Pharmacokinetics and pharmacodynamics of levofloxacin in intensive care patients

Clinical Pharmacokinetics of Antitubercular Drugs in the Overweight and Obese Population: Implications for Dosage Adjustments

The rise in global obesity prevalence has increased the need to understand the pharmacokinetics of drugs in overweight and obese individuals. Tuberculosis remains a significant health challenge, and its treatment outcomes can be influenced by the pharmacokinetic profiles of antitubercular agents. This literature review aims to point out the clinical pharmacokinetics of antitubercular drugs in the overweight and obese patient population, highlighting considerations for potential dosage adjustments. We conducted a comprehensive search of the PubMed US National Library of Medicine from inception to January 2024. Articles focusing on the pharmacokinetics of antitubercular agents used for both drug-susceptible and multidrug-resistant tuberculosis in overweight and obese adults were included. In total, 349 scientific articles were identified and examined for human pharmacokinetic parameters. Of these, 19 were included in this article. To highlight potential differences, pharmacokinetic data for normal-weight tuberculosis patients are also presented, albeit selectively. In general, pharmacokinetic studies of antitubercular agents in overweight and obese individuals are lacking. Fixed-dose combinations often used in the treatment of drug-susceptible tuberculosis are not recommended when treating these population groups. Rather, individual dosing based on therapeutic drug monitoring and the known solubility of the substance should be considered. To improve the management of tuberculosis in overweight and obese patients, there is an urgent need for pharmacokinetic studies and, ultimately, adequate dosing in this patient population, especially given the increasing prevalence of obesity.

Risk Factors Associated with Antibiotic Exposure Variability in Critically Ill Patients: A Systematic Review

(1) Background: Knowledge about the behavior of antibiotics in critically ill patients has been increasing in recent years. Some studies have concluded that a high percentage may be outside the therapeutic range. The most likely cause of this is the pharmacokinetic variability of critically ill patients, but it is not clear which factors have the greatest impact. The aim of this systematic review is to identify risk factors among critically ill patients that may exhibit significant pharmacokinetic alterations, compromising treatment efficacy and safety. (2) Methods: The search included the PubMed, Web of Science, and Embase databases. (3) Results: We identified 246 observational studies and ten clinical trials. The most studied risk factors in the literature were renal function, weight, age, sex, and renal replacement therapy. Risk factors with the greatest impact included renal function, weight, renal replacement therapy, age, protein or albumin levels, and APACHE or SAPS scores. (4) Conclusions: The review allows us to identify which critically ill patients are at a higher risk of not reaching therapeutic targets and helps us to recognize the extensive number of risk factors that have been studied, guiding their inclusion in future studies. It is essential to continue researching, especially in real clinical practice and with clinical outcomes.

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.

Rapid Antibiotic Combination Testing for Carbapenem-Resistant Gram-Negative Bacteria within Six Hours Using ATP Bioluminescence

To guide the timely selection of antibiotic combinations against carbapenem-resistant Gram-negative bacteria (CR-GNB), an in vitro test with a short turnaround time is essential. We developed an in vitro ATP bioluminescence assay to determine effective antibiotic combinations against CR-GNB within 6 h. We tested 42 clinical CR-GNB strains (14 Acinetobacter baumannii, 14 Pseudomonas aeruginosa, and 14 Klebsiella pneumoniae strains) against 74 single antibiotics and two-antibiotic combinations. Bacteria (approximately 5 log₁₀ CFU/ml) were incubated with an antibiotic(s) at 35°C; ATP bioluminescence was measured at 6 h and 24 h; and the measurements were compared to viable counts at 24 h. Receiver operating characteristic (ROC) curves were used to determine the optimal luminescence thresholds (T_RLU) for distinguishing between inhibitory and noninhibitory combinations. The areas under the 6-h and 24-h ROC curves were compared using the DeLong method. Prospective validation of the established thresholds was conducted using 18 additional CR-GNB. The predictive accuracy of T_RLU for the 6-h ATP bioluminescence assay was 77.5% when all species were analyzed collectively. Predictive accuracies ranged from 73.7% to 82.7% when each species was analyzed individually. Upon comparison of the areas under the 6-h and 24-h ROC curves, the 6-h assay performed significantly better than the 24-h assay (P < 0.01). Predictive accuracy remained high upon prospective validation of the 6-h ATP assay (predictive accuracy, 79.8%; 95% confidence interval [CI], 77.6 to 81.9%), confirming the external validity of the assay. Our findings indicate that our 6-h ATP bioluminescence assay can provide guidance for prospective selection of antibiotic combinations against CR-GNB in a timely manner and may be useful in the management of CR-GNB infections.

