Fluid shifts have no influence on ciprofloxacin pharmacokinetics in intensive care patients with intra-abdominal sepsis

Clinical pharmacokinetics of antimicrobials in critical care: a narrative review

INTRODUCTION

The management of critically ill septic patients presents considerable challenges due to multifaceted physiological alterations. Rapid changes such as fluid shifts, hyperdynamic states, and altered renal clearance often require special attention for better clinical outcomes. Vital organ dysfunction, with or without MODS, often necessitates supportive management like RRT, ventilatory support, and ECMO. These interventions can significantly affect the PK/PD of administered antimicrobials, complicating effective treatment.

AREA COVERED

Patient-specific parameters such as age, weight, and comorbid illnesses (e.g. cystic fibrosis, burns, and immunocompromised states) are critical determinants of antimicrobial pharmacokinetics. Understanding PK/PD determinants is crucial for developing optimized dosing regimens that enhance therapeutic efficacy and minimize toxicity in critically ill patients.

EXPERT OPINION

Incorporating pharmacometrics approaches in dose optimization can significantly improve patient outcomes. This review focuses on the nuances of PK/PD for optimized antimicrobial dosing in critically ill septic patients, emphasizing the importance of individualized treatment plans to address the complex and dynamic needs of this patient population. The adoption of these advanced pharmacokinetic and pharmacodynamic principles into clinical practice is essential for advancing patient care and optimizing therapeutic outcomes in critically ill patients.

Feasibility of Continuous Infusion of Cefiderocol in Conjunction with the Establishment of Therapeutic Drug Monitoring in Patients with Extensively Drug-Resistant Gram-Negative Bacteria

BACKGROUND AND OBJECTIVE

Resistance to antibacterial substances is a huge and still emerging issue, especially with regard to Gram-negative bacteria and in critically ill patients. We report a study in six patients infected with extensively drug-resistant Gram-negative bacteria in a limited outbreak who were successfully managed with a quasi-continuous infusion of cefiderocol.

METHODS

Patients were initially treated with prolonged infusions of cefiderocol over 3 h every 8 h, and the application mode was then switched to a quasi-continuous infusion of 2 g over 8 h, i.e. 6 g in 24 h. Therapeutic drug monitoring (TDM) was established using an in-house liquid chromatography-tandem mass spectrometry (LC-MS/MS) method.

RESULTS

Determined trough plasma concentrations were a median of 50.00 mg/L [95% confidence interval (CI) 27.20, 74.60] and steady-state plasma concentrations were a median of 90.96 mg/L [95% CI 37.80, 124]. No significant differences were detected with respect to acute kidney injury/continuous renal replacement therapy. Plasma concentrations determined from different modes of storage were almost equal when frozen or cooled, but markedly reduced when stored at room temperature.

CONCLUSIONS

(Quasi) continuous application of cefiderocol 6 g/24 h in conjunction with TDM is a feasible mode of application; the sample for TDM should either be immediately analyzed, cooled, or frozen prior to analysis.

Tissue Penetration of Antimicrobials in Intensive Care Unit Patients: A Systematic Review-Part II

In patients that are admitted to intensive care units (ICUs), the clinical outcome of severe infections depends on several factors, as well as the early administration of chemotherapies and comorbidities. Antimicrobials may be used in off-label regimens to maximize the probability of therapeutic concentrations within infected tissues and to prevent the selection of resistant clones. Interestingly, the literature clearly shows that the rate of tissue penetration is variable among antibacterial drugs, and the correlation between plasma and tissue concentrations may be inconstant. The present review harvests data about tissue penetration of antibacterial drugs in ICU patients, limiting the search to those drugs that mainly act as protein synthesis inhibitors and disrupting DNA structure and function. As expected, fluoroquinolones, macrolides, linezolid, and tigecycline have an excellent diffusion into epithelial lining fluid. That high penetration is fundamental for the therapy of ventilator and healthcare-associated pneumonia. Some drugs also display a high penetration rate within cerebrospinal fluid, while other agents diffuse into the skin and soft tissues. Further studies are needed to improve our knowledge about drug tissue penetration, especially in the presence of factors that may affect drug pharmacokinetics.

Ensuring target concentrations of antibiotics in critically ill patients through dose adjustment

INTRODUCTION

Antibiotics are commonly prescribed in critical care, and given the large variability of pharmacokinetic (PK) parameters in these patients, drug PK frequently varies during therapy with the risk of either treatment failure or toxicity. Therefore, adequate antibiotic dosing in critically ill patients is very important.

