Ceftazidime/avibactam serum concentration in patients on ECMO

OBJECTIVES

The use of extracorporeal membrane oxygenation (ECMO) may alter blood levels of several drugs, including antibiotics, leading to under dosing of these drugs and thus to potential treatment failure. No data exist on pharmacokinetics of new antimicrobial, in particular ceftazidime/avibactam. We therefore perform this study to evaluate ceftazidime/avibactam blood levels in ECMO patients and find factors associated with underdosing.

METHODS

Retrospective observational study of patients on ECMO having received ceftazidime/avibactam and in whom trough blood levels of ceftazidime and avibactam were available. Main outcome measurement was the number of patients with ceftazidime and avibactam blood levels above predefined cut-off values, derived from the European Committee on Antimicrobial Susceptibility Testing (EUCAST) breakpoints for Enterobacteriaceae and Pseudomonas aeruginosa, namely 8 mg/L for ceftazidime and 4 mg/L for avibactam, and explored factors associated with underdosing.

RESULTS

Twenty-three ceftazidime/avibactam trough levels were available in 14 ECMO patients, all of them having received veno-venous ECMO for SARS-CoV-2-associated pneumonia. Although ceftazidime levels were above 8 mg/L in all except one patient, nine (39%) of the avibactam dosages were below 4 mg/L. Increased renal clearance (creatinine clearance > 130 mL/min) was the main factor associated with under dosing, since 7 out of the 10 dosages below the predefined cut-offs were measured in patients with this condition.

CONCLUSIONS

In ECMO patients receiving ceftazidime/avibactam, ceftazidime and avibactam serum levels are above EUCAST breakpoints in most cases, justifying the use of normal dosing in ECMO patients. Increased renal clearance may lead to ceftazidime and avibactam under dosing.

Subcutaneous administration of ceftazidime at 20 and 40 mg/kg produces theoretically therapeutic plasma concentrations for at least 120 hours in red-eared sliders (Trachemys scripta elegans)

OBJECTIVE

To evaluate and compare the pharmacokinetic parameters of SC ceftazidime administered at 20 and 40 mg/kg to red-eared sliders.

ANIMALS

8 adult red-eared sliders (Trachemys scripta elegans).

METHODS

In a sequential, 2-period study with a 3-week washout period between treatments, ceftazidime was administered SC to turtles at 20 and 40 mg/kg. Blood samples were collected from the subcarapacial sinus at 0, 24, 48, 72, 96, and 120 hours after ceftazidime administration. Plasma ceftazidime concentrations were quantified using reversed-phase HPLC.

RESULTS

Mean plasma half-life after 20- and 40-mg/kg dosing was 39.75 ± 8.0 hours and 33.03 ± 6.56 hours, respectively. Mean maximum plasma concentration after 20- and 40-mg/kg dosing was 71.0 ± 15.93 µg/mL and 120.0 ± 30.62 µg/mL, respectively. Mean plasma ceftazidime concentrations remained ≥ 8 µg/mL, the theoretical MIC for various reptile pathogens for all time points.

CLINICAL RELEVANCE

Results indicate that ceftazidime dosed at either 20 or 40 mg/kg produces plasma concentrations exceeding the theoretical MIC of various reptile pathogens for at least 120 hours. An ideal dosing interval could not be determined, as all plasma concentrations remained above the threshold of interest for all time points. Follow-up studies should focus on establishing a dosing interval and more rigorous monitoring for potential adverse effects.

Simultaneous determination of ceftazidime and pyridine in human plasma by LC-UV

A sensitive, accurate and precise liquid chromatography (LC) method for the simultaneous determination of ceftazidime and pyridine in human plasma has been developed and validated. Acetonitrile (ACN) was employed to precipitate the proteins in the plasma samples. Chromatographic separation was performed with a Kinetex® C18 (150 mm × 3 mm, 2.6 µm) column with gradient elution. Ammonium formate 20 mM and ACN were mixed in a ratio of 98:2 (v/v) for mobile phase A and 85:15 (v/v) for mobile phase B. Both were adjusted to pH 4.5 with formic acid. The flow rate was 0.4 mL/min. UV detection was performed at 254 nm. Calibration curves were linear in the range from 0.3 to 225 μg/mL for ceftazidime and from 0.2 to 10 μg/mL for pyridine with correlation coefficients ≥ 0.999. Within- and between-run precision and accuracy were satisfactory with coefficients of variation (CV) ≤ 8.0% and deviations ≤ 7.0%, respectively. The method fulfilled all validation criteria prescribed by the European Medicines Agency guidelines. Next, it has been used successfully to analyze plasma samples of patients who received ceftazidime under intermittent and continuous administration. With intermittent administration, the concentration of the antibiotics reached a peak and then dropped quickly, which may be below the minimal inhibitory concentration (MIC). With continuous administration, the concentration of the antibiotics remained stable over 24 h, certainly above the MIC. Although the same tendency in ceftazidime concentration changes over time was observed, a difference in concentration amongst the patients was noticeable. The concentration of pyridine in plasma was negligible.

Measurement of Free Plasma Concentrations of Beta-Lactam Antibiotics: An Applicability Study in Intensive Care Unit Patients

BACKGROUND

The antibacterial effect of antibiotics is linked to the free drug concentration. This study investigated the applicability of an ultrafiltration method to determine free plasma concentrations of beta-lactam antibiotics in ICU patients.

METHODS

Eligible patients included adult ICU patients treated with ceftazidime (CAZ), meropenem (MEM), piperacillin (PIP)/tazobactam (TAZ), or flucloxacillin (FXN) by continuous infusion. Up to 2 arterial blood samples were drawn at steady state. Patients could be included more than once if they received another antibiotic. Free drug concentrations were determined by high-performance liquid chromatography with ultraviolet detection after ultrafiltration, using a method that maintained physiological conditions (pH 7.4/37°C). Total drug concentrations were determined to calculate the unbound fraction. In a post-hoc analysis, free concentrations were compared with the target value of 4× the epidemiological cut-off value (ECOFF) for Pseudomonas aeruginosa as a worst-case scenario for empirical therapy with CAZ, MEM or PIP/tazobactam and against methicillin-sensitive Staphylococcus aureus for targeted therapy with FXN.

RESULTS

Fifty different antibiotic treatment periods in 38 patients were evaluated. The concentrations of the antibiotics showed a wide range because of the fixed dosing regimen in a mixed population with variable kidney function. The mean unbound fractions (fu) of CAZ, MEM, and PIP were 102.5%, 98.4%, and 95.7%, with interpatient variability of <6%. The mean fu of FXN was 11.6%, with interpatient variability of 39%. It was observed that 2 of 12 free concentrations of CAZ, 1 of 40 concentrations of MEM, and 11 of 23 concentrations of PIP were below the applied target concentration of 4 × ECOFF for P. aeruginosa. All concentrations of FXN (9 samples from 6 patients) were >8 × ECOFF for methicillin-sensitive Staphylococcus aureus.

CONCLUSIONS

For therapeutic drug monitoring purposes, measuring total or free concentrations of CAZ, MEM, or PIP is seemingly adequate. For highly protein-bound beta-lactams such as FXN, free concentrations should be favored in ICU patients with prevalent hypoalbuminemia.

Population Pharmacokinetic Modelling of Ceftazidime and Avibactam in the Plasma and Epithelial Lining Fluid of Healthy Volunteers

OBJECTIVES

Our objective was to develop population pharmacokinetic (PK) models for ceftazidime and avibactam in the plasma and epithelial lining fluid (ELF) of healthy volunteers and to compare ELF concentrations to plasma PK/pharmacodynamic (PD) targets.

METHODS

Plasma and ELF population PK models were developed for ceftazidime and avibactam concentration data from 42 subjects (NCT01395420). Two- and three-compartment plasma PK models were fitted to ceftazidime and avibactam plasma PK data, and different plasma-ELF linked models were evaluated. Using best-fitting models, plasma and ELF concentration-time profiles were simulated for 1000 subjects. ELF concentration-time profiles for ceftazidime/avibactam 2000-500 mg every 8 h were compared with plasma PK/PD targets for ceftazidime (50% of time above [fT >] 8 mg/l) and avibactam (50% fT > 1 mg/l).

