Effect of pharmacokinetic/pharmacodynamic ratio on tigecycline clinical response and toxicity in critically ill patients with multidrug-resistant Gram-negative infections.

INTRODUCTION: The information about the pharmacokinetics and optimal dose of tigecycline in critically ill patients with severe underlying diseases is limited and controversial. In this study, we evaluate the pharmacokinetic parameters of tigecycline in critically ill patients with multidrug-resistant Gram-negative infection and explore the association between the pharmacokinetic/pharmacodynamic ratio and treatment response. METHODS: A prospective study was designed including critically ill patients treated with tigecycline for multidrug-resistant Gram-negative infections. Blood samples were collected at day 3-5 of treatment, and pharmacokinetics parameters were evaluated using NONMEM® software. Relationship between area under the free concentration-time curve and minimum inhibitory concentration ratio (fAUC/MIC) and treatment failure was evaluated. Association between tigecycline fAUC and hepatobiliary toxicity was also investigated. RESULTS: Twenty-five critically ill patients were included in the study. In the pharmacokinetic model, weight and total bilirubin level were found to be significant predictors of tigecycline clearance. Fifteen (60.0%) patients achieved an fAUC/MIC ratio >4.5, seven (28.0%) an fAUC/MIC > 6.96 and only three (12.0%) an fAUC/MIC > 17.9. No differences in fAUC/MIC ratio were obtained between those patients with and without clinical failure (5.28 (IC95%: 2.57-7.94) vs 8.71 (3.57-13.84)). fAUC values were higher in those patients who suffered hepatobiliary disorders (7.63 (3.93-11.34) vs 17.63 (7.85-26.28) mg/L/h). CONCLUSION: An important percentage of critically ill patients with multidrug-resistant Gram-negative infection treated with tigecycline do not achieve an appropriate pharmacokinetic/pharmacodynamic value. Tigecycline fAUC seems to be associated with hepatobiliary disorders in this study population. The effect of fAUC/MIC ratio on clinical response remains unclear.

Vasopressin antagonist efficacy and safety in volume-overloaded critically ill patients: a new therapeutic alternative.

Objectives: To assess tolvaptan's efficacy and safety in critical care patients with volume overload. Methods: Prospective observational study. Twenty-eight patients in the recovery phase from multiple organ failure and with volume overload refractory to conventional therapy treated with tolvaptan were included. Results: Patients received an initial daily dose of 3.75 (n=1), 7.5 (n=8) and 15 (n=19) mg of tolvaptan. Median treatment duration was 2 days (range: 1 to 12). All patients presented an increase in 24 hours diuresis after the first dose (median increase from baseline (IQR)=1114 (285-1943) mL), with a median net daily fluid loss of 1007 mL (456-2380) mL after 24 hours. High diuretic efficacy (daily fluid loss higher than 0.5 L with tolvaptan first dose) was detected in 18 patients (64.3%). Initial hyponatraemia was present in 16 (57.1%) patients, while overly rapid correction with tolvaptan treatment occurred in two patients without clinical consequences. Two patients presented hypophosphataemia after treatment. Conclusion: Tolvaptan is an effective therapeutic option in critically ill patients with volume overload refractory to conventional diuretics. Further studies are required to evaluate its safety profile and its effect on short-term outcomes and mortality.

Ceftolozane/Tazobactam Dosing Requirements Against Pseudomonas aeruginosa Bacteremia.

OBJECTIVES: To assess the probability of reaching adequate pharmacokinetic/pharmacodynamics values for ceftolozane/tazobactam at different doses and degrees of renal functions in patients with Pseudomonas aeruginosa bacteremia. METHODS: Six dosing regimens were evaluated: 0.5/0.25 g, 1/0.5 g, and 2/1 g every 8 hours given as 1 hour or 3 hours infusions. Pharmacokinetic data were obtained from the literature. Susceptibility data to ceftolozane were collected from patients with P aeruginosa infection treated with ceftolozane-tazobactam. Probability of reaching a fraction of time (fT) >40% minimum inhibitory concentration (MIC) and fT >100%MIC value for ceftolozane at 3 different renal clearance values was evaluated. For tazobactam, the probability of reaching an fT >40% and >70% for 3 limit values was calculated. RESULTS: Thirty-seven strains were included. For ceftolozane, the probability of reaching a fT >40%MIC was greater than 90% for any degree of renal function. The probability of reaching a fT >100%MIC for 1 g dose infused over 1 hour and 3 hours was 82.2% and 86.4% for a creatinine clearance (ClCr) >90 mL/min. Using a 2 g dose, the probability was greater than 90% for both infusions rates. For tazobactam, the probability of reaching a value of fT >50% of the limit concentrations was greater than 90% for a ClCr of 70 mL/min. In the case of a ClCr >90 mL/min and limit concentration values ≥ 0.25 mg/mL, only extended infusions showed a probability >90%. CONCLUSIONS AND RELEVANCE: The standard doses of ceftolozane/tazobactam achieve an adequate fT >40%MIC value. However, doses of 2 g in extended infusion is necessary to reach a value of fT >100%MIC, especially in patients with an increased renal clearance and high levels of beta-lactamases expression.