AREAS COVERED

This review provides an overview of the basic principles of PK and pharmacodynamics of antibiotics and the main patient and pathogen characteristics that may affect the dosage of antibiotics and different approaches to adjust doses.

EXPERT OPINION

Dose adjustment should be done for aminoglycosides and glycopeptides based on daily drug concentration monitoring. For glycopeptides, in particular vancomycin, the residual concentration (Cres) should be assessed daily. For beta-lactam antibiotics, a loading dose should be administered, followed by three different possible approaches, as TDM is rarely available in most centers: 1) antibiotic regimens should be adapted according to renal function and other risk factors; 2) nomograms or software can be used to calculate daily dosing; 3) TDM should be performed 24-48 h after the initiation of treatment; however, the results are required within 24 hours to appropriately adjust dosage regimens. Drug dosing should be reduced or increased according to the TDM results.

Optimizing Antimicrobial Drug Dosing in Critically Ill Patients

A fundamental step in the successful management of sepsis and septic shock is early empiric antimicrobial therapy. However, for this to be effective, several decisions must be addressed simultaneously: (1) antimicrobial choices should be adequate, covering the most probable pathogens; (2) they should be administered in the appropriate dose, (3) by the correct route, and (4) using the correct mode of administration to achieve successful concentration at the infection site. In critically ill patients, antimicrobial dosing is a common challenge and a frequent source of errors, since these patients present deranged pharmacokinetics, namely increased volume of distribution and altered drug clearance, which either increased or decreased. Moreover, the clinical condition of these patients changes markedly over time, either improving or deteriorating. The consequent impact on drug pharmacokinetics further complicates the selection of correct drug schedules and dosing during the course of therapy. In recent years, the knowledge of pharmacokinetics and pharmacodynamics, drug dosing, therapeutic drug monitoring, and antimicrobial resistance in the critically ill patients has greatly improved, fostering strategies to optimize therapeutic efficacy and to reduce toxicity and adverse events. Nonetheless, delivering adequate and appropriate antimicrobial therapy is still a challenge, since pathogen resistance continues to rise, and new therapeutic agents remain scarce. We aim to review the available literature to assess the challenges, impact, and tools to optimize individualization of antimicrobial dosing to maximize exposure and effectiveness in critically ill patients.

Population pharmacokinetics and target attainment of ciprofloxacin in critically ill patients

Purpose

To develop and validate a population pharmacokinetic model of ciprofloxacin intravenously in critically ill patients, and determine target attainment to provide guidance for more effective regimens.

Methods

Non-linear mixed-effects modelling was used for the model development and covariate analysis. Target attainment of an ƒAUC_0–24/MIC ≥ 100 for different MICs was calculated for standard dosing regimens. Monte Carlo simulations were performed to define the probability of target attainment (PTA) of several dosing regimens.

Results

A total of 204 blood samples were collected from 42 ICU patients treated with ciprofloxacin 400–1200 mg/day, with median values for age of 66 years, APACHE II score of 22, BMI of 26 kg/m², and eGFR of 58.5 mL/min/1.73 m². The median ƒAUC_0–24 and ƒC_max were 29.9 mg•h/L and 3.1 mg/L, respectively. Ciprofloxacin pharmacokinetics were best described by a two-compartment model. We did not find any significant covariate to add to the structural model. The proportion of patients achieving the target ƒAUC_0–24/MIC ≥ 100 were 61.9% and 16.7% with MICs of 0.25 and 0.5 mg/L, respectively. Results of the PTA simulations suggest that a dose of ≥ 1200 mg/day is needed to achieve sufficient ƒAUC_0–24/MIC ratios.

Conclusions

The model described the pharmacokinetics of ciprofloxacin in ICU patients adequately. No significant covariates were found and high inter-individual variability of ciprofloxacin pharmacokinetics in ICU patients was observed. The poor target attainment supports the use of higher doses such as 1200 mg/day in critically ill patients, while the variability of inter-individual pharmacokinetics parameters emphasizes the need for therapeutic drug monitoring to ensure optimal exposure.

Electronic supplementary material

The online version of this article (10.1007/s00228-020-02873-5) contains supplementary material, which is available to authorized users.

