Population pharmacokinetics of single-dose amikacin in critically ill patients with suspected ventilator-associated pneumonia.

AIMS: Modifications of antimicrobials' pharmacokinetic parameters have been reported in critically ill patients, resulting in a risk of treatment failure. We characterized amikacin pharmacokinetic variability in critically ill patients with ventilator-associated pneumonia (VAP) and evaluated several dosing regimens.
METHODS: We conducted a prospective multicenter study in critically ill patients with presumptive diagnosis of Gram-negative bacilli (GNB) VAP. Patients empirically received imipenem and a single-dose of amikacin, which was administered as a 30-min infusion (20 mg/kg). Concentrations were measured 0.5, 1, 8, 16, and 24 h after beginning of infusion. Pharmacokinetic parameters were estimated using a population approach. Main pharmacodynamic target was a ratio ≥ 10 between the concentration achieved 1 h after beginning of infusion (C 1h) and the minimal inhibitory concentration of the liable bacteria (MIC). We simulated individual C 1h for several dosing regimens by Monte Carlo method and computed C 1h/MIC ratios for MICs from 0.5 to 64 mg/L.
RESULTS: Sixty patients (47 males), median (range) age, and body weight, 61.5 years (28-84) and 78 kg (45-126), respectively, were included. Amikacin median C 1h was 45 mg/L (22-87). Mean value (between-patients variability) for CL, V1, Q, and V2 were 4.3 L/h (31 %), 15.9 L (22 %), 12.1 L/h (27 %), and 21.4 L (47 %), respectively. CL increased with CrCL (p<0.001) and V1 with body weight (p<0.001) and PaO2/FIO2 ratio (p<0.001). With a 25 mg/kg regimen, the pharmacodynamic target was achieved in 20 and 96 % for a MICs of 8 and 4 mg/L, respectively.
CONCLUSION: Amikacin clearance was decreased and its volume of distribution was increased as previously reported. A ≥ 25 mg/kg single-dose is needed for empirical treatment of GNB-VAP.