In vitro study of antimicrobial activity on Klebsiella Pneumoniae biofilms in endotracheal tubes.

Effective treatment approaches for biofilms in endotracheal tubes (ETTs) are lacking. In this study, we evaluated the in vitro effects of five antimicrobials against biofilms formed by Klebsiella pneumoniae in ETTs. K. pneumoniae was added to minimal mucin medium prior to inoculation in microtiter plates containing ETT fragments. Biofilm susceptibility was assessed by crystal violet staining. At 24 h, the antimicrobials significantly reduced biofilm formation. At 48 h, all of the antimicrobial agents exhibited significant reductions in biofilm formation, even at concentrations above the minimum inhibitory concentration (MIC). Tigecycline and fosfomycin showed the greatest inhibition capacity, with good activity at concentrations twofold greater than the MIC. K. pneumoniae exhibited excellent biofilm formation ability, with formation in the first 24 h and significantly reduced antimicrobial activity. These results contribute to the establishment of new antibiotic breakpoints for the adequate management of infections associated with biofilm formation. Abbreviations ETT Endotracheal tube MIC Minimum inhibitory concentration MBIC Minimum biofilm inhibitory concentration OD Optical density PBS Phosphate-buffered saline VAP Ventilator-associated pneumonia.

Impact of voriconazole plasma concentrations on treatment response in critically ill patients.

WHAT IS KNOWN AND OBJECTIVE: Several authors have demonstrated the relationship between voriconazole concentrations and the risk of therapeutic failure and adverse events However, the information about voriconazole concentrations in the critically ill patient is scarce. The aim of this study was to analyse the plasma concentrations and pharmacokinetic behaviour of voriconazole in critically ill patients and their association with the treatment response and development of toxicity. METHODS: A prospective, observational study was conducted. Patients admitted to an intensive care unit and on treatment with intravenous voriconazole were included. Plasma concentrations were measured between days 4 and 7 from the start of the treatment. The pharmacokinetic analysis was performed using the NONMEM® software. A regression model was used to evaluate the variables associated with the values outside the therapeutic range, as well as the relationship between the plasma concentrations and the treatment response and the development of hepatotoxicity. RESULTS AND DISCUSSION: A total of 33 patients were included. Plasma concentrations outside the therapeutic range (1-5.5 mg/L) were observed in 15 patients, being above the established range in 9 (27.3%) cases, and below it in 6 (18.2%) cases. The presence of a bilirubin value of >1.5 mg/dL and a C-reactive protein >100 mg/dL was associated with supra-therapeutic concentrations. Voriconazole concentrations greater than 5.5 mg/dL were associated with the development of hepatotoxicity. WHAT IS NEW AND CONCLUSIONS: There is a wide variation in voriconazole concentrations in critically ill patients, being associated with a high frequency of adverse events. Close monitoring of these values is required in order to decrease the risk of therapeutic failure and toxicity.

Influence of antibiotic pressure on multi-drug resistant Klebsiella pneumoniae colonisation in critically ill patients.

