, 1989) of treatment of intermittent infection with P. aeruginosa, which consists of a combination of inhaled colistin and oral ciprofloxacin used with

increasing dosage and for increased duration at reinfections (Hansen et al., 2008). However, inhaled tobramycin and oral ciprofloxacin, both of which target the metabolically active biofilm subpopulation, have been shown to have similar good results as inhaled colistin check details and oral ciprofloxacin in the early treatment of CF patients (Taccetti et al., 2012). This is probably due to the predominant effect of oral therapy on bacteria situated in the respiratory zone of the airways and of inhaled therapy on bacteria situated in the conducting zones of the respiratory tree. The synergistic effect of colistin and ciprofloxacin observed in in vitro biofilm studies might be tested only when quinolones become available for inhalation (Geller et al., 2011; Hoiby, 2011) and their combination therapy learn more can be investigated. Recently is has been shown in CF patients that combined colistin–tobramycin inhalation significantly decreased bacterial burden and that in animal and in vitro studies colistin–tobramycin combination was superior to monotherapy with regard to the killing of biofilm

P. aeruginosa (Herrmann et al., 2010). The rationale behind recommending combination therapy is, in addition to attacking various biofilm bacterial subpopulations, prevention of the development of antibiotic resistance especially when hypermutable isolates are selected (Macia et al., 2005, 2006). Biofilm susceptibility testing of 100 CF isolates demonstrated diminished activity of several antipseudomonal antibiotics compared with standard in vitro susceptibility testing,

and suggested that the use of standard drug dosages result in suboptimal drug concentrations at the site of infection (Moskowitz et al., 2004). Moriarty et al. (2007) measured sputum and serum concentrations of antibiotics in CF patients and showed that key PD parameters associated with clinical effectiveness for ceftazidime and tobramycin were not achieved at Reverse transcriptase the site of infection in the lung after intravenous administration. The negative effects of biofilm subinhibitory concentration are multiple: lack of bacterial killing, development of antibiotic resistance due to exposure of bacterial cells at concentrations lower than the mutant-preventing concentration, and enhancement of biofilm formation. It has been shown that sub-MIC concentrations of aminoglycosides (Bagge et al., 2004; Hoffman et al., 2005), beta-lactam antibiotics (Bagge et al., 2004) and quinolones (Takahashi et al., 1995) upregulate genes involved in biofilm formation. So high dosages are required to achieve effective treatment of biofilms based on in vivo PK/PD studies (Hengzhuang et al., 2012). In addition, the low oxygen concentrations present in the CF mucus (Worlitzsch et al., 2002; Kolpen et al.