudomonas infections based on in vitro susceptibility patterns. Arch Otolaryngol Head Neck Surg1995;121:1022–1025.
 
10. Mirza N. Otitis externa: Management in the primary care office. Post-grad Med 1996;99:153–158.
 
11. Sundström J, Jacobson K, Munck-Wikland E, et al. Pseudomonas aeruginosa in otitis externa: A particular variety of the bacteria?Arch Otolaryngol Head Neck Surg 1996;122:833–836.
 
12. Jones RN, Milazzo J, Seidlin M. Ofloxacin otic solution for treatment of otitis externa in children and adults. Arch Otolaryngol Head Neck Surg 1997;123:1193–1200.
 
13. Ohyama M, Furuta S, Ueno K, et al. Ofloxacin otic solution in patients with otitis media: An analysis of drug concentrations. Arch Otolaryngol Head Neck Surg 1999;125:337–340.
 
14. Ostrowski VB, Wiet RJ. Pathologic conditions of the external ear and auditory canal. Postgrad Med1996;100:223–228, 233–237.