Evaluation of Amikacin Pharmacokinetics in Critically Ill Patients with Intra-abdominal Sepsis

Purpose: Although the current widespread use of amikacin is in intra-abdominal sepsis treatment, its pharmacokinetic changes in the present setting are not yet well known. This study was aimed to evaluate the amikacin pharmacokinetic profile in critically ill patients with intraabdominal sepsis compared to pneumosepsis.

Methods: Adult septic patients received amikacin therapy were studied. Patients with intraabdominal sepsis were enrolled in group 1 (n=16), and patients with pneumosepsis were enrolled in group 2 (n=13). The amikacin serum concentrations were evaluated in the first, second, fourth and sixth hours after initiating 30-minute infusion. The pharmacokinetic parameters were calculated for each patient.

Results: There was no significant difference in the volume of distribution between the two groups (0.33±0.08 vs. 0.28±0.10 L/kg, P=0.193). The amikacin clearance was significantly lower in group 1 compared to group 2 (58.5±21.7 vs. 83.9±37.0 mL/min, P=0.029). There was no significant correlation between amikacin clearance and creatinine clearance estimated by Cockcroft-Gault formula in all patients (P=0.206). The half-life was significantly longer in group 1 compared to group 2 (5.3±2.8 vs. 3.4±3.2 hours, P=0.015).

Conclusion: Pathophysiologic changes following intra-abdominal sepsis can affect amikacin pharmacokinetics behavior. The clearance and half-life may change, but the alteration of the volume of distribution is not significantly different in comparison with pneumosepsis. Further studies are required to evaluate the pharmacokinetic variables of amikacin in critically ill patients with intra-abdominal sepsis.

Antibiotic Stewardship: Strategies to Minimize Antibiotic Resistance While Maximizing Antibiotic Effectiveness

Empiric therapy of the septic patient in the hospital is challenging. Antibiotic stewardship is concerned with optimizing antibiotic use and minimizing resistance. Clinicians should avoid overcovering and overtreating colonizing organisms in respiratory secretions and urinary catheters. Empiric therapy should take into account the prevalence of multidrug-resistant organisms in the hospital setting. The most effective resistance prevention strategies is to preferentially select a low resistance potential antibiotic, which should be administered in the highest possible dose without toxicity for the shortest duration to eliminate the infection.

New paradigm for rapid achievement of appropriate therapy in special populations: coupling antibiotic dose optimization rapid microbiological methods

INTRODUCTION

Some special patient populations (e.g. critically ill, burns, hematological malignancy, post-major surgery, post-major trauma) have characteristics that lead to higher rates of failure and mortality associated with infection. Choice of effective antibiotics and optimized doses are challenging in these patients that are commonly infected by multidrug-resistant pathogens. Areas covered: A review of the importance of diagnosis and the place of newer microbiological methods (e.g. whole-genome sequencing) to ensure rapid transition from empiric to directed antibiotic therapy is provided. The effects of pathophysiological changes on antibiotic pharmacokinetics are also provided. Expert opinion: Product information dosing regimens do not address the pharmacokinetic alterations that can occur in special patient populations and increase the likelihood of therapeutic failure and the emergence of bacterial resistance. Altered dosing approaches, supplemented with the use of dosing software and therapeutic drug monitoring, may be needed to ensure optimal antibiotic exposure and better therapeutic outcomes in these patients with severe infection. Dose optimization needs to be coupled with advanced microbiological techniques that enable rapid microbiological identification and characterization of resistance mechanism to ensure that maximally effective directed therapy can be chosen.

Pharmacokinetics of Antibiotics in Sub-Saharan African Patient Populations: A Systematic Review

BACKGROUND

In sub-Saharan Africa (SSA), severe febrile illness accounts for a large majority of medical admissions. SSA patients may also suffer from cachexia and organ dysfunction resulting from tuberculosis, hepatitis B, and hypertension. It is hard to tell how these conditions influence the pharmacokinetics (PK) of antibiotics in this population. The aim of this systematic review was to summarize antibiotic PK data of SSA adult patient populations to clarify whether inappropriate drug concentrations that may also lead to antimicrobial resistance are likely to occur.

METHODS

An electronic search was conducted in Ovid MEDLINE, Embase, and the African Index Medicus collecting studies from 1946 to May 2016. Reviewers independently selected studies reporting outcome data on volume of distribution (V), clearance, and half-life. Relevant information was abstracted and quality assessed.

