Serum pharmacokinetics and sputum penetration of amikacin 30 mg/kg once daily and of ceftazidime 200 mg/kg/day as a continuous infusion in cystic fibrosis patients

[A pharmacologic approach to treatment of Mycobacterium abscessus pulmonary disease]

Mycobacterium abscessus is a fast-growing non-tuberculous mycobacteria complex causing pulmonary infections, comprising the subspecies abscessus, massiliense and bolletii. Differences are based predominantly on natural inducible macrolide resistance, active in most Mycobacterium abscessus spp abscessus species and in Mycobacterium abscessus spp bolletii but inactive in Mycobacterium abscessus spp massiliense. Therapy consists in long-term treatment, combining multiple antibiotics. Prognosis is poor, as only 40% of patients experience cure. Pharmacodynamic and pharmacokinetic data on M. abscessus have recently been published, showing that therapy ineffectiveness might be explained by intrinsic bacterial resistance (macrolides…) and by the unfavorable pharmacokinetics of the recommended antibiotics. Other molecules and inhaled antibiotics are promising.

Clinical Pharmacokinetic and Pharmacodynamic Considerations in the Drug Treatment of Non-Tuberculous Mycobacteria in Cystic Fibrosis

Non-tuberculous mycobacteria (NTM) are an emerging group of pulmonary infectious pathogens of increasing importance to the management of patients with cystic fibrosis (CF). NTM include slow-growing mycobacteria such as Mycobacterium avium complex (MAC) and rapidly growing mycobacteria such as Mycobacterium abscessus. The incidence of NTM in the CF population is increasing and infection contributes to significant morbidity to the patient and costs to the health system. Treating M. abscessus requires the combination of multiple costly antibiotics for months, with potentially significant toxicity associated with treatment. Although international guidelines for the treatment of NTM infection in CF are available, there are a lack of robust pharmacokinetic studies in CF patients to inform dosing and drug choice. This paper aims to outline the pharmacokinetic and pharmacodynamic factors informing the optimal treatment of NTM infections in CF.

Population Pharmacokinetic Evaluation of Amikacin Liposome Inhalation Suspension in Patients with Treatment-Refractory Nontuberculous Mycobacterial Lung Disease

Background and Objectives

Use of parenteral amikacin to treat refractory nontuberculous mycobacterial (NTM) lung disease is limited by systemic toxicity. A population pharmacokinetic model was developed using data pooled from two randomized trials to evaluate the pharmacokinetic properties of once-daily amikacin liposome inhalation suspension (ALIS) in patients with treatment-refractory NTM lung disease.

Methods

In phase 2 (TR02-112) and phase 3 (CONVERT) studies, patients with sputum cultures positive for Mycobacterium avium complex (both studies) or M. abscessus (TR02-112) despite ≥ 6 months of guideline-based therapy were treated with once-daily ALIS 590 mg.

Results

Fifty-three patients (28 Japanese; 25 White) were assessed. At baseline and ≈ 6 months after daily dosing, median maximum concentration (C_max) was < 2 mg/L and median area under the concentration-time curve (AUC_0–24) was < 20 mg·h/L, suggesting low systemic exposure at both time points. Exposure estimates were similar between Japanese and White patients. The median unchanged amikacin fraction excreted in urine was < 10% of inhaled dose throughout the TR02-112 study, indicating that relatively small amounts reached systemic circulation. Median t_1/2 was 5.5 h. Amikacin concentrations were much higher in sputum than in serum, demonstrating the ability to achieve higher drug concentration at the site of infection. Median sputum amikacin concentrations in the CONVERT study were high at 1–4 h postdose (range 242–426 μg/g) and decreased by 8 h (median 7 μg/g).

Conclusions

Systemic exposure to amikacin in serum and urine following once-daily ALIS administration in patients with treatment-refractory NTM lung disease was notably lower than that previously reported for parenteral amikacin.

Trial registration

ClinicalTrials.gov NCT01315236 (registered March 15, 2011) and NCT02344004 (registered January 22, 2015)

Supplementary Information

The online version contains supplementary material available at 10.1007/s13318-020-00669-7.

