Table 1.

Effect of Azithromycin in Planktonic Growth Conditions

	MIC without azithromycin	MIC with azithromycin
tobramycin	1.0 mcg/mL	0.5 mcg/mL
ciprofloxacin	1.0 mcg/mL	0.5 mcg/mL

Addition of azithromycin to tobramycin or ciprofloxacin had no significant effect on the minimal inhibitory concentration (MIC) of these antibiotics after 24 hours in a shaking liquid culture at 37 C (Table 1). The slight reduction in MIC for both ciprofloxacin and tobramycin is unlikely to be a significant change but clearly does not indicate antagonism of tobramycin during planktonic bacterial growth conditions. These experiments used the same P. aeruginosa bacterial strain and concentration of azithromycin as that used in the biofilm culture model above. Data were replicated 3 times to ensure consistency. Azithromycin alone did not provide an MIC break point through 20 mcg/mL indicating a lack of antimicrobial effect as monotherapy (data not shown).