The effect of ofloxacin on the intracellular growth of Legionella pneumophila in guinea pig alveolar phagocytes.

Ofloxacin was evaluated as an antibiotic for possible use in the therapy of Legionnaires' disease in relation to its ability to penetrate alveolar phagocytes and inhibit Legionella pneumophila intracellular replication. A comparison with two other antibiotics used in the treatment of Legionnaires' disease, ciprofloxacin and erythromycin, was also made. Ofloxacin was found to be the most effective antibiotic, eliminating viable L. pneumophila from alveolar phagocytes at 0.001 mg/l. This was followed by ciprofloxacin, eliminating intracellular organisms at 0.01 mg/l. Erythromycin was shown to be much less effective, requiring a much higher concentration, of 0.1 mg/l. All three antibiotics had approximately similar MIC values and the considerable differences in intracellular penetration shown by these antibiotics indicate how discrepancies between in-vitro and in-vivo estimates of efficacy can occur.