Antibiotic pharmacokinetic and pharmacodynamic considerations in critical illness

Antibiotic-Drug Interactions in the Intensive Care Unit: A Literature Review

Interactions between drugs are a common problem in Intensive Care Unit patients, as they mainly have a critical condition that often demands the administration of multiple drugs simultaneously. Antibiotics are among the most frequently used medications, as infectious diseases are often observed in ICU patients. In this review, the most important antibiotic-drug interactions, based on the pharmacokinetic and pharmacodynamic mechanisms, were gathered together and described. In particular, some of the most important interactions with main groups of antibacterial drugs were observed in patients simultaneously prescribed oral anticoagulants, NSAIDs, loop diuretics, and valproic acid. As a result, the activity of drugs can be increased or decreased, as dosage modification might be necessary. It should be noted that these crucial interactions can help predict and avoid negative consequences, leading to better patient recovery. Moreover, since there are other factors, such as fluid therapy or albumins, which may also modify the effectiveness of antibacterial therapy, it is important for anaesthesiologists to be aware of them.

Antimicrobial Drug Penetration Is Enhanced by Lung Tissue Inflammation and Injury

Rationale: Pneumonia is a frequent and feared complication in intubated critically ill patients. Tissue concentrations of antimicrobial drugs need to be sufficiently high to treat the infection and also prevent development of bacterial resistance. It is uncertain whether pulmonary inflammation and injury affect antimicrobial drug penetration into lung tissue.Objectives: To determine and compare tissue and BAL fluid concentrations of ceftaroline fosamil and linezolid in a model of unilateral acute lung injury in pigs and to evaluate whether dose adjustment is necessary to reach sufficient antimicrobial concentrations in injured lung tissue.Methods: After induction of unilateral acute lung injury, ceftaroline fosamil and linezolid were administered intravenously. Drug concentrations were measured in lung tissue through microdialysis and in blood and BAL fluid samples during the following 8 hours. The primary endpoint was the tissue concentration area under the concentration curve in the first 8 hours (AUC0-8 h) of the two antimicrobial drugs.Measurements and Main Results: In 10 pigs, antimicrobial drug concentrations were higher in inflamed and injured lung tissue compared with those in uninflamed and uninjured lung tissue (median ceftaroline fosamil AUC0-8 h [and interquartile range] = 26.7 mg ⋅ h ⋅ L-1 [19.7-39.0] vs. 16.0 mg ⋅ h ⋅ L-1 [13.6-19.9], P = 0.02; median linezolid AUC0-8 h 76.0 mg ⋅ h ⋅ L-1 [68.1-96.0] vs. 54.6 mg ⋅ h ⋅ L-1 [42.7-60.9], P = 0.01), resulting in a longer time above the minimal inhibitory concentration and in higher peak concentrations and dialysate/plasma ratios. Penetration into BAL fluid was excellent for both antimicrobials, but without left-to-right differences (ceftaroline fosamil, P = 0.78; linezolid, P = 1.00).Conclusions: Tissue penetration of two commonly used antimicrobial drugs for pneumonia is enhanced by early lung tissue inflammation and injury, resulting in longer times above the minimal inhibitory concentration. Thus, lung tissue inflammation ameliorates antimicrobial drug penetration during the acute phase.

Towards optimization of ceftazidime dosing in obese ICU patients: the end of the 'one-size-fits-all' approach?

BACKGROUND

Ceftazidime is commonly used as a key antibiotic against Pseudomonas aeruginosa in critically ill patients. ICU patients have severely altered and variable antibiotic pharmacokinetics, resulting in lower antimicrobial concentrations and potentially poor outcome. Several factors, including obesity and renal function, may influence pharmacokinetics. Thus, the objective of the study was to evaluate the impact of obesity and renal function on ceftazidime plasma concentrations and dosing regimen in ICU patients.

METHODS

All consecutive adult patients from six ICUs, treated with continuous ceftazidime infusion and under therapeutic drug monitoring evaluation, were included. Obesity was defined as BMI ≥30 kg/m². Glomerular filtration rate (GFR) was estimated by the Chronic Kidney Disease Epidemiology Collaboration formula. The ceftazidime recommended target for plasma concentrations was between 35 and 80 mg/L.

RESULTS

A total of 98 patients (45 obese), with an average weight of 90 (±25) kg, were included. Mean GFR was 84.1 (±40.4) mL/min/1.73 m2. Recommended ceftazidime plasma concentrations were achieved for only 48.0% of patients, with median dosing regimen of 6 g/day. Obese patients had lower ceftazidime plasma concentrations compared with non-obese patients (37.8 versus 56.3 mg/L; P = 0.0042) despite similar dosing regimens (5.83 g/day versus 5.52 g/day, P = 0.2529). Almost all augmented renal clearance patients were underdosed despite ceftazidime dosing of 6.6 (±0.8) g/day. Weight-based ceftazidime dosing seemed to attenuate such obesity-related discrepancies, regardless of GFR.

CONCLUSIONS

Obese ICU patients required significantly greater ceftazidime doses to achieve the target range. A tailored dosing regimen may be considered based on weight and GFR. Future prospective studies should be performed to confirm this individualized dosing approach.

Heterostructured piezocatalytic nanoparticles with enhanced ultrasound response for efficient repair of infectious bone defects

Infection of bone defects remains a challenging issue in clinical practice, resulting in various complications. The current clinical treatments include antibiotic therapy and surgical debridement, which can cause drug-resistance and potential postoperative complications. Therefore, there is an urgent need for an efficient treatment to sterilize and promote bone repair in situ. In this work, an ultrasound responsive selenium modified barium titanate nanoparticle (Se@BTO NP) was fabricated, which exhibited significant antibacterial and bone regeneration effects. Selenium nanoparticle (Se NP) was modified on the surface of barium titanate nanoparticle (BTO NP) to form heterostructure, which facilitated the second distribution of piezo-induced carriers under ultrasound (US) irradiation and improved the separation of electron-hole pairs. The Se@BTO NPs exhibited remarkable antibacterial efficiency with an antibacterial rate of 99.23 % against Staphylococcus aureus (S.aureus) and significantly promoted the osteogenic differentiation under ultrasound irradiation. The in vivo experiments exhibited that Se@BTO NPs successfully repaired the femoral condylar bone defects of rats infected by S.aureus, resulting in significant promotion of bone regeneration. Overall, this work provided an innovative strategy for the utilization of US responsive nanomaterials in efficient bacteria elimination and bone regeneration. STATEMENT OF SIGNIFICANCE: Infectious bone defects remain a challenging issue in clinical practice. Current antibiotic therapy and surgical debridement has numerous limitations such as drug-resistance and potential complications. Herein, we designed an innovative ultrasound responsive selenium modified barium titanate nanoparticle (Se@BTO NP) to achieve efficient non-invasive bacteria elimination and bone regeneration. In this work, Se@BTO nanoparticles can enhance the separation of electrons and holes, facilitate the transfer of free carriers due to the cooperative effect of ultrasound induced piezoelectric field and heterojunction construction, and thus exhibit remarkable antibacterial and osteogenesis effect. Overall, our study provided a promising strategy for the utilization of piezocatalytic nanomaterials in efficient antibacterial and bone regeneration.

"CATCH" Study: Correct Antibiotic Therapy in Continuous Hemofiltration in the Critically Ill in Continuous Renal Replacement Therapy: A Prospective Observational Study

The proper posology of antibiotics in the critically ill in CRRT is difficult to assess. We therefore performed a prospective observational cohort study to make clear hints in this topic. Our results reveal a high Sieving Coefficient for all antibiotics, equal to or higher than those described in previous papers. CVVH clearance in relation to total body clearance was significant, (i.e., >than 25% for all classes). A strong correlation between the antibiotic concentrations obtained in plasma and ultrafiltrate was found both at the peak and in the valley, with the determination of two equations that allow a new method for calculating the amount of antibiotic lost in CVVH both for trough levels and peak. Based on the results of our study and considering the limitations we believe that we can extrapolate the following final considerations: (1) it is likely to carry out a loading dose for the main antibiotics (2) subsequent administrations must take into account the daily loss identified by the linear regression equation. This angular coefficient gives the idea that the average daily loss of given antibiotic is about 25%; this implies that on the basis of the linear regression equation that correlates ultrafiltered/plasma antibiotic concentration, the dosage should be increased by 25% every day, while still ensuring a daily plasma TDM of the drug.

