Antibacterial Dosing in Intensive Care

Comparison of the pharmacokinetic properties of vancomycin, linezolid, tigecyclin, and daptomycin

The rapid antibiotic resistance development has created a major demand for new antimicrobial agents that can combat resistant strains such as methicillin-resistant S. aureus (MRSA). Until a short time ago, the glycopeptide vancomycin was the only therapeutic choice in this situation. However, in recent years some newer agents with different mechanisms of actions have been added to the arsenal, and more are on the horizon. For a successful therapy it is of vital importance that these compounds are used judiciously and dosed appropriately. The present article reviews the pharmacokinetic properties of vancomycin, linezolid, tigecycline and daptomycin. The first major difference between these compounds is their oral bioavailability. Only linezolid can be administered orally, whereas vancomycin, daptomycin and tigecycline are limited to parenteral use. Once in the body, they show very different disposition. Daptomycin has a very small volume of distribution of 7L indicating very little tissue distribution whereas tigecycline has a very large volume of distribution of 350-500 L. Vancomycin and linezolid are in-between with volumes of distribution of approximately 30 and 50 L, close to total body water. However, studies have shown that linezolid shows better tissue penetration than vancomycin. Newer studies using microdialysis, a new technique that allows direct monitoring of unbound tissue levels, support this finding. As far as drug elimination, daptomycin and vancomycin are mainly eliminated into the urine and require dosing adjustments in renally impaired patients, whereas tigecycline is eliminated into the bile and linezolid is metabolized so that in renal patients no dosing adjustments are needed for these compounds. Although the elimination pathways are very different, the resulting half-lives of linezolid, vancomycin, and daptomycin are not greatly different and vary from 4-8 h. Tigecycline, however, has a much longer half-life of up to 1-2 days due to the slow redistribution from tissue binding sites.

Chitosan sponges to locally deliver amikacin and vancomycin: a pilot in vitro evaluation

BACKGROUND

Open orthopaedic wounds are ideal sites for infection. Preventing infection in these wounds is critical for reducing patient morbidity and mortality, controlling antimicrobial resistance and lowering the cost of treatment. Localized drug delivery has the potential to overcome the challenges associated with traditional systemic dosing. A degradable, biocompatible polymer sponge (chitosan) that can be loaded with clinician-selected antibiotics at the point of care would provide the patient and clinician with a desirable, adjunctive preventive modality.

QUESTIONS/PURPOSES

We asked (1) if an adaptable, porous chitosan matrix could absorb and elute antibiotics for 72 hours for potential use as an adjunctive therapy to débridement and lavage; and (2) if the sponges could elute levels of antibiotic that would inhibit growth of Staphylococcus aureus and Pseudomonas aeruginosa?

METHODS

We fabricated a degradable chitosan sponge that can be loaded with antibiotics during a 60-second hydration in drug-containing solution. In vitro evaluation determined amikacin and vancomycin release from chitosan sponges at six time points. Activity tests were used to assess the release of inhibitory levels of amikacin and vancomycin.

RESULTS

Amikacin concentration was 881.5 microg/mL after 1 hour with a gradual decline to 13.9 microg/mL after 72 hours. Vancomycin concentration was 1007.4 microg/mL after 1 hour with a decrease to 48.1 microg/mL after 72 hours. Zone of inhibition tests were used to verify inhibitory levels of drug release from chitosan sponges. A turbidity assay testing activity of released amikacin and vancomycin indicated inhibitory levels of elution from the chitosan sponge.

CLINICAL RELEVANCE

Chitosan sponges may provide a potential local drug delivery device for preventing musculoskeletal infections.

Using population pharmacokinetics to determine gentamicin dosing during extended daily diafiltration in critically ill patients with acute kidney injury