Pharmacokinetic and Pharmacodynamic Optimization of Antibiotic Therapy in Cystic Fibrosis Patients: Current Evidences, Gaps in Knowledge and Future Directions

Antibiotic therapy is one of the main treatments for cystic fibrosis (CF). It aims to eradicate bacteria during early infection, calms down the inflammatory process, and leads to symptom resolution of pulmonary exacerbations. CF can modify both the pharmacokinetic (PK) and pharmacodynamic (PD) profiles of antibiotics, therefore specific PK/PD endpoints should be determined in the context of CF. Currently available data suggest that optimal PK/PD targets cannot be attained in sputum with intravenous aminoglycosides. Continuous infusion appears preferable for β-lactam antibiotics, but optimal concentrations in sputum are unlikely to be reached, with some possible exceptions such as meropenem and ceftolozane. Usual doses are likely suboptimal for fluoroquinolones and linezolid, whereas daily doses of 45-60 mg/kg and 200 mg could be convenient for vancomycin and doxycycline, respectively. Weekly azithromycin doses of 22-30 mg/kg could also be appropriate for its anti-inflammatory effect. The difficulty with achieving optimal concentrations supports the use of combined treatments and the inhaled administration route, as very high local concentrations, concomitantly with low systemic exposure, can be obtained with the inhaled route for aminoglycosides, colistin, and fluoroquinolones, thus minimizing the risk of toxicity.

Population pharmacokinetics of amikacin in patients with pediatric cystic fibrosis

INTRODUCTION

Amikacin is commonly used in patients with pediatric cystic fibrosis (CF) for the treatment of pulmonary exacerbations. Amikacin efficacy is related to maximum plasma concentration/minimum inhibitory concentration (Cmax/MIC) ratio >8. Pharmacokinetic data in patients with pediatric CF are scarce. The aim of this study was to develop a population pharmacokinetic (PopPK) model describing amikacin disposition in patients with pediatric CF.

METHODS

CF patients under 18 years of age with pulmonary exacerbation who received amikacin were enrolled. Patients received different amikacin regimens (30 mg^-1  kg^-1  day^-1 every 8, 12, or 24 hours) depending on the patient's status and hospital protocols. Amikacin serum levels were obtained for therapeutic drug monitoring. PopPK model was developed using MONOLIX Suite-2018R1 (Lixoft).

RESULTS

A total of 39 patients (114 amikacin concentrations) were included in this study. Population estimates for the elimination rate constant (k) and the volume of distribution (V) were 0.541 hours^-1 and 0.451 L/kg, respectively. Between-subject and between-occasion variability were 53% and 16.5% for k and 31% and 22% for V, respectively. Bodyweight was a significant covariate associated with V. Based on simulations, almost 70% of the patients receiving 30 mg^-1  kg^-1  day^-1 every 24 hours would achieve a Cmax/MIC ratio >8 which is an appropriate therapeutic goal while no patient in the other two groups (Q8 and Q12) would achieve that objective.

CONCLUSIONS

The regimen of 30  mg^-1  kg^-1  day^-1 every 24 hours more adequately fulfilled the therapeutic target for amikacin. Although all our patients had good clinical results and a good adverse-events profile, further studies are necessary to redefine the optimal treatment strategy.

Amikacin target achievement in adult cystic fibrosis patients utilizing Monte Carlo simulation

AIM

Pseudomonas aeruginosa (PsA) is a common pathogen in cystic fibrosis (CF). Management of an acute pulmonary exacerbation (APE) caused by PsA is dual anti-pseudomonal antibiotics, a beta-lactam plus aminoglycoside. Aminoglycoside dosing in CF differs from the general population due to altered pharmacokinetics. The primary objective of this study was to utilize pharmacokinetic data from adult CF patients that received amikacin to determine the probability of target attainment for APEs caused by PsA.

METHODS

This was a single-center, non-randomized, retrospective cohort study of patients >18 years with CF that received intravenous amikacin between January 2010 and July 2016. Amikacin dose, frequency, and serum concentrations were used to calculate pharmacokinetic parameters assuming a one-compartment model. Monte Carlo simulation was conducted with MIC values from CF patients with a PsA positive sputum culture between January 2014 and September 2016 to predict concentration-time profiles for different doses of amikacin.

RESULTS

This study included pharmacokinetic parameters for 14 amikacin courses administered to six unique patients. The average empiric dose of amikacin was 24.3 ± 14.6 mg/kg, achieving a peak:MIC ratio ≥8 at a rate of 37% (median 5.87; IQR 3.05-10.96). A dose of 45 mg/kg/day was needed to achieve target peak:MIC ratios 90% of the time for a PsA MIC of 8 mg/L.