Antibiotic Therapy in the Critically Ill with Acute Renal Failure and Renal Replacement Therapy: A Narrative Review

The outcome for critically ill patients is burdened by a double mortality rate and a longer hospital stay in the case of sepsis or septic shock. The adequate use of antibiotics may impact on the outcome since they may affect the pharmacokinetics (Pk) and pharmacodynamics (Pd) of antibiotics in such patients. Acute renal failure (ARF) occurs in about 50% of septic patients, and the consequent need for continuous renal replacement therapy (CRRT) makes the renal elimination rate of most antibiotics highly variable. Antibiotics doses should be reduced in patients experiencing ARF, in accordance with the glomerular filtration rate (GFR), whereas posology should be increased in the case of CRRT. Since different settings of CRRT may be used, identifying a standard dosage of antibiotics is very difficult, because there is a risk of both oversimplification and failing the therapeutic efficacy. Indeed, it has been seen that, in over 25% of cases, the antibiotic therapy does not reach the necessary concentration target mainly due to lack of the proper minimal inhibitory concentration (MIC) achievement. The aim of this narrative review is to clarify whether shared algorithms exist, allowing them to inform the daily practice in the proper antibiotics posology for critically ill patients undergoing CRRT.

Distribution of therapeutic monoclonal antibodies into ascites in advanced gastric cancer patients with peritoneal metastasis: case reports and literature review

BACKGROUND

Therapeutic monoclonal antibodies, including ramucirumab and nivolumab, are used to treat advanced gastric cancer (AGC). Malignant ascites is often accompanied by peritoneal metastasis in AGC patients. However, the distribution of therapeutic monoclonal antibodies into ascites has yet to be adequately investigated.

METHODS

We determined serum and ascites concentrations of ramucirumab or nivolumab and total IgG in three AGC patients with massive ascites. When serum and ascites samples were obtained on the same day, the ascites-to-serum ratio (A/S ratio) of the concentration of monoclonal antibodies was evaluated. The relationship between time after last infusion and the A/S ratio of therapeutic monoclonal antibodies was examined using 15 datasets from the present study and the literature.

RESULTS

Ramucirumab and nivolumab were detected in massive ascites at considerable amounts (A/S ratios of 0.24-0.35 for ramucirumab and 0.17-0.55 for nivolumab). A positive correlation was detected between the A/S ratios of the therapeutic monoclonal antibodies and the time after last infusion (r = 0.747). Removal of ascites using paracentesis eliminated at least 15.3%-30.3% and 5.2-27.4% of the injected ramucirumab and nivolumab, respectively. Endogenous IgG, as well as therapeutic monoclonal antibodies, were distributed into ascites; the A/S ratios for IgG were 0.22-0.45.

CONCLUSION

Our results suggest that therapeutic monoclonal antibodies, including ramucirumab and nivolumab, are distributed into massive ascites in AGC patients concomitantly with endogenous IgG. In these patients, retention of ascites and its removal may result in decreased systemic drug exposure to ramucirumab and nivolumab.

Applying pharmacokinetic/pharmacodynamic measurements for linezolid in critically ill patients: optimizing efficacy and reducing resistance occurrence

PURPOSE

Linezolid (LZD) levels are frequently insufficient in intensive care unit (ICU) patients receiving standard dose, which is predictive of a poor prognosis. Alternative dosing regimens are suggested to address these insufficient levels, which are substantial factors contributing to the emergence of multidrug-resistant bacteria, resulting in increased morbidity and mortality among people who are critically ill.

METHODS

Forty-eight patients admitted to the intensive care unit were enrolled in an open-label, prospective, randomized study and assigned to one of three LZD administration modes: intermittent groupI (GpI) (600 mg/12 h), continuous infusion groupII (GpII) (1200 mg/24 h) or continuous infusion with loading dose groupIII (GpIII) (on Day 1, 300 mg intravenously plus 900 mg continuous infusion, followed by 1200 mg/24 h on Day 2). We evaluated serum levels of LZD using a validated ultra-performance liquid chromatography (UPLC) technique.

RESULTS

Time spent with a drug concentration more than 85% over the minimum inhibitory concentration (T > MIC) was substantially more common in GpII and III than in GpI (P < 0.01). AUC/MIC values greater than 80 were obtained more frequently with continuous infusion GpIII and GpII than with intermittent infusion GpI, at 62.5%, 37.5% and 25%, respectively (P < 0.01). In GpI, the mortality rate was significantly higher than in the other groups.

CONCLUSION

In critically ill patients, continuous infusion with a loading dose (GpIII) is obviously superior to continuous infusion without a loading dose (GpII) or intermittent infusion (GpI) for infection therapy. Additionally, it might limit fluctuations in plasma concentrations, which may help overcome LZD resistance.

A narrative review on antimicrobial therapy in septic shock: updates and controversies

PURPOSE OF REVIEW

Antibiotics are an essential treatment for septic shock. This review provides an overview of the key issues in antimicrobial therapy for septic shock. We include a summary of available evidence with an emphasis on data published in the last few years.

RECENT FINDINGS

We examine apparently contradictory data supporting the importance of minimizing time to antimicrobial therapy in sepsis, discuss approaches to choosing appropriate antibiotics, and review the importance and challenges presented by antimicrobial dosing. Lastly, we evaluate the evolving concepts of de-escalation, and optimization of the duration of antimicrobials.

SUMMARY

The topics discussed in this review provide background to key clinical decisions in antimicrobial therapy for septic shock: timing, antibiotic choice, dosage, de-escalation, and duration. Although acknowledging some controversy, antimicrobial therapy in septic shock should be delivered early, be of the adequate spectrum, appropriately and individually dosed, rationalized when possible, and of minimal effective duration.

Idiosyncratic variation in the fitness costs of tetracycline-resistance mutations in Escherichia coli

A bacterium's fitness relative to its competitors, both in the presence and absence of antibiotics, plays a key role in its ecological success and clinical impact. In this study, we examine whether tetracycline-resistant mutants are less fit in the absence of the drug than their sensitive parents, and whether the fitness cost of resistance is constant or variable across independently derived lines. Tetracycline-resistant lines suffered, on average, a reduction in fitness of almost 8%. There was substantial among-line variation in the fitness cost. This variation was not associated with the level of resistance conferred by the mutations, nor did it vary significantly across several genetic backgrounds. The two resistant lines with the most extreme fitness costs involved functionally unrelated mutations on different genetic backgrounds. However, there was also significant variation in the fitness costs for mutations affecting the same pathway and even different alleles of the same gene. Our findings demonstrate that the fitness costs of antibiotic resistance do not always correlate with the phenotypic level of resistance or the underlying genetic changes. Instead, these costs reflect the idiosyncratic effects of particular resistance mutations and the genetic backgrounds in which they occur.

