**6. Combination therapy**

The application of combination therapy instead of monotherapy in cases of non-MDR *P. aeruginosa* remains to date a controversial issue [14]. Combination treatment against MDR strains instead seems to be some times necessary (for example in cases of pan-resistance or resistance to all except a single agent). In such cases better results are expected by the additive or subadditive activity of a combination or by the enhancement of a single active agent by an otherwise inactive drug [142].

Several old and newer studies have showed the increased activity *in vitro* of various antibiotic combinations against MDR *P. aeruginosa* (Table 7) even though, the mechanisms of positive interaction between the various agents are rarely known [142].


**Table 7.** Enhanced activity of antibiotic combinations against MDR *P. aeruginosa*.