RESULTS

Three-compartment PK models best fitted the plasma concentration data for ceftazidime and avibactam. ELF data for both drugs were best described by a direct response (instantaneous equilibrium) model. Ceftazidime plasma-ELF relationships were best described by a saturable Michaelis-Menten model. For avibactam, departure from plasma-ELF relationship linearity was more modest than for ceftazidime. ELF:plasma penetration ratios of both ceftazidime (52%) and avibactam (42%) at plasma concentrations relevant for efficacy (~ 8 mg/l for ceftazidime and ~ 1 mg/l for avibactam) were greater than previously calculated using non-compartmental area under the curve (AUC) methods, which average across the entire concentration range. Ceftazidime and avibactam ELF exposures exceeded their respective plasma PK/PD time-above-threshold targets by the dosing interval mid-point in most subjects.

CONCLUSIONS

This compartmental modelling analysis suggests ELF exposures of both ceftazidime and avibactam exceed levels required for efficacy in plasma.

Population Pharmacokinetics and Dosing Simulations of Ceftazidime in Chinese Neonates

An accurate dosage determination is required in neonates when antibiotics are used. The adult data cannot be simply extrapolated to the pediatric population due to significant individual differences. We aimed to identify factors impacting ceftazidime exposure in neonates and to provide drug dosing guidance to clinicians. Forty-three neonates aged less than 60 days with proven or suspected infections were enrolled in this study. After intravenous administration, blood samples were collected, and plasma ceftazidime concentration was determined using a HPLC method. Pharmacokinetic data were fitted using a nonlinear mixed-effects model approach. One-compartmental model could nicely characterize the ceftazidime in vivo behavior. The covariate test found that the postmenstrual age (day) was strongly associated with systemic drug clearance (L/h), and the effect of body weight (kg) was identified as the covariate on distribution volume (L). Compared with the base model, the addition of covariates improved the goodness-of-fit of the final model. Model validation (bootstrap, visual predictive check, and prediction-corrected visual predictive check) suggested a robust and reliable pharmacokinetic model was developed. Personalized dosage regimens were provided based on model simulations. The intravenous dose should be adjusted according to postmenstrual age, body weight, and minimum inhibitory concentration.

Simultaneous Determination of Eight β-Lactam Antibiotics, Amoxicillin, Cefazolin, Cefepime, Cefotaxime, Ceftazidime, Cloxacillin, Oxacillin, and Piperacillin, in Human Plasma by Using Ultra-High-Performance Liquid Chromatography with Ultraviolet Detection

A simple and rapid ultra-high-performance liquid chromatography (UHPLC) method using UV detection was developed for the simultaneous determination of eight β-lactam antibiotics in human plasma, including four penicillins, amoxicillin (AMX), cloxacillin (CLX), oxacillin (OXA), and piperacillin (PIP), and four cephalosporins, cefazolin (CFZ), cefepime (FEP), cefotaxime (CTX), and ceftazidime (CAZ). One hundred-microliter samples were spiked with thiopental as an internal standard, and proteins were precipitated by acetonitrile containing 0.1% formic acid. Separation was achieved on a pentafluorophenyl (PFP) column with a mobile phase composed of phosphoric acid (10 mM) and acetonitrile in gradient elution mode at a flow rate of 500 μl/min. Detection was performed at 230 nm for AMX, CLX, OXA, and PIP and 260 nm for CFZ, FEP, CTX, and CAZ. The total analysis time did not exceed 13 min. The method was found to be linear at concentrations ranging from 2 to 100 mg/liter for each compound, and all validation parameters fulfilled international requirements. Between- and within-run accuracy errors ranged from -5.2% to 11.4%, and precision was lower than 14.2%. This simple method requires small-volume samples and can easily be implemented in most clinical laboratories to promote the therapeutic drug monitoring of β-lactam antibiotics. The simultaneous determination of several antibiotics considerably reduces the time to results for clinicians, which may improve treatment efficiency, especially in critically ill patients.

Pharmacodynamics of Ceftazidime and Avibactam in Neutropenic Mice with Thigh or Lung Infection

Avibactam is a new non-β-lactam β-lactamase inhibitor that shows promising restoration of ceftazidime activity against microorganisms producing Ambler class A extended-spectrum β-lactamases (ESBLs) and carbapenemases such as KPCs, class C β-lactamases (AmpC), and some class D enzymes. To determine optimal dosing combinations of ceftazidime-avibactam for treating infections with ceftazidime-resistant Pseudomonas aeruginosa, pharmacodynamic responses were explored in murine neutropenic thigh and lung infection models. Exposure-response relationships for ceftazidime monotherapy were determined first. Subsequently, the efficacy of adding avibactam every 2 h (q2h) or q8h to a fixed q2h dose of ceftazidime was determined in lung infection for two strains. Dosing avibactam q2h was significantly more efficacious, reducing the avibactam daily dose for static effect by factors of 2.7 and 10.1, whereas the mean percentage of the dosing interval that free drug concentrations remain above the threshold concentration of 1 mg/liter (%fT>C(T) 1 mg/liter) yielding bacteriostasis was similar for both regimens, with mean values of 21.6 (q2h) and 18.5 (q8h). Dose fractionation studies of avibactam in both the thigh and lung models indicated that the effect of avibactam correlated well with %fT>C(T) 1 mg/liter. This parameter of avibactam was further explored for four P. aeruginosa strains in the lung model and six in the thigh model. Parameter estimates of %fT>C(T) 1 mg/liter for avibactam ranged from 0 to 21.4% in the lung model and from 14.1 to 62.5% in the thigh model to achieve stasis. In conclusion, addition of avibactam enhanced the effect of ceftazidime, which was more pronounced at frequent dosing and well related with %fT>C(T) 1 mg/liter. The thigh model appeared more stringent, with higher values, ranging up to 62.5% fT>C(T) 1 mg/liter, required for a static effect.

Randomized, placebo-controlled study to assess the impact on QT/QTc interval of supratherapeutic doses of ceftazidime-avibactam or ceftaroline fosamil-avibactam

Potential effects of supratherapeutic doses of intravenous (IV) ceftazidime-avibactam and ceftaroline fosamil-avibactam on cardiac repolarization were assessed in a thorough QT/QTc study. This was a double-blind, randomized, placebo-controlled, four-period crossover Phase I study (NCT01290900) in healthy males (n = 51). Subjects received, in randomized order and separated by ≥3 days washout: single doses of IV ceftaroline fosamil 1,500 mg with avibactam 2,000 mg; IV ceftazidime 3,000 mg with avibactam 2,000 mg; oral moxifloxacin 400 mg (open-label positive control); and IV placebo (saline). Least square mean and two-sided 90% confidence intervals (CI) for change from baseline in Fridericia-corrected QT interval (ΔQTcF) for active treatments versus placebo were estimated at 10 time points over 24 hours. The upper bound of the two-sided 90% CI for placebo-corrected ΔQTcF did not exceed 10 milliseconds at any time point over 24 hours for ceftaroline fosamil-avibactam or ceftazidime-avibactam. The lower bound of the two-sided 90% CI for the difference between moxifloxacin and placebo in ΔQTcF over 1-4 hours was >5 milliseconds, confirming assay sensitivity. Pharmacokinetics results confirmed achievement of supratherapeutic plasma concentrations. No safety concerns were raised. In conclusion, supratherapeutic doses of ceftaroline fosamil-avibactam or ceftazidime-avibactam were not associated with QT/QTc prolongation in this study population.

[Study on the blood concentration and clinical efficacy of ceftazidime, a cephem antibiotic at dose of one gram q.i.d, for adult hospital-acquired pneumonia patients]

Ceftazidime (CAZ), a cephem antibiotic for injection, was administered at dose of one gram q.i.d. to adult hospital-acquired pneimonia patients, and the clinical efficacy and blood concentration of CAZ was studied in five cases. The assessment of clinical efficacy was "efficacy" in all cases, and early improvement of examination value including body temperature, the value of CRP, and white blood cell counts were obtained. Abnormality of hepatic function as adverse effect was noted in two cases. However, the severity was mild and didn't affect the treatment in both cases. The maximum drug concentration immediately after the end of infusion was 72.1-176.5 microg/mL (median, 82.7 microg/mL) and the trough level was 5.1-72.1 microg/mL (median, 26.6 microg/mL), therefore the blood concentration was maintained a higher level than the MIC of bacteria estimated to be causative. From these results, administration method of ceftazidime one gram q.i.d. was considered to be a good way with increase of drug efficacy by maintaining highly blood concentration over prolonged period, and expected to be a good effect for hospital-acquired pneumonia.