Megalin-targeting liposomes for placental drug delivery

Every year, complications during pregnancy affect more than 26 million women. Some of those diseases are associated with significant morbidity and mortality, as is the case of preeclampsia, the main cause of maternal deaths globally. The ability to improve the delivery of drugs to the placenta upon administration to the mother may offer new opportunities in the treatment of diseases of pregnancy. The objective of this study was to develop megalin-targeting liposome nanocarriers for placental drug delivery. Megalin is a transmembrane protein involved in clathrin-mediated endocytic processes, and is expressed in the syncytiotrophoblast (SynT), an epithelial layer at maternal-fetal interface. Targeting megalin thus offers an opportunity for the liposomes to hitchhike into the SynT, thus enriching the concentration of any associated therapeutic cargo in the placental tissue. PEGylated (2 KDa) lipids were modified with gentamicin (GM), a substrate to megalin receptors as we have shown in earlier studies, and used to prepare placental-targeting liposomes. The ability of the targeting liposomes to enhance accumulation of a fluorescence probe was assessed in an in vivo placental model - timed-pregnant Balb/c mice at gestational day (GD) 18.5. The targeting liposomes containing 10 mol% GM-modified lipids increased the accumulation of the conjugated fluorescence probe in the placenta with a total accumulation of 2.8% of the initial dose, which corresponds to a 94 fold increase in accumulation compared to the free probe (p < .0001), and 2-4 fold accumulation compared to the non-targeting control liposomes (p < .0001), as measured by both tissue extraction assay and ex vivo imaging. Furthermore, confocal images of placental SynT cross-sections show a 3-fold increase of the targeting liposomes compared with the non-targeting liposomes. The rate and extent of uptake of a fluorescent probe encapsulated within targeting liposomes was also probed in an in vitro model of the human placental barrier (polarized BeWo monolayers) using flow cytometry. Targeting liposomes containing 5 mol% GM-modified lipids enhanced the uptake of the probe by 1.5 fold compared to the non-targeting control. An increase to 10 mol% of the modified lipid resulted in further enhancement in uptake, which was 2 fold greater compared to control. In a competition assay, inhibition of the megalin receptors resulted in a significant reduction in uptake of the fluorescence probe encapsulated in GM-modified liposomes compared to the uptake without free inhibitor (p < .0001), implicating the involvement of megalin receptor in the internalization of the liposomes. Taken together, these results demonstrate that megalin-targeted liposomes may offer an opportunity to enhance the delivery of therapeutics to the placenta for the treatment of diseases of pregnancy.

TDM-guided medication of polymyxin B in a patient with CRKP-induced bloodstream infection: a case report

The narrow therapeutic window of polymyxin B constrains its clinical use against the multidrug-resistant organisms (MDRO). A 45-year-old patient was suffering with bloodstream infection with high fever and received a combined treatment with polymyxin B and tigecycline. Therapeutic drug monitoring (TDM) was applied to polymyxin B to develop a personalized medication against MDRO. The dose adjustment of polymyxin B with TDM successfully alleviated the infection and reduced the incident of acute kidney injury as caused in case of the original doses of polymyxin B. TDM of polymyxin B represents a valid treatment to ensure the efficiency and safety.

Antibiotics can be used to contain drug-resistant bacteria by maintaining sufficiently large sensitive populations

Standard infectious disease practice calls for aggressive drug treatment that rapidly eliminates the pathogen population before resistance can emerge. When resistance is absent, this elimination strategy can lead to complete cure. However, when resistance is already present, removing drug-sensitive cells as quickly as possible removes competitive barriers that may slow the growth of resistant cells. In contrast to the elimination strategy, a containment strategy aims to maintain the maximum tolerable number of pathogens, exploiting competitive suppression to achieve chronic control. Here, we combine in vitro experiments in computer-controlled bioreactors with mathematical modeling to investigate whether containment strategies can delay failure of antibiotic treatment regimens. To do so, we measured the "escape time" required for drug-resistant Escherichia coli populations to eclipse a threshold density maintained by adaptive antibiotic dosing. Populations containing only resistant cells rapidly escape the threshold density, but we found that matched resistant populations that also contain the maximum possible number of sensitive cells could be contained for significantly longer. The increase in escape time occurs only when the threshold density-the acceptable bacterial burden-is sufficiently high, an effect that mathematical models attribute to increased competition. The findings provide decisive experimental confirmation that maintaining the maximum number of sensitive cells can be used to contain resistance when the size of the population is sufficiently large.

The effect of therapeutic drug monitoring of beta-lactam and fluoroquinolones on clinical outcome in critically ill patients: the DOLPHIN trial protocol of a multi-centre randomised controlled trial

BACKGROUND

Critically ill patients undergo extensive physiological alterations that will have impact on antibiotic pharmacokinetics. Up to 60% of intensive care unit (ICU) patients meet the pharmacodynamic targets of beta-lactam antibiotics, with only 30% in fluoroquinolones. Not reaching these targets might increase the chance of therapeutic failure, resulting in increased mortality and morbidity, and antibiotic resistance. The DOLPHIN trial was designed to demonstrate the added value of therapeutic drug monitoring (TDM) of beta-lactam and fluoroquinolones in critically ill patients in the ICU.

METHODS

A multi-centre, randomised controlled trial (RCT) was designed to assess the efficacy and cost-effectiveness of model-based TDM of beta-lactam and fluoroquinolones. Four hundred fifty patients will be included within 24 months after start of inclusion. Eligible patients will be randomly allocated to either study group: the intervention group (active TDM) or the control group (non-TDM). In the intervention group dose adjustment of the study antibiotics (cefotaxime, ceftazidime, ceftriaxone, cefuroxime, amoxicillin, amoxicillin with clavulanic acid, flucloxacillin, piperacillin with tazobactam, meropenem, and ciprofloxacin) on day 1, 3, and 5 is performed based upon TDM with a Bayesian model. The primary outcome will be ICU length of stay. Other outcomes amongst all survival, disease severity, safety, quality of life after ICU discharge, and cost effectiveness will be included.

DISCUSSION

No trial has investigated the effect of early TDM of beta-lactam and fluoroquinolones on clinical outcome in critically ill patients. The findings from the DOLPHIN trial will possibly lead to new insights in clinical management of critically ill patients receiving antibiotics. In short, to TDM or not to TDM?

TRIAL REGISTRATION

EudraCT number: 2017-004677-14. Sponsor protocol name: DOLPHIN. Registered 6 March 2018 . Protocol Version 6, Protocol date: 27 November 2019.

Moxifloxacin in Chronic Obstructive Pulmonary Disease: Pharmacokinetics and Penetration into Bronchial Secretions in Ward and Intensive Care Unit Patients

This study aimed to evaluate the pharmacokinetic profile of moxifloxacin (MXF) in serum and sputum/bronchial secretions of 22 patients with acute exacerbation of chronic obstructive pulmonary disease (AECOPD) hospitalized in the ward and intensive care unit (ICU). The data showed that ICU patients had lower concentrations in secretions (P = 0.01). However, no other statistically significant differences were observed in pharmacokinetic parameters and penetration in secretions between ward and ICU patients. MXF showed a favorable pharmacokinetic profile, and the pharmacodynamic targets for common pathogens for AECOPD were achieved.

A Randomized Pharmacokinetic and Pharmacodynamic Evaluation of Every 8-Hour and 12-Hour Dosing Strategies of Vancomycin and Cefepime in Neurocritically ill Patients

PURPOSE

Neurocritically ill patients have clinically significant alterations in pharmacokinetic parameters of renally eliminated medications that may result in subtherapeutic plasma and cerebrospinal fluid antibiotic concentrations.

METHODS

We conducted a prospective randomized open-label study of adult neurocritically ill patients treated with vancomycin and cefepime. Vancomycin 15 mg/kg and cefepime 2 g were dosed at every-8- or 12-hour intervals. The primary outcomes were the achievement of pharmacodynamic (PD) targets related to time of unbound drug above minimum inhibitory concentrations (MIC) for 60% or more of the dosing interval (fT > MIC ≥ 60%) for β-lactams and ratio of 24-hour area under the curve (AUC):MIC of 400 or greater for vancomycin.

RESULTS

Twenty patients were included in the study. They were divided equally between the every-12-hour and every-8-hour dosing groups. Patients (mean age 51.8 ± 11 yrs) were primarily male (60%) and white (95%), and most had an admission diagnosis of intracranial hemorrhage (80%). Compared with the every-12-hour group, the every-8-hour vancomycin group achieved target trough concentrations (higher than 15 μg/ml) significantly more frequently at initial measurement (0% vs 80%, p<0.01) and at 7-10 days (0% vs 90%, p=0.045) and achieved PD targets more frequently at increasing MICs. Similarly, compared with every-12-hour dosing, the every-8-hour cefepime dosing strategy significantly increased PD target attainment (fT > MIC ≥ 60%) at an MIC of 8 μg/ml (20% vs 70%, p=0.02).