Application of Antibiotic Pharmacodynamics and Dosing Principles in Patients With Sepsis

Sepsis is associated with marked mortality, which may be reduced by prompt initiation of adequate, appropriate doses of antibiotic. Critically ill patients often have physiological changes that reduce blood and tissue concentrations of antibiotic and high rates of multidrug-resistant pathogens, which may affect patients' outcomes. All critical care professionals, including critical care nurses, should understand antibiotic pharmacokinetics and pharmacodynamics to ensure sound antibiotic dosing and administration strategies for optimal microbial killing and patients' outcomes. Effective pathogen eradication occurs when the dose of antibiotic reaches or maintains optimal concentrations relative to the minimum inhibitory concentration for the pathogen. Time-dependent antibiotics, such as β-lactams, can be given as extended or continuous infusions. Concentration-dependent antibiotics such as aminoglycosides are optimized by using high, once-daily dosing strategies with serum concentration monitoring. Vancomycin and fluoroquinolones are dependent on both time and concentration above the minimum inhibitory concentration.

Pharmacokinetics and Pharmacodynamics of Antimicrobials in Critically Ill Patients

Critically ill patients with severe infections often have altered pharmacokinetic and pharmacodynamic variables that lead to challenging treatment decisions. These altered variables can often lead to inadequate dosing and poor treatment outcomes. The pharmacokinetic parameters include absorption, distribution, metabolism, and excretion. Pharmacodynamics is the relationship between drug serum concentrations and pharmacologic and toxicologic properties of the medication. In addition to these altered parameters, these critically ill patients frequently are receiving organ support in the forms of continuous renal replacement therapy or extra-corporeal membrane oxygenation. Altered pharmacodynamics can lead to decreased end-organ perfusion, which can ultimately lead to treatment failure or exposure-related toxicity. The most common antimicrobials utilized in the intensive care unit are classified by the pharmacodynamic principles of time-dependent, concentration-dependent, and concentration dependent with time-dependence. Thus, the aim of this review is to outline pharmacokinetic and pharmacodynamic changes of critically ill patients with severe infections and provide strategies for optimal antibiotic agent dosing in these patients.

Evaluating Polymyxin B-Based Combinations against Carbapenem-Resistant Escherichia coli in Time-Kill Studies and in a Hollow-Fiber Infection Model

Polymyxin B-based combinations have emerged as a mainstay treatment against carbapenem-resistant Escherichia coli (CREC). We investigated the activity of polymyxin B-based two-antibiotic combinations against CREC using time-kill studies (TKS) and validated the findings in a hollow-fiber infection model (HFIM). TKS were conducted using 5 clinical CREC strains at 5 log₁₀ CFU/ml against 10 polymyxin B-based two-antibiotic combinations at maximum clinically achievable concentrations. HFIMs simulating dosing regimens with polymyxin B (30,000U/kg/day) and tigecycline (100 mg every 12 h) alone and in combination were conducted against two CREC strains at 5 log₁₀ CFU/ml over 120 h. Emergence of resistance was quantified using antibiotic-containing media. Phenotypic characterization (growth rate and stability of resistant phenotypes) of the resistant isolates was performed. All five CREC strains harbored carbapenemases. Polymyxin B and tigecycline MICs ranged from 0.5 mg/liter to 2 mg/liter and from 0.25 mg/liter to 8 mg/liter, respectively. All antibiotics alone did not have bactericidal activity at 24 h in the TKS, except for polymyxin B against two strains. In combination TKS, only polymyxin B plus tigecycline demonstrated both bactericidal activity and synergy in two out of five strains. In the HFIM, polymyxin B alone was bactericidal against both CREC strains before regrowth was observed at 8 h. Phenotypically stable polymyxin B-resistant mutants were observed for both strains, with a reduced growth rate observed in one strain. Tigecycline alone resulted in a slow reduction in bacterial counts. Polymyxin B plus tigecycline resulted in rapid and sustained bactericidal killing up to 120 h. Polymyxin B plus tigecycline is a promising combination against CREC. The clinical relevance of our results warrants further investigations.

