Population pharmacokinetics and pharmacodynamics of piperacillin/tazobactam in patients with complicated intra-abdominal infection

OBJECTIVES

We investigated the population pharmacokinetics and pharmacodynamics of piperacillin and tazobactam in hospitalized patients.

PATIENTS AND METHODS

A multicentre, randomized clinical trial was conducted in hospitalized patients with complicated intra-abdominal infection. Patients received piperacillin/tazobactam administered by either continuous infusion (13.5 g over 24 h, n = 130) or intermittent infusion (3.375 g every 6 h, n = 132). NONMEM was used to perform population pharmacokinetic analysis in a subset of patients (n = 56) who had serum samples obtained at steady-state for drug concentration analyses. Classification and regression tree analysis was used to identify the breakpoints of piperacillin PK-PD indexes in 94 patients with causative pathogen's MIC.

RESULTS

A one-compartment model was applied to fit the data. Creatinine clearance and body weight were the most significant variables to explain patient variability in piperacillin and tazobactam clearance and volume of distribution. The infusion method had no influence on PK parameters. For patients (n = 30) receiving intermittent infusion in the pharmacokinetic study, mean Cmax and half-life were 122.22 mg/L and 1.17 h for piperacillin, and 15.74 mg/L and 1.81 h for tazobactam. For patients (n = 26) receiving continuous infusion in the pharmacokinetic study, mean steady-state concentration was 35.31 +/- 12.15 mg/L for piperacillin and 7.29 +/- 3.28 mg/L for tazobactam. As a result of a low rate of failures (<11%) observed in the trial and the low MICs for infecting pathogens, no association could be established between clinical/microbiological outcome and drug exposure.

CONCLUSIONS

Intermittent infusion and continuous infusion of piperacillin and tazobactam provided sufficient drug exposure to treat those pathogens commonly implicated in intra-abdominal infections.

Effect of opsonophagocytosis mediated by specific antibodies on the co-amoxiclav serum bactericidal activity against Streptococcus pneumoniae after administration of a single oral dose of pharmacokinetically enhanced 2000/125 mg co-amoxiclav to healthy volunteers

OBJECTIVES

To measure the effect of opsonophagocytosis mediated by complement activated by specific antibodies on the co-amoxiclav serum bactericidal activity against Streptococcus pneumoniae strains with reduced susceptibility to beta-lactams (amoxicillin MICs of 2, 4, 8 and 16 mg/L).

METHODS

An open Phase I study measuring ex vivo bactericidal activity after anti-pneumococcal vaccination and an oral dose of 2000/125 mg sustained-release co-amoxiclav was carried out. The ex vivo bactericidal activity was investigated through killing curves over 3 h [assuring polymorphonuclear neutrophil (PMN) viability] with serum samples collected 1.5 h and 5 h after dosing. Global killing was measured as the area under the killing curve (AUKC; log cfu x h/mL). The AUKC of the control growth curve of S. pneumoniae in Hanks' balanced salt solution (AUKC(K)) was used as control. The effect of the presence of complement and/or PMN was evaluated by the difference in the AUKC(K) and the different AUKCs obtained in the presence of inactivated serum (AUKC(IS)), active serum (AUKC(S)), inactivated serum plus PMN (AUKC(IS+PMN)) and active serum plus PMN (AUKC(S+PMN)).

RESULTS

Significant differences were found in all cases between the bactericidal activity of active serum+PMN (AUKC(K) - AUKC(S+PMN)) and that of inactivated serum (AUKC(K) - AUKC(IS)) with therapeutic indexes ranging from 0.56 to 3.04. At 1.5 h after dosing, a significantly higher bactericidal activity of co-amoxiclav was obtained when opsonophagocytosis occurred (samples with active serum and PMN) than when not occurring (killing curves with inactivated serum and without PMN), for all amoxicillin non-susceptible strains.

CONCLUSIONS

The results of this ex vivo study suggest that the collaboration of co-amoxiclav and complement-mediated opsonophagocytosis activated by specific antibodies may lay new approaches to overcome in vivo amoxicillin non-susceptibility.