RESULTS

Twelve studies were selected, addressing 6 antibiotic classes. There were 6 studies on fluoroquinolones and 1 on β-lactam antibiotics. Nine out of 12 originated from South Africa and 6 of those dealt with intensive care unit (ICU) populations. The quality of most studies was low. Studies on amikacin, teicoplanin, and ertapenem (n = 4) displayed a pattern of a large V with low drug concentrations. Fluoroquinolone PK changes were less prominent and more diverse whereas the probability of pharmacodynamic target attainment was low for the treatment of tuberculosis in South Africa. Interindividual variability of V was high for 10/12 studies.

CONCLUSIONS

Antibiotic PK data of SSA adult patient populations are scarce, but disease-induced inappropriate drug concentrations do occur. Data from non-ICU, severely ill patients, and β-lactam data are particularly lacking, whereas β-lactam antibiotics are commonly used, and typically vulnerable to disease-induced PK changes. Studies investigating the PK and pharmacodynamics of β-lactam antibiotics in severely ill, adult SSA patient populations are needed to improve local antibiotic dosing strategies.

[Therapeutic drug monitoring and individual dosing of antibiotics during sepsis : Modern or just "trendy"?]

Pharmacokinetic variability of anti-infective drugs due to pathophysiological changes by severe sepsis and septic shock is a well-known problem for critically ill patients resulting in suboptimal serum and most likely tissue concentrations of these agents.To cover a wide range of potential pathogens, high concentrations of broad spectrum anti-infectives have to reach the site of infection. Microbiological susceptibility testing (susceptible, intermediate, resistant) don't take the pharmacokinetic variability into account and are based on data generated by non-critically ill patients. But inter-patient variability in distribution and elimination of anti-infective drugs in ICU patients is extremely high and also highly unpredictable. Drug clearance of mainly renally eliminated drugs and thus the required dose can differ up to 10-fold due to the variability in renal function in patients with severe infections. To assure a timely and adequate anti-infective regime, individual dosing and therapeutic drug monitoring (TDM) seem to be appropriate tools in the setting of pathophysiological changes in pharmacokinetics (PK) and pharmakodynamics (PD) due to severe sepsis. In the case of known minimal inhibitory concentration, PK/PD indices (time or peak concentration dependent activity) and measured serum level can provide an optimal target concentration for the individual drug and patient.Modern anti-infective management for ICU patients includes more than the choice of drug and prompt application. Individual dosing, optimized prolonged infusion time and TDM give way to new and promising opportunities in infection control.

Pharmacokinetic and Pharmacodynamic Principles of Anti-infective Dosing

PURPOSE

An understanding of the pharmacokinetic (PK) and pharmacodynamic (PD) principles that determine response to antimicrobial therapy can provide the clinician with better-informed dosing regimens. Factors influential on antibiotic disposition and clinical outcome are presented, with a focus on the primary site of infection. Techniques to better understand antibiotic PK and optimize PD are acknowledged.

METHODS

PubMed (inception-April 2016) was reviewed for relevant publications assessing antimicrobial exposures within different anatomic locations and clinical outcomes for various infection sites.

FINDINGS

A limited literature base indicates variable penetration of antibiotics to different target sites of infection, with drug solubility and extent of protein binding providing significant PK influences in addition to the major clearing pathway of the agent. PD indices derived from in vitro studies and animal models determine the optimal magnitude and frequency of dosing regimens for patients. PK/PD modeling and simulation has been shown an efficient means of assessing these PD endpoints against a variety of PK determinants, clarifying the unique effects of infection site and patient characteristics to inform the adequacy of a given antibiotic regimen.

IMPLICATIONS

Appreciation of the PK properties of an antibiotic and its PD measure of efficacy can maximize the utility of these life-saving drugs. Unfortunately, clinical data remain limited for a number of infection site-antibiotic exposure relationships. Modeling and simulation can bridge preclinical and patient data for the prescription of optimal antibiotic dosing regimens, consistent with the tenets of personalized medicine.