CONCLUSION

Our data suggests it may not be clinically feasible to utilize amikacin for PsA isolates with a MIC of 16 mg/L. Current guideline dosing recommendations of amikacin 30-35 mg/kg/day are only adequate for PsA with a MIC ≤4 mg/L.

Pharmacokinetics of Continuous Infusion Beta-lactams in the Treatment of Acute Pulmonary Exacerbations in Adult Patients With Cystic Fibrosis

BACKGROUND

Several clinical trials have shown the efficacy of continuous infusion beta-lactam (BL) antibiotics in patients with cystic fibrosis (CF); however, little is known about pharmacokinetic changes during the treatment of an acute pulmonary exacerbation (APE). Identifying and understanding these changes may assist in optimizing antibiotic dosing during APE treatment.

METHODS

This study was a retrospective cohort study of 162 adult patients with CF admitted to the University of Utah Hospital between January 1, 2008, and May 15, 2014, for treatment of an APE with both a continuous infusion BL and IV tobramycin. We extracted the administered doses of continuous infusion BLs and tobramycin along with serum drug concentrations and calculated medication clearance rates. The primary outcome was change in clearance rates of continuous infusion BLs between day 2 and day 7 of APE treatment.

RESULTS

The BL clearance rate increased 20.7% (95% CI, 11.42 to 32.49; P < .001), whereas the tobramycin clearance rate decreased 6.3% (95% CI, -12.29 to -4.45; P < .001). The mean percent predicted FEV₁ increased between admission and discharge by 12.2% (95% CI, -13.81 to -10.55; P < .001).

CONCLUSIONS

Clinicians should monitor BL levels along with aminoglycoside levels and make dose adjustments to maximize the chance of optimal antibiotic treatment. Continuous infusion BL and tobramycin clearance can change dramatically during the treatment of an APE, which may necessitate significant changes in dosing to achieve optimal antibiotic levels. Clearance rates of these antibiotics may change in opposite directions, requiring specific monitoring of each medication.

Pharmacokinetic-Pharmacodynamic Target Attainment Analyses To Determine Optimal Dosing of Ceftazidime-Avibactam for the Treatment of Acute Pulmonary Exacerbations in Patients with Cystic Fibrosis

Acute pulmonary exacerbations (APE) involving Pseudomonas aeruginosa are associated with increased morbidity and mortality in cystic fibrosis (CF) patients. Drug resistance is a significant challenge to treatment. Ceftazidime-avibactam (CZA) demonstrates excellent in vitro activity against isolates recovered from CF patients, including drug-resistant strains. Altered pharmacokinetics (PK) of several beta-lactam antibiotics have been reported in CF patients. Therefore, this study sought to characterize the PK of CZA and perform target attainment analyses to determine the optimal treatment regimen. The PK of CZA in 12 adult CF patients administered 3 intravenous doses of 2.5 g every 8 h infused over 2 h were determined. Population modeling utilized the maximum likelihood expectation method. Monte Carlo simulations determined the probability of target attainment (PTA). An exposure target consisting of the cumulative percentage of a 24-h period that the free drug concentration exceeds the MIC under steady-state pharmacokinetic conditions (fT_>MIC) was evaluated for ceftazidime (CAZ), and an exposure target consisting of the cumulative percentage of a 24-h period that the free drug concentration exceeds a 1-mg/liter threshold concentration (fT_{>1 mg/liter}) was evaluated for avibactam (AVI). Published CAZ and CZA MIC distributions were incorporated to evaluate cumulative response probabilities. CAZ and AVI were best described by one-compartment models. The values of total body clearance (CL; CAZ CL, 7.53 ± 1.28 liters/h; AVI CL, 12.30 ± 1.96 liters/h) and volume of distribution (V; CAZ V, 18.80 ± 6.54 liters; AVI V, 25.30 ± 4.43 liters) were broadly similar to published values for healthy adults. CZA achieved a PTA (fT_>MIC, 50%) of >0.9 for MICs of ≤16 mg/liter. The overall likelihood of a treatment response was 0.82 for CZA, whereas it was 0.42 for CAZ. These data demonstrate improved pharmacodynamics of CZA in comparison with those of CAZ and provide guidance on the optimal dosing of CZA for future studies. (This study has been registered at ClinicalTrials.gov under registration no. NCT02504827.).