[Pharmacokinetic/pharmacodynamic analysis of antibiotic therapy in dentistry and stomatology]

INTRODUCTION

This study evaluates the efficacy of various antimicrobial treatments for orofacial infections on the basis of pharmacokinetic/pharmacodynamic (PK/PD) criteria.

METHODS

A complete a literature search was undertaken to establish the MIC90 values of the five microorganisms most frequently isolated in odontogenic infections and the pharmacokinetic parameters of 13 antibiotics used in these infections. Pharmacokinetic simulations were then carried out with mean population parameters and efficacy indexes were calculated for the 47 treatment regimens analyzed. For drugs showing time-dependent antibacterial killing, the time above MIC (t > MIC) was calculated. For drugs with concentration-dependent bactericidal activity, the AUC/MIC was calculated.

RESULTS

Amoxicillin-clavulanic (500 mg/8 h or 1000 mg/12 h) and clindamycin (300 mg/6 h) in the time-dependent killing group and moxifloxacin (400 mg/24 h) in the concentration-dependent group showed adequate efficacy indexes against the five pathogens considered to be the most commonly implicated in odontogenic infections. The spiramycin plus metronidazole combination, present in the commercial formulation Rhodogyl, did not reach satisfactory PK/PD indexes.

CONCLUSION

PK/PD indexes, which are useful predictors of the potential efficacy of antibacterial therapy, were used with ontogenic infections in the present study. The PK/PD simulations showed that amoxicillin-clavulanic, clindamycin and moxifloxacin were the most suitable antibiotics for this kind of infection. Clinical trials are required to confirm that this methodology is useful in these pathologic processes.

Pharmacokinetics of a combination preparation of ampicillin and sulbactam in turkeys

OBJECTIVE

To investigate the disposition kinetics of ampicillin and sulbactam after IV and IM administration of an ampicillin-sulbactam (2:1) preparation and determine the bioavailability of the combined preparation after IM administration in turkeys.

ANIMALS

10 healthy large white turkeys.

PROCEDURE

In a crossover study, turkeys were administered the combined preparation IV (20 mg/kg) and IM (30 mg/kg). Blood samples were collected before and at intervals after drug administrations. Plasma ampicillin and sulbactam concentrations were measured by use of high-performance liquid chromatography; plasma concentration-time curves were analyzed via compartmental pharmacokinetics and noncompartmental methods.

RESULTS

The drugs were distributed according to an open 2-compartment model after IV administration and a 1-compartment model (first-order absorption) after IM administration. For ampicillin and sulbactam, the apparent volumes of distribution were 0.75+/-0.11 L/kg and 0.74+/-0.10 L/kg, respectively, and the total body clearances were 0.67+/-0.07 L x kg(-1) x h(-1) and 0.56+/-0.06 L x kg(-1) x h(-), respectively. The elimination half-lives of ampicillin after IV and IM administration were 0.78+/-0.12 hours and 0.89+/-0.17 hours, respectively, whereas the corresponding half-lives of sulbactam were 0.91+/-0.12 hours and 0.99+/-0.16 hours, respectively. Bioavailability after IM injection was 58.87+/-765% for ampicillin and 53.75+/-5.35% for sulbactam.

CONCLUSIONS AND CLINICAL RELEVANCE

Results indicated that a regimen of loading and maintenance doses of 300 mg of the ampicillin-sulbactam (2:1) combination/kg every 8 hours could be clinically useful in turkeys. This dosage regimen maintained plasma concentrations of ampicillin > 0.45 microg/mL in turkeys.

Pharmacodynamic studies of amoxicillin against Streptococcus pneumoniae: comparison of a new pharmacokinetically enhanced formulation (2000 mg twice daily) with standard dosage regimens

OBJECTIVES

To compare the pharmacodynamic effects of a pharmacokinetically enhanced formulation of amoxicillin 2000 mg twice daily, with amoxicillin 875 mg twice daily, 875 mg three times daily and 500 mg three times daily against Streptococcus pneumoniae with different susceptibility to amoxicillin in an in vitro kinetic model.