Antibiotic dose optimization in critically ill patients

The judicious use of existing antibiotics is essential for preserving their activity against infections. In the era of multi-drug resistance, this is of particular importance in clinical areas characterized by high antibiotic use, such as the ICU. Antibiotic dose optimization in critically ill patients requires sound knowledge not only of the altered physiology in serious infections - including severe sepsis, septic shock and ventilator-associated pneumonia - but also of the pathogen-drug exposure relationship (i.e. pharmacokinetic/pharmacodynamic index). An important consideration is the fact that extreme shifts in organ function, such as those seen in hyperdynamic patients or those with multiple organ dysfunction syndrome, can have an impact upon drug exposure, and constant vigilance is required when reviewing antibiotic dosing regimens in the critically ill. The use of continuous renal replacement therapy and extracorporeal membrane oxygenation remain important interventions in these patients; however, both of these treatments can have a profound effect on antibiotic exposure. We suggest placing emphasis on the use of therapeutic drug monitoring and dose individualization when optimizing therapy in these settings.

How do we use therapeutic drug monitoring to improve outcomes from severe infections in critically ill patients?

High mortality and morbidity rates associated with severe infections in the critically ill continue to be a significant issue for the healthcare system. In view of the diverse and unique pharmacokinetic profile of drugs in this patient population, there is increasing use of therapeutic drug monitoring (TDM) in attempt to optimize the exposure of antibiotics, improve clinical outcome and minimize the emergence of antibiotic resistance. Despite this, a beneficial clinical outcome for TDM of antibiotics has only been demonstrated for aminoglycosides in a general hospital patient population. Clinical outcome studies for other antibiotics remain elusive. Further, there is significant variability among institutions with respect to the practice of TDM including the selection of patients, sampling time for concentration monitoring, methodologies of antibiotic assay, selection of PK/PD targets as well as dose optimisation strategies. The aim of this paper is to review the available evidence relating to practices of antibiotic TDM, and describe how TDM can be applied to potentially improve outcomes from severe infections in the critically ill.

The effect of pathophysiology on pharmacokinetics in the critically ill patient--concepts appraised by the example of antimicrobial agents

Critically ill patients are at high risk for development of life-threatening infection leading to sepsis and multiple organ failure. Adequate antimicrobial therapy is pivotal for optimizing the chances of survival. However, efficient dosing is problematic because pathophysiological changes associated with critical illness impact on pharmacokinetics of mainly hydrophilic antimicrobials. Concentrations of hydrophilic antimicrobials may be increased because of decreased renal clearance due to acute kidney injury. Alternatively, antimicrobial concentrations may be decreased because of increased volume of distribution and augmented renal clearance provoked by systemic inflammatory response syndrome, capillary leak, decreased protein binding and administration of intravenous fluids and inotropes. Often multiple conditions that may influence pharmacokinetics are present at the same time thereby excessively complicating the prediction of adequate concentrations. In general, conditions leading to underdosing are predominant. Yet, since prediction of serum concentrations remains difficult, therapeutic drug monitoring for individual fine-tuning of antimicrobial therapy seems the way forward.

Emergency department antimicrobial considerations in severe sepsis

Severe sepsis and septic shock are common problems in the emergency department patient population and require expert clinical skill by members of the emergency department team to maximize optimal patient outcomes. Although various guidelines have been developed for the management of these patients, issues around antimicrobial-related considerations in critically ill patients require further evidence-based attention. In this review article, important factors related to patient illness, microorganism, timing of antimicrobial administration, and source control are discussed.

Individualised antibiotic dosing for patients who are critically ill: challenges and potential solutions

Infections in critically ill patients are associated with persistently poor clinical outcomes. These patients have severely altered and variable antibiotic pharmacokinetics and are infected by less susceptible pathogens. Antibiotic dosing that does not account for these features is likely to result in suboptimum outcomes. In this Review, we explore the challenges related to patients and pathogens that contribute to inadequate antibiotic dosing and discuss how to implement a process for individualised antibiotic therapy that increases the accuracy of dosing and optimises care for critically ill patients. To improve antibiotic dosing, any physiological changes in patients that could alter antibiotic concentrations should first be established; such changes include altered fluid status, changes in serum albumin concentrations and renal and hepatic function, and microvascular failure. Second, antibiotic susceptibility of pathogens should be confirmed with microbiological techniques. Data for bacterial susceptibility could then be combined with measured data for antibiotic concentrations (when available) in clinical dosing software, which uses pharmacokinetic/pharmacodynamic derived models from critically ill patients to predict accurately the dosing needs for individual patients. Individualisation of dosing could optimise antibiotic exposure and maximise effectiveness.