Study on the resonance Rayleigh scattering spectra of the interactions of palladium (II)–cephalosporins chelates with 4,5-dibromofluorescein and their analytical applications

In pH 2.8-3.8 BR buffer medium, the third generation cephalosporin antibiotics (TGCs) such as ceftazidime (CZD), ceftriaxone (CTRX), cefoperazone (CPZ), and cefotaxime (CFTM) react with palladium(II) (Pd(II)) to form 1:2 yellowish-brown cationic chelates, which further react with 4,5-dibromofluorescein (DBF) to form 1:3 brown ion-association complexes. As a result, not only the spectra of absorption and fluorescence are changed, but also the resonance Rayleigh scattering (RRS) is enhanced greatly and the new RRS spectra are observed. The four TGCs products have similar spectral characteristics and their maximum RRS wavelengths are all located at 291 nm. The quantitative determination ranges and the detection limits of the four TGCs are 0.0065-1.0 microg mL(-1) and 2.0 ng mL(-1) for CZD, 0.0070-1.1 microg mL(-1) and 2.2 ng mL(-1) for CTRX, 0.0090-1.6 microg mL(-1) and 2.7 ng mL(-1) for CPZ, and 0.014-2.2 microg mL(-1) and 4.2 ng mL(-1) for CFTM, respectively. The optimum conditions of the reactions and the effects of foreign substances are investigated, and the composition of ion-association complexes is discussed also. Based on the ion-association reaction, a highly sensitive, simple and rapid method has been proposed to the determination of TGCs.

Intermittent administration of ceftazidime to burns patients: influence of glomerular filtration

OBJECTIVE

The pharmacokinetics of ceftazidime, the antibiotic of choice for treating acute P. aeruginosa infections, may be modified in burns patients. The aim of this study was to identify the factors causing variations in the serum antibiotic concentrations in bums patients.

METHODS

30 patients with serious burns were randomly divided into two groups. Group 1 received a dose of ceftazidime of 2 x 3 g/24 hours. The second group received the same dose but divided into 6 administrations. Blood samples were taken at 24 (M1) and 48 hours (M2) after the start of treatment and the peak and trough serum concentrations of ceftazidime measured by HPLC. Depending on the results, frequency and/or dose was modified to obtain trough concentrations (Cmin) equal to 16 mg/l, i.e. 4 times the MIC. Either the same dose was maintained, but mostly divided up, or it was increased to 1 g x 8 administrations or it was decreased to 1 g x 4 or 1 g x 3. The serum concentrations of ceftazidime obtained were analyzed taking into account the characteristics of the burns patients (multivariate correlation).

RESULTS

From the first sample (M1) Cmin was lower than the target concentration in 50% of the patients in Group 1 and 20% in Group 2. The modification of the dosing regimen put into place after the first analysis, led to the patients being further divided into four groups before the second blood sampling. Finally, 5 patients ended up in Group 1. In all patients and for all administration times, a negative correlation was found between Cmin and the creatinine clearance, calculated by using Cockcroft's formula.

CONCLUSION

This study highlights the peculiarities of ceftazidime pharmacokinetics seen in burns patients with high interindividual variability. Based on Cmin monitoring and a predefined therapeutic range, dose adjustment was often required. Ceftazidime clearance is correlated with creatinine clearance (Cockcroft's formula), suggesting that this parameter could be used for a priori or a posteriori dose individualization. To respect the summary of the product characteristics (SPC) and reduce the variability in trough concentrations, the dose should be fractionated (1 g x 6) over a 24-hour period or even given as a continuous infusion. Trough concentrations must be evaluated to adapt the dosage regimen to attain target concentrations of 4 x the MIC.

Influence of high mutation rates on the mechanisms and dynamics of in vitro and in vivo resistance development to single or combined antipseudomonal agents

We studied the mechanisms and dynamics of the development of resistance to ceftazidime (CAZ) alone or combined with tobramycin (TOB) or ciprofloxacin (CIP) in vitro and in vivo (using a mouse model of lung infection with human antibiotic regimens). Pseudomonas aeruginosa strain PAO1 and its hypermutable derivative PAODeltamutS were used, and the results were compared with those previously obtained with CIP, TOB, and CIP plus TOB (CIP-TOB) under the same conditions. An important (200-fold) amplification of the number of resistant mutant cells was documented for PAODeltamutS-infected mice that were under CAZ treatment compared to the number for mice that received placebo, whereas the median number of resistant mutant cells was below the detection limits for mice infected by PAO1. These results were intermediate between the high amplification with CIP (50,000-fold) and the low amplification with TOB (10-fold). All CAZ-resistant single mutant cells selected in vitro or in vivo hyperproduced AmpC. On the other hand, the three combinations studied were found to be highly effective in the prevention of in vivo resistance development in mice infected with PAODeltamutS, although the highest therapeutic efficacy (in terms of mortality and total bacterial load reduction) compared to those of the individual regimens was obtained with CIP-TOB and the lowest was with CAZ-CIP. Nevertheless, mutant cells that were resistant to the three combinations tested were readily selected in vitro for PAODeltamutS (mutation rates from 1.2 x 10(-9) to 5.8 x 10(-11)) but not for PAO1, highlighting the potential risk for antimicrobial resistance development associated with the presence of hypermutable strains, even when combined therapy was used. All five independent CAZ-TOB-resistant PAODeltamutS double mutants studied presented the same resistance mechanism (AmpC hyperproduction plus an aminoglycoside resistance mechanism not related to MexXY), whereas four different combinations of resistance mechanisms were documented for the five CAZ-CIP-resistant double mutants.

A population pharmacokinetic approach to ceftazidime use in burn patients: influence of glomerular filtration, gender and mechanical ventilation

AIMS

The aim of this study was to evaluate the disposition of ceftazidime in burn patients using a population pharmacokinetic approach, and to identify the clinical and biological parameters influencing its pharmacokinetics.

METHODS

The development of the pharmacokinetic model was based on 237 serum ceftazidime concentrations from 50 burn patients. The determination of the pharmacokinetic parameters and the selection of covariates were performed using a nonlinear mixed-effect modelling method.

RESULTS

A two-compartment model with first order elimination incorporating a proportional error model best fitted the data. Ceftazidime clearance (CL, l h(-1)) was significantly correlated with creatinine clearance (CL(CR)), and the distribution volume of the peripheral compartment (V2, l) was correlated with gender, mechanical ventilation and the CL(CR). The final model was defined by the following equations: Ceftazidime clearance was 6.1 and 5.7 l h(-1) for mechanically ventilated males and females, respectively, and 7.2 and 6.6 l h(-1) for nonventilated patients. The total volume of distribution was 31.6 and 49.4 l for mechanically ventilated males and females, respectively, and 22.8 and 28.1 l h (-1)for nonventilated patients.

CONCLUSIONS

We have shown that gender, mechanical ventilation and CL(CR) significantly influence the disposition of ceftazidime in burn patients. Interindividual variability in the pharmacokinetics of ceftazidime was significant and emphasizes the need for therapeutic monitoring.

Role of ceftazidime dose regimen on the selection of resistant Enterobacter cloacae in the intestinal flora of rats treated for an experimental pulmonary infection

OBJECTIVES

The effect of ceftazidime dosing increments and frequency of dosing on the selection of ceftazidime-resistant Enterobacter cloacae in the intestine was studied in rats, during treatment of a pulmonary infection caused by Klebsiella pneumoniae.

METHODS

Rats with pulmonary infection (n = 10 per group) received therapy with doses of ceftazidime at 3.1 to 400 mg/kg per day at a frequency of every 6,12 or 24 h for 18 days, starting 24 h after bacterial inoculation of the lung. Emergence of resistance in intestinal E. cloacae was monitored by culturing fresh stool specimens at days 0, 8, 15, 22, 29, 36 and 43 on agar plates with (6.4 mg/L) and without ceftazidime. Pharmacodynamic indices and time within the mutant selection window (MSW) were assessed in infected rats for each regimen. Ceftazidime-resistant E. cloacae mutants were characterized by determination of the beta-lactamase activity under cefoxitin-induced and non-induced conditions.

RESULTS

A reduction of intestinal ceftazidime-susceptible E. cloacae was observed and showed a significant correlation with the fAUC/MIC at days 8, 15 and 22 and with the fCmax on days 8, 15, 22, 29 and 36. More rats treated with 12-25 and 50-100 mg/kg per day every 6 h were found colonized with ceftazidime-resistant E. cloacae mutants than animals treated every 12 h or every 24 h. The proportion of rats colonized with ceftazidime-resistant E. cloacae mutants at days 15, 36 and 43 correlated with the time during which ceftazidime plasma concentrations were within the boundaries of the MSW. Only at day 15 was a correlation demonstrated between the fCmax and significantly fewer rats colonized with ceftazidime-resistant E. cloacae. Ceftazidime-resistant E. cloacae mutants (MIC >or= 128 mg/L) were characterized as stable derepressed mutants.

