Topical ciprofloxacin and antibiotic resistance

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Editor, – A generation or so ago, I was taught that if one wanted to render antibiotics useless, due to resistance, as quickly as possible, apply them topically. Why is ciprofloxacin being marketed in this way? Should there not be a full re-evaluation of the use and misuse of all topical antibiotics? Is there any convincing evidence that any of them are a good idea?

Peter Rout
General Practitioner
Darlington, NSW

Professor J. Turnidge, Microbiology and Infectious Diseases, Women's and Children's Hospital, Adelaide, comments:

The concern expressed by Dr Rout about the topical use of ciprofloxacin is shared by many others. The standard teaching comes from the early experience with the use of topical antibiotics to treat infected burns, where resistance emerged rapidly. It is possible that the very high counts of bacteria in infected burns made the selection of resistance easier. Whether this problem occurs with all topical antibiotic use is not clear. The concentrations of topical antibiotics are often 1000 fold higher than the minimal inhibitory concentrations of the bacteria. Thus, in theory, there should be a lower risk of resistance selection than with systemic use.

However, there is another principle that must be taken into account. The rate of resistance selection is related to the total amount of antibiotic use in the community. We should prefer topical drugs which, when resistance is selected, do not jeopardise the valuable systemic antibiotics. Indeed, in the case of fluoroquinolones, strenuous efforts have been made to ensure that availability of the systemic drug is restricted to cases of proven need. Topical application should follow the same principle. Dr Rout will be pleased to know that the availability of topical ciprofloxacin (and other topical quinolones) has been taken up with national regulators. Although the outcome is not known, we hope that these drugs will be restricted to (rare) cases of proven need.