TABLE 2.

Half-lives of ciprofloxacin in J774 macrophages as measured during efflux studies under conditions that caused a 2.5- to 4-fold increase in drug accumulation at equilibrium^a

Condition	Half-life (min)b
Ciprofloxacin (17 mg/liter; 50 μM)c	1.68 ± 0.30a
Ciprofloxacin (68 mg/liter; 200 μM)c	4.08 ± 0.74b
Exposure to pH 6d	9.26 ± 0.53c
ATP depletiond	10.72 ± 0.24c
Addition of probenecid (10 mM)d	9.51 ± 0.53c
Addition of MK571 (100 μM)d	7.70 ± 1.19c

^aSee Fig. 3 to 6 and the text for details.

^bGroups with the same letter are not different from one another but are significantly different from those with a different letter (paired t test analysis; P < 0.05)

^cDrug extracellular concentration during uptake only.

^dCiprofloxacin extracellular concentration during uptake was 50 μM; indicated treatment applied during uptake and efflux.