CONCLUSIONS

Colonization with stable derepressed ceftazidime-resistant E. cloacae mutants particularly occurred when rats were exposed to moderate doses of ceftazidime (12-25 or 50-100 mg/kg per day) administered every 6 h. Emergence of resistance was correlated with time within the MSW.

Continuous infusion of ceftazidime in critically ill patients undergoing continuous venovenous haemodiafiltration: pharmacokinetic evaluation and dose recommendation

Introduction

In seriously infected patients with acute renal failure and who require continuous renal replacement therapy, data on continuous infusion of ceftazidime are lacking. Here we analyzed the pharmacokinetics of ceftazidime administered by continuous infusion in critically ill patients during continuous venovenous haemodiafiltration (CVVHDF) in order to identify the optimal dosage in this setting.

Method

Seven critically ill patients were prospectively enrolled in the study. CVVHDF was performed using a 0.6 m² AN69 high-flux membrane and with blood, dialysate and ultrafiltration flow rates of 150 ml/min, 1 l/hour and 1.5 l/hour, respectively. Based on a predicted haemodiafiltration clearance of 32.5 ml/min, all patients received a 2 g loading dose of ceftazidime, followed by a 3 g/day continuous infusion for 72 hours. Serum samples were collected at 0, 3, 15 and 30 minutes and at 1, 2, 4, 6, 8, 12, 24, 36, 48 and 72 hours; dialysate/ultrafiltrate samples were taken at 2, 8, 12, 24, 36 and 48 hours. Ceftazidime concentrations in serum and dialysate/ultrafiltrate were measured using high-performance liquid chromatography.

Results

The mean (± standard deviation) elimination half-life, volume of distribution, area under the concentration-time curve from time 0 to 72 hours, and total clearance of ceftazidime were 4 ± 1 hours, 19 ± 6 l, 2514 ± 212 mg/h per l, and 62 ± 5 ml/min, respectively. The mean serum ceftazidime steady-state concentration was 33.5 mg/l (range 28.8–36.3 mg/l). CVVHDF effectively removed continuously infused ceftazidime, with a sieving coefficient and haemodiafiltration clearance of 0.81 ± 0.11 and 33.6 ± 4 mg/l, respectively.

Conclusion

We conclude that a dosing regimen of 3 g/day ceftazidime, by continuous infusion, following a 2 g loading dose, results in serum concentrations more than four times the minimum inhibitory concentration for all susceptible pathogens, and we recommend this regimen in critically ill patients undergoing CVVHDF.

Ceftazidime overdose-related nonconvulsive status epilepticus after intraperitoneal instillation

We report a case of ceftazidime-related nonconvulsive status epilepticus (NCSE) in a 70-year-old female patient with continuous ambulatory peritoneal dialysis (CAPD)-related peritonitis. She was given ceftazidime intravenously which was then changed to intraperitoneal installation after clinical improvement. She received 11 g of ceftazidime via intraperitoneal installation for two days after being discharged from the hospital. Her consciousness was altered with mutism, asterisxis, and horizontal nystagmus. Her EEG showed continuous generalized three spikes-and-wave per second that were abolished after intravenous diazepam. Ceftazidime-related NCSE was suggested and ceftazidime therapy was stopped. Hemodialysis was done while phenytoin was also given to control the convulsions. Her consciousness improved after hemodialysis. Serum ceftazidime measured before and after hemodialysis on the second and third day were 105.2/39.4, 36.2/5.2 microg/mL (normal peak level 55 microg/mL), respectively. Repeated evaluation on day 6 showed normal EEG without epileptiform activity. She was later discharged with full recovery.

A simple formula for individualising ceftazidime dosage administered by continuous infusion in patients with haematological malignancies

A formula is proposed for individualising ceftazidime dosage administered by continuous infusion in patients with haematological malignancies. Sixty patients were retrospectively randomised into Group A (n=30) to establish the formula and Group B (n=30) to evaluate this formula. Individual ceftazidime clearances were estimated from the ratio between the rate of infusion and plasma concentration at steady state. In Group A, ceftazidime clearance was significantly correlated with creatinine clearance. From this result, a formula (rate of infusion (g/day)=0.00133x[creatinine clearance (mL/min)]x[target concentration at steady state (mg/L)]) is proposed. This formula provided consistent estimations of ceftazidime plasma concentrations in Group B and should help clinicians to define the optimum ceftazidime dosage, particularly in patients with disturbed renal function.

Trough serum concentrations of β-lactam antibiotics in cancer patients: inappropriateness of conventional schedules to pharmacokinetic/pharmacodynamic properties of β-lactams

Serum concentrations of beta-lactams that continuously exceed the minimum inhibitory concentration may improve therapeutic outcomes for immunosuppressed patients. The trough serum levels of ceftazidime (CAZ), cefepime (FEP) or imipenem (IMP) were prospectively determined on days 1 and 3 of treatment in cancer patients. Seventy-eight episodes of suspected infection were analysed. Trough serum levels were higher than 4 mg/L in 62%, 24% and 0% of cases in the CAZ, FEP and IMP groups, respectively, and were higher than 20 mg/L in 24% of cases in the CAZ group compared with 0% both in the FEP and IMP groups. For suspected infectious episodes in cancer patients, the traditional intermittent regimen of beta-lactams does not appear to be appropriate for the pharmacokinetic/pharmacodynamic properties of these antibiotics.

Time-kill curves as a tool for targeting ceftazidime serum concentration during continuous infusion for treatment of septicaemic melioidosis

Melioidosis is a fatal community-acquired infection endemic in tropical areas. Ten isolates of the causative microorganism were subjected to time-kill study using a range of ceftazidime concentrations. This study demonstrated that a ceftazidime concentration of eight times the minimum inhibitory concentration yielded an optimal bactericidal effect and should be the target concentration administered by continuous infusion.

Determination of ceftazidime and cefepime in plasma and dialysate-ultrafiltrate from patients undergoing continuous veno-venous hemodiafiltration by HPLC

We have developed and validated a new, rapid and reproducible HPLC method for the determination of cefepime and ceftazidime in plasma and dialysate-ultrafiltrate samples obtained from intensive care unit (ICU) patients undergoing continuous veno-venous hemodiafiltration (CVVHDF). The method for plasma samples involved protein precipitation with acetonitrile, followed by washing with dichloromethane to remove apolar lipophilic compounds. Dialysate-ultrafiltrate samples did not require any preparation. Separation was performed on a muBondapak C18 (30 cm x 3.9 mm x 10 microm) with UV detection. The mobile phase contained acetate buffer: ACN and was delivered at 2 ml/min. The coefficients of determination of the calibration curves were always > or = 0.998 and R.S.D.% of the response factors <10%. The intra and inter-assay precision and accuracy of the quality controls (QC) and limit of quantification (LOQ) were satisfactory in all cases. Plasma and dialysate-ultrafiltrate samples were stable at -20 and -80 degrees C for 2 months and also after three freeze/thaw cycles. Dialysate-ultrafiltrate samples were stable in the chromatographic rack for 24h at room temperature, but we recommend storing processed plasma samples at 4 degrees C until the analysis. The described method has proved to be useful to give accurate measurements of ceftazidime and cefepime in samples obtained from patients undergoing CVVHDF.

Determination of ceftazidime in plasma and cerebrospinal fluid by micellar electrokinetic chromatography with direct sample injection

A simple micellar electrokinetic chromatography (MEKC) with UV detection at 254 nm for analysis of ceftazidime in plasma and in cerebrospinal fluid (CSF) by direct injection without any sample pretreatment is described. The separation of ceftazidime from biological matrix was performed at 25 degrees C using a background electrolyte consisting of Tris buffer with sodium dodecyl sulfate (SDS) as the electrolyte solution. Under optimal MEKC condition, good separation with high efficiency and short analyses time is achieved. Several parameters affecting the separation of the drug from biological matrix were studied, including pH and concentration of the Tris buffer and SDS. Using cefazolin as an internal standard (IS), the linear ranges of the method for the determination of ceftazidime in plasma and in CSF were all over the range of 3-90 microg/mL; the detection limit of the drug in plasma and in CSF (signal-to-noise ratio = 3; injection 0.5 psi, 5 s) was 2.0 microg/mL. The applicability of the proposed method for determination of ceftazidime in plasma and CSF collected after intravenous administration of 2 g ceftazidime in patients with meningitis was demonstrated.