Extended-Interval Aminoglycoside Use in Cystic Fibrosis Exacerbation in Children and Young Adults: A Prospective Quality Improvement Project

This is a prospective quality improvement project for patients with cystic fibrosis who are 5 years of age and older who were admitted for intravenous antibiotic administration as part of treatment of cystic fibrosis exacerbation. The goal of this project was to compare the pharmacokinetics of once-daily versus thrice-daily aminoglycoside use when treating cystic fibrosis exacerbation in different age groups. Of the total of 119 patient encounters, 82.4% were started on once-daily dosing, and the remainder were started on thrice-daily dosing. Patients with pharmacokinetics allowing the continuation of once-daily dosing differed from patients who required a switch to thrice-daily dosing in terms of baseline forced expiratory volume in 1 second, forced expiratory flow from 25% to 75% of vital capacity, age, and body mass index (BMI) but were similar in BMI percentiles. The once-daily dosing group had higher mean 18-hour level, higher mean half-life, higher mean area under the curve, and lower mean elimination constant. This study showed that aminoglycoside clearance is higher in younger children.

Antipseudomonal agents exhibit differential pharmacodynamic interactions with human polymorphonuclear leukocytes against established biofilms of Pseudomonas aeruginosa

Pseudomonas aeruginosa is the most common pathogen infecting the lower respiratory tract of cystic fibrosis (CF) patients, where it forms tracheobronchial biofilms. Pseudomonas biofilms are refractory to antibacterials and to phagocytic cells with innate immunity, leading to refractory infection. Little is known about the interaction between antipseudomonal agents and phagocytic cells in eradication of P. aeruginosa biofilms. Herein, we investigated the capacity of three antipseudomonal agents, amikacin (AMK), ceftazidime (CAZ), and ciprofloxacin (CIP), to interact with human polymorphonuclear leukocytes (PMNs) against biofilms and planktonic cells of P. aeruginosa isolates recovered from sputa of CF patients. Three of the isolates were resistant and three were susceptible to each of these antibiotics. The concentrations studied (2, 8, and 32 mg/liter) were subinhibitory for biofilms of resistant isolates, whereas for biofilms of susceptible isolates, they ranged between sub-MIC and 2 × MIC values. The activity of each antibiotic alone or in combination with human PMNs against 48-h mature biofilms or planktonic cells was determined by XTT [2,3-bis(2-methoxy-4-nitro-5-sulfophenyl)-2H-tetrazolium-5-carboxanilide] assay. All combinations of AMK with PMNs resulted in synergistic or additive effects against planktonic cells and biofilms of P. aeruginosa isolates compared to each component alone. More than 75% of CAZ combinations exhibited additive interactions against biofilms of P. aeruginosa isolates, whereas CIP had mostly antagonistic interaction or no interaction with PMNs against biofilms of P. aeruginosa. Our findings demonstrate a greater positive interaction between AMK with PMNs than that observed for CAZ and especially CIP against isolates of P. aeruginosa from the respiratory tract of CF patients.

Pharmacokinetics and pharmacodynamics of aerosolized antibacterial agents in chronically infected cystic fibrosis patients

Bacteria adapt to growth in lungs of patients with cystic fibrosis (CF) by selection of heterogeneously resistant variants that are not detected by conventional susceptibility testing but are selected for rapidly during antibacterial treatment. Therefore, total bacterial counts and antibiotic susceptibilities are misleading indicators of infection and are not helpful as guides for therapy decisions or efficacy endpoints. High drug concentrations delivered by aerosol may maximize efficacy, as decreased drug susceptibilities of the pathogens are compensated for by high target site concentrations. However, reductions of the bacterial load in sputum and improvements in lung function were within the same ranges following aerosolized and conventional therapies. Furthermore, the use of conventional pharmacokinetic/pharmacodynamic (PK/PD) surrogates correlating pharmacokinetics in serum with clinical cure and presumed or proven eradication of the pathogen as a basis for PK/PD investigations in CF patients is irrelevant, as minimization of systemic exposure is one of the main objectives of aerosolized therapy; in addition, bacterial pathogens cannot be eradicated, and chronic infection cannot be cured. Consequently, conventional PK/PD surrogates are not applicable to CF patients. It is nonetheless obvious that systemic exposure of patients, with all its sequelae, is minimized and that the burden of oral treatment for CF patients suffering from chronic infections is reduced.