The objective of the present prospective pharmacokinetic study was to describe the variability of plasma gentamicin concentrations in critically ill patients with acute kidney injury (AKI) necessitating extended daily diafiltration (EDD-f) using a population pharmacokinetic model and to subsequently perform Monte Carlo dosing simulations to determine which dose regimen achieves the pharmacodynamic targets the most consistently. We collected data from 28 gentamicin doses in 14 critically ill adult patients with AKI requiring EDD-f and therapeutic gentamicin. Serial plasma samples were collected. A population pharmacokinetic model was used to describe the pharmacokinetics of gentamicin and perform Monte Carlo simulations with doses of between 3 mg/kg of body weight and 7 mg/kg and at various time points before commencement of EDD-f to evaluate the optimal dosing regimen for achieving pharmacodynamic targets. A two-compartment pharmacokinetic model adequately described the gentamicin clearance while patients were on and off EDD-f. The plasma half-life of gentamicin during EDD-f was 13.8 h, whereas it was 153.4 h without EDD-f. Monte Carlo simulations suggest that dosing with 6 mg/kg every 48 h either 30 min or 1 h before the commencement of EDD-f results in 100% attainment of the target maximum concentration drug in plasma (<10 mg/liter) and sufficient attainment of the target area under the concentration-time curve from 0 to 24 h (AUC(0-24); 70 to 120 mg.h/liter). None of the simulated dosing regimens satisfactorily achieved the targets of the minimum concentrations of drug in plasma (<1.0 mg/liter) at 24 h. In conclusion, dosing of gentamicin 30 min to 1 h before the commencement of an EDD-f treatment enables attainment of target peak concentrations for maximal therapeutic effect while enhancing drug clearance to minimize toxicity. Redosing in many patients should occur after 48 h, and we recommend the use of therapeutic drug monitoring to guide dosing to optimize achievement of the AUC(0-24) targets.

An Official ATS/ERS/ESICM/SCCM/SRLF Statement: Prevention and Management of Acute Renal Failure in the ICU Patient: an international consensus conference in intensive care medicine

OBJECTIVES

To address the issues of Prevention and Management of Acute Renal Failure in the ICU Patient, using the format of an International Consensus Conference.

METHODS AND QUESTIONS

Five main questions formulated by scientific advisors were addressed by experts during a 2-day symposium and a Jury summarized the available evidence: (1) Identification and definition of acute kidney insufficiency (AKI), this terminology being selected by the Jury; (2) Prevention of AKI during routine ICU Care; (3) Prevention in specific diseases, including liver failure, lung Injury, cardiac surgery, tumor lysis syndrome, rhabdomyolysis and elevated intraabdominal pressure; (4) Management of AKI, including nutrition, anticoagulation, and dialysate composition; (5) Impact of renal replacement therapy on mortality and recovery.

RESULTS AND CONCLUSIONS

The Jury recommended the use of newly described definitions. AKI significantly contributes to the morbidity and mortality of critically ill patients, and adequate volume repletion is of major importance for its prevention, though correction of fluid deficit will not always prevent renal failure. Fluid resuscitation with crystalloids is effective and safe, and hyperoncotic solutions are not recommended because of their renal risk. Renal replacement therapy is a life-sustaining intervention that can provide a bridge to renal recovery; no method has proven to be superior, but careful management is essential for improving outcome.

Diagnosis and management of complicated intra-abdominal infection in adults and children: guidelines by the Surgical Infection Society and the Infectious Diseases Society of America

Evidence-based guidelines for managing patients with intra-abdominal infection were prepared by an Expert Panel of the Surgical Infection Society and the Infectious Diseases Society of America. These updated guidelines replace those previously published in 2002 and 2003. The guidelines are intended for treating patients who either have these infections or may be at risk for them. New information, based on publications from the period 2003-2008, is incorporated into this guideline document. The panel has also added recommendations for managing intra-abdominal infection in children, particularly where such management differs from that of adults; for appendicitis in patients of all ages; and for necrotizing enterocolitis in neonates.

Diagnosis and Management of Complicated Intra-abdominal Infection in Adults and Children: Guidelines by the Surgical Infection Society and the Infectious Diseases Society of America

Evidence-based guidelines for managing patients with intra-abdominal infection were prepared by an Expert Panel of the Surgical Infection Society and the Infectious Diseases Society of America. These updated guidelines replace those previously published in 2002 and 2003. The guidelines are intended for treating patients who either have these infections or may be at risk for them. New information, based on publications from the period 2003–2008, is incorporated into this guideline document. The panel has also added recommendations for managing intra-abdominal infection in children, particularly where such management differs from that of adults; for appendicitis in patients of all ages; and for necrotizing enterocolitis in neonates.

Vancomycin dosing for pneumonia in critically ill trauma patients

BACKGROUND

Vancomycin has been recommended as the treatment of choice for methicillin-resistant Staphylococcus aureus (MRSA) pneumonia with a desired trough concentration of 15 to 20 mg/L. The purpose of this study was to evaluate the initial dosing of vancomycin for MRSA pneumonia in critically ill adult trauma patients.

METHODS

Critically ill adult trauma patients were retrospectively identified for inclusion into the study. Patients initiated at a dose of 1 g intravenously (i.v.) every 8 hours were compared with patients initiated at a dose of 1 g i.v. every 12 hours. Baseline continuous demographic variables and steady-state vancomycin trough concentrations were compared between the two groups using a Student's t test (alpha = 0.05).