METHODS

Strains of S. pneumoniae with amoxicillin MICs of 1, 2, 4 and 8 mg/L at an initial inoculum of approximately 10(5) cfu/mL were exposed to amoxicillin in an in vitro kinetic model simulating the human serum concentration-time profile of the pharmacokinetically enhanced formulation twice daily (C(max) 17 mg/L after 1.5 h). All isolates were also exposed to amoxicillin with concentration-time profiles correlating to the human dosage of 875 mg twice daily (C(max) 15 mg/L after 1 h), 875 mg three times daily and 500 mg (C(max) 8 mg/L after 1 h) three times daily with simulated half-life of 1 h. Repeated samples were taken regularly during 24 h and viable counts were carried out.

RESULTS

Overall, the pharmacokinetically enhanced formulation was more effective at reducing bacterial counts than any of the other formulations evaluated. Eradication was achieved with the enhanced formulation for strains with a MIC of < or =2 mg/L, however, regrowth occurred with the other dosing regimens. In the experiments with the strain with a MIC of 4 mg/L, the enhanced formulation kept the bacterial counts < or =10(2) cfu/mL for at least 14 out of 24 h tested. In contrast, none of the other formulations reduced the bacterial counts down to < or =10(2) cfu/mL at any point. None of the regimens was able to eradicate the strain with an MIC of 8 mg/L, even though an initial substantial kill was noted with the enhanced formulation after both doses. The least effective dosage regimen for all strains was 875 mg twice daily.

Double-blind, randomized study of the efficacy and safety of oral pharmacokinetically enhanced amoxicillin-clavulanate (2,000/125 milligrams) versus those of amoxicillin-clavulanate (875/125 milligrams), both given twice daily for 7 days, in treatment of bacterial community-acquired pneumonia in adults

This randomized, double-blind, noninferiority trial was designed to demonstrate that pharmacokinetically enhanced amoxicillin-clavulanate (2,000/125 mg) was at least as effective clinically as amoxicillin-clavulanate 875/125 mg, both given twice daily for 7 days, in the treatment of community-acquired pneumonia in adults. In total, 633 clinically and radiologically confirmed community-acquired pneumonia patients (intent-to-treat population) were randomized to receive either oral amoxicillin-clavulanate 2,000/125 mg (n = 322) or oral amoxicillin-clavulanate 875/125 mg (n = 311). At screening, 160 of 633 (25.3%) patients had at least one typical pathogen isolated from expectorated or invasive sputum samples or blood culture (bacteriology intent-to-treat population). Streptococcus pneumoniae (58 of 160, 36.3%), methicillin-susceptible Staphylococcus aureus (34 of 160, 21.3%), and Haemophilus influenzae (33 of 160, 20.6%) were the most common typical causative pathogens isolated in both groups in the bacteriology intent-to-treat population. Clinical success in the clinical per protocol population at test of cure (days 16 to 37), the primary efficacy endpoint, was 90.3% (223 of 247) for amoxicillin-clavulanate 2,000/125 mg and 87.6% (198 of 226) for amoxicillin-clavulanate 875/125 mg (treatment difference, 2.7; 95% confidence interval, -3.0, 8.3). Bacteriological success at test of cure in the bacteriology per protocol population was 86.6% (58 of 67) for amoxicillin-clavulanate 2,000/125 mg and 78.4% (40 of 51) for amoxicillin-clavulanate 875/125 mg (treatment difference, 8.1%; 95% confidence interval, -5.8, 22.1). Both therapies were well tolerated. Amoxicillin-clavulanate 2,000/125 mg twice daily was shown to be as clinically effective as amoxicillin-clavulanate 875/125 mg twice daily for 7 days in the treatment of adult patients with community-acquired pneumonia, without a noted increase in the reported rate of adverse events.