Continuous infusion meropenem and ticarcillin-clavulanate in pediatric cystic fibrosis patients

Aztreonam, cefepime, and ceftazidime are anti-pseudomonal beta-lactam antibiotics which have been previously reported to be administered by continuous infusion (CI) in pediatric CF patients. We present two cases administering intravenous (IV) meropenem and ticarcillin-clavulanate by CI in pediatric CF patients. The delivery of beta-lactam antibiotics via CI should be considered in order to optimize the pharmacodynamics (PD) of beta-lactams in the treatment of acute pulmonary exacerbations (APE).

Optimization of anti-pseudomonal antibiotics for cystic fibrosis pulmonary exacerbations: V. Aminoglycosides

Intravenous (IV) anti-pseudomonal aminoglycosides (i.e., amikacin and tobramycin) have been shown to be tolerable and effective in the treatment of acute pulmonary exacerbations (APEs) in both pediatric and adult patients with cystic fibrosis. The aim of this review is to provide an evidence-based summary of pharmacokinetic/pharmacodynamic, tolerability, and efficacy studies utilizing IV amikacin, gentamicin, and tobramycin in the treatment of APE and to highlight areas where further investigation is needed. The Cystic Fibrosis Foundation Pulmonary Guidelines recommend that once-daily administration of aminoglycosides is preferred over three times per day in the treatment of an APE. The literature supports dosing ranges for amikacin and tobramycin of 30-35 and 7-15 mg/kg/day, respectively, given once daily, with subsequent doses determined by therapeutic drug concentration monitoring. The literature does not support the routine use of gentamicin in the treatment of APE due to a lack of studies showing efficacy and evidence indicating an increased risk of nephrotoxicity. Further studies are needed to determine the optimal dosing strategy of amikacin in the treatment of an APE, and to further identify risk factors and determinants that influence the development of P. aeruginosa resistance with once-daily administration of tobramycin.

Current use for old antibacterial agents: polymyxins, rifamycins, and aminoglycosides

This article reviews three classes of antibacterial agents that are uncommonly used in bacterial infections and therefore can be thought of as special-use agents. The polymyxins are reserved for gram-negative bacilli that are resistant to virtually all other classes of drugs. Rifampin is used therapeutically, occasionally as a companion drug in treatment of refractory gram-positive coccal infections, especially those involving foreign bodies. Rifaximin is a new rifamycin that is a strict enteric antibiotic approved for treatment of traveler's diarrhea and is showing promise as a possible agent for refractory Clostridium difficile infections. The aminoglycosides are used mainly as companion drugs for the treatment of resistant gram-negative bacillary infections and for gram-positive coccal endocarditis.

Current use for old antibacterial agents: polymyxins, rifamycins, and aminoglycosides

This article reviews three classes of antibacterial agents that are uncommonly used in bacterial infections and therefore can be thought of as special-use agents. The polymyxins are reserved for gram-negative bacilli that are resistant to virtually all other classes of drugs. Rifampin is used therapeutically, occasionally as a companion drug in treatment of refractory gram-positive coccal infections, especially those involving foreign bodies. Rifaximin is a new rifamycin that is a strict enteric antibiotic approved for treatment of traveler's diarrhea and is showing promise as a possible agent for refractory Clostridium difficile infections. The aminoglycosides are used mainly as companion drugs for the treatment of resistant gram-negative bacillary infections and for gram-positive coccal endocarditis.

Continuous versus intermittent infusions of ceftazidime for treating exacerbation of cystic fibrosis

