Efficacy of loading dose of colistin in Acinetobacter baumannii ventilator-associated pneumonia

Colistin loading dose (LD) has been postulated as an advance in therapy. The clinical, microbiological effectiveness and nephrotoxicity of adding an LD to systemic colistin in ventilator-associated pneumonia (VAP) caused by multidrug-resistant (MDR) Acinetobacter baumannii remain unknown. In this quasi experimental study, the efficacy, outcomes and nephrotoxicity in 30 adults who received intravenous colistin with LD for MDR A. baumannii ventilator associated pneumonia were compared with 22 in absence of LD. Adding LD, the clinical cure rate at 14 days of therapy increased from 47.6% to 56.7% (p>0.397). No significant differences in bacteriological clearance (80 vs 81%), ICU mortality (50% vs 54.2%) or ICU length of stay (median: 32 vs 36 days) were identified. Mortality increased (76.2% vs 35.5%, p=0.004) in patients with nephrotoxicity, with age (median 67.0 vs. 50.0 years, p=0.002) being the only risk factor for nephrotoxicity. The nephrotoxicity rate increased from 27.3% in absence of LD to 35.3% with LD and SOFA <8, and 69.2% (p= 0.065) with LD and SOFA >7. Overall, nephrotoxicity was more severe in the LD group according to RIFLE criteria (p=0.015). Adding LD to systemic colistin for MDR A. baumannii VAP had no significant effect on clinical cure rates, bacteriologic clearance or pre-defined outcomes. However, the nephrotoxicity rate increased with LD, with special risk in adults with high organ failure development or advanced age. Further evidence regarding the risks and benefits of LD is required. The development of newer agents and strategies is urgently needed.