RESULTS

There were 36 patients who satisfied criteria for inclusion, 17 patients in the 1 g every 8 hour group and 19 patients in the 1 g every 12 hour group. The mean steady-state trough concentration was higher in the 1 g every 8 hour group versus the 1 g every 12 hour group (11.1 vs. 6.8 mg/L, p = 0.014). A steady-state trough concentration greater than 15 mg/L was achieved in 23.5% of the patients in the 1 g every 8 hour group and none of the patients in the 1 g every 12 hour group.

CONCLUSION

A vancomycin regimen of 1 g i.v. every 12 hours in critically ill trauma patients with MRSA pneumonia and normal renal function is unlikely to achieve trough concentrations of 15 to 20 mg/L. Doses of at least 1 g i.v. every 8 hours are needed.

Pharmacokinetics of gentamicin in critically ill patients: pilot study evaluating the first dose

Gentamicin is extensively used in the treatment of severe Gram-negative bacterial infections. A loading dose of 7 mg/kg is recommended to achieve a maximum concentration (C(max)) above 16 mg/L. We studied gentamicin pharmacokinetic data from patients treated between January 2006 and June 2008 in two intensive-care units. The Sawchuk and Zaske one-compartment pharmacokinetic model was used to estimate the gentamicin volume of distribution (the 32 patients had a median age of 68 years (23 men)). The median volume of distibution (V(d)) per kilogram of body weight (V(d)/kg) was 0.41 L/kg (interquartile range of 0.36-0.46 L/kg), with no correlations with age, Charlson comorbidity score, sequential organ failure assessment (SOFA) score and creatinine serum level (r(2) = 0.016, 0.058, 0.037, and 0.067, respectively). Women had a significantly higher median V(d)/kg (0.50 vs. 0.40 L/kg, p 0.002) and lower C(max) (15.2 vs. 18.5 mg/L, p 0.016), despite similar dose/kg. In a logistic regression model, only sex (female: OR 0.032; 95% CI 0.03-0.387) and dose/kg (per mg/kg: OR 3.21; 95% CI 1.17-8.79) were significantly associated with the achievement of C(max) above 16 mg/L. Gentamicin clearance was 57 mL/min (interquartile range of 44.7-78 mL/min) and decreased with age (r(2) = 0.178, p 0.016), SOFA score (r(2) = 0.199, p 0.011) and creatinine clearance (r(2) = 0.258, p 0.003). Gentamicin V(d) was increased in critically ill patients, particularly in women. Therefore, high gentamicin loading doses should be given to all patients, especially women, independently of organ failure. Gentamicin clearance decreases with age, SOFA score, and renal failure.

Management of ventilator-associated pneumonia

Ventilator-associated pneumonia (VAP) management depends on the interaction between the infective agent, the host response, and the antimicrobial drug used. After the pathogen reaches the lungs, two outcomes are possible: either the microorganisms are eliminated by the host immune system, or they overcome the immune system and cause pulmonary infection. When a patient is thought to have VAP, two steps are strongly recommended: etiologic diagnostic testing and the immediate initiation of antibiotics. The daily management of VAP remains a challenge for physicians in the ICU. In recent years, a more dynamic approach has evolved, updating local epidemiology, evaluating VAP and diagnostic tools every day, and assessing host response using clinical and biochemical parameters.

Unbound cephalothin pharmacokinetics in adult burn patients are related to the elapsed time after injury

Cephalothin (cefalotin) pharmacokinetics were evaluated for nine severely burned patients (42% +/- 9% mean burn areas) and five healthy volunteers by using non-plasma-protein-bound concentration-time profiles. Burn patients gave increased mean residence times (36%) and reduced total clearances (25%). Mean residence times and distribution volumes increased between 1 and 4 days posttrauma, suggesting that burn patient pharmacokinetics change during the initial fluid resuscitation phase of treatment.

Vancomycin dosage optimization in patients with malignant haematological disease by pharmacokinetic/pharmacodynamic analysis

BACKGROUND

The use of vancomycin against Staphylococcus aureus is currently debated because of the increasing resistance developed by this pathogen. Nevertheless, antibacterial effectiveness is a limited resource that must be protected and restored. Novel dosage strategies based on pharmacokinetic/pharmacodynamic analyses are needed to retain effectiveness that could improve drug exposure in patients infected with such pathogens.