Population pharmacokinetics of ceftazidime in burn patients

AIM

The aim of this study was to characterize, via a population pharmacokinetic approach, the pharmacokinetics of ceftazidime in burn patients who were not in the acute post-injury phase.

METHODS

The development of the pharmacokinetic model was based on data from therapeutic drug monitoring (41 patients, 94 samples). The estimation of population pharmacokinetic parameters and the selection of covariates (age, gender, body weight, size of burn and creatinine plasma concentration) that could affect the pharmacokinetics were performed with a nonlinear mixed effect modelling method.

RESULTS

No relationship between covariates and the pharmacokinetic parameters was established with the exception of an inverse-linear relationship between creatinine plasma concentration and ceftazidime total clearance. The total clearance of ceftazidime was 2.72 l h-1[coefficient variation (CV) = 56.3%] and the distribution volume of the central compartment was 0.28 l kg-1 (CV = 13.2%) The transfer rate constants (k12, k 21) between the central and peripheral compartments were 0.06718 h-1 (CV = 87.2%) and 0.001823 h-1 (CV = 82.7%), respectively. From these parameters, the total ceftazidime volume of distribution (10.64 l kg-1) was calculated.

CONCLUSION

The population parameters were different from those obtained in a previous study performed in fewer patients and in the early period after burn injury. In our study, the lower ceftazidime clearance could be explained by the relative decrease in ceftazidime elimination in relation to the burn area, and the higher ceftazidime volume of distribution in the presence of interstitial oedema, which could act as a reservoir from which ceftazidime returns slowly to the circulation.

Plasma and lung concentrations of ceftazidime administered in continuous infusion to critically ill patients with severe nosocomial pneumonia

OBJECTIVE

To determine the steady-state plasma and epithelial lining fluid (ELF) concentrations of ceftazidime administered in continuous infusion to critically ill patients with severe nosocomial pneumonia.

DESIGN

Prospective, open-label study.

SETTING

An intensive care unit and research ward in a university hospital.

PATIENTS

A total of 15 adult patients with severe nosocomial bacterial pneumonia on mechanical ventilation were enrolled.

INTERVENTIONS

All subjects received a 30 min intravenous infusion of 2 g ceftazidime followed by a continuous infusion of 4 g over 24 h. The concentrations of ceftazidime in plasma and ELF were determined at steady-state after 2 days of therapy by high performance liquid chromatography.

MEASUREMENTS AND MAIN RESULTS

The mean +/-SD steady-state plasma and ELF concentrations of 4 g ceftazidime in continuous infusion were 39.6+/-15.2 microg/mL and 8.2+/-4.8 microg/mL, respectively, showing a mean +/-SD percentage penetration of ceftazidime into ELF of 20.6+/-8.9%.

CONCLUSION

The administration of 4 g ceftazidime in continuous infusion in critically ill patients with severe nosocomial pneumonia provides concentrations in excess of the minimal inhibitory concentration of many susceptible organisms over the course of therapy both in serum and ELF. However, for some pathogens such as P. aeruginosa, higher doses of ceftazidime should be administered, or another agent should be used in combination.

Pharmacokinetic interactions of ceftazidime, imipenem and aztreonam with amikacin in healthy volunteers

The common usage of extended spectrum beta-lactams co-administered with amikacin in everyday clinical practice for infections by multidrug-resistant isolates has created the need to search for pharmacokinetic interaction. Eighteen healthy volunteers were enrolled in the study; six were administered 1g of ceftazidime singly intravenously or combined with 0.5 g of amikacin; six received 0.5 g of imipenem singly or combined with 0.5 g of amikacin and six 1g of aztreonam singly or combined with 0.5 g of amikacin. Blood and urine samples were collected at regular time intervals and apparent serum levels were determined by a microbiological assay. Co-administration of ceftazidime and amikacin resulted in higher C(max) and AUC for amikacin than when administered alone. Co-administration of imipenem and amikacin resulted in higher C(max) for imipenem than when administered alone. The tested interactions did not affect plasma half-life (t(1/2)) and clearance rate of any antimicrobial compared with its single administration. All tested drugs were mainly eliminated by glomerular filtration. It is concluded that co-administration of ceftazidime, imipenem or aztreonam with amikacin in healthy volunteers might affect C(max) and AUC without influencing any other pharmacokinetic parameter. The probable clinical endpoint is that giving ceftazidime, imipenem or aztreonam with amikacin might result in a transient elevation of beta-lactam serum levels without further affecting the complete pharmacokinetic profile of each drug as obtained after administration of the drug alone.

Ceftazidime determination in serum by high-pressure liquid chromatography

A rapid and sensitive high-pressure liquid chromatographic method with simple sample preparation was developed for the quantitative analysis of the beta-lactam antibiotic ceftazidime (CAS 78439-06-2, Fortum). A good linear relationship was established between the peak area and the amount of ceftazidime injected over a concentration range of 1 to 200 microg/ml. The detection limit of the method was calculated to be 0.9 microg/ml. Stability was shown at 4 degrees C and at -196 degrees C for time periods of 2 h and 84 days, respectively.

Pharmacokinetics of ceftazidime in CAPD-related peritonitis

OBJECTIVE

The aim of this study was to measure and evaluate the appropriateness of the actual concentrations of serum and dialysate ceftazidime in Thai continuous ambulatory peritoneal dialysis (CAPD) patients.

DESIGN

Prospective and descriptive study of patients treated following the International Society for Peritoneal Dialysis (ISPD) 2000 recommendation for the empiric therapy of CAPD-related peritonitis.

SETTING

Institutional level of clinical care.

PATIENTS

CAPD-related peritonitis patients were diagnosed by dialysate effluent white blood cell count of more than 100/mm3 and polymorphonuclear leukocytes of at least 50%. There were 10 patients, all at least 18 years of age, entered; all completed the study.

INTERVENTION

In accordance with the ISPD 2000 recommendations, the antibiotic regimen comprised continuous intraperitoneal (i.p.) cefazolin and once-daily i.p. ceftazidime. Cefazolin was administered as loading and continuous maintenance doses of 500 and 125 mg/L dialysate respectively. Ceftazidime (20 mg/kg body weight) was given i.p. once daily. Duration of treatment was 96 hours.

MAIN OUTCOME MEASURES

Serum and dialysate effluent samples of the 10 CAPD patients with peritonitis were measured for ceftazidime levels, which were used for the development of pharmacokinetic equations that could predict drug concentrations at any treatment time.

RESULTS

Following ceftazidime administration as in the ISPD 2000 recommendation, serum ceftazidime levels were above 8 microg/mL, the minimum inhibitory concentration (MIC) recommended by NCCLS, throughout 24 hours. Dialysate ceftazidime levels were below the MIC for total periods of 4.19 and 6.26 hours in day 1 and day 4 respectively. The clinical response rate to the empiric regimen was 90%.

CONCLUSIONS

Once-daily i.p. administration of ceftazidime according to the ISPD 2000 recommendation could not provide adequately therapeutic levels of ceftazidime in dialysate throughout 24 hours. Despite this finding and the poor post-antibiotic property of ceftazidime, the empiric regimen including once-daily i.p. ceftazidime could yield good clinical outcome.

Clinical pharmacokinetics of cefamandole and ceftazidime administered by continuous intravenous infusion

In view of the results of animal studies as well as theoretical considerations, continuous administration of beta-lactam antibiotics should be superior to intermittent administration because of the close relationship between efficacy and the duration of time in which the concentration of unbound antibiotics in plasma remains above the MIC. The aim of the present study was to establish the pharmacokinetic parameters of cefamandole and ceftazidime for patients receiving these cephalosporins by continuous infusion. The interindividual differences in the concentrations in plasma at the steady state were mainly attributable to variations in renal function, as estimated by the rate of creatinine clearance. Using these results, we derived formulas for both cephalosporins that can be used to determine on an individual basis the total daily dose needed to obtain a therapeutic concentration in plasma. These formulas were tested with a group of subsequent patients and proved to be practical and fairly reliable. For some patients, a correction for a possible underestimation of the renal clearance at presentation might be required.

Optimizing ceftazidime pharmacodynamics in patients with acute exacerbation of severe chronic bronchitis

OBJECTIVES

Implementation of current pharmacodynamic knowledge could enhance clinical results, avoid resistance development and reduce treatment costs. In this open, randomized, multicentre study, we evaluated the clinical and bacteriological outcome and pharmacokinetic as well as pharmacodynamic parameters of two ceftazidime therapy regimens in patients with acute exacerbation of severe chronic bronchitis (AECB).