The present multicenter, randomized crossover study compared the safety and efficacy of continuous infusion with those of short infusions of ceftazidime in patients with cystic fibrosis. Patients with chronic Pseudomonas aeruginosa colonization received two successive courses of intravenous tobramycin and ceftazidime (200 mg/kg of body weight/day) for pulmonary exacerbation administered as thrice-daily short infusions or as a continuous infusion. The primary endpoint was the variation in the forced expiratory volume in 1 s (FEV1) during the course of antibiotic treatment. Sixty-nine of the 70 patients enrolled in the study received at least one course of antibiotic treatment. The improvement in FEV1 at the end of therapy was not statistically different between the two treatment procedures (+7.6% after continuous infusion and +5.5% after short infusions) but was better after continuous ceftazidime treatment in patients harboring resistant isolates (P < 0.05). The interval between the course of antibiotic treatments was longer after the continuous infusion than after the short infusion of ceftazidime (P = 0.04). The mean serum ceftazidime concentration during the continuous infusion was 56.2 +/- 23.2 microg/ml; the mean peak and trough concentrations during the short infusions were 216.3 +/- 71.5 and 12.1 +/- 8.7 microg/ml, respectively. The susceptibility profiles of the P. aeruginosa isolates remained unchanged and were similar for both regimens. Quality-of-life scores were similar whatever the treatment procedure, but 82% of the patients preferred the continuous-infusion regimen. Adverse events were not significantly different between the two regimens. In conclusion, the continuous infusion of ceftazidime did not increase its toxicity and appeared to be as efficient as short infusions in patients with cystic fibrosis as a whole, but it gave better results in patients harboring resistant isolates of P. aeruginosa.

Pharmacokinetic and pharmacodynamic evaluation of liposomal amikacin for inhalation in cystic fibrosis patients with chronic pseudomonal infection

The pharmacokinetics and pharmacodynamics of a novel liposomal amikacin for inhalation were evaluated in cystic fibrosis patients with chronic pseudomonas infection. Twenty-four patients from two studies received 500 mg of liposomal amikacin by inhalation once daily for 14 days. Serum, sputum, and 24-h urine samples were collected on days 1 and 14 of therapy; pulmonary function tests (PFT) and sputum for quantitative microbiology were assessed at baseline and serially for 14 days. Relationships between amikacin exposure in serum and sputum and absolute change in PFT endpoints and log10 CFU of Pseudomonas aeruginosa from baseline on days 7 and 14 of therapy were assessed. On days 7 and 14, absolute change from baseline in forced expiratory volume in 1 s (FEV1), percent predicted forced expiratory volume in 1 s (FEV1 % predicted), and forced expiratory flow between 25 and 75% of forced vital capacity (FEF(25-75%)) increased by 0.24 (P = 0.002) and 0.13 (P = 0.10) liters, 7.49 (P < 0.001) and 4.38 (P = 0.03), and 0.49 (P < 0.001) and 0.42 (P = 0.02) liters/s, respectively. In addition, relative change from baseline in FEV1 % predicted was 10.8% (P < 0.001) and 5.62% (P = 0.073) on days 7 and 14, respectively. While significant relationships between absolute change in PFT endpoints and the ratio of serum or sputum area under the concentration-time curve to the MIC (AUC/MIC) were not observed, relationships between change in log10 CFU and serum AUC/MIC ratio and change in log10 CFU and absolute changes in all PFT endpoints were significant. Together, these findings likely represent drug effect and warrant the further development of liposomal amikacin for inhalation.

Continuous versus intermittent infusion of temocillin, a directed spectrum penicillin for intensive care patients with nosocomial pneumonia: stability, compatibility, population pharmacokinetic studies and breakpoint selection

BACKGROUND AND AIMS

Temocillin, a 6alpha-methoxy-penicillin stable towards most beta-lactamases (including extended-spectrum beta-lactamase), is presented as an alternative to carbapenems for susceptible Enterobacteriaceae in microbiological surveys. We aimed at documenting its potential clinical usefulness in intensive care (IC) patients using pharmacokinetic/pharmacodynamic approaches applied to conventional (twice daily) and continuous infusion (CI) modes of administration.

METHODS

(i) In vitro evaluation of temocillin stability and compatibility with other drugs under conditions pertinent of CI in IC patients; (ii) pharmacokinetic study in patients treated by CI (4 g/day; n = 6) versus [twice daily (2 g every 12 h); n = 6]; (iii) population pharmacokinetic analysis of twice daily with Monte Carlo simulations to determine 95% probability of target attainment (PTA(95)) versus MIC (based on time above MIC > or = 40% for measured free drug).

RESULTS

Temocillin was stable at 37 degrees C in 8.34% solutions for 24 h and compatible with flucloxacillin and aminoglycosides, but not with several other antibiotic and non-antibiotic drugs. With CI, stable total serum concentrations were 73.5 +/- 3.0 mg/L (SEM) and free concentration 29.3 +/- 2.8 mg/L. With twice daily, Cmax (total drug) was 147 +/- 12.3 mg/L (SEM; free drug: 50.3 +/- 15.8 mg/L), lowest trough (total drug) 12.3 mg/L, and PTA(95) (free drug) obtained for MIC < or = 8 mg/L.