OBJECTIVE

The aim of this study was to assess whether standard or higher vancomycin dosages are required to increase the probability of attaining a target pharmacokinetic/pharmacodynamic index for several staphylococcal strains and thus to estimate the minimum vancomycin daily dose related to a high probability of effective treatment in patients with malignant haematological disease.

METHODS

Monte Carlo simulation was performed to calculate the cumulative fraction of response (CFR) for different vancomycin daily dosages, using a population pharmacokinetic model previously defined in patients with malignant haematological disease and the minimum inhibitory concentration (MIC) distribution for vancomycin against several staphylococcal species (vancomycin-susceptible S. aureus and vancomycin-intermediate S. aureus [VISA], S. epidermidis, S. haemolyticus and coagulase-negative Staphylococcus [CNS] species) obtained from the European Committee on Antimicrobial Susceptibility Testing (EUCAST) in order to predict the dose that would achieve the pharmacokinetic/pharmacodynamic index value associated with efficacy (the area under the concentration-time curve from 0 to 24 hours divided by the MIC [AUC(24)/MIC >/=400]).

RESULTS

CFR values showed dependence on the renal function of the patient and the causative pathogen. Only in patients with a creatinine clearance (CL(CR)) <60 mL/min did the standard vancomycin dosage (2000 mg/day) induce CFRs >60% for all staphylococci, except the VISA strains. CFRs for S. aureus of 90.6%, 47.3% and 31.2% for CL(CR) values of <60, 60-120 and >120 mL/min, respectively, were obtained, whereas for the VISA strains, the corresponding values were only 14.0%, 0.3% and 0%. The impact of potential pathogens on CFRs is also significant. According to our pharmacokinetic/pharmacodynamic analysis, in patients with normal renal function (CL(CR) between 60 and 120 mL/min) vancomycin 2000 mg/day leads to a risk of not achieving the recommended AUC(24)/MIC breakpoint of 52.7%, 70.4%, 74.9% and 80.3% for S. aureus, S. haemolyticus, CNS and S. epidermidis, respectively. Application of our results to clinical practice graphically allows us to obtain the recommended dose for any a priori-selected probability of attaining the AUC(24)/MIC ratio of >/=400 and to evaluate the CFRs for any dosing regimen used in this population group, depending on the patients' renal function.

CONCLUSIONS

Application of pharmacokinetic/pharmacodynamic analysis based on Monte Carlo simulation offers an excellent tool for selecting the therapeutic option with the highest probability of clinical success in patients with malignant haematological disease. Thus, for vancomycin-susceptible S. aureus, if a CFR >/=80 is assumed as clinically acceptable, vancomycin doses of 1500, 3000 and 4000 mg/day for a CL(CR) of <60, 60-120 and >120 mL/min, respectively, will be required.

Variations in MIC value caused by differences in experimental protocol

The minimal inhibitory concentration (MIC) of an antibiotic for a microorganism quantifies the effectiveness in reducing growth or the bactericidal ability of the compound. Measurements of MIC's carried out using different protocols should be comparable. Several of the factors that influence the outcome of the measurement vary between protocols. Variations in the MIC estimate were examined for E. coli and amoxicillin as well as tetracycline and for Pseudomonas putida and enrofloxacin. Duration of the measurement, density of the starting culture, the use of optical density or cell counts to determine growth and the induction of resistance can cause differences of a factor of up to 8 in the MIC value. While this does not hamper the reporting of trends by researchers adhering to the same protocol, it may affect assessments based on the absolute value of the MIC of a given combination of microorganism and antibiotic.

Meropenem dosing in critically ill patients with sepsis and without renal dysfunction: intermittent bolus versus continuous administration? Monte Carlo dosing simulations and subcutaneous tissue distribution

OBJECTIVES

To compare the plasma and subcutaneous tissue concentration-time profiles of meropenem administered by intermittent bolus dosing or continuous infusion to critically ill patients with sepsis and without renal dysfunction, and to use population pharmacokinetic modelling and Monte Carlo simulations to assess the cumulative fraction of response (CFR) against Gram-negative pathogens likely to be encountered in critical care units.

PATIENTS AND METHODS

We randomized 10 patients with sepsis to receive meropenem by intermittent bolus administration (n = 5; 1 g 8 hourly) or an equal dose administered by continuous infusion (n = 5). Serial subcutaneous tissue concentrations were determined using microdialysis and compared with plasma data for first-dose and steady-state pharmacokinetics. Population pharmacokinetic modelling of plasma data and Monte Carlo simulations were then undertaken with NONMEM.