METHODS

Eighty-one patients (56 males, 25 females, age 65.3 +/- 10.1 years) with AECB were included. A subgroup of 21 patients underwent pharmacokinetic and pharmacodynamic examination. The patients received either ceftazidime 2 g every 8 h (C3 x 2) or ceftazidime 2 g as a loading dose, followed by ceftazidime 2 g over 7 h every 12 h (C2 x 2) for 8-14 days. Clinical and bacteriological responses were monitored at day 8 or 9, and 72 h after the end of therapy (EOT).

RESULTS

At EOT, clinical success was recorded in 90% and 90.2% of clinically evaluable patients receiving C3 x 2 and C2 x 2, respectively. Bacteriological success at EOT was achieved in 87.5% and 90.2% of evaluable patients treated with C3 x 2 and C2 x 2, respectively. C(max) (mg/L) varied between 168.9 +/- 34.1 and 144.0 +/- 9.8 in the C3 x 2 group, and between 60.1 +/- 34.1 and 54.2 +/- 30.4 at steady-state in the C2 x 2 group. Minimal concentrations were between 9.1 and 13.4 mg/L in the C3 x 2 group, and between 16.6 and 17.7 mg/L in the C2 x 2 group. Concentrations >4-5 x MIC were seen in all pathogens, except Staphylococcus aureus, during 100% of infusion time.

CONCLUSION

The 2 x 7 h infusion of ceftazidime 2 g (C2 x 2) was clinically and bacteriologically as effective as the usual 3 x 2 g ceftazidime short-term infusion in the treatment of AECB, and demonstrated advantages in terms of pharmacodynamic parameters compared with the C3 x 2 regimen.

A comparison of antibiotic regimens in the treatment of acute melioidosis in a mouse model

Melioidosis is caused by the Gram-negative bacillus Burkholderia pseudomallei. Most clinical reports of disease are from south-east Asia and northern Australia. The organism is intrinsically resistant to most commonly available antibiotics. Standard therapy includes ceftazidime either alone or in combination with co-trimoxazole. The clinical advantage in adding co-trimoxazole has never been determined; nor has the activity of newer, fourth-generation cephalosporins, such as cefepime, been studied in the treatment of this condition. BALB/c mice have been shown to represent an animal model of melioidosis. This animal model was used in this study to compare the efficacy of ceftazidime and cefepime alone or with co-trimoxazole, in the therapy of melioidosis. Antibiotic levels in the mice were determined by HPLC, and dosing was modified to keep plasma antibiotic levels at or above the MIC for the organism-antibiotic combination for a significant part of a 12 h period. Bacterial load, as determined by splenic counts, showed that ceftazidime in combination with co-trimoxazole was the most effective therapeutic option. The animal model described in this study can be used as a preliminary evaluation of therapeutic options for melioidosis.

Continuous infusion of ceftazidime in the empiric treatment of febrile neutropenic children with cancer

PURPOSE

Infection remains one of the most important complications in cancer therapy. The choice of antibiotics and the method of administration can affect results. Beta-lactam antibiotics can be administered by several short injections per day or by continuous infusion. The latter modality may provide superior pharmacokinetics.

PATIENTS AND METHODS

The authors studied the pharmacokinetics of ceftazidime in children treated for malignancy and in febrile aplasia after chemotherapy. They received a continuous infusion of ceftazidime (200 mg/kg/day) after a loading dose (65 mg/kg/day) administered with amikacin (25 mg/kg/day) and vancomycin (50 mg/kg/day). RESULTS Twenty-three pharmacokinetic studies were performed. Mean ceftazidime serum levels were 31.1 +/- 11.9, 31.2 +/- 10, 32.4 +/- 11.6, 33 +/- 11.6, and 30.4 +/- 12.1 mg/L at 25, 27, 30, 36, and 43 hours, respectively. Treatment was tolerated well. There were no toxic or infectious deaths.

CONCLUSIONS

Ceftazidime's time-dependent pharmacokinetics shows the advantage of continuous infusion. This study confirmed the feasibility and safety of this administration schedule in the empiric treatment of febrile neutropenic children with cancer.

Clearance of ceftazidime during continuous venovenous haemofiltration in critically ill patients

Published recommendations for the optimal dosing regimen of ceftazidime in critically ill patients with continuous venovenous haemofiltration (CVVH) differ. The aim of this prospective study was to analyse the pharmacokinetic and pharmacodynamic parameters of ceftazidime during CVVH with a high-flux polysulphone membrane, and derive a dosage recommendation. Twelve critically ill patients (five female, seven male) with acute renal failure undergoing CVVH using a 0.7 m(2) polysulphone high-flux membrane were investigated. All patients received ceftazidime 2 g i.v. q8h. Peak ceftazidime concentrations were 58.2 +/- 11.6 mg/L, with trough concentrations 14.0 +/- 3.2 mg/L at the arterial port. The elimination half-life, haemofiltration clearance, volume of distribution and total removal were 4.3 +/- 0.6 h, 32.1 +/- 7.9 mL/min, 36.4 +/- 6.4 L and 74.5 +/- 6.5%, respectively. Based on these pharmacokinetic parameters and that maximal killing is at 4 x MIC we recommend at least ceftazidime 2 g i.v. q8h.

Pharmacokinetics of ceftazidime in serum and peritoneal exudate during continuous versus intermittent administration to patients with severe intra-abdominal infections

Ceftazidime demonstrates time-dependent killing, which is maximal at 4 x or 5 x MIC for the organism, consequently continuous infusion (CI) has been proposed to ensure adequate ceftazidime concentrations for the entire course of therapy. Severe intra-abdominal infections (IAIs) require surgical or percutaneous drainage for management, and ceftazidime is frequently prescribed. Cardiovascular or metabolic changes and renal or liver dysfunction may alter drug pharmacokinetics during severe IAIs, and no data exist on concentrations of ceftazidime reached in the peritoneal fluid. The objectives here were to determine the pharmacokinetics of ceftazidime during continuous and intermittent administration in patients with severe IAIs, and to measure the concentrations of ceftazidime in the peritoneal exudate. Eighteen surgical patients with severe IAI and a creatinine clearance of >30 mL/min were studied. A non-randomized pilot study of six patients treated with CI alone was followed by a prospective, randomized comparative study of 12 patients. Pilot study patients received ceftazidime 1 g iv followed by a 4.5 g CI over 24 h. Randomized patients received either ceftazidime continuously as above or 1.5 g tds. Samples for pharmacokinetic analyses were collected on days 2 and 4. Ceftazidime concentrations were determined by high-performance liquid chromatography. CI resulted in a mean serum concentration >40 mg/L and a T> 4 x MIC for most pathogens encountered in severe IAIs for >90% of the course of therapy in both serum and peritoneal exudate. Eight-hourly administration resulted in T> 4 x MIC for most pathogens encountered in severe IAIs for >90% of the dosing interval, but in peritoneal exudate for only 44% of the dosing interval. During CI, AUCs in the peritoneal exudate were c. 60% of the concomitant serum AUCs. In critically ill surgical patients with severe IAIs, CI of ceftazidime resulted in more favourable concentrations in serum and peritoneal exudate than 8-hourly bolus infusion.

Effect of serum from different patient populations on the serum bactericidal test

We evaluated the effect of serum from normal and uraemic volunteers, neutropenic patients and burn patients on the serum bactericidal test. Serum samples were spiked with ceftazidime to mimic in vivo peak (75 mg/L) and trough (5 mg/L) concentrations. Serum inhibitory and bactericidal titres (SIT and SBT) were performed in triplicate using Escherichia coli ATCC 25922 and Pseudomonas aeruginosa ATCC 27853. For E. coli, the trough SIT and SBT were significantly higher in serum from burn patients compared with normal volunteers (P < or = 0.024). The trough SIT was significantly higher in serum from burn patients compared with neutropenic patients (P = 0.022) and in uraemic patients compared with normal volunteers (P = 0.04). No significant differences between subject populations were found for P. aeruginosa.

Vancomycin and ceftazidime bioactivities persist for at least 2 weeks in the lumen in ports: simplifying treatment of port-associated bloodstream infections by using the antibiotic lock technique

The residual antibiotic concentration of vancomycin (2 mg/ml)- or ceftazidime (2 mg/ml)-heparin solutions instilled in ports in pediatric hematology-oncology patients 1 to 34 days earlier was measured. Antibiotic concentrations of > or = 100 microg of either antibiotic per ml persisted for at least 21 days. For treatment of lumenal port infections, antibiotic-heparin dwell times of > or = 2 weeks may be appropriate.