CONCLUSIONS

This study demonstrated that more frequent dosing of vancomycin and cefepime is required to achieve optimal PD targets in adult neurocritically ill patients. The need for increased total daily doses is potentially secondary to the development of augmented renal clearance.

Pharmacokinetics of cefuroxime in infants and neonates undergoing cardiac surgery

AIMS

Very little data exist regarding the effect of cardiopulmonary bypass (CPB) on cefuroxime (CXM) pharmacokinetics in children less than one year of age.

METHODS

50 mg kg^-1 CXM i.v. after induction were followed by 75 mg kg^-1 into the CPB circuit. In 42 patients undergoing cardiac surgery, 15-20 samples were obtained between 5 and 360 min after the first dose. Total CXM concentrations were measured by high-performance liquid chromatography and a pharmacokinetic/pharmacodynamic (PK/PD) modelling was performed.

RESULTS

Using a fixed protein binding of 15.6% for CXM, peak plasma concentrations of unbound CXM were 229 ± 52 μg ml^-1 after the first bolus and 341 ± 86 μg ml^-1 on CPB. Nadir concentrations before CPB were 69 ± 20 μg ml^-1 and six hours later decreased to 41 ± 19 μg ml^-1 with and 24 ± 14 μg ml^-1 without CPB. A two-compartment model was fitted with the main covariates body weight, CPB and postmenstrual age (PMA). PK parameters were as follows: systemic clearance, 5.15 [95% CI 4.5-5.8] l h^-1 ; central volume of distribution, 11.25 [9.41-13.09] l; intercompartmental clearance, 18.19 [14.79-21.58] l h^-1 ; and peripheral volume, 17.07 [15.7-18.5] L. ƒT > MIC of 32 μg ml^-1 for an 8-h time period was between 70 and 100% (2.5-10 kg BW). According to our simulation, 25 mg ml^-1 CXM as a primary bolus and into the prime plus a 5 mg kg^-1  h^-1 infusion maintain CXM concentrations continuously above 32 μg ml^-1 .

CONCLUSIONS

The routine dosing regimen provided was sufficient for prophylaxis, but continuous dosing can provide a higher percentage of ƒT > MIC.

Closed-Loop- and Decision-Assist-Guided Fluid Therapy of Human Hemorrhage

OBJECTIVES

We sought to evaluate the efficacy, efficiency, and physiologic consequences of automated, endpoint-directed resuscitation systems and compare them to formula-based bolus resuscitation.

DESIGN

Experimental human hemorrhage and resuscitation.

SETTING

Clinical research laboratory.

SUBJECTS

Healthy volunteers.

INTERVENTIONS

Subjects (n = 7) were subjected to hemorrhage and underwent a randomized fluid resuscitation scheme on separate visits 1) formula-based bolus resuscitation; 2) semiautonomous (decision assist) fluid administration; and 3) fully autonomous (closed loop) resuscitation. Hemodynamic variables, volume shifts, fluid balance, and cardiac function were monitored during hemorrhage and resuscitation. Treatment modalities were compared based on resuscitation efficacy and efficiency.

MEASUREMENTS AND MAIN RESULTS

All approaches achieved target blood pressure by 60 minutes. Following hemorrhage, the total amount of infused fluid (bolus resuscitation: 30 mL/kg, decision assist: 5.6 ± 3 mL/kg, closed loop: 4.2 ± 2 mL/kg; p < 0.001), plasma volume, extravascular volume (bolus resuscitation: 17 ± 4 mL/kg, decision assist: 3 ± 1 mL/kg, closed loop: -0.3 ± 0.3 mL/kg; p < 0.001), body weight, and urinary output remained stable under decision assist and closed loop and were significantly increased under bolus resuscitation. Mean arterial pressure initially decreased further under bolus resuscitation (-10 mm Hg; p < 0.001) and was lower under bolus resuscitation than closed loop at 20 minutes (bolus resuscitation: 57 ± 2 mm Hg, closed loop: 69 ± 4 mm Hg; p = 0.036). Colloid osmotic pressure (bolus resuscitation: 19.3 ± 2 mm Hg, decision assist, closed loop: 24 ± 0.4 mm Hg; p < 0.05) and hemoglobin concentration were significantly decreased after bolus fluid administration.

CONCLUSIONS

We define efficacy of decision-assist and closed-loop resuscitation in human hemorrhage. In comparison with formula-based bolus resuscitation, both semiautonomous and autonomous approaches were more efficient in goal-directed resuscitation of hemorrhage. They provide favorable conditions for the avoidance of over-resuscitation and its adverse clinical sequelae. Decision-assist and closed-loop resuscitation algorithms are promising technological solutions for constrained environments and areas of limited resources.

Phenobarbital in intensive care unit pediatric population: predictive performances of population pharmacokinetic model

An external evaluation of phenobarbital population pharmacokinetic model described by Marsot et al. was performed in pediatric intensive care unit. Model evaluation is an important issue for dose adjustment. This external evaluation should allow confirming the proposed dosage adaptation and extending these recommendations to the entire intensive care pediatric population. External evaluation of phenobarbital published population pharmacokinetic model of Marsot et al. was realized in a new retrospective dataset of 35 patients hospitalized in a pediatric intensive care unit. The published population pharmacokinetic model was implemented in nonmem 7.3. Predictive performance was assessed by quantifying bias and inaccuracy of model prediction. Normalized prediction distribution errors (NPDE) and visual predictive check (VPC) were also evaluated. A total of 35 infants were studied with a mean age of 33.5 weeks (range: 12 days-16 years) and a mean weight of 12.6 kg (range: 2.7-70.0 kg). The model predicted the observed phenobarbital concentrations with a reasonable bias and inaccuracy. The median prediction error was 3.03% (95% CI: -8.52 to 58.12%), and the median absolute prediction error was 26.20% (95% CI: 13.07-75.59%). No trends in NPDE and VPC were observed. The model previously proposed by Marsot et al. in neonates hospitalized in intensive care unit was externally validated for IV infusion administration. The model-based dosing regimen was extended in all pediatric intensive care unit to optimize treatment. Due to inter- and intravariability in pharmacokinetic model, this dosing regimen should be combined with therapeutic drug monitoring.

Pharmacokinetics and pharmacodynamics of meropenem in children with severe infection

This study aimed to describe the pharmacokinetic (PK) characteristics of meropenem in children with severe infections and to assess the pharmacokinetic/pharmacodynamic (PK/PD) profiles of various meropenem dosage regimens in these patients. Fourteen children with severe infections received intravenous (i.v.) bolus doses of meropenem (20 mg/kg/dose) every 8 h (q8h). Serum samples were obtained before and serially after the second dose of meropenem, and a population PK analysis was performed. The final model was used to simulate serum concentration-time profiles with various dosage regimens. The PK/PD target was to achieve a serum meropenem concentration higher than the minimum inhibitory concentration (MIC) of the causative organism (i.e. Pseudomonas aeruginosa and Enterobacteriaceae) for ≥40% of the dosing interval (40%T>MIC). The median age and weight of the children were 6.0 years and 20.0 kg, respectively. Meropenem serum concentration-time profiles were best described by a two-compartmental model with first-order elimination. The simulations showed that the probabilities of target attainment (PTAs) for organisms with an MIC of 1 mg/L were 0.678 and 1.000 following i.v. bolus and 3-h infusion of meropenem (20 mg/kg/dose), respectively. Using a 3-h infusion of a 20 mg/kg/dose, the PTA was 0.999 and 0.765 for organisms with MICs of 4 mg/L and 8 mg/L, respectively. Meropenem given as i.v. bolus doses of 20 mg/kg/dose q8h appeared to be inadequate for PK/PD target attainment for organisms with an MIC of 1 mg/L. The simulations showed that meropenem administration via a 3-h infusion using the same dose improved the PTA.