Effect of the formulation on the bioequivalence of sultamicillin: tablets and suspension

Sultamicillin (CAS 76497-13-7) is a pro-drug of a combination of ampicillin and sulbactam linked as a double ester. The aim of the present studies, performed in two different groups of volunteers, was to compare the bioavailability of 750 mg sultamicillin tablets (Duobaktam 750 mg tablets, study 1) and sultamicillin 250 mg/5mL suspensions (Duobaktam 250 mg/5mL, study 2). Each study was conducted according to an open, randomized, single-dose, two-period cross-over design in 24 healthy volunteers with a wash-out period from 7 to 14 days. Blood samples were taken up to 12 h post dosing, and concentrations of ampicillin and sulbactam were determined by a HPLC-UV method. In the first study, the 90% confidence interval for intra-individual ratios of AUC0-t and Cmax of ampicillin and sulbactam were between 1.01-1.18 and 0.95-1.09 (AUC0-t) as well as between 0.87-1.04 and 0.80-0.96 (Cmax), respectively, and thus within the acceptance ranges. The 90% confidence interval for intra-individual ratios of AUC0-t and Cmax of sultamicillin suspensions (2nd study) were between 0.94-1.16 (ampicillin) and 0.92-1.14 (sulbactam) for AUC0-t and between 0.96-1.23 (ampicillin) and 0.97-1.24 (sulbactam) for Cmax. These values were also within the acceptance range for bioequivalence studies. Concerning the secondary parameter tmax the 90%-confidence interval for the intra-individual differences for both ampicillin and sulbactam were between 0.00-0.50 in the first and between -0.17-0.00 in the second study, respectively. In the light of the present studies it can be concluded that the sultamicillin test formulations, i.e. tablet and suspension are bioequivalent to the respective reference formulations.

[Optimization of amoxicillin/clavulanate therapy based on pharmacokinetic/pharmacodynamic parameters in patients with diabetic foot infection]

AIM OF THE STUDY

Individualized optimization of amoxicillin/clavulanate (AMC) antimicrobial therapy in diabetic foot infection.

METHODS

Pharmacokinetic analysis of individual steady-state plasma amoxicillin concentrations was done both in the i.v. infusion phase and in the oral phase of AMC, administered on the basis of the quantitative susceptibility of the detected microbe(s). The in vitro growth/killing dynamic parameters on model of Staphylococcus aureus as the most frequent isolate were evaluated. Therapeutic protocol optimization, leading to prediction of the earliest time to reduce the number of viable bacteria to 10-6 as a surrogate criterion of efficacy, was performed.

RESULTS

Based on individual plasma amoxicillin oscillations in 17 patients suffering from infected diabetic foot ulcers and the model microbial dynamic parameters, the reduction of the number of viable bacteria was reached significantly earlier after the administration of continuous i.v. AMC infusion than after the same daily AMC dose administered intermittently. In case of highly susceptible staphylococcal strain, highly frequent oral therapy of AMC (not longer than 8 hrs dosing interval) was also sufficiently effective. Decreasing plasma amoxicillin concentrations exponentially extended the time required for effective reduction of microbes.

CONCLUSION

Individualized optimization of amoxicillin/clavulanate dosage on the basis of growth/killing microbial dynamic parameters and antibiotic concentration/time fluctuations may enhance the antimicrobial effect and the treatment of infected non-critical ischemic diabetic foot ulcers.

Antibacterial effects of amoxicillin-clavulanate against Streptococcus pneumoniae and Haemophilus influenzae strains for which MICs are high, in an in vitro pharmacokinetic model