RESULTS

It was found that continuous infusion maintains higher median trough concentrations, in both plasma (intermittent bolus 0 versus infusion 7 mg/L) and subcutaneous tissue (0 versus 4 mg/L). All simulated intermittent bolus, extended and continuous infusion dosing achieved 100% of pharmacodynamic targets against most Gram-negative pathogens. Superior obtainment of pharmacodynamic targets was achieved using administration by extended or continuous infusion against less susceptible Pseudomonas aeruginosa and Acinetobacter species.

CONCLUSIONS

This is the first study to compare the relative concentration-time data of bolus and continuous administration of meropenem at the subcutaneous tissue and plasma levels. We found that the administration of meropenem by continuous infusion maintains higher concentrations in subcutaneous tissue and plasma than by intermittent bolus dosing. Administration by extended or continuous infusion will achieve superior CFR against less-susceptible organisms in patients without renal dysfunction.

Piperacillin penetration into tissue of critically ill patients with sepsis--bolus versus continuous administration?

OBJECTIVE

To describe a pharmacokinetic model of piperacillin concentrations in plasma and subcutaneous tissue when administered by bolus dosing and continuous infusion in critically ill patients with sepsis on days 1 and 2 of antibiotic therapy and to compare results against previous results for piperacillin from a cohort of patients with septic shock.

DESIGN

Prospective randomized controlled trial.

SETTING

Eighteen-bed intensive care unit at 918-bed tertiary referral hospital.

PATIENTS

Thirteen critically ill adult patients with known or suspected sepsis in whom the treating physician deemed piperacillin-tazobactam appropriate therapy were conveniently sampled.

INTERVENTIONS

Patients were randomized to receive different daily doses of piperacillin-tazobactam by bolus dosing or continuous infusion (continuous infusion--six patients; bolus dosing--seven patients). Serial plasma and tissue concentrations were determined on days 1 and 2 of treatment. Tissue concentrations of piperacillin were determined using a subcutaneously inserted microdialysis catheter. Separate pharmacokinetic models were developed for both bolus and continuous dosing.

MEASUREMENTS AND MAIN RESULTS

This is the first known article to report concurrent plasma and subcutaneous tissue concentrations of a beta-lactam antibiotic administered by bolus and continuous dosing in critically ill patients with sepsis. With a 25% lower piperacillin dose administered to the continuous infusion group, the infusion group had statistically significantly higher median plasma concentrations than the bolus group on day 2 (16.6 vs. 4.9 mg/L; p = 0.007). There was a trend to higher median plasma concentrations on day 1 in the bolus dosing group (8.9 vs. 4.9 mg/L; p = 0.078). Median tissue concentrations were not statistically different on day 1 (infusion group 2.4 mg/L vs. bolus group 2.2 mg/L; p = 0.48) and day 2 (infusion group 5.2 mg/L vs. bolus group 0.8 mg/L; p = 0.45). A two-compartment pharmacokinetic model was found to describe the data best. Tissue pharmacodynamic targets were achieved more successfully with infusion dosing.

CONCLUSIONS

Patients with sepsis do not seem to have the same level of impairment of tissue distribution as described for patients with septic shock. A 25% lower dose of piperacillin administered by continuous infusion seems to maintain higher trough concentrations compared with standard bolus dosing. It is likely that the clinical advantages of continuous infusion are most likely to be evident when treating pathogens with high minimum inhibitory concentration, although without therapeutic drug monitoring and subsequent dose adjustment, infusions may never achieve target concentrations of organisms with very high minimum inhibitory concentrations in a small number of patients.

Mortality in ICU patients with bacterial community-acquired pneumonia: when antibiotics are not enough

BACKGROUND

It remains uncertain why immunocompetent patients with bacterial community-acquired pneumonia (CAP) die, in spite of adequate antibiotics.

METHODS

This is a secondary analysis of the CAPUCI database which was a prospective observational multicentre study. Two hundred and twelve immunocompetent patients admitted to 33 Spanish ICUs for CAP were analyzed. Comparisons were made for lifestyle risk factors, comorbidities and severity of illness. ICU mortality was the principal outcome variable.

