Infections caused by antimicrobial-resistant bacteria are a
serious public health problem, particularly those caused
by multidrug-resistant gram-negative bacilli (MDR-GNB).
The escalation of resistance is a difficult problem to manage;
with resistance to cephalosporins first appearing,
more recently followed by carbapenems and finally the
appearance and spread of pandrug-resistant bacteria.
Acinetobacter baumannii, Pseudomonas aeruginosa and
the Enterobacteriaceae are the main MDR-GNB producing
serious infections. The treatment of these infections
is difficult due to the lack of active antimicrobials [1]. In
addition, carbapenem-resistant Klebsiella pneumoniae has
become a new antibiotic resistance problem in countries
such as, Greece, Italy and Spain. This context is likely the
best example of the denominated ‘Post-Antibiotic Era’,
with relevance even in non-specialized media [2].
MDR A. baumannii has turned into one of the main
causes of hospital-acquired infection. MDR A. baumannii
frequently produces hospital-acquired infection and
endemic situations in intensive care units (ICUs) all over
the world [3,4]. P. aeruginosa has a similar trajectory.
Ventilator-associated pneumonia (VAP) is one of the most
common and severe hospital-acquired infections. The most
common etiologies of VAP are GNB, and among them
MDR-GNB are very frequently isolated. VAP is associated
with increased attributable mortality, length of stay and use
of resources in the ICU [5]. In addition, the risk of inappropriate
empiric antimicrobial treatment is higher in areas
with a high prevalence of MDR-GNB. The inappropriate
empiric treatment of VAP is a risk factor for a poorer prognosis
[6-8]. It has been suggested that combined treatment
could help improve the results of VAP, since it broadens the
antibacterial spectrum [9]. This hypothesis has not been
confirmed in a clinical trial that compared meropenem plus
ciprofloxacin with meropenem in monotherapy [10]. In
many ICUs the proportion of resistance to all the betalactams
(including carbapenems) and quinolones is so high
(over 30 to 50%) [11,12] that empirical treatment with these
antimicrobials, even if combined, results in inappropriate
treatment in a high percentage of cases.
This scenario of multi-resistance has resulted in colistin
being the antimicrobial with greater in vitro activity