Personalized therapeutics for levofloxacin: a focus on pharmacokinetic concerns

Background

Personalized medicine should be encouraged because patients are complex, and this complexity results from biological, medical (eg, demographics, genetics, polypharmacy, and multimorbidities), socioeconomic, and cultural factors. Levofloxacin (LVX) is a broad-spectrum fluoroquinolone antibiotic. Awareness of personalized therapeutics for LVX seems to be poor in clinical practice, and is reflected in prescribing patterns. Pharmacokinetic–pharmacodynamic studies have raised concerns about suboptimal patient outcomes with the use of LVX for some Gram-negative infections. Meanwhile, new findings in LVX therapeutics have only been sporadically reported in recent years. Therefore, an updated review on personalized LVX treatment with a focus on pharmacokinetic concerns is necessary.

Methods

Relevant literature was identified by performing a PubMed search covering the period from January 1993 to December 2013. We included studies describing dosage adjustment and factors determining LVX pharmacokinetics, or pharmacokinetic–pharmacodynamic studies exploring how best to prevent the emergence of resistance to LVX. The full text of each included article was critically reviewed, and data interpretation was performed.

Results

In addition to limiting the use of fluoroquinolones, measures such as reducing the breakpoints for antimicrobial susceptibility testing, choice of high-dose short-course of once-daily LVX regimen, and tailoring LVX dose in special patient populations help to achieve the validated pharmacokinetic–pharmacodynamic target and combat the increasing LVX resistance. Obese individuals with normal renal function cleared LVX more efficiently than normal-weight individuals. Compared with the scenario in healthy subjects, standard 2-hour spacing of calcium formulations and oral LVX was insufficient to prevent a chelation interaction in cystic fibrosis patients. Inconsistent conclusions were derived from studies of the influence of sex on the pharmacokinetics of LVX, which might be associated with sample size and administration route. Children younger than 5 years cleared LVX nearly twice as fast as adults. Patients in intensive care receiving LVX therapy showed significant pharmacokinetic differences compared with healthy subjects. Creatinine clearance explained most of the population variance in the plasma clearance of LVX. Switching from intravenous to oral delivery of LVX had economic benefits. Addition of tamsulosin to the LVX regimen was beneficial for patients with bacterial prostatitis because tamsulosin could increase the maximal concentration of LVX in prostatic tissue. Coadministration of multivalent cation-containing drugs and LVX should be avoided. For patients receiving warfarin and LVX concomitantly, caution is needed regarding potential changes in the international normalized ratio; however, it is unnecessary to seek alternatives to LVX for the sake of avoiding drug interaction with warfarin. It is unnecessary to proactively reduce the dose of cyclosporin or tacrolimus when comedicated with LVX. Transporters such as organic anion-transporting polypeptide 1A2, P-glycoprotein, human organic cation transporter 1, and multidrug and toxin extrusion protein 1 are involved in the pharmacokinetics of LVX.

Conclusion

Personalized LVX therapeutics are necessary for the sake of better safety, clinical success, and avoidance of resistance. New findings regarding individual dosing of LVX in special patient populations and active transport mechanisms in vivo are opening up new horizons in clinical practice.