Pharmacokinetic considerations for drugs administered in the critically ill

Significant physiological changes are common among critically ill patients. This case-based review describes the consequences of these changes on the selection and dosing of medications.

Population pharmacokinetics of imipenem in critically ill patients with suspected ventilator-associated pneumonia and evaluation of dosage regimens

AIMS

Significant alterations in the pharmacokinetics (PK) of antimicrobials have been reported in critically ill patients. We describe PK parameters of imipenem in intensive care unit (ICU) patients with suspected ventilator-associated pneumonia and evaluate several dosage regimens.

METHODS

This French multicentre, prospective, open-label study was conducted in ICU patients with a presumptive diagnosis of ventilator-associated pneumonia caused by Gram-negative bacilli, who empirically received imipenem intravenously every 8 h. Plasma imipenem concentrations were measured during the fourth imipenem infusion using six samples (trough, 0.5, 1, 2, 5 and 8 h). Data were analysed with a population approach using the stochastic approximation expectation maximization algorithm in Monolix 4.2. A Monte Carlo simulation was performed to evaluate the following six dosage regimens: 500, 750 or 1000 mg with administration every 6 or 8 h. The pharmacodynamic target was defined as the probability of achieving a fractional time above the minimal inhibitory concentration (MIC) of >40%.

RESULTS

Fifty-one patients were included in the PK analysis. Imipenem concentration data were best described by a two-compartment model with three covariates (creatinine clearance, total bodyweight and serum albumin). Estimated clearance (between-subject variability) was 13.2 l h(-1) (38%) and estimated central volume 20.4 l (31%). At an MIC of 4 μg ml(-1) , the probability of achieving 40% fractional time > MIC was 91.8% for 0.5 h infusions of 750 mg every 6 h, 86.0% for 1000 mg every 8 h and 96.9% for 1000 mg every 6 h.

CONCLUSIONS

This population PK model accurately estimated imipenem concentrations in ICU patients. The simulation showed that for these patients, the best dosage regimen of imipenem is 750 mg every 6 h and not 1000 mg every 8 h.

Role of an electronic antimicrobial alert system in intensive care in dosing errors and pharmacist workload

BACKGROUND

Critically ill patients are vulnerable to dosing errors. We developed an electronic Antimicrobial Dose alert based upon Creatinine clearance (ADC-alert), which gives daily antimicrobial dosing advice based upon the 24-h creatinine clearance (CLcr).

OBJECTIVE

Primary objective: to verify the correctness of the ADC-alert output and its benefit for the workload of the clinical pharmacist (CP). Secondary objective to compare the ADC-alert output between patients with normal and impaired CLcr.

SETTING

The 36-bed surgical and medical intensive care unit (ICU) of the Ghent University Hospital, Ghent, Belgium.

METHOD

In a single centre prospective observational 44-day study, prescriptions were reviewed by CP and compared with the ADC-alert output advice. CP workload was calculated with and without the use of the ADC-alert. Impaired renal function was defined as a CLcr < 50 mL/min for at least 1 day during antimicrobial treatment in the ICU or the need for renal replacement therapy (RRT).

MAIN OUTCOME MEASURES

Correct dosing recommendation by ADC-alert compared to CP review and time spent by CP with and without the ADC-alert.

RESULTS

A total of 87 patients (554 daily antimicrobial prescriptions; 435 patient days) were both screened by CP and ADC-alert. Renal function impairment occurred in 39 patients (44.8 %) with 12 patients requiring RRT. The ADC-alert gave a correct dosage advice in 483 prescriptions (87.2 %). The overall sensitivity was 77.3 %; specificity was 89.9 %. Use of the ADC-alert reduces CP workload with 76.5 % (average time spent per patient: 17 vs. 4 min). Patients with a CLcr < 50 mL/min less frequently received a correct recommendation than patients with normal CLcr (P = 0.001). This was due to configuration problems in dialysis patients.

CONCLUSION

We developed and evaluated an electronic alert system to generate dynamic antimicrobial dose adaptation based on the daily calculation of the 24-h CLcr of ICU patients. Its use led to substantial time savings for clinical pharmacists. However, the alert advice suffered from some developmental and other flaws. Despite resolving some of these shortcomings, bedside interpretation of the results and clinical judgement remain necessary.

Impact of imipenem and amikacin pharmacokinetic/pharmacodynamic parameters on microbiological outcome of Gram-negative bacilli ventilator-associated pneumonia

OBJECTIVES

Despite recent advances, antibiotic therapy of ventilator-associated pneumonia (VAP) in ICU patients is still challenging. We assessed the impact of imipenem and amikacin pharmacokinetic and pharmacodynamic parameters on microbiological outcome in these patients.

PATIENTS AND METHODS

Patients with Gram-negative bacilli (GNB) VAP were prospectively included. Blood samples for pharmacokinetic analysis were collected after empirical administration of a combination of imipenem three times daily and one single dose of amikacin. MICs were estimated for each GNB obtained from respiratory samples. Microbiological success was defined as a ≥10(3) cfu/mL decrease in bacterial count in quantitative cultures between baseline and the third day of treatment.

RESULTS

Thirty-nine patients [median (min-max) age = 60 years (28-84) and median SAPS2 at inclusion = 40 (19-73)] were included. Median MICs of imipenem and amikacin were 0.25 mg/L (0.094-16) and 2 mg/L (1-32), respectively. Median times over MIC and over 5× MIC for imipenem were 100% (8-100) and 74% (3-100), respectively. The median C1/MIC ratio for amikacin was 23 (1-76); 34 patients (87%) achieved a C1/MIC ≥10. Microbiological success occurred in 29 patients (74%). No imipenem pharmacodynamic parameter was significantly associated with the microbiological success. For amikacin, C1/MIC was significantly higher in the microbiological success group: 26 (1-76) versus 11 (3-26) (P = 0.004).

CONCLUSIONS

In ICU patients with VAP, classic imipenem pharmacodynamic targets are easily reached with usual dosing regimens. In this context, for amikacin, a higher C1/MIC ratio than previously described might be necessary.

Optimizing antimicrobial therapy in critically ill patients

Critically ill patients with infection in the intensive care unit (ICU) would certainly benefit from timely bacterial identification and effective antimicrobial treatment. Diagnostic techniques have clearly improved in the last years and allow earlier identification of bacterial strains in some cases, but these techniques are still quite expensive and not readily available in all institutions. Moreover, the ever increasing rates of resistance to antimicrobials, especially in Gram-negative pathogens, are threatening the outcome for such patients because of the lack of effective medical treatment; ICU physicians are therefore resorting to combination therapies to overcome resistance, with the direct consequence of promoting further resistance. A more appropriate use of available antimicrobials in the ICU should be pursued, and adjustments in doses and dosing through pharmacokinetics and pharmacodynamics have recently shown promising results in improving outcomes and reducing antimicrobial resistance. The aim of multidisciplinary antimicrobial stewardship programs is to improve antimicrobial prescription, and in this review we analyze the available experiences of such programs carried out in ICUs, with emphasis on results, challenges, and pitfalls. Any effective intervention aimed at improving antibiotic usage in ICUs must be brought about at the present time; otherwise, we will face the challenge of intractable infections in critically ill patients in the near future.

Reducing medication errors in critical care: a multimodal approach

The Institute of Medicine has reported that medication errors are the single most common type of error in health care, representing 19% of all adverse events, while accounting for over 7,000 deaths annually. The frequency of medication errors in adult intensive care units can be as high as 947 per 1,000 patient-days, with a median of 105.9 per 1,000 patient-days. The formulation of drugs is a potential contributor to medication errors. Challenges related to drug formulation are specific to the various routes of medication administration, though errors associated with medication appearance and labeling occur among all drug formulations and routes of administration. Addressing these multifaceted challenges requires a multimodal approach. Changes in technology, training, systems, and safety culture are all strategies to potentially reduce medication errors related to drug formulation in the intensive care unit.