RESULTS

Bacteremic CAP (43.3 vs. 21.1%) and empyema (11.5 vs. 2.2%) were more frequent (P < 0.05) in patients with Streptococcus pneumoniae CAP. Higher rates of adequate empiric therapy (95.8 vs. 75.5%, P < 0.05) were observed in patients with S. pneumoniae CAP. Patients with non-pneumococcal CAP experienced more shock (66.7 vs. 50.8%, P < 0.05), and need for mechanical ventilation (83.3 vs. 61.5%, P < 0.05). ICU mortality was 20.7 and 28% [OR 1.49(0.74-2.98)] among immunocompetent patients with S. pneumoniae (n = 122) and non-pneumococci (n = 90), in spite of initial adequate antibiotic. Multivariable regression analysis in these 184 immunocompetent patients with adequate empirical antibiotic treatment identified the following variables as independently associated with mortality: shock (HR 13.03); acute renal failure (HR 4.79), and APACHE II score higher than 24 (HR 2.22).

CONCLUSIONS

Mortality remains unacceptably high in immunocompetent patients admitted to the ICU with bacterial pneumonia, despite adequate initial antibiotics and comorbidities management. Patients with shock, acute renal failure and APACHE II score higher than 24 should be considered for inclusion in trials of adjunctive therapy in order to improve CAP survival.

Clinical relevance of pharmacokinetics and pharmacodynamics in cardiac critical care patients

Pharmacokinetics is a discipline aimed at predicting the best dosage and dosing regimen for each single drug in order to ensure and maintain therapeutically effective concentrations at the action sites. In cardiac critical care patients, various pathophysiological conditions may significantly alter the pharmacokinetic behaviour of drugs. Gastrointestinal drug absorption may be erratic and unpredictable in the early postoperative period, and so patients may be unresponsive to oral therapy; thus the intravenous route should be preferred for life-saving drugs whenever feasible. Variations in the extracellular fluid content as a response to the trauma of surgery and the fluid load or significant drug loss through thoracic drainages may significantly lower plasma concentrations of extracellularly distributed hydrophilic antimicrobials (beta-lactams, aminoglycosides and glycopeptides). Drug metabolism may be altered by the systemic inflammatory response and/or multiple organ failure and/or drug-drug pharmacokinetic interactions that can potentially occur during polytherapy, especially in immunosuppressed cardiac transplant patients. Instability of renal function may promote significant changes in body fluid concentrations of renally eliminated drugs, even in a brief period of hours. Finally, the application of extracorporeal circulation by means of cardiopulmonary bypass may significantly alter the disposition of several drugs during the operation because of acute haemodilution, hypoalbuminaemia, hypothermia and/or adsorption to the bypass equipment. Accordingly, to avoid either overexposure and the consequent increased risk of toxicity or underexposure and the consequent risk of therapeutic failure in critically ill cardiac patients, the dosing regimens of several drugs are expected to be significantly different from those suggested for clinically stable patients. Additionally, therapeutic drug monitoring may be helpful in the management of drug therapy and should be routinely used to guide individualized dose adjustments for (i) immunosuppressants whenever cytochrome P450 3A4 isoenzyme inhibitors (e.g. macrolide antibacterials, azole antifungals) or inducers (e.g. rifampicin [rifampin]) are added to or withdrawn from the regimen; and (ii) glycopeptide and aminoglycoside antibacterials whenever haemodynamically active agents (such as dopamine, dobutamine and furosemide [frusemide]) are added to or withdrawn from the regimen, and also whenever significant changes of haemodynamics and/or of renal function occur.

High performance liquid chromatographic determination of plasma free and total tazobactam and piperacillin

A high-pressure liquid chromatography (HPLC) method with ultraviolet detection was developed for the measurement of plasma free and total tazobactam and piperacillin. This method is simple and fast, requiring only 11 min for the HPLC run and a sample preparation of about 11 min for total drugs and 10 min for free drugs. The procedure for the assay involves the treatment of plasma with acetonitrile for total drugs determination, and the use of a centrifugal filter device to deproteinize plasma for free drugs determination. The HPLC column, a Hypersil-ODS, was equilibrated with an eluent mixture composed of acetonitrile-potassium phosphate (pH 2.6). CVs for repeatability of tazobactam and piperacillin measurements ranged from 4.30 to 6.60; CVs for reproducibility ranged from 5.60 to 9.40. Mean analytical recoveries ranged from 100.4 to 103%. A linear relationship was obtained between peak area and drugs concentration in the range studied (0-62.5mg/L for tazobactam and 0-500mg/L for piperacillin). The equation for regression line were y=19x-1.4 for tazobactam and y=1.7x-0.9 for piperacillin; correlation coefficients were >0.999. The lower limit of quantitation (LLQ) for standard samples was about 0.12 mg/L for tazobactam and 0.49 mg/L for piperacillin, respectively. The lower limit of detection (LLD) was 0.06 mg/L for tazobactam and 0.24 mg/L for piperacillin. This HPLC assay for tazobactam and piperacillin is sensitive and accurate, and provides a reliable determination of both free and total tazobactam and piperacillin in human plasma, thus allowing the determination of these analytes in patients receiving tazocillin therapy.