Importance of relating efficacy measures to unbound drug concentrations for anti-infective agents

For the optimization of dosing regimens of anti-infective agents, it is imperative to have a good understanding of pharmacokinetics (PK) and pharmacodynamics (PD). Whenever possible, drug efficacy needs to be related to unbound concentrations at the site of action. For anti-infective drugs, the infection site is typically located outside plasma, and a drug must diffuse through capillary membranes to reach its target. Disease- and drug-related factors can contribute to differential tissue distribution. As a result, the assumption that the plasma concentration of drugs represents a suitable surrogate of tissue concentrations may lead to erroneous conclusions. Quantifying drug exposure in tissues represents an opportunity to relate the pharmacologically active concentrations to an observed pharmacodynamic parameter, such as the MIC. Selection of an appropriate specimen to sample and the advantages and limitations of the available sampling techniques require careful consideration. Ultimately, the goal will be to assess the appropriateness of a drug and dosing regimen for a specific pathogen and infection.

Pharmacokinetics and pharmacodynamics of ciprofloxacin in critically ill patients after the first intravenous administration of 400 mg

PURPOSE

To investigate the pharmacokinetics and pharmacodynamics of ciprofloxacin in critically ill patients after the first intravenous administration of 400 mg.

MATERIAL/METHODS

Plasma concentrations were measured in 20 critically ill patients (mean [SD]; age, 55.5 [16.5] years; weight, 80.3 [16.9] kg; and creatinine clearance, 110.0 [71.5] mL/min). Four blood samples were drawn at the following time points 0, 0.5, 6 , 8 hours after infusion. Ciprofloxacin concentrations were determined by high-performance liquid chromatography.

RESULTS

In the cases where ciprofloxacin was applied in targeted antibiotic therapy the minimum inhibitory concentrations (MIC) were ≤0.5 mg/l. The maximum and minimum plasma concentrations of ciprofloxacin were 1.74 (0.58-7.90) and 0.45 (0.16-2.96) mg/l, respectively. The main pharmacokinetic parameters for ciprofloxacin in the analyzed patients were as follows: k(el), 0.21 h-1; t(1/2kel), 3.37 h; AUC(0-inf), 10.10 mg×h/l; AUMC(0-last), 15.36 mg×h(2)/l; MRT, 1.71 h; V(d), 214.8 l; Cl, 39.70 l/h. Considering the maximum value of MIC (0.5 mg/l) only 30% and 25% of analyzed patients had desired values of the PK/PD indexes AUIC>125 and C(max) /MIC>10, respectively.

CONCLUSIONS

The target plasma concentrations after the first dose of ciprofloxacin were reached only in a few critically ill patients. Considerable inter-subject variability for PK/PD parameters in ICU patients requires systematic monitoring.

Therapeutic drug monitoring of antimicrobials

Optimizing the prescription of antimicrobials is required to improve clinical outcome from infections and to reduce the development of antimicrobial resistance. One such method to improve antimicrobial dosing in individual patients is through application of therapeutic drug monitoring (TDM). The aim of this manuscript is to review the place of TDM in the dosing of antimicrobial agents, specifically the importance of pharmacokinetics (PK) and pharmacodynamics (PD) to define the antimicrobial exposures necessary for maximizing killing or inhibition of bacterial growth. In this context, there are robust data for some antimicrobials, including the ratio of a PK parameter (e.g. peak concentration) to the minimal inhibitory concentration of the bacteria associated with maximal antimicrobial effect. Blood sampling of an individual patient can then further define the relevant PK parameter value in that patient and, if necessary, antimicrobial dosing can be adjusted to enable achievement of the target PK/PD ratio. To date, the clinical outcome benefits of a systematic TDM programme for antimicrobials have only been demonstrated for aminoglycosides, although the decreasing susceptibility of bacteria to available antimicrobials and the increasing costs of pharmaceuticals, as well as emerging data on pharmacokinetic variability, suggest that benefits are likely.

Do we understand the impact of altered physiology, consequent interventions and resultant clinical scenarios in the intensive care unit? The antibiotic story

Early, appropriate antibacterial therapy is a key factor in effectively managing septic critically ill patients1. The prescriber must not only employ an agent of appropriate spectrum, but also in an adequate dose to achieve bacterial eradication at the site of infection. However, the relationship between drug administration and therapeutic success is complex in the critically ill, such that a patient's physiology heavily influences the way drugs distribute into tissue and are eliminated. This represents a significant challenge to the emergency or intensive care physician, and in this manner, personalising therapy, through a greater understanding of how a drug will behave in an individual patient, is likely to lead to improved outcomes.

