Staphylococcus epidermidis develops resistance to ciprofloxacin rapidly. That this antibiotic is excreted in apocrine and eccrine sweat of healthy individuals might be the reason for the development of such resistance. We assessed whether S epidermidis isolated from the axilla and nasal flora of healthy people could develop resistance to ciprofloxacin after a 1-week course of this antibiotic.

The concentration of ciprofloxacin in sweat was measured in seven volunteers after oral administration of 750 mg ciprofloxacin twice daily for 7 days, and the development of resistance in S epidermidis from axilla and nostrils was monitored during and 2 months after the treatment. Genotyping of S epidermidis was done by restriction fragment length polymorphism.

The mean concentration of ciprofloxacin in sweat increased during the 7 days of treatment—from 2·2 μg/mL 2·5 h after the first tablet to 2·5 μg/mL after the fifth tablet, and 5·5 μg/mL after the 13th tablet. All persons harboured susceptible S epidermidis (minimal inhibitory concentration [MIC] 0·25 μg/mL) in axilla and nostrils before treatment. Four resistant strains were detected, two intermediate-level (MIC 4–12 μg/mL) and two high-level (MIC >32 μg/mL). Three of these strains were found in all the participants, and a ciprofloxacin-sensitive variant of one of the high-level resistant strains was also found before the start of the treatment. The high-level resistant strains were also resistant to methicillin, erythromycin, gentamicin, sulphonamide, and trimethoprim. A mean of 2·7 days after the start of the treatment, development of ciprofloxacin resistance was detected in S epidermidis from the axilla of all persons, compared with 11 days for the appearance of resistant S epidermidis in nostrils. The resistant strains persisted for an average of 37 and 39 days in axilla and nostrils, respectively, after the end of the treatment.

The rapid development of resistance to ciprofloxacin due to excretion of this drug into the sweat might be involved in the development of multiresistant S epidermidis and possibly other skin bacteria in hospitals and in communities with high use of ciprofloxacin or related drugs.