Development and validation of a UHPLC diode array detector method for meropenem quantification in human plasma

OBJECTIVES

Meropenem is a β-lactam antibiotic frequently used to treat serious infections in intensive care unit patients. The main objective was to develop and validate a sensitive and specific ultra high performance liquid chromatography method with photodiode array detection for the quantitation of meropenem in human plasma. The applicability of the method for meropenem monitoring was also examined.

DESIGN AND METHODS

The validation of the method was performed following the FDA's guidelines for bioanalytical methods. In parallel, the method was applied for monitoring meropenem in forty plasma samples from ten critically ill patients treated intravenously at a total dose of 1 g. Drug levels were measured in each patient at 0 h, 2 h, 4 h and 8 h after meropenem infusion.

RESULTS

With this method, intraday and day-to-day variation was below 10%; intraday and day-to-day accuracy was between 94% and 114%; the limit of quantification was 0.5 μg/mL and recovery was above 70%. The method was successfully applied to quantitate meropenem concentrations and the results showed significant pharmacokinetic interindividual variability. Of special interest is that 50% of treated patients had meropenem plasma levels below the minimum inhibitory concentration at 8h after the start of infusion, which was strongly related to creatinine clearance >60 mL/min.

CONCLUSIONS

The method meets the requirements to be applied for meropenem concentration measurements in pharmacokinetics studies and clinical routine. The results suggest the need for therapeutic drug monitoring of meropenem in treated critically-ill patients.

Estimation of glomerular filtration rate to adjust vancomycin dosage in critically ill patients: superiority of the Chronic Kidney Disease Epidemiology Collaboration equation?

The purpose of this study was to determine the best estimate of glomerular filtration rate (GFR) to adjust vancomycin (VAN) dosage in critically ill patients. Seventy-eight adult intensive care unit patients received a 15 mg/kg loading dose of VAN plus a 30 mg/kg/day continuous infusion. Steady-state concentration was measured 48 hours later and the dose was adjusted to obtain a target concentration ranging from 20 to 25 mg/l. GFR was estimated by measured creatinine clearance (CLCR), Cockcroft, Modification of Diet in Renal Disease and Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equations. The required dose providing the target concentration was 36±17 mg/kg/day. The first dosage had to be increased in 51% of all patients and in 84% of trauma patients (highest GFR), but had to be decreased in 17% of patients. The closest relationship between clearances of vancomycin was observed with CKD-EPI to GFR. The correlation between clearances of vancomycin and measured CLCR was significant but was rather poor with Cockcroft and Modification of Diet in Renal Disease equation. On the Bland and Altman plots, measured CLCR provided a lower bias but a larger confidence interval and a weaker precision than CKD-EPI. For VAN dose adjustments in intensive care unit patients, Cockcroft formula and Modification of Diet in Renal Disease should be used with caution. In clinical practice, the physician does not have at their disposal the patient's measured CLCR when prescribing. The CKD-EPI appears to be the best predictor of clearances of vancomycin for calculation of a therapeutic VAN regimen.

[Tarragona strategy--appropriate antibiotic therapy in the ICU]

BACKGROUND

Appropriate antibiotic initial therapy remarkably decreases the mortality of patients with infections in the ICU. The establishment of an appropriate initial therapy follows empirical aspects. This practice was first done for the treatment of nosocomial pneumonia. Since that time the practice became known as Tarragona strategy.

RESULTS

The basic elements of the strategy are based on the initial antibiotic treatment of patients with infections in the ICU in general and include the following: view the patient and his/her medical history, consider the microbiologic environment, in which the patient became ill, test for possible causative microorganisms and initiate high-dose antibiotics immediately, evaluate pharmacokinetic/pharmacodynamic aspects influenced by the pathophysiologic processes in the critically ill patient, the specifics of the microorganisms, the peculiarity of the antibiotics in the patient and due to therapeutic procedures, and tailor the initial broad spectrum therapy as necessary according to the microbiological results.

CONCLUSION

This procedure is safe, reduces mortality, limits the development of resistance, and is economic.

Relevance of Liver Failure for Anti-Infective Agents: From Pharmacokinetic Alterations to Dosage Adjustments

The liver is a complex organ with great ability to influence drug pharmacokinetics. Due to its wide array of function, its impairment has the potential to affect bioavailability, enterohepatic circulation, drug distribution, metabolism, clearance, and biliary elimination. These alterations differ widely depending on the cause of the liver failure, if it is acute or chronic in nature, the extent of impairment, and comorbid conditions. In addition, effects on liver functions do not occur in a proportional or predictable manner for escalating degrees of liver impairment. The ability of hepatic alterations to influence PK is also dependent on drug characteristics, such as administration route, chemical properties, protein binding, and extraction ratio, among others. This complexity makes it difficult to predict what these effects have on drugs. Unlike certain classes of agents, efficacy of anti-infectives is most often dependent on fulfilling pharmacokinetic/pharmacodynamic targets, such as C_max/MIC, AUC/MIC, T_>MIC, IC₅₀/EC₅₀, or T>EC₉₅. Loss of efficacy, or conversely, increased risk of toxicity may occur in certain circumstances of liver injury. Although important to consider these potential alterations and their effects on specific anti-infectives, many lack data to constitute specific dosing adjustments, making it important to monitor patients for effectiveness and toxicities of therapy.

Treatment ofPseudomonas aeruginosainfection in critically ill patients

Critically ill patients are on the increase in the present clinical setting. Aging of our population and increasingly aggressive medical and therapeutic interventions, including implanted foreign bodies, organ transplantation and advances in the chemotherapy of malignant diseases, have created a cohort of particularly vulnerable patients. Pseudomonas aeruginosa is one of the leading gram-negative organisms associated with nosocomial infections. This organism is frequently feared because it causes severe hospital-acquired infections, especially in immunocompromised hosts, and is often antibiotic resistant, complicating the choice of therapy. The epidemiology, microbiology, mechanisms of resistance and currently available and future treatment options for the most relevant infections caused by P. aeruginosa are reviewed.

Effect of experimentally induced hypovolemia on ertapenem tissue distribution using microdialysis in rats

Hypovolemia is a common event in critical care patients that may affect drug distribution and elimination. In order to better understand this issue the effect of hypovolemia on the plasma protein binding and tissue distribution of ertapenem was investigated in rats using microdialysis. Microdialysis probes were inserted into the jugular vein and hind leg muscle. Ertapenem recoveries in muscle and blood were determined in each rat by retrodialysis by drug before drug administration. Hypovolemia was induced in 6 rats by removing 40% of the initial blood volume over 30 min. Ertapenem was infused intravenously at a dose of 40 mg kg(-1) over 30 min, and microdialysis samples were collected for 310 min. The unbound concentration profiles in muscle and blood were virtually superimposed in both groups except at early time points. The ratios of the area under the concentration-time curve (AUC) for tissue to the AUC for blood were 0.7±0.2 and 0.8±0.2 for control and hypovolemic rats, respectively. Hypovolemia induced a 40% decrease in the clearance of ertapenem, with no statistically significant alteration of its volume of distribution. This study showed that ertapenem elimination was altered in hypovolemic rats, probably due to decreased renal blood flow, but its distribution characteristics were not. Unbound concentrations of ertapenem in blood and muscle were always virtually identical.

Approaches for dosage individualisation in critically ill patients

INTRODUCTION

Pharmacokinetic variability in critically ill patients is the result of the overlapping of multiple pathophysiological and clinical factors. Unpredictable exposure from standard dosage regimens may influence the outcome of treatment. Therefore, strategies for dosage individualisation are recommended in this setting.