Optimal dosing of antibiotics in critically ill patients by using continuous/extended infusions: a systematic review and meta-analysis

Introduction

The aim of this study was to determine whether using pharmacodynamic-based dosing of antimicrobials, such as extended/continuous infusions, in critically ill patients is associated with improved outcomes as compared with traditional dosing methods.

Methods

We searched Medline, HealthStar, EMBASE, Cochrane Clinical Trial Registry, and CINAHL from inception to September 2013 without language restrictions for studies comparing the use of extended/continuous infusions with traditional dosing. Two authors independently selected studies, extracted data on methodology and outcomes, and performed quality assessment. Meta-analyses were performed by using random-effects models.

Results

Of 1,319 citations, 13 randomized controlled trials (RCTs) (n = 782 patients) and 13 cohort studies (n = 2,117 patients) met the inclusion criteria. Compared with traditional non-pharmacodynamic-based dosing, RCTs of continuous/extended infusions significantly reduced clinical failure rates (relative risk (RR) 0.68; 95% confidence interval (CI) 0.49 to 0.94, P = 0.02) and intensive care unit length of stay (mean difference, −1.5; 95% CI, −2.8 to −0.2 days, P = 0.02), but not mortality (RR, 0.87; 95% CI, 0.64 to 1.19; P = 0.38). No significant between-trial heterogeneity was found for these analyses (I² = 0). Reduced mortality rates almost achieved statistical significance when the results of all included studies (RCTs and cohort studies) were pooled (RR, 0.83; 95% CI, 0.69 to 1.00; P = 0.054).

Conclusions

Pooled results from small RCTs suggest reduced clinical failure rates and intensive care unit length-of-stay when using continuous/extended infusions of antibiotics in critically ill patients. Reduced mortality rates almost achieved statistical significance when the results of RCTs were combined with cohort studies. These results support the conduct of adequately powered RCTs to define better the utility of continuous/extended infusions in the era of antibiotic resistance.

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.

Clearance of levofloxacin by an in vitro model of continuous venovenous hemodialysis (CVVHD)

Information about the elimination and the adequate dosing of levofloxacin during renal replacement therapy is scarce. The aim of this study was to characterize in vitro the elimination of levofloxacin during continuous venovenous hemodialysis (CVVHD) and to investigate whether the CVVHD clearances of creatinine and urea are correlated with the levofloxacin clearance in order to facilitate dosage adjustments. An in vitro model of CVVHD was established using five dialyzer membranes at varying dialysate flow rates applied in the clinical setting (8, 16, 25, 33 and 41 ml/min). Plasma and dialysate samples were drawn for determination of levofloxacin, creatinine and urea concentrations to evaluate clearances by CVVHD. During CVVHD, the clearance of levofloxacin varied between 9.02 and 33.30 ml/min, depending on the chosen setup. Positive correlations (p<0.001) were received for: dialysate flow rate (QD) and creatinine/ urea clearances (R(2)>0.93); QD and levofloxacin clearance (R(2) 0.59-0.71); levofloxacin and creatinine clearance (R(2) 0.69-0.75); and levofloxacin and urea clearance (R(2) 0.56-0.75) as well. When dosing critically ill patients, therefore, extracorporeal as well as total clearance of levofloxacin should be considered.

Pharmacokinetics and pharmacodynamics of levofloxacin in critically ill patients with ventilator-associated pneumonia

The pharmacokinetics of levofloxacin and outcome of levofloxacin therapy in critically ill patients with ventilator-associated pneumonia (VAP) were assessed. Further theoretical considerations regarding the pharmacokinetic/pharmacodynamic (PK/PD) appropriateness of levofloxacin therapy were made. Twelve patients completed the study, all of whom were treated with a standard intravenous levofloxacin regimen (2x500 mg on Day 1, then 1x500 mg daily). The maximum free plasma levofloxacin concentration (fC(max,ss)) and the area under the free concentration-time curve (fAUC) were 8.13+/-1.64 mg/L and 49.63+/-15.60 mgh/L, respectively. Optimal PK/PD target parameters were achieved in 10 patients; clinical success was attained in 11 of the 12 patients who completed the study. Bacterial eradication was obtained in 9 of the 11 cases with microbiologically confirmed bacteriological aetiology. Intravenous levofloxacin therapy (500 mg/day) was proven to be an effective regimen in this limited number of patients with VAP. However, theoretical considerations based on PK/PD indices predict that, with the current susceptibility breakpoint of 2mg/L, even higher levofloxacin doses (e.g. 1000 mg) could result in treatment failures in infections caused by pathogens labelled as levofloxacin-susceptible in the microbiology report.