Therapeutic challenges of urosepsis

Urosepsis accounts for approximately 25% of all sepsis cases and may develop from a community or nosocomial acquired urinary tract infection (UTI). The underlying UTI is almost exclusively a complicated one with involvement of parenchymatous urogenital organs (e.g. kidneys, prostate). In urosepsis, as in other types of sepsis, the severity of sepsis depends mostly upon the host response. The treatment of urosepsis comprises four major aspects: Early goal directed therapy, early optimal pharmacodynamic exposure to antimicrobials, early control of the complicating factor in the urinary tract and specific sepsis therapy. Following these prerequisites there appear two major challenges that need to be addressed: Firstly, time from admission to therapy is critical; the shorter the time to effective treatment, the higher the success rate. This aspect has to become incorporated into the organisational process. Secondly, adequate initial antibiotic therapy has to be insured. This goal implies however, a wide array of measures to ensure rational antibiotic policy. Both challenges are best targeted if an interdisciplinary approach at any level of the process is established, encompassing urologists, intensive care specialists, radiologists, microbiologists and clinical pharmacologists working tightly together at any time.

Antibiotic resistance--what's dosing got to do with it?

OBJECTIVE

This review seeks to identify original research articles that link antibiotic dosing and the development of antibiotic resistance for different antibiotic classes. Using this data, we seek to apply pharmacodynamic principles to assist clinical practice for suppressing the emergence of resistance. Concepts such as mutant selection window and mutant prevention concentration will be discussed.

DATA SOURCES

PubMed, EMBASE, and the Cochrane Controlled Trial Register.

STUDY SELECTION

All articles that related antibiotic doses and exposure to the formation of antibiotic resistance were reviewed.

DATA SYNTHESIS

The escalation of antibiotic resistance continues worldwide, most prominently in patients in intensive care units. Data are emerging from in vitro and in vivo studies that suggest that inappropriately low antibiotic dosing may be contributing to the increasing rate of antibiotic resistance. Fluoroquinolones have widely been researched and publications on other antibiotic classes are emerging. Developing dosing regimens that adhere to pharmacodynamic principles and maximize antibiotic exposure is essential to reduce the increasing rate of antibiotic resistance.

CONCLUSIONS

Antibiotic dosing must aim to address not only the bacteria isolated, but also the most resistant subpopulation in the colony, to prevent the advent of further resistant infections because of the inadvertent selection pressure of current dosing regimens. This may be achieved by maximizing antibiotic exposure by administering the highest recommended dose to the patient.

Altered pharmacology in the Intensive Care Unit patient

Critically ill patients, not infrequently present alterations of physiological parameters that determine the success/failure of therapeutic interventions as well as the final outcome. Sepsis and polytrauma are two of the most common and complex syndromes occurring in Intensive Care Unit (ICU) and affect drug absorption, disposition, metabolism and elimination. Pharmacological management of ICU patients requires consideration of the unique pharmacokinetics associated with these clinical conditions and the likely occurrence of drug interaction. Rational adjustment in drug choice and dosing contributes to the appropriateness of treatment of those patients.

Ideal microbiological and pharmacological characteristics of a quality antimicrobial agent: comparing original and generic molecules

This article critically evaluates the main in vitro and in vivo studies published which compare generic with the original molecules, both those administered orally and parenterally. The authors indicate that caution should be used in assuming bioequivalence of the generic drug with its clinical efficacy in clinical practice. In fact, mild differences in the content of the active ingredient, less relevant in healthy volunteers, may have an impact in the actual population, which is heterogeneous for age, sex, weight, concomitant risk factors and severity of the underlying disease, as in critically ill patients, with consequences for the patient and ecosystem. Nowadays the requirements for authorization to commercialize a generic antimicrobial agent are focused on demonstration of bioequivalence to the original molecule, with a range variability of +/-20%. However this kind of trial is not sufficient to predict the actual profile in clinical practice, particularly in critically ill patients. Thus while generics can represent an opportunity for physicians, patients and healthcare systems the regulatory procedures do not seem exhaustive, and it is probably necessary to define an ad hoc technical standard of quality before their commercialization and to perform adequate clinical trials regarding efficacy and safety of the "equivalent molecule", especially for drugs used in critically ill patients.

