Compared with placebo , erythromycin reduced the rate of pulmonary exacerbations over the @ weeks of the study in patients with P. aeruginosa-dominated infection ( median @ -LSB- IQR @-@ -RSB- vs @ -LSB- @-@ -RSB- ; median difference -@ , @ % CI -@ to -@ ; p = @ ) , but not in those without P. aeruginosa-dominated infection ( @ -LSB- @-@ -RSB- vs @ -LSB- @-@ -RSB- ; median difference @ , -@ to @ ; p = @ ; interaction p = @ ) .