Use of pharmacodynamic principles to optimise dosage regimens for antibacterial agents in the elderly

Throughout most of the world we are witnessing an ever increasing number of aged people as a percentage of the general population. In the coming years, the unique spectrum of infections presented by an elderly population, particularly those in long-term care facilities, will challenge our ability to maintain an effective battery of antibacterials. The pharmacokinetic parameters of most antibacterial agents are altered when assessed in the elderly due in part to non-pathological physiological changes. The inability to clear a drug from the body due to declining lung, kidney/bladder, gastrointestinal and circulatory efficiency can cause accumulation in the body of drugs given in standard dosages. While this may have the potential benefit of achieving therapeutic concentrations at a lower dose, there is also a heightened risk of attaining toxic drug concentrations and an increased chance of unfavourable interactions with other medications. Pharmacodynamic issues in the elderly are related to problems that arise from treating elderly patients who may have a history of previous antibacterial treatment and exposure to resistant organisms from multiple hospitalisations. Furthermore, the elderly often acquire infections in tandem with other common disease states such as diabetes mellitus and heart disease. Thus, it is essential that optimised dosage strategies be designed specifically for this population using pharmacodynamic principles that take into account the unique circumstances of the elderly. Rational and effective dosage and administration strategies based on pharmacodynamic breakpoints and detailed understanding of the pharmacokinetics of antibacterials in the elderly increase the chances of achieving complete eradication of an infection in a timely manner. In addition, this strategy helps prevent selection of drug-resistant bacteria and minimises the toxic effects of antibacterial therapy in the elderly patient.

New formulations of amoxicillin/clavulanic acid: a pharmacokinetic and pharmacodynamic review

The pharmacokinetic properties of amoxicillin and clavulanic acid when used alone or in combination are extensively reviewed and discussed in this article. The reported data support a nonlinear absorption process for amoxicillin. Saturable transport mechanisms, limited solubility and the existence of an absorption window are possibly involved in the gastrointestinal absorption of this antibacterial, all leading to a decrease in the peak plasma concentration (Cmax)/dose ratio, a prolongation of the time to reach Cmax, and broad variability for high doses of amoxicillin. Data available in the literature also suggest a possible interaction between amoxicillin and clavulanic acid that might decrease the absolute bioavailability of clavulanic acid. In the present review the intrinsic pharmacodynamics of each drug, together with the synergism produced by the amoxicillin/clavulanic acid association, are also reviewed and analysed. Not only beta-lactamase-producing strains, but also Streptococcus pneumoniae strains, seem to be more efficiently eradicated by the association of amoxicillin and clavulanic acid, and a relevant post-antibacterial effect and post-beta-lactamase inhibitor effect are likely to operate when amoxicillin is administered together with clavulanic acid. The principles of pharmacokinetic/pharmacodynamic analysis applied to amoxicillin are reviewed, with special emphasis being placed on the results obtained from in vitro studies and animal models regarding the new pharmacokinetically enhanced formulation. Theoretical considerations concerning the efficacy of this formulation provided by the application of pharmacokinetic/pharmacodynamic analysis to the scarce pharmacokinetic data available are also included. The broad pharmacokinetic variability of both amoxicillin and clavulanic acid, particularly when administered together and at high doses of amoxicillin, is highlighted and the interest in considering this aspect to improve predictions based on pharmacokinetic/pharmacodynamic analyses for the new formulations is indicated. Methodological recommendations such as the Monte Carlo simulation are proposed in order to obtain more realistic predictions in clinical practice.