Pharmacokinetics/pharmacodynamics of antibacterials in the Intensive Care Unit: setting appropriate dosing regimens

Patients admitted to Intensive Care Units (ICUs) are at very high risk of developing severe nosocomial infections. Consequently, antimicrobials are among the most important and commonly prescribed drugs in the management of these patients. Critically ill patients in ICUs include representatives of all age groups with a range of organ dysfunction related to severe acute illness that may complicate long-term illness. The range of organ dysfunction, together with drug interactions and other therapeutic interventions (e.g. haemodynamically active drugs and continuous renal replacement therapies), may strongly impact on antimicrobial pharmacokinetics in critically ill patients. In the last decade, it has become apparent that the intrinsic pharmacokinetic (PK) and pharmacodynamic (PD) properties are the major determinants of in vivo efficacy of antimicrobial agents. PK/PD parameters are essential in facilitating the translation of microbiological activity into clinical situations, ensuring a successful outcome. In this review, we analyse the typical patterns of antimicrobial activity and the corresponding PK/PD parameters, with a special focus on a PK/PD dosing approach of the antimicrobial agent classes commonly utilised in the ICU setting.

A novel way to investigate the effects of plasma exchange on antibiotic levels: use of microdialysis

Plasma exchange (PE) is a treatment modality frequently used for many autoimmune diseases and may cause extracorporeal elimination of antibiotics. No data currently exist on antibiotic concentrations in extracellular fluid during PE. The aim of this study is to describe the effect of PE on the serum and subcutaneous tissue pharmacokinetics of piperacillin administered as a continuous infusion in a critically ill 17-year-old patient with Guillain-Barré syndrome and ventilator-associated pneumonia on Days 1 and 4 of antibiotic therapy. The effect of PE on piperacillin concentrations appears to be small. On Day 1, an estimated 7% of total piperacillin eliminated during PE was attributable to PE. On Day 4 this was estimated to be 11%. Using the in vivo sampling technique microdialysis, we have been able to show that a small redistribution of piperacillin from tissue to serum occurs in response to the reducing serum concentrations caused by PE. In critically ill patients, we believe that administration of a beta-lactam antibiotic by continuous infusion should be considered to maintain serum and tissue concentrations of these time-dependent antibiotics.

Optimal management of urosepsis from the urological perspective

Urosepsis in adults comprises approximately 25% of all sepsis cases and in most cases is due to complicated urinary tract infections (UTIs). In this paper we review the optimal management of urosepsis from the urological point of view. Urosepsis is often due to obstructed uropathy of the upper or lower urinary tract. The treatment of urosepsis comprises four major aspects: 1. Early goal-directed therapy; 2. Optimal pharmacodynamic exposure to antimicrobials both in blood and in the urinary tract; 3. Control of complicating factors in the urinary tract; 4. Specific sepsis therapy. Early tissue oxygenation, appropriate initial antibiotic therapy and rapid identification and control of the septic focus in the urinary tract are critical steps in the successful management of a patient with severe urosepsis. To achieve this goal an optimal interdisciplinary approach encompassing the emergency unit, urological specialties and intensive-care medicine is necessary.

Inadequate antimicrobial prophylaxis during surgery: a study of beta-lactam levels during burn debridement

OBJECTIVES

To determine how long single-dose prophylactic antibiotic regimens for burns surgery maintained plasma concentrations above the MICs for target organisms during surgery.

PATIENTS AND METHODS

We monitored antibiotic plasma concentrations in 12 patients (mean +/- SD 43 +/- 12% total burn surface area) throughout debridement surgery after administration of the standard prophylactic antibiotic dosing regimens of either 1 g of intravenous cefalotin or 4.5 g of intravenous piperacillin/tazobactam.

RESULTS

The eschar debridement and grafting procedures ranged in duration from 2.25 to over 8.5 h. The duration of total plasma cefalotin concentration above an MIC of 0.2 mg/L for Staphylococcus aureus was 6.49 +/- 2.85 h, whereas the mean duration of total plasma piperacillin concentration above an MIC of 64 mg/L for Pseudomonas aeruginosa was only 1.15 +/- 0.59 h. None of the patients dosed with piperacillin/tazobactam was adequately protected for the duration of their surgery and adequate prophylaxis was only evident in four of the nine patients administered cefalotin.

CONCLUSIONS

These results suggest a need to review antibiotic prophylaxis dosage regimens for burns surgery and the adoption of regimens that will minimize the risk of infection in this high-risk patient group. It is suggested that the antibiotic prophylaxis guideline for burn debridement surgery be modified to include re-dosing or a continuous infusion of beta-lactam antibiotics.