CONCLUSIONS

Temocillin (4 g/day) by CI yields stable free serum concentrations above the current breakpoint (16 mg/L), although individual variations may suggest lowering the breakpoint to 8 mg/L (as for twice daily) unless the daily dose or the frequency of administration is increased.

Sputum antibiotic concentrations: implications for treatment of cystic fibrosis lung infection

BACKGROUND

The success of antibiotic therapy may be predicted based on the achievement of pharmacodynamic indices (PDIs), which are determined by the susceptibility of the infecting bacteria and the concentrations of antibiotics achieved at the site of infection. The aim of this study was to determine whether PDIs associated with clinical effectiveness for ceftazidime and tobramycin were achieved at the site of infection in the lungs of cystic fibrosis (CF) patients following intravenous administration during treatment of an acute exacerbation.

METHODS

Serum and sputum samples were collected from 14 CF patients and the concentration of both antibiotics in the samples determined. The susceptibility of bacteria cultured from sputum samples to both antibiotics alone and in combination was also determined.

RESULTS

A total of 22 Pseudomonas aeruginosa isolates and 4 Burkholderia cepacia complex isolates were cultured from sputum samples with 55% and 4% of isolates susceptible to ceftazidime and tobramycin, respectively. Target PDIs for ceftazidime and tobramycin, an AUC/MIC ratio of 100 and a C(max)/MIC ratio of 10, respectively, were not achieved in serum or sputum simultaneously or even individually for any patient. Although the combination of ceftazidime and tobramycin was synergistic against 20 of the 26 isolates cultured, the concentrations of both antibiotics required for synergy were achieved simultaneously in only 38% of serum and 14% of sputum samples.

CONCLUSION

Key PDIs associated with clinical effectiveness for ceftazidime and tobramycin were not achieved at the site of infection in the lungs of CF patients.

Lung deposition of continuous and intermittent intravenous ceftazidime in experimental Pseudomonas aeruginosa bronchopneumonia

OBJECTIVE

Lung tissue deposition of intravenous ceftazidime administered either continuously or intermittently was compared in ventilated piglets with experimental bronchopneumonia.

DESIGN

Prospective experimental study

ANIMALS

Eighteen anesthetized and ventilated piglets

INTERVENTIONS

Bronchopneumonia was produced by the intrabronchial inoculation of Pseudomonas aeruginosa characterized by an impaired sensitivity to ceftazidime (MIC 16 mg/l). Ceftazidime was administered either through a continuous infusion of 90 mg/kg per 24 h after a bolus of 30 mg/kg or by an intermittent infusion of 30 mg/kg per 8 h.

MEASUREMENTS AND RESULTS

Piglets were killed 24 h after the initiation of continuous ceftazidime (n = 6), and 1 h (peak, n = 6) and 8 h (trough, n = 6) after the third dose following intermittent administration. Lung tissue concentrations of ceftazidime, measured by HPLC, and lung bacterial burden were assessed on multiple postmortem lung specimens. During continuous administration ceftazidime lung tissue concentrations were 9.7 +/- 3.8 microg/g. Following intermittent administration peak and trough lung tissue concentrations were, respectively, 7.1 +/- 2.4 microg/g and 0.6 +/- 1 microg/g. Lung bacterial burden was different after continuous and intermittent administration (median 7.10(3) vs. 4.10(2) cfu/g).

CONCLUSIONS

Continuous infusion of ceftazidime maintained higher tissue concentrations than intermittent administration.