AREAS COVERED

The authors focus on several approaches for dosage individualisation that have been developed, ranging from the well-established therapeutic drug monitoring (TDM) up to the innovative application of pharmacogenomics criteria. Furthermore, the authors summarise the specific population pharmacokinetic models for different drugs developed for critically ill patients to improve the initial dosage selection and the Bayesian forecasting of serum concentrations. The authors also consider the use of Monte Carlo simulation for the selection of dosage strategies.

EXPERT OPINION

Pharmacokinetic/pharmacodynamics (PK/PD) modelling and dosage individualisation methods based on mathematical and statistical criteria will contribute in improving pharmacologic treatment in critically ill patients. Moreover, substantial effort will be necessary to integrate pharmacogenomics criteria into critical care practice. The lack of availability of target biomarkers for dosage adjustment emphasizes the value of TDM which allows a large part of treatment outcome variability to be controlled.

Drug absorption, distribution, metabolism and excretion considerations in critically ill adults

INTRODUCTION

All critically ill patients require medication to treat organ dysfunction. However, the pharmacokinetics of drugs used to treat these patients is complex due to frequent alterations in drug absorption, distribution, metabolism, and excretion (ADME).

AREAS COVERED

This review examines pharmacokinetic aspects of drug administration for adult intensive care unit (ICU) patients. Specifically, the authors examine the ADME changes that occur and which should be considered by clinicians when delivering drug therapy to critically ill patients.

EXPERT OPINION

Dosage pharmacokinetics determined from single-dose or limited-duration administration studies in healthy volunteers may not apply to critically ill patients. Organ dysfunction among these patients may be due to pre-existing disease or the effects of a systemic or locoregional inflammatory response precipitated by their illness. Alterations in pharmacokinetics observed among the critically ill include altered bioavailability after enteral administration, increased volume of distribution and blood-brain barrier permeability and changes in P-glycoprotein and cytochrome P450 enzyme function. However, the effect of these changes on clinically important outcomes remains uncertain and poorly studied. Future investigations should examine not only pharmacokinetic changes among the critically ill, but also whether recognition of these changes and alterations in drug therapy directed as a consequence of their observation alters patient outcomes.

Oseltamivir pharmacokinetics in critically ill adults receiving extracorporeal membrane oxygenation support

Extracorporeal membrane oxygenation (ECMO) is known to affect pharmacokinetics and hence optimum dosing. The aim of this open label, prospective study was to investigate the pharmacokinetics of oseltamivir (prodrug) and oseltamivir carboxylate (active metabolite) during ECMO. Fourteen adult patients with suspected or confirmed H1N1 influenza were enrolled in the study. Oseltamivir 75 mg was enterally administered twice daily and blood samples for pharmacokinetic assessment were taken on day 1 and 5. A multi-compartmental model to describe the pharmacokinetics of oseltamivir and oseltamivir carboxylate was developed using a non-linear mixed effects modelling approach. The median (range) clearance of oseltamivir carboxylate was 15.8 (4.8-36.6) l/hour, lower than the reported mean value of 21.5 l/hour in healthy adults. The median (range) steady state volume of distribution of oseltamivir carboxylate was 179 (61-436) litres, much greater than healthy adults but similar to previous reports in critically ill patients. Substantial 'between subject' variability in systemic exposure to oseltamivir carboxylate was revealed; median (range) area under the curve and Cmax were 4346 (644-13660) ng/hour/ml and 509 (54-1277) ng/ml, respectively. Both area under the curve and Cmax were significantly correlated with serum creatinine (r2=0.37, P=0.02 and r2=0.29, P=0.02, respectively). Systemic exposure to oseltamivir carboxylate following the administration of enteral oseltamivir 75 mg twice daily in adult ECMO patients is comparable to those in ambulatory patients and far in excess of concentrations required to maximally inhibit neuraminidase activity of the H1N1 virus. Dosage adjustment for ECMO, per se, appears not to be necessary; however, doses should be reduced in patients with renal dysfunction.

Amikacin population pharmacokinetics in critically ill Kuwaiti patients

Amikacin pharmacokinetic data in Kuwaiti (Arab) intensive care unit (ICU) patients are lacking. Fairly sparse serum amikacin peak and trough concentrations data were obtained from adult Kuwaiti ICU patients. The data were analysed using a nonparametric adaptive grid (NPAG) maximum likelihood algorithm. The estimations of the developed model were assessed using mean error (ME) as a measure of bias and mean squared error (MSE) as a measure of precision. A total of 331 serum amikacin concentrations were obtained from 56 patients. The mean (± SD) model parameter values found were Vc = 0.2302 ± 0.0866 L/kg, kslope = 0.004045 ± 0.00705 min per unit of creatinine clearance, k12 = 2.2121 ± 5.506 h(-1), and k21 = 1.431 ± 2.796 h(-1). The serum concentration data were estimated with little bias (ME = -0.88) and good precision (MSE = 13.08). The present study suggests that amikacin pharmacokinetics in adult Kuwaiti ICU patients are generally rather similar to those found in other patients. This population model would provide useful guidance in developing initial amikacin dosage regimens for such patients, especially using multiple model (MM) dosage design, followed by appropriate Bayesian adaptive control, to optimize amikacin dosage regimens for each individual patient.

Rapid quantification of six β-lactams to optimize dosage regimens in severely septic patients

A fast analytical procedure was developed for the simultaneous quantification of cefepime (CEF), meropenem (MEM), ceftazidime (CZA), cefuroxime (CFX), aztreonam (AZT), and piperacillin (PIP) in serum of intensive care patients. The β-lactam pharmacokinetic parameters can be altered in severe sepsis due to changes in the distribution, the metabolism and the elimination process. Therapeutic drug monitoring (TDM) of β-lactams is therefore recommended in critically ill patients. The plasma samples were spiked with cefoperazone as internal standard and proteins were precipitated with methanol. The different β-lactams were separated with high performance liquid chromatography within 18 min, and quantified by UV spectrophotometry with a diode array detector. The method was validated by means of the accuracy profile approach based on β expectation tolerance intervals. The acceptance limits were settled at ± 30% according to the regulatory requirements. Assay validation demonstrated good performance for all β-lactams analyzed in terms of trueness, repeatability, linearity and intermediate precision over the range of 2-200 μg/mL. The simple extraction procedure provides respective absolute and relative recoveries ranging from 70% to 86% and from 66% to 89% for all the β-lactams analyzed. Few interferences were observed and the method was easily applicable to TDM in intensive care patients. The quantification of β-lactams should allow for antibiotic regimen adjustment in critically ill patients.

Antibiotics in critically ill patients: a systematic review of the pharmacokinetics of β-lactams

INTRODUCTION

Several reports have shown marked heterogeneity of antibiotic pharmacokinetics (PK) in patients admitted to ICUs, which might potentially affect outcomes. Therefore, the pharmacodynamic (PD) parameter of the efficacy of β-lactam antibiotics, that is, the time that its concentration is above the bacteria minimal inhibitory concentration (T > MIC), cannot be safely extrapolated from data derived from the PK of healthy volunteers.

METHODS

We performed a full review of published studies addressing the PK of intravenous β-lactam antibiotics given to infected ICU patients. Study selection comprised a comprehensive bibliographic search of the PubMed database and bibliographic references in relevant reviews from January 1966 to December 2010. We selected only English-language articles reporting studies addressing β-lactam antibiotics that had been described in at least five previously published studies. Studies of the PK of patients undergoing renal replacement therapy were excluded.

RESULTS

A total of 57 studies addressing six different β-lactam antibiotics (meropenem, imipenem, piperacillin, cefpirome, cefepime and ceftazidime) were selected. Significant PK heterogeneity was noted, with a broad, more than twofold variation both of volume of distribution and of drug clearance (Cl). The correlation of antibiotic Cl with creatinine clearance was usually reported. Consequently, in ICU patients, β-lactam antibiotic half-life and T > MIC were virtually unpredictable, especially in those patients with normal renal function. A better PD profile was usually obtained by prolonged or even continuous infusion. Tissue penetration was also found to be compromised in critically ill patients with septic shock.