Rapid antibiotic drug monitoring: meropenem and ceftazidime determination in serum and bronchial secretions by high-performance liquid chromatography-integrated sample preparation

A sensitive and rapid HPLC assay for the determination of the beta-lactam antibiotics ceftazidime and meropenem in serum and bronchial secretions is described. HPLC-integrated sample preparation allows direct injection of serum samples without any pretreatment. Sputum samples need only a simple homogenisation and volume measurement but no liquefying reagents are necessary. The inline extraction technique is realized by automatically switching from the extraction column to the analytical column. After the matrix passed the extraction column, the retained analyte is quantitatively transferred to the analytical column where separation by isocratic HPLC is performed. Ceftazidime and meropenem are detected according to their absorption maxima at 258 and 296 nm, respectively. The detection limit of both antibiotics is estimated to be better than 0.5 microg/ml in serum as well as in sputum samples. The described procedure allows determination of the antibiotics within 30-45 min, thereby facilitating drug monitoring in clinical routine.

Measurement and pharmacokinetic analysis of unbound ceftazidime in rat blood using microdialysis and microbore liquid chromatography

To evaluate the biodisposition of ceftazidime in rat blood, a rapid and simple microbore liquid chromatographic technique together with a microdialysis sampling technique were developed. This method involves an on-line design for blood dialysate directly injected into a microbore liquid chromatographic system. The chromatographic conditions consisted of a mobile phase of methanol-acetonitrile-100 mM monosodium phosphoric acid (pH 3.0) (10:10:80, v/v/v) pumped through a microbore reversed-phase column at a flow-rate of 0.05 ml/min. With the detection wavelength set at 254 nm, a good linear correlation was observed between the peak area and the ceftazidime concentration at 0.1 to 50 microg/ml (r=0.999). Microdialysis probes, being custom-made, were screened for acceptable in vivo recovery while chromatographic resolution and detection were validated for response linearity, as well as intra-day and inter-day variabilities. This method was then applied to the pharmacokinetic profiling of ceftazidime in blood following intravenous 50 mg/kg administration to rats. The pharmacokinetics was calculated from the corrected data for dialysate concentrations of ceftazidime versus time. This method has been used to study ceftazidime pharmacokinetics in rats and has proven to be rapid and reproducible.

Pharmacokinetics of ceftazidime in dogs following subcutaneous administration and continuous infusion and the association with in vitro susceptibility of Pseudomonas aeruginosa

OBJECTIVE

To determine the pharmacokinetics of ceftazidime following subcutaneous administration and continuous IV infusion to healthy dogs and to determine the minimum inhibitory concentration (MIC) of ceftazidime for clinical isolates of Pseudomonas aeruginosa.

ANIMALS

10 healthy adult dogs.

PROCEDURE

MIC of ceftazidime for 101 clinical isolates of P aeruginosa was determined in vitro. Serum concentrations of ceftazidime were determined following subcutaneous administration of ceftazidime (30 mg/kg of body weight) to 5 dogs and continuous IV infusion of ceftazidime (loading dose, 4.4 mg/kg; infusion rate, 4.1 mg/kg/h) for 36 hours to 5 dogs.

RESULTS

The MIC of ceftazidime for P aeruginosa was < or = 8 microg/ml; all isolates were considered susceptible. Following SC administration of ceftazidime, mean beta disappearance half-life was 0.8 hours, and mean serum ceftazidime concentration exceeded the MIC for P aeruginosa for only 4.3 hours. Two dogs had gastrointestinal tract effects. Mean serum ceftazidime concentration exceeded 16 microg/ml during continuous IV infusion. None of the dogs developed adverse effects.

CONCLUSIONS AND CLINICAL RELEVANCE

Administration of ceftazidime subcutaneously (30 mg/kg, q 4 h) or as a constant IV infusion (loading dose, 4.4 mg/kg; rate, 4.1 mg/kg/h) would maintain serum ceftazidime concentrations above the MIC determined for 101 clinical isolates of P aeruginosa. Use of these dosages may be appropriate for treatment of dogs with infections caused by P aeruginosa.

Changes of the serum antibiotic levels during open heart surgery (ceftazidim, ciprofloxacin, clindamycin)

BACKGROUND

Wound, mediastinal and intracardiac infections are still very serious complications of open-heart surgery. The incidence of it is still in the range of 0.4%-5%. The aims of our study were to assess the adequacy of regimen using ceftazidim (CTZ), ciprofloxacin (CPF) and clindamycin (CLIN) as prophylactic antibiotics and to verify whether cardiopulmonary bypass (CPB) can modify the time of antibiotic serum concentrations. That is why the serum levels of them were measured during open heart procedures.

METHODS

The prospective study comprised 75 consequent coronary patients randomized in to three groups receiving 1 g of CTZ or 400 mg of CPF or 900 mg of CLIN i.v. with anesthesia induction. Routine coronary surgery with left internal mammary artery harvesting, moderate body hypothermic (30 degrees C) CPB with crystaloid cardioplegia was performed. Serum antibiotic levels were determined before application, with skin incision, prior CPB induction, after cardioplegia infusion, every 20 minutes of CPB, prior end of CPB, in time of chest closure. Conventional cylinder-plate microbiological assay was used for antibiotic level measurement.

RESULTS

All serum antibiotic concentrations showed a sharp decrease immediately after starting CPB and lasted until CPB ended. After initiating of CPB after cardioplegia administration serum concentrations of CTZ (105 min after initial dose) decreased by, on average 55%, CPF (97 min) by 42% and CLIN (116 min) by 78%.

CONCLUSION

CPB can modify the time course of antibiotic serum concentrations. The serum levels of CTZ at the end of the longest procedures were found to be below the MICs for some of the suspected pathogens. We recommend to use higher antibiotic doses for prophylaxis and to administer the second dose with protamin sulphate to obtain maximum concentration in newly formed blood clots.

Serum bactericidal and inhibitory titres in the management of melioidosis

A retrospective evaluation of the relationship between serum bactericidal and inhibitory titres and treatment outcome in 195 adult Thai patients with severe melioidosis was conducted. Drug regimens included ceftazidime (52% of patients), co-amoxiclav (24%), imipenem (11%) or the conventional four-drug combination (11%). Pre- and 1 h post-dose serum samples were collected after 48-72 h of therapy, and serum inhibitory and bactericidal titrations determined. Median post-dose titres were: bactericidal 1:8 (range 0-1:128) and inhibitory 1:16 (range 0-1:128). Overall mortality was 26% and outcome was not influenced by either inhibitory or bactericidal titres. Pre-dose titres correlated with renal function; renal function was the most important predictor of mortality. Determination of serum inhibitory or bactericidal titres is unhelpful in the management of severe melioidosis.

Comparison of five beta-lactam antibiotics against common nosocomial pathogens using the time above MIC at different creatinine clearances

STUDY OBJECTIVE

To compare the time above the minimum inhibitory concentration (T>MIC) for five parenteral beta-lactam antibiotics against common nosocomial bacterial pathogens at different creatinine clearances (Clcr).

INTERVENTIONS

Serum concentration-time profiles were simulated for cefepime, ceftazidime, piperacillin, piperacillin-tazobactam, and imipenem at Clcr ranging from 120-30 ml/minute. The MIC data for 90% of organisms (MIC90) were collected for Escherichia coli, Klebsiella pneumoniae, Serratia marcescens, Citrobacter freundii, Enterobacter aerogenes, Enterobacter cloacae, Pseudomonas aeruginosa, and oxacillin-susceptible Staphylococcus aureus, and a weighted geometric mean MIC90 was calculated. The T>MIC was calculated as percentage of the dosing interval in which free concentrations exceeded the weighted geometric mean MIC90. A T>MIC of 70% or greater was considered desirable for all organisms except S. aureus (> or = 50%).