Continuous versus intermittent intravenous administration of antibacterials with time-dependent action: a systematic review of pharmacokinetic and pharmacodynamic parameters

We performed a systematic review of randomised clinical trials to evaluate the comparative pharmacokinetic and pharmacodynamic properties of the continuous versus intermittent mode of intravenous administration of various antibacterials. Data were identified from PubMed (January 1950 to January 2005), Current Contents, the Cochrane central register of controlled trials, and references from relevant articles and reviews. Seventeen randomised clinical trials comparing continuous with intermittent intravenous administration of the same antibacterial regimen and examining the pharmacokinetic and pharmacodynamic properties were included in this systematic review. We reviewed data regarding the clinical setting, number of participants, antibacterial agents and dosages used, as well as maximum serum concentration (Cmax), trough serum concentration (Cmin), steady-state or plateau serum concentration (Css), area under the concentration-time curve (AUC), time above the minimum inhibitory concentration (MIC) [T>MIC], AUC: MIC, elimination rate constant, elimination half-life, volume of distribution and systematic clearance. The mean Cmax of the intermittently administered antibacterials was higher compared with Css achieved by the continuous infusion of the same antibacterial in all eligible studies (Cmax was on average 5.5 times higher than Css, range 1.9-11.2). Css was on average 5.8 times higher than the Cmin of the intermittently administered antibacterials (range 1.2-15.6). In three of six studies the length of time that the drug concentration was above the MIC of the responsible pathogens was longer in patients receiving the antibacterials continuously. In conclusion, the reviewed data suggest that the continuous intravenous infusion of antibacterials with time-dependent bacterial killing seems to be superior than the intermittent intravenous administration, from a pharmacodynamic point of view, at least when treating bacteria with high MIC values for the studied antibacterials.

Continuous versus intermittent intravenous administration of antibiotics: a meta-analysis of randomised controlled trials

Intermittent intravenous administration of antibiotics is the first-line approach in the management of severe infections worldwide. However, the potential benefits of alternate modes of administration of antibiotics, including continuous intravenous infusion, deserve further evaluation. We did a meta-analysis of randomised controlled trials comparing continuous intravenous infusion with intermittent intravenous administration of the same antibiotic regimen. Nine randomised controlled trials studying beta-lactams, aminoglycosides, and vancomycin were included. Clinical failure was lower, although without statistical significance, in patients receiving continuous infusion of antibiotics (pooled OR 0.73, 95% CI 0.53-1.01); the difference was statistically significant in a subset of randomised controlled trials that used the same total daily antibiotic dose for both intervention arms (0.70, 0.50-0.98, fixed and random effects models). Regarding mortality and nephrotoxicity, no differences were found (mortality 0.89, 0.48-1.64; nephrotoxicity 0.91, 0.56-1.47). In conclusion, the data suggest that the administration of the same total antibiotic dose by continuous intravenous infusion may be more efficient, with regard to clinical effectiveness, compared with the intermittent mode. In an era of gradually increasing resistance among most pathogens, the potential advantages of continuous intravenous administration of antibiotics on several clinical outcomes should be further investigated.

Current use for old antibacterial agents: polymyxins, rifampin, and aminoglycosides

This article discusses three classes of antibacterial agents that are uncommonly used in bacterial infections (other than mycobacterial infections) and can be thought of as special-use agents. These are the polymyxins, rifampin, and the aminoglycosides.

Empiric Treatment of Multidrug-ResistantBurkholderia cepaciaLung Exacerbation in a Patient with Cystic Fibrosis: Application of Pharmacodynamic Concepts to Meropenem Therapy

A 31-year-old man with cystic fibrosis was diagnosed with multidrug-resistant Burkholderia cepacia pneumonia. Meropenem 2000 mg every 8 hours was administered as a 3-hour infusion to maximize pharmacodynamic exposure; oral minocycline 100 mg twice/day was also given. Blood samples were collected to confirm meropenem concentrations. Concentrations above the mimimum inhibitory concentration (MIC) of 8 microg/ml were achieved for 52% of the dosing interval, which is greater than what is required for a bactericidal effect. The patient's condition improved, he was discharged, and completed a 3-week course of the antibiotic regimen. After 6 months, he had remained at his baseline level of health. This case demonstrates that pharmacodynamic principles can be used to design an antibiotic dosing regimen that can achieve optimal exposures when the MIC is above that considered susceptible to conventional dosing strategies.

Pharmacodynamics and dosing of aminoglycosides

Aminoglycosides are concentration-dependent killing agents whose pharmacodynamic predictors of efficacy are the area-under-the-curve to minimum inhibitory concentration ratio and the peak to minimum inhibitory concentration ratio. Prospective studies have shown that these agents can be given once-daily or less frequently in most clinical settings, with equal efficacy and possible reduced toxicity. Dosages for different clinical settings have been studied and methods are available to monitor once-daily dosing.