Influence of low dose ciprofloxacin on microbial colonization of the digestive tract in healthy volunteers during normal and during impaired colonization resistance.

Ciprofloxacin in low doses is, in volunteers, effective for decontaminating the digestive tract [elimination of aerobic Gram-negative bacilli (GNB)] without disturbing colonization resistance. Before using this concept in neutropenic patients, we investigated if a low dose quinolone is still effective when the colonization resistance is disturbed by another antimicrobial agent. Ciprofloxacin 20 mg daily was effective in eliminating Gram-negative bacilli from the digestive tract in 4/5 volunteers, in 1 volunteer the GNB persisted in low concentration. No colonization with exogenous resistant GNB occurred. Following impairment of colonization resistance by addition of clindamycin 300 mg daily, 3/5 volunteers became colonized by spontaneously acquired exogenous GNB resistant to ciprofloxacin. We conclude that selective decontamination with a quinolone in low dosage cannot be recommended in neutropenic patients because there is, in the case of disturbed colonization resistance, a real risk of acquisition of quinolone-resistant strains.