MEASUREMENTS AND MAIN RESULTS

Cefepime 2 g every 12 hours (Clcr > or = 70 ml/min) and every 24 hours (Clcr < or = 60 ml/min) achieved desirable T>MIC for all Enterobacteriaceae and S. aureus at every Clcr. Imipenem 0.5 g achieved desirable T>MIC for E. coli, K. pneumoniae, C. freundii, and S. aureus at every Clcr. However, imipenem T>MIC was less than 70% for the following regimens and organisms: S. marcescens 0.5 g every 6 hours (Clcr > or = 90 ml/min), E. aerogenes 0.5 g every 6 hours (Clcr > or = 80 ml/min), E. cloacae 0.5 g every 6 hours (Clcr > or = 100 ml/min), S. marcescens 0.5 g every 8 hours (Clcr 60-70 ml/min), E. cloacae 0.5 g every 8 hours (Clcr 60-70 ml/min), and E. aerogenes 0.5 g every 8 hours (Clcr 50-70 ml/min). Ceftazidime 2 g every 8 hours (Clcr 60-100 ml/min) and every 12 hours (Clcr 40-50 ml/min) achieved desirable T>MIC for E. coli, K. pneumoniae, S. marcescens, and S. aureus only. At every dose and Clcr, piperacillintazobactam achieved desirable T>MIC for S. aureus but not for any Enterobacteriaceae at Clcr > 50 ml/minute. Piperacillin did not achieve desirable T>MIC for any organism, and none of the beta-lactams attained a T>MIC of 70% or above for P. aeruginosa at any Clcr.

CONCLUSION

At every Clcr, cefepime achieved a desirable T>MIC for more nosocomial pathogens than any other beta-lactam evaluated. Based on pharmacodynamic data, cefepime is an appropriate empiric choice for treatment of nosocomial infections. However, when P. aeruginosa is a potential pathogen, empiric combination therapy should be considered.

Microdialysis for pharmacokinetic studies of ceftazidime in rabbit vitreous

The method of microdialysis was used for collecting series of samples from the rabbit vitreous after systemic and intravitreous administration of ceftazidime. The purpose of the study was to compare the method with traditional pharmacokinetic sampling. Ceftazidime was injected intramuscularly (1 mg/kg) or intravitreally (1 mg) in rabbits, with a previously implanted microdialysis probe in the vitreous. The membrane was perfused with a buffer, and the dialysate was collected in samples where the concentration of the drug was analyzed by HPLC. After intramuscular administration, blood samples were taken to calculate systemic pharmacokinetics. The same procedures were repeated with rabbits with mild intraocular inflammation induced by the injection of 400 EU of endotoxin into the vitreous, 12-15 hr before drug administration. Pharmacokinetic parameters, such as half-life and AUC, were calculated. The penetration into the vitreous after intramuscular injection was higher (42%) in inflamed than in non-inflamed eyes (20%), suggesting an interference with the blood retinal barrier. Other kinetic parameters did not differ significantly between the groups. The advantage of the method is that fewer experimental animals can be used to obtain the necessary data compared to traditional pharmacokinetic methods. In conclusion, intraocular dialysis with chronically implanted probes is a technique well suited for pharmacokinetic studies of systemically administered ceftazidime or other drugs that will pass a dialysis membrane.

Antibiotic dosing issues in lower respiratory tract infection: population-derived area under inhibitory curve is predictive of efficacy

Several lower respiratory tract infection (LRTI) trials have documented a correlation between clinical response and area under the inhibitory curve (24 h AUC/MIC; AUIC). The AUIC values in these studies were based on measured MICs and measured serum concentrations. This study evaluates AUIC estimates made using population pharmacokinetic parameters, and MICs from an automated microbiological susceptibility testing system. A computer database review over 2 years yielded 81 patients at Millard Fillmore Hospital with a culture-documented gram-negative LRTI who had been treated with piperacillin and an aminoglycoside, ceftazidime, ciprofloxacin or imipenem. Their AUIC values were estimated using renal function, drug dosages and MIC values. Outcome groups (clinical and microbiological cures and failures) were related to the AUIC values using Kruskal-Wallis ANOVA, linear regression and classification and regression tree (CART) analysis. A significant breakpoint for clinical cures was an AUIC value at least 72 SIT(-1) x 24 h (inverse serum inhibitory titre integrated over time). All antibiotics performed significantly better above this value than below it. Clinical cure was well described by a Hill-type equation. Within the piperacillin/aminoglycoside regimen, most of the activity came from the piperacillin, which had a higher overall AUIC value than the aminoglycoside. AUIC estimations based upon MIC values derived from the automated susceptibility testing method differed from NCCLS breakpoint data and from tube dilution derived values in this hospital by as much as three tube dilutions. These automated methods probably overestimated the MIC values of extremely susceptible organisms. The lack of precise MIC estimates in automated clinical microbiology methods impairs the use of AUIC to prospectively optimize microbiological outcome. Even ignoring this limitation and using the values as they are reported, the results of this analysis suggest that AUIC targets between 72 and 275 SIT(-1) x 24 h are useful in predicting clinical outcome.

Continuous infusion ceftazidime in intensive care: a randomized controlled trial

We randomized 18 critically ill patients to receive ceftazidime 6 g/day by continuous infusion or bolus dosing (2 g 8 hourly), each with a loading dose of 12 mg/kg ceftazidime. During the first 8 h, plasma ceftazidime concentration fell below 40 mg/L in only one patient (trough 38 mg/L) from the infusion group, compared with eight from the bolus group (2-33 mg/L) for periods ranging from 73 to 369 min. Thereafter all infusion patients remained above 40 mg/L for 40 h of study versus 20-30% of bolus patients. The pharmacokinetic and pharmacodynamic characteristics of ceftazidime suggest that continuous infusions should be clinically investigated in outcome studies.

Comparison of ex-vivo serum bactericidal activity of cefepime, ceftazidime and cloxacillin against Staphylococcus aureus

Cefepime (1 g), ceftazidime (1 g), and cloxacillin (2 g) were administered intravenously to 10 volunteers each. After infusion of a single dose over 30 min, blood samples were obtained at 0.5, 1, 2, 3, 4, 5, 6, 8, 10, and 12 h (for ceftazidime at 0.5 and 4 h) after dosing. Drug levels were determined by the bioassay method. Serum bactericidal activity against five clinical isolates of cloxacillin-susceptible Staphylococcus aureus were determined by the microdilution method according to the National Committee for Clinical Laboratory Standards guidelines. The mean peak serum level was 76.88 +/- 24.71 mg/L for cefepime, 42.8 +/- 15.98 mL/L for ceftazidime, and 92.81 +/- 24.7 mg/L for cloxacillin. Concentrations of cefepime were detected during the whole testing period (mean trough level, 1.43 +/- 0.9 mg/L at 12 h), whereas concentrations of cloxacillin were measurable up to 5 h after administration (mean trough level, 0.90 +/- 0.97 mg/L). The mean peak reciprocal bactericidal titers were 29.41 for cefepime, 5.6 for ceftazidime, and 377 for cloxacillin. Effective bactericidal titers were detected as long as 5 h for cefepime (approximately 40% of the dosing interval) and 3 h for cloxacillin (at least 50% of the dosing interval). For ceftazidime, serum bactericidal activity was markedly lower compared with that of cefepime. Although cefepime has demonstrated an improved antistaphylococcal bactericidal activity compared with ceftazidime, it was somewhat lower than that of cloxacillin.

Determination of ceftazidime in plasma using high-performance liquid chromatography and electrochemical detection. Application for individualizing dosage regimens in elderly patients

This study describes a sensitive HPLC-electrochemical detection method for the analysis of ceftazidime, a third-generation cephalosporin, in human plasma. The extraction procedure involved protein precipitation with 30% trichloroacetic acid. The separation was achieved on a reversed-phase column (250X4.6 mm I.D., 5 microm) packed with C18 Kromasil with isocratic elution and a mobile phase consisting of acetonitrile-25 mM KH2PO4-Na2HPO4 buffer, pH 7.4 (10:90, v/v). The proposed analytical method is selective, reproducible and reliable. The assay has a precision of 0.2-15.1% (C.V.) in the range of 5-200 microg mil(-1). (corresponding to 0.5 to 20 ng of ceftazidime injected onto the column), and is optimised for assaying 50 microl of plasma. The extraction recovery from plasma was approximately 100%. The method was highly specific for ceftazidime and there was no interference from either commonly administered drugs or endogenous compounds. This assay was used to measure ceftazidime in elderly patients for therapeutic drug monitoring.

Alternative method for determination of ceftazidime in plasma by high-performance liquid chromatography

A high-performance liquid chromatography procedure was developed to analyze ceftazidime concentrations in plasma. The procedure consisted of solid phase extraction followed by ion-pairing reverse-phase chromatography. An excellent linear relationship between ceftazidime peak height measurements and concentrations was demonstrated over the concentration range of 1-200 microg ml(-1). The advantage of this assay is the elimination of interference at the ceftazidime elution time that has been noted in previous studies and in our experience. Thus, this study describes an alternative, simple methodology that is clinically useful for analyzing ceftazidime in the research setting.