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Data taken from [11-15,120-128].

MICs for E. coli (mode) are usually <0.1 mg/liter for all agents, but resistance emergence has elevated the MIC90 to the values shown.

between the fluoroquinolones, some of which have broad-spectrum activity against both Gram-negative and Gram-positive species. Others (e.g., norfloxacin and pefloxacin) are less active against Gram-positive pathogens. Ciprofloxacin retains preeminence against Gram-negative isolates, notably against P. aerugi-nosa, for which it is the drug of choice. Levofloxacin has similar overall activity to ofloxacin (of which it is the L-isomer) but is possibly twice as active against Gram-positive isolates. Sparfloxacin is more active against the pneumococci but has been superseded by the newest agents. Trovafloxacin, moxifloxacin, and gatifloxacin have high potency and a wide spectrum including S. pneumoniae, against which they are 10-fold more active than ciprofloxacin and two- to fourfold more active than sparfloxacin [11-14]. Gemifloxacin continues the trend of increasing activity against respiratory pathogens [15].

The newer fluoroquinolones and naphthyridones have been specifically targeted at respiratory infections, and activity against drug- (penicillin-) resistant S. pneumoniae (DRSP) is of paramount importance. In this respect, all agents probably have activity against DRSP similar to their activity against sensitive strains [14,15].

Development of resistance has been a feature of fluoroquinolone therapy of staphylococcal infections [16,17]. Later agents such as clinafloxacin appear to have good activity against strains resistant to, for example, ciprofloxacin [18]. However, experience suggests that resistance would develop quickly in clinical use [15].

The new quinolones are significantly more potent than earlier class members against both Mycoplasma pneumoniae (MICs 0.01-0.6 mg/liter) and Legionella pneumophila (MICs usually <0.06 mg/liter) [14,19]. They also have improved potency against Chlamydia pneumoniae (14).

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