Background: The aim of this study is to evaluate the risk factors for colonisation by multidrug resistant (MDR) K. pneumoniae in a critical care unit and the relationship between colonisation and the antibiotic pressure exerted by the antimicrobial treatments received by patients. Methods: A prospective observational was designed. Patients admitted for more than 48 h to an intensive care unit were included. Samples for surveillance cultures were obtained from all the patients upon admission and once a week. The association between risk factors and colonisation by MDR K. pneumoniae was determined by logistic regression. A Cox regression model was used to evaluate the effect of the use of antimicrobials on the colonisation rate. An ARMIA model was used to investigate the association between the incidence of colonisation by MDR strains and the global consumption of antimicrobials in the unit. Results: One thousand seven hundred twenty-five patients were included, from which 308 (17.9%) were positive for MDR K. pneumoniae. In the multivariate analysis, hospitalisation for longer than 7 days together with respiratory infection and administration of any antibiotic was associated with increased MR K. pneumoniae colonisation. Patients who received antibiotics for more than 48 h were colonised earlier than patients who did not receive antibiotic treatment [HR: 2.16 (95%CI:1.55-3.03)]. The ARIMA model found a significant association between the monthly colonisation rate for MR K. pneumoniae and the consumption of cephalosporins and carbapenems in the previous month. Conclusion: Individual antibiotic administration and the global antibiotic pressure of cephalosporins and carbapenems are associated to an increased colonisation by MDR K. pneumoniae strains.

Vancomycin and daptomycin minimum inhibitory concentrations as a predictor of outcome of methicillin-resistant Staphylococcus aureus bacteraemia.

OBJECTIVES: The aim of this study was to determine the persistence of the adverse prognostic effect of elevated vancomycin minimum inhibitory concentration (MIC) in methicillin-resistant Staphylococcus aureus (MRSA) bacteraemia in a setting with low vancomycin use. METHODS: A retrospective study focusing on episodes of bacteraemia due to MRSA diagnosed from January 2010 through December 2015 was designed. The main outcome measures were 30-day mortality and treatment failure. Multivariate logistic regression analysis was used to identify variables associated with patient mortality and treatment outcome. RESULTS: In total, 79 MRSA bacteraemia episodes were included. The vancomycin MIC was >1.0µg/mL in 53 episodes (67.1%). The presence of high vancomycin MIC was not associated with a higher mortality rate or treatment success. A daptomycin MIC≥0.5µg/mL was present in 16 (26.2%) of 61 episodes for which the daptomycin MIC was obtained and was associated with 30-day mortality in the multivariate analysis (odds ratio=4.72, 95% confidence interval 1.19-18.71). None of the antimicrobials used were associated with a lower risk of treatment failure or mortality. CONCLUSIONS: The pernicious effect of high vancomycin MIC disappears in the absence of a predominant use of this antibiotic. However, a high daptomycin MIC in MRSA bacteraemia is associated with higher mortality in patients with bacteraemia, irrespective of antimicrobial treatment choice.

Implication of Haemodiafiltration Flow Rate on Amikacin Pharmacokinetic Parameters in Critically Ill Patients.

BACKGROUND: To analyse the effect of haemodiafiltration (CVVHDF) flow rate on amikacin pharmacokinetics and blood concentrations. METHODS: Prospective observational study. Patients receiving CVVHDF and amikacin treatment were included. Pharmacokinetic parameters were calculated using Bayesian analysis. Spearman correlation test was used in order to assess the influence of CVVHDF flux on amikacin minimum concentration (Cmin) and plasma clearance. RESULTS: Thirty patients undergoing CVVHDF procedures were included. The treatment with amikacin started at an initial mean dose of 12.4 (4.1) mg/kg/day. An association between the flow rate and Cmin value (r = 0.261; p = 0.161) and plasma clearance was found (r = 0.268; p = 0.152). Four patients (13.3%) were not able to achieve peak concentration over MIC value higher than 8. In 4 patients, amikacin had to be discontinued due to a high Cmin value. CONCLUSIONS: Amikacin clearance in patients with CVVHDF is affected by the flow rate used. Therefore, CVVHDF dose should be taken into account when dosing amikacin.

Pharmacokinetics of Amikacin in Critical Care Patients on Extracorporeal Device.

In this study, we evaluate the effect of extracorporeal membrane oxygenation (ECMO) and ventricular assist devices (Levitronix) on the pharmacokinetic of amikacin in critically ill patients. Twelve patients with ECMO and three with Levitronix devices who started treatment with amikacin were included. Amikacin pre (Cmax) and post (Cmin) dose serum concentrations were measured during the first 72-96 hours of treatment initiation. Pharmacokinetic parameters were performed by Bayesian adjustment. The median initial dose was 1,000 mg (range: 600-1,400 mg). Mean plasma concentrations were Cmax 58.6 mg/L (17.0 mg/L); Cmin 9.58 mg/L (7.8 mg/L). Patients with an ECMO device had a higher volume of distribution (0.346 [0.033] vs. 0.288 [0.110] L/kg) and a lower plasma clearance (1.58 [0.21] vs. 3.73 [1.03] L/h) than the control group. This phenomenon was also observed in those patients with simultaneous use of ECMO and hemodilafiltration. For patients with Levitronix system, no significant alterations in the volume of distribution were observed, although a lower plasma clearance was noticed. Placement of ECMO devices alters the pharmacokinetic parameters of amikacin in the critically ill patients and should be considered when selecting the initial dose.

