Population pharmacokinetics of cefotaxime in intensive care patients.

PURPOSE: To characterise the pharmacokinetics and associated variability of cefotaxime in adult intensive care unit (ICU) patients and to assess the impact of patient covariates. METHODS: This work was based on data from cefotaxime-treated patients included in the ACCIS (Antibiotic Concentrations in Critical Ill ICU Patients in Sweden) study. Clinical data from 51 patients at seven different ICUs in Sweden, given cefotaxime (1000-3000 mg given 2-6 times daily), were collected from the first day of treatment for up to three consecutive days. In total, 263 cefotaxime samples were included in the population pharmacokinetic analysis. RESULTS: A two-compartment model with linear elimination, proportional residual error and inter-individual variability (IIV) on clearance and central volume of distribution best described the data. The typical individual was 64 years, with body weight at ICU admission of 92 kg and estimated creatinine clearance of 94 mL/min. The resulting typical value of clearance was 11.1 L/h, central volume of distribution 5.1 L, peripheral volume of distribution 18.2 L and inter-compartmental clearance 14.5 L/h. The estimated creatinine clearance proved to be a significant covariate on clearance (p < 0.001), reducing IIV from 68 to 49%. CONCLUSION: A population pharmacokinetic model was developed to describe cefotaxime pharmacokinetics and associated variability in adult ICU patients. The estimated creatinine clearance partly explained the IIV in cefotaxime clearance. However, the remaining unexplained IIV is high and suggests a need for dose individualisation using therapeutic drug monitoring where the developed model, after evaluation of predictive performance, may provide support.

Therapeutic drug monitoring of vancomycin and meropenem: Illustration of the impact of inaccurate information in dose administration time.

OBJECTIVES: To illustrate the impact of errors in documented dose administration time on therapeutic drug monitoring (TDM)-based target attainment evaluation for vancomycin and meropenem, and to explore the influence of drug and patient characteristics, and TDM sampling strategies. METHODS: Bedside observations of errors in documented dose administration times were collected. Population pharmacokinetic simulations were performed for vancomycin and meropenem, evaluating different one- and two-sampling strategies for populations with estimated creatinine clearance (CLcr) of 30, 80 or 130 mL/min. The impact of errors was evaluated as the proportion of individuals incorrectly considered to have reached the target. RESULTS: Of 143 observed dose administrations, 97% of doses were given within ±30 min of the documented time. For vancomycin, a +30 min error was predicted to result in a 0.1-3.9 percentage point increase of cases incorrectly evaluated as reaching area under the concentration-time curve during a 24-hour period (AUC24)/minimum inhibitory concentration (MIC) >400, with the largest increase for patients with augmented renal clearance and peak and trough sampling. For meropenem, a +30 min error resulted in a 1.3-6.4 and 0-20 percentage point increase of cases incorrectly evaluated as reaching 100% T>MIC, and 50% T>MIC, respectively. Overall, mid-dose and trough sampling was most favourable for both antibiotics. CONCLUSIONS: For vancomycin, simulations indicate that TDM-based target attainment evaluation is robust with respect to the observed errors in dose administration time of ±30 min; however, the errors had a potentially clinically important impact in patients with augmented renal clearance. For meropenem, extra measures to promote correct documentation are warranted when using TDM, as the impact of errors was evident even in patients with normal renal function.

Short term impact of guidelines on vancomycin dosing and therapeutic drug monitoring.

BACKGROUND: After medical center implementation of 2009 ASHP/IDSA guidelines, we evaluated the appropriateness of vancomycin dosing and TDM. OBJECTIVE: Our primary objectives were to assess short term effects on (1) appropriateness of initial vancomycin dosing, (2) appropriateness of sampling of plasma levels, before and after implementation of guidelines. METHOD: The study was conducted in two phases, pre-guideline and post-guideline implementation. The interventions included (1) Nurses and phlebotomist education regarding the appropriate timing of vancomycin sampling, (2) A nomogram for appropriate initial dosing that was distributed to medical staff. Patient demographics, dosing and timing of sampling were collected in eligible patients and assessed for appropriateness. RESULTS: The appropriateness of the prescribed dose increased from 51% (128/253) of patients during the pre period to 78% (155/200) (p < 0.0001) during the post period. Similarly, overall appropriateness of sampling of vancomycin troughs at steady state improved from 36% (63/173) pre to 55% (106/191) (p < 0.03) post. Specifically, the appropriate timing of troughs (within 30 min of the next dose) increased from 37% (64/173) during the pre period to 78% (149/191) during the post period (p < 0.0001). Conclusion Adoption of the guidelines with associated training resulted in significant short term improvement in vancomycin dosing and TDM.