Appropriateness of Ciprofloxacin Dosing Based on a Population Pharmacokinetic Model

Purpose

Over the past two decades, the minimum inhibitory concentrations (MICs) of ciprofloxacin have been steadily increasing for gram-negative bacteria. One major reason cited for this “MIC creep” is underdosing of ciprofloxacin due to a lack of understanding of its pharmacodynamic properties. The primary objective of this study was to evaluate the frequency of underdosing of ciprofloxacin in a tertiary acute care medical center based on a population pharmacokinetic model. Secondary objectives included evaluation of appropriateness of dosing based on renal function and approved product labeling.

Methods

Seventy-six patients were included in this single-center, retrospective study. Data collection included demographic, laboratory, and microbiology data along with details on antibiotic administration. Patient-specific predicted 24-hour area under the curve/MIC (AUC24/MIC) values were estimated using a population pharmacokinetic model with a goal predicted AUC24/MIC of at least 100 and a preferred target value of 250.

Results

Only 8% of the subjects obtained a predicted AUC24/MIC higher than 250, while 34% of the subjects achieved a predicted AUC24/MIC of 100 or less. The majority of patients (79%) received a total daily intravenous-equivalent dose of 800 mg, whereas only 8% of subjects received an initial total daily intravenous-equivalent dose of 1,200 mg, which is the recommended dose for most severe infections. Overall 26% of subjects were prescribed an appropriate initial dose for their estimated renal function based on infection type and severity.

Conclusion

Ciprofloxacin for acute infection treatment was frequently underdosed based on US Food and Drug Administration–approved labeling and estimated predicted AUC24/MIC at a tertiary acute care medical center.

Ciprofloxacin use in critically ill patients: pharmacokinetic and pharmacodynamic approaches

The objective of this study was to evaluate the properties of ciprofloxacin in intensive care patients using a population approach. Seventy patients received ciprofloxacin. On Day 1, three to eight blood samples were taken over a 12-h period. Peak drug concentration (Cmax) and 24-h area under the concentration-time curve (AUC) were compared with the French breakpoint defining antibiotic susceptibility. A population pharmacokinetic modelling approach was then carried out. A two-compartment open model with a proportional error model best fitted the data. A relationship between the elimination constant rate and the Cockcroft creatinine clearance was found. Ciprofloxacin clearance was 13.6+/-5.8L/h, the volume of distribution was 62.0+/-10.7 L and the ciprofloxacin half-life was 3.7+/-1.8h. When the minimum inhibitory concentration (MIC) was equal to 1mg/L the inhibitory ratio (IR) was > or = 8 in only 10.8% of cases, and the AUC/MIC ratio (AUIC) was 42.0+/-36. In conclusion, this study highlights that the Cockcroft clearance significantly influences ciprofloxacin elimination. Target plasma concentrations for ciprofloxacin, the IR and AUIC were rarely reached with a standard dosing regimen. In critically ill patients, the observed pharmacokinetic variability is mainly responsible for the overly frequent low concentrations of ciprofloxacin, emphasising the need for therapeutic monitoring.

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.

Systematic review: fluoroquinolones for the treatment of intra-abdominal surgical infections

BACKGROUND

Intra-abdominal infections result in substantial morbidity and mortality. Fluoroquinolones are among the various regimens that are used for the treatment of these infections.

AIM

To evaluate the available data from laboratory and clinical studies regarding the use of fluoroquinolones for the treatment of patients with intra-abdominal infections.

METHODS

We searched for relevant laboratory and clinical studies in the PubMed and the Cochrane Library databases.

RESULTS

Good pharmacokinetic and pharmacodynamic properties of fluoroquinolones in inflamed abdominal tissue are reported in several laboratory studies. In six prospective non-randomized clinical studies of patients with intra-abdominal infections, the clinical success achieved with the use of fluoroquinolones ranged from 77% to 94%. In 10 randomized-controlled trials fluoroquinolone-based regimens were compared with other commonly used (mainly beta-lactam-based) regimens. Clinical success, bacterial eradication, withdrawal because of toxicity and mortality were similar between the compared treatment arms except from two randomized-controlled trials, in which clinical success was statistically higher in the fluoroquinolone treatment arm.

CONCLUSIONS

Fluoroquinolones seem to be an effective and relatively safe option for the treatment of patients with intra-abdominal infections.