Impact of amikacin pharmacokinetic/pharmacodynamic index on treatment response in critically ill patients.

OBJECTIVES: This study evaluated the association between the pharmacokinetic/pharmacodynamic index and treatment response to amikacin in critically ill patients. METHODS: An observational prospective study was designed. Critically ill adult patients with infection due to amikacin-sensitive Gram-negative bacteria treated with amikacin were included. Amikacin maximum (Cmax) and minimum (Cmin) plasma concentration samples were taken during the first 48-96h after the beginning of treatment. The impact of Cmax/MIC ratio and area under the concentration-time curve (AUC)/MIC ratio on early and final clinical response, microbiological eradication, development of resistant strains and renal toxicity was analysed using a multivariate model. RESULTS: A total of 85 patients received amikacin treatment, of whom 71 (83.5%) achieved a Cmax/MIC >6, 66 (77.6%) a Cmax/MIC >8, 64 (75.3%) a Cmax/MIC >10 and 72 (84.7%) an AUC/MIC >65. Clinical response at the end of treatment was significantly greater in patients with Cmax/MIC >6 [OR=5.48 (95% CI 1.28-11.40)], Cmax/MIC >8 [OR=6.01 (2.41-12.2)] and Cmax/MIC >10 [OR=8.02 (2.21-14.2)]. Cmax/MIC >10 was associated with a non-significant increase in microbiological eradication [OR=2.84 (0.76-10.61)]. Achieving Cmax/MIC >6 was associated with a lower proportion of patients with selection of resistant strains or with an increase in amikacin MIC (27.8% vs. 10.2%). Amikacin AUC was associated with development of nephrotoxicity [ROC curve 0.77 (0.66-0.87)]. CONCLUSIONS: The Cmax/MIC ratio of amikacin in critically ill patients is directly related to the response to treatment and the selection of resistant strains.

Individualised antimicrobial dosing in critically ill patients undergoing continuous renal replacement therapy: focus on total drug clearance.

BACKGROUND: Continuous renal replacement therapy (CRRT) is common practice in critical care patients with acute renal failure. OBJECTIVES: To evaluate the adequacy of antimicrobial doses calculated based on the total drug clearance and dose recommended by different guides in critically ill patients undergoing CRRT. METHODS: Retrospective observational study. Patients admitted to a critical care unit during May 2014 to May 2016 and subjected to CRRT were included. The recommended dose was established as the product of the usual dose of the drug by total drug clearance. RESULTS: 177 antimicrobial agents, used in 64 patients were analysed; 45 (25.4%) antimicrobials were given in an insufficient dose (<20%) according to the theoretical calculation. Following the recommendations in the revised guidelines, between 10% and 20% of antimicrobials were given in insufficient doses. A higher success rate of treatment in those patients not receiving a low drug dosage was seen (35.2% vs 24.0%). CONCLUSIONS: There is a great disparity between the antimicrobial dose prescribed, recommended and calculated based on drug clearance in critically ill patients undergoing CRRT.

Daily bathing strategies and cross-transmission of multidrug-resistant organisms: Impact of chlorhexidine-impregnated wipes in a multidrug-resistant gram-negative bacteria endemic intensive care unit.

BACKGROUND: Health-care associated infections are a major cause of morbidity and mortality in critical care units. The aim of this study is to evaluate the effectiveness of chlorhexidine gluconate (CHG)-impregnated wipes in the daily bathing of patients in an intensive care unit (ICU) to prevent cross-transmission and colonization by multidrug-resistant organisms (MDROs) METHODS: Prospective cohort study with an intervention of 11 months. The intervention consisted of using CHG-impregnated wipes for the daily bathing of patients on mechanical ventilation or colonized by MDROs. Monthly trends in the number of patients colonized by MDROs and the incidence of nosocomial infections were evaluated. RESULTS: A total of 1,675 patients were admitted to the unit during the intervention period, and 430 (25.7%) were bathed with chlorhexidine wipes. A significant decrease was observed in the incidence of colonization by MDROs over the months (ß = -0.209; r2 = 0.549; P = .027), and in the number of patients colonized compared with the equivalent period of the previous year (22.0% vs 18.4%; P = .01). No significant decrease was observed in the incidence of nosocomial infection between the two periods (4.11% vs 4.57%; P = .355). No dermatologic problems were observed in the treated patients. CONCLUSIONS: The use of CHG-impregnated wipes reduces cross-transmission and colonization by MDROs in the ICUs in an endemic situation because of multidrug-resistant Enterobacteriaceae.