The antibacterial effect of amoxicillin-clavulanate in two formulations, pharmacokinetically enhanced 16:1 amoxicillin-clavulanate twice a day (b.i.d.) and standard 7:1 amoxicillin-clavulanate b.i.d., were studied in an in vitro pharmacokinetic model of infection. Five strains of Streptococcus pneumoniae and two of Haemophilus influenzae, all associated with raised MICs (2 to 8 mg/liter), were used. The antibacterial effect was measured over 24 h by the area under the bacterial kill curve (AUBKC) and the log change in viable count at 24 h (Delta24). A high 10(8) CFU/ml and low 10(6) CFU/ml initial inocula were used. Employing the Delta24 effect measure, the time above MIC (T>MIC) 50% maximum effect (EC(50)) for S. pneumoniae was in the range 21 to 28% with an 80% maximal response of 41 to 51%, for the AUBKC measure, the value was 26 to 39%, irrespective of inoculum. For H. influenzae, the T>MIC EC(50) was 28 to 37%, and the 80% maximum response was 32 to 48% for the Delta24 measure and 20 to 48% for AUBKC. The maximum response occurred at a T>MIC of 50 to 60% for both species and inocula. The S. pneumoniae data were analyzed by analysis of variance to assess the effect of inoculum, formulation, and MIC on antibacterial effect. Standard and enhanced formulations had different effects depending on MIC, with the standard formulation less effective at higher amoxicillin-clavulanate MICs. This is explained by the greater T>MICs of the enhanced formulation. Although resistant to amoxicillin-clavulanate by conventional breakpoints, S. pneumoniae and H. influenzae strains for which MICs are 2 or 4 mg/liter may well respond to therapy with pharmacokinetically enhanced formulation amoxicillin-clavulanate.

Amoxicillin/clavulanic acid (875/125): bioequivalence of a novel Solutab tablet and rationale for a twice-daily dosing regimen

A new amoxicillin/clavulanic acid tablet formulation (Solutab tablet, Forcid Solutab) containing amoxicillin/clavulanic acid (875/125) has been developed. The aim of the present study was to demonstrate bioequivalence between the new tablet formulation (test), taken as an intact tablet and after prior dispersal, versus the originator product viz. Augmentan film-coated tablet (875/125) used as reference. The study was performed in 48 healthy volunteers according to an open, single-dose, crossover design. Bioequivalence was demonstrated using Cmax and AUC(0-infinity) as primary parameters of evaluation for both amoxicillin and clavulanic acid with 90% confidence intervals of the ratios Solutab tablet/Augmentan within the range of 0.8-1.25. The duration of the plasma concentration exceeding the amoxicillin minimal inhibitory concentration (MICs) was calculated using individual plasma concentration-time curves and compartmental analysis. The data showed that the bioavailability characteristics of the test tablet, taken intact or in dispersed form, and the reference tablets were very similar. The analysis, moreover, also confirmed the appropriateness of using a b.i.d. dosage regimen for both formulations, taking into account the pharmacodynamic breakpoint values for some major pathogens.

Effect of antibiotic sequence on combination regimens against Pseudomonas aeruginosa in a multiple-dose, in vitro infection model

The goal of this study was to investigate the effect of antibiotic sequence on combination regimens against Pseudomonas aeruginosa in an in vitro infection model. Ceftazidime plus ciprofloxacin and ceftazidime plus tobramycin were dosed every 12 h for 48 h using simultaneous or staggered administration. Simultaneous dosing and ceftazidime followed by ciprofloxacin or tobramycin were significantly more active at both 24 h (p = 0.03) and 48 h (p < 0.0001) than ciprofloxacin or tobramycin followed by ceftazidime. Final bacterial kill was sixfold greater with the former regimens. This study showed that antibiotic sequence had a significant and class dependent effect on antibacterial response. The clinical relevance of these observations warrants further investigations in animal models.

Augmentin (amoxicillin/clavulanate) in the treatment of community-acquired respiratory tract infection: a review of the continuing development of an innovative antimicrobial agent

Amoxicillin/clavulanate (Augmentin) is a broad-spectrum antibacterial that has been available for clinical use in a wide range of indications for over 20 years and is now used primarily in the treatment of community-acquired respiratory tract infections. Amoxicillin/clavulanate was developed to provide a potent broad spectrum of antibacterial activity, coverage of beta-lactamase-producing pathogens and a favourable pharmacokinetic/pharmacodynamic (PK/PD) profile. These factors have contributed to the high bacteriological and clinical efficacy of amoxicillin/clavulanate in respiratory tract infection over more than 20 years. This is against a background of increasing prevalence of antimicrobial resistance, notably the continued spread of beta-lactamase-mediated resistance in Haemophilus