Acinetobacter baumannii is a gram-negative aerobic bacillus; that primarily causes hospital-acquired infections affecting specially to debilitated patients with prolonged hospitalization and with long-term exposition to antimicrobials. Until now, the ICUs have been considered as the epicenters of A. baumannii infections. Nevertheless, spread to general wards and long-term care facilities have also been shown to play an important role.
A. baumannii as ‘priority 1’
A. baumannii exhibits a wide variety of mechanisms of resistance to antimicrobial agents. This phenomenon has increasingly become a cause for serious concern for stakeholders and the scientific community worldwide. Thus, the WHO published its first list of ‘priority pathogens’ resistant to antibiotics; which includes the 12 families of bacteria most dangerous for human health and for that new antibiotics are in urgent need. In this list, A. baumannii, considered as ‘priority 1’ (critical).
A. baumannii is a major cause of nosocomial infections affecting mainly to debilitating patients in the ICU, although the spread to regular wards and to long-term care facilities is increasing. It has the characteristic of its great persistence in the environment; and to have an extraordinary capability to develop resistance to all antimicrobials. Carbapenems may not under consideration the treatment of choice in areas with high rates of carbapenem-resistant A. baumannii.
Nowadays, polymyxins are the antimicrobials with the greatest level of in-vitro activity against A. baumannii. Colistin, the most widely used in clinical practice, although polymyxin B seems to be associated with less renal toxicity. Colistin, administered intravenously, as it is an inactive prodrug colistimethate. Doctors recommend a loading dose of 9 million IU and subsequently high, extended-interval maintenance doses (4.5 million IU/12 h).
No clinical study showing reduction in clinical outcomes
Combination therapy instead of monotherapy increases the rates of microbiological eradication although no clinical study has demonstrated a reduction in clinical outcomes (mortality or length of stay). The optimal treatment for multidrug-resistant A. baumanniinosocomial infections doesn’t have any proof. There are no compelling data to recommend combination therapy for severe A. baumanniiinfections.
The treatment for A. baumannii infections often represents a challenge because of the paucity of active agents; the limited data about their efficacy and concerns about serious side-effects. As carbapenem and sulbactam resistances are rising worldwide; polymyxins in monotherapy or combined with other agents are in use. Colistin is a suboptimal to β-lactams or sulbactam but it represents frequently the last resort for drug resistant A. baumannii infection.
Recent meta-analyses coincide in the lack of clinical efficacy (cure rate or mortality) using combination therapy instead of monotherapy for A. baumannii severe infections although microbiological eradication rates are significantly higher with the use of two active antimicrobials. Furthermore, side-effects can be significantly higher with some of these combinations.