Septic Participation in Cardiogenic Shock: Exposure to Bacterial Endotoxin.

OBJECTIVE: In cardiogenic shock (CS), presence of fever, leukocytosis, relatively low systemic vascular resistances, and high serum procalcitonin levels are quite frequent and recurrently involve the search for an infectious complication. We hypothesized that endotoxin exposure in CS could explain this sepsis-like syndrome. DESIGN AND SETTING: Prospective observational study of consecutive CS patients admitted to our intensive care unit (ICU). Patients were followed during the first 3 days after CS onset. All clinical, hemodynamic, and microbiological data were collected. Inflammatory biomarkers and anti-endotoxin antibodies (IgM EndoCAb) were daily measured. PATIENTS: We included 37 consecutive CS patients. MEASUREMENTS AND MAIN RESULTS: Twenty-two patients (60%) had body temperature >38.3°C or <35°C; and 23 patients (62%) had a leucocyte count >14,000/mm or <4,000/mm. Microbiological study was performed in 30 patients (81%). No infection was diagnosed in the studied patients. All the patients had serum inflammatory biomarkers levels above normal values including procalcitonin (19 patients [51%] had serum procalcitonin above 2 ng/mL). All the patients had IgM EndoCAb below the normal median value; 22 patients (59.5%) had IgM anti-endotoxin value below 10th percentile range for healthy people. Hemodynamic and respiratory stabilization was achieved in 23 patients (62%) and the ICU mortality rate was 38%, only procalcitonin and interleuquin-6 were associated with higher mortality rate. CONCLUSION: We have detected extremely low titers of IgM EndoCAb in CS suggesting endotoxin exposure. However, only inflammatory biomarkers were related to ICU mortality.

From starting mechanical ventilation to ventilator-associated pneumonia, choosing the right moment to start antibiotic treatment.

BACKGROUND: Ventilator-associated pneumonia (VAP) can have a clear onset or may be a result of the gradual appearance of symptoms and signs of VAP (gradual VAP). The aim of this paper is to describe the VAP development process with the intention of discriminating between those pneumonias with a clear beginning and those that are diagnosed after a period of maturation. In addition, we evaluate the effect of the starting time of antibiotic treatment in both situations. METHODS: Consecutive ventilated patients fulfilling VAP criteria were included. The patients were monitored for clinical, microbiological, and inflammatory signs. Patients with VAP were classified into two groups: (1) nongradual VAP (patients in whom all VAP criteria were detected for the first time on the day of diagnosis) and (2) gradual VAP (progressive appearance of signs and symptoms throughout the pre-VAP period [<96 h to >24 h before VAP diagnosis]). RESULTS: A total of 71 patients with VAP were identified, of whom 43 (61 %) had gradual VAP, most of whom (n = 38, 88 %) had late-onset VAP. Antibiotic treatment was given to 34 (79 %) patients with gradual VAP in the pre-VAP period, and empirical antibiotic treatment was appropriate in 22 patients (51 %). The patients with an appropriate empirical treatment had a higher percentage of early clinical response to treatment (68 % [n = 15] vs. 28 % [n = 7]; p = 0.009). An attempt was made to find a diagnostic test capable of identifying the infectious process underway, but clinical scales and biomarkers of inflammation helped us to achieve acceptable results. CONCLUSIONS: Gradual emergence of VAP, mainly of late onset, is a common condition. Clinicians should be aware of this gradual onset of the infection to establish an early antibiotic treatment, even before the classic diagnostic criteria for VAP are applied.

Blood culture contamination rate in an intensive care setting: Effectiveness of an education-based intervention.

