Antimicrobial activity of glycerine-ichthammol in otitis externa.

The clinical efficacy of glycerine-ichthammol in otitis externa may be due to an anti-inflammatory action of ichthammol or a dehydrating effect of glycerine on the oedematous ear canal. Its antimicrobial activity, if any, against the common organisms in otitis externa is not well known. A study of the antibacterial property of glycerine-ichthammol as measured by a growth inhibition test and a modified cidal assay, showed inhibition of selected gram positive organisms (Streptococcus pyogenes and Staphylococcus aureus) by ichthammol and glycerine-ichthammol combination, but only negligible antibacterial activity against Pseudomonas aeruginosa and Escherichia coli. Candida albicans was also weakly inhibited. As the activity against gram negative organisms is minimal, incorporation of an anti-gram negative antibiotic such as gentamicin in the glycerine-ichthammol compound to enhance its antibacterial spectrum is suggested.