CONCLUSIONS

The PK of β-lactam antibiotics are heterogeneous and largely unpredictable in ICU patients. Consequently, the dosing of antibiotics should be supported by PK concepts, including data derived from studies of the PK of ICU patients and therapeutic drug monitoring.

Simultaneous determination of 12 beta-lactam antibiotics in human plasma by high-performance liquid chromatography with UV detection: application to therapeutic drug monitoring

A rapid and specific high-performance liquid chromatography method with UV detection (HPLC-UV) for the simultaneous determination of 12 beta-lactam antibiotics (amoxicillin, cefepime, cefotaxime, ceftazidime, ceftriaxone, cloxacillin, imipenem, meropenem, oxacillin, penicillin G, piperacillin, and ticarcillin) in small samples of human plasma is described. Extraction consisted of protein precipitation by acetonitrile. An Atlantis T3 analytical column with a linear gradient of acetonitrile and a pH 2 phosphoric acid solution was used for separation. Wavelength photodiode array detection was set either at 210 nm, 230 nm, or 298 nm according to the compound. This method is accurate and reproducible (coefficient of variation [CV] < 8%), allowing quantification of beta-lactam plasma levels from 5 to 250 μg/ml without interference with other common drugs. This technique is easy to use in routine therapeutic drug monitoring of beta-lactam antibiotics.

Tobramycin disposition in ICU patients receiving a once daily regimen: population approach and dosage simulations

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT? It is well known that tobramycin given as an once daily dose according to the usual recommendations needs therapeutic drug monitoring by measurement of peak and trough concentrations. In the literature, there are only few published studies on the population pharmacokinetics of once daily tobramycin in critically ill patients. Glomerular filtration rate and bodyweight were identified as covariates contributing to the inter-individual variability in the disposition of aminoglycosides. The study, by Peris-Marti et al. [24], only evaluated the pharmacodynamic effectiveness of a 4 mg kg(-1) dose of tobramycin given once daily in critically ill patients. The authors concluded with a simulation showing that for a theoretical MIC of 1 or 2 mg l(-1) , a 7 mg kg(-1) dose was required.

WHAT THIS STUDY ADDS

Our results confirm the high variability of tobramycin disposition in intensive care patients and consequently the possible lack of effectiveness. By using a population pharmacokinetic approach, two explicative covariates (height and Cockcroft creatinine clearance) added to a two-compartment model with proportional error, explained much of the inter-individual variability of tobramycin disposition in the critically ill patient population. In a median ICU patient, simulations were performed at various dosage regimens and peak and AUC pharmacodynamic targets could not be reached simultaneously in more than 45% of the ICU patient population. Drug monitoring is required to manage efficacy and toxicity.

AIM

The aim of this study was to evaluate the disposition of tobramycin (TOB) in critically ill patients (ICU) by a population pharmacokinetic approach, to determine the covariates involved, and to simulate tobramycin dosage regimens.

METHODS

Forty-nine adult ICU patients received TOB (5 mg kg(-1) ) once daily. NonMem modelling was performed on 32 patients. The 17 other patients were used for the qualification process by normalized prediction distribution error. Then Monte Carlo simulations (MCS) were performed.

RESULTS

A two-compartment model with a proportional error best fitted the data. TOB total clearance (CL(TOB) ) was significantly correlated with Cockcroft creatinine clearance (COCK) and height. TOB clearance was 4.8 ± 1.9 l h(-1) (range 1.22-8.95), the volume of distribution of the central compartment was 24.7 ± 3.7 l (range 17.34-32.83) and that of the peripheral compartment and the inter-compartmental clearance were 30.6 l and 4.74 l h(-1) , respectively. Only 29% of the patients presented a target AUC between 80 and 125 mg l(-1) h and 61% were lower than 80 mg l(-1)  h. After considering COCK and height, MCS showed that only 50% of the population could achieve the target AUC for the 375 and 400 mg dosages.

CONCLUSION

Even after taking into account COCK and height, for strains with an MIC ≤ 1 mg l(-1) , MCS doses evidenced that peak and AUC pharmacodynamic targets could not be reached simultaneously in more than 45% of the ICU patient population. Combination therapy in addition to drug monitoring are required to manage efficacy and toxicity.

Management of aminoglycosides in the intensive care unit

Antibacterial resistance is increasing throughout the world, while the development of new agents is slowly progressing. In addition, the increasing prevalence of fluoroquinolone resistance may force many practitioners to choose an aminoglycoside agent in gram-negative regimens. Aminoglycosides are bactericidal agents with potent activity against gram-negative infections and activity against gram-positive infections when added to a cell wall active antimicrobial-based regimen. These agents may be dosed multiple times a day or consolidated as high-dose, extended-interval dosing to maximize pharmacokinetic and pharmacodynamic properties to achieve possible improved efficacy with reduced toxicity. Clinical application includes the treatment of bacteremia, endocarditis, health-care and nosocomial pneumonias, intra-abdominal infections, and others. Nephrotoxicity and ototoxicity are potential risks of aminoglycoside therapy that may be minimized with serum monitoring and short courses of therapy.

Steady-state pharmacokinetics and BAL concentration of colistin in critically Ill patients after IV colistin methanesulfonate administration

BACKGROUND

Infections caused by multidrug-resistant gram-negative bacteria have caused a resurgence of interest in colistin. To date, information about pharmacokinetics of colistin is very limited in critically ill patients, and no attempts have been made to evaluate its concentration in BAL.

METHODS

In this prospective, open-label study, 13 adult patients with ventilator-associated pneumonia caused by gram-negative bacteria were treated with colistin methanesulfonate (CMS) IV, 2 million International Units (174 mg) q8h, a usually recommended dose, for at least 2 days. Blood samples were collected from each patient at time intervals after the end of infusion. BAL was performed at 2 h. Colistin was measured by a selective, sensitive high-performance liquid chromatography-based method. Pharmacokinetic parameters were determined by noncompartmental analysis.

RESULTS

Patients received 2.19 ± 0.38 mg/kg (range, 1.58-3.16) of CMS per dose. At steady state, mean ± SD plasma colistin maximum (Cmax) and trough (Ctrough) concentrations were 2.21 ± 1.08 and 1.03 ± 0.69 μg/mL, respectively. Mean ± SD area under the plasma concentration-time curve from 0 to 8 h (AUC(0-8)), apparent elimination half-life, and apparent volume of distribution were 11.5 ± 6.2 μg × h/mL, 5.9 ± 2.6 h, and 1.5 ± 1.1 L/kg, respectively. Cmax/minimum inhibitory concentration (MIC) ratio and AUC(0-24)/MIC ratio (MIC = 2 μg/mL) were 1.1 ± 0.5 and 17.3 ± 9.3, respectively. Colistin was undetectable in BAL. Nephrotoxicity was not observed.

CONCLUSIONS

Although the pharmacodynamic parameters that better predict the efficacy of colistin are not known in humans, in critically ill adult patients the IV administration of CMS 2 million International Units (174 mg) q8h results in apparently suboptimal plasma concentrations of colistin, which is undetectable in BAL. A better understanding of the pharmacokinetic-pharmacodynamic relationship of colistin is urgently needed to determine the optimal dosing regimen.

Pharmacokinetic and pharmacodynamic parameters of antimicrobials: potential for providing dosing regimens that are less vulnerable to resistance

Whereas infections caused by multidrug-resistant micro-organisms are increasing worldwide, there are few new molecules, especially ones that are active against Gram-negative strains. There are extensive data showing that the administration of antimicrobials according to pharmacokinetic/pharmacodynamic parameters improves the possibility of a positive clinical outcome, particularly in severely ill patients. Evidence is growing that when pharmacokinetic/pharmacodynamic parameters are used to target not only clinical cure but also eradication, the spread of resistance will also be contained. The present paper summarizes the most relevant papers published in this field and provides some suggestions for dosing regimens that can be adopted in the clinical setting to limit the spread of resistance.