BACKGROUND: Blood culture (BC) contamination rate is an indicator of quality of care scarcely explored in intensive care units (ICUs). We analyzed the BC contamination rate in our ICU to assess the effectiveness of an education-based intervention. METHODS: We conducted an interventional study with concurrent controls. Consecutive BCs drawn during a 6-month period were included. An education-based intervention was presented to case nurses (optimal technique). The remaining nurses comprised the control group (standard technique). Two independent observers assessed clinical significance of saprophytic skin bacteria isolated in BCs. RESULTS: Six hundred fifty-six BCs were obtained: 308 (47%) via optimal technique and 348 (53%) via standard technique (47%). One hundred eighty-seven BCs were positive for saprophytic microorganisms; 127 (89%) were considered unrelated to infection. Coagulase-negative staphylococci isolation was lower in the optimal technique group (14% vs 26%; P < .001), as well as contamination due to coagulase-negative staphylococci (12% vs 21%; P = .002) or Acinetobacter baumannii (0.3% vs 2%; P = .013). BC contamination rate was 13% in the optimal technique group versus 23% in the standard group (P < .005). In the optimal technique group, BC contamination rate was higher in BCs drawn through the catheter (17% vs 7%; P = .028). CONCLUSIONS: An education-based intervention significantly reduced the BC contamination rate in our ICU. It seems necessary to design a tool to extract BCs through the catheter to minimize the risk of contamination.

Diagnosing external ventricular drain-related ventriculitis by means of local inflammatory response: soluble triggering receptor expressed on myeloid cells-1.

INTRODUCTION: External ventricular drainage (EVD)-related ventriculitis is one of the most severe complications associated with the use of EVDs. Establishing an early and certain diagnosis can be difficult in critically ill patients. We performed this prospective study to evaluate the usefulness of soluble triggering receptor expressed on myeloid cells-1 (sTREM-1) determination in cerebrospinal fluid (CSF) in the diagnosis of ventriculitis. METHODS: A prospective observational study was conducted of 73 consecutive patients with EVD. Samples of CSF for culture, cytobiochemical analysis and sTREM-1 determination were extracted three times a week. Ventriculitis diagnosis required a combination of microbiological, cytobiochemical and clinical criteria. RESULTS: Seventy-three consecutive patients were included. EVD-related ventriculitis was diagnosed in six patients and EVD-colonization in ten patients. Patients without clinical or microbiological findings were considered controls. The median CSF sTREM-1 was 4,320 pg/ml (interquartile range (IQR): 2,987 to 4,886) versus 266 pg/ml (118 to 689); P <0.001. There were no differences when comparing colonized-patients and controls. The best cut-off sTREM-1 value for the diagnosis of ventriculitis was 2,388.79 pg/ml (sensitivity 100%, specificity 98.5%, positive predictive value 85.71%, negative predictive value 100%). CSF proteins, glucose and the ratio CSF/serum glucose were also significantly different (P = 0.001). Serum biomarkers were not useful to diagnose EVD-related infection. These results were confirmed by a case-control study with ventriculitis patients (cases) and non-ventriculitis (control subjects) matched by age, comorbidities, severity scales and EVD duration (P = 0.004). CONCLUSIONS: CSF sTREM-1 was useful in the diagnosis of ventriculitis, in a similar measure to classical CSF parameters. Furthermore, CSF sTREM-1 could prove the diagnosis in uncertain cases and discriminate between EVD-colonization and infection.

Impact of microbial ecology on accuracy of surveillance cultures to predict multidrug resistant microorganisms causing ventilator-associated pneumonia.

OBJECTIVES: The objective of this study was to assess surveillance cultures (SC) prediction accuracy in two periods and settings of the same Department with a different microbiological epidemiology (high and low prevalence of multi-drug resistant microorganisms (MDRM)). METHODS: Prospective and observational study. SC were obtained twice a week in consecutive mechanically ventilated patients. Patients fulfilling VAP criteria were analyzed. RESULTS: 440 patients were followed up, 71 patients had VAP (50 in period I and 21 in period II). MDRM causing VAP were more prevalent in the first period (48% vs. 19%; p = 0.033). The rate of empirical appropriate treatment in period I was lower than in period II (52% vs.76%; p = 0.031). SC prediction accuracy was similar in the two periods (80% vs. 81%; p = 0.744). However, if antibiotic treatment had been guided by SC, the percentage of appropriate treatment would have increased by 28% in the first period but only by 5% in the second; p = 0.024. CONCLUSIONS: SC were able to predict VAP etiology in 80% of cases regardless the prevalence of MDRM. However, the potential benefit of SC in terms of appropriate empirical treatment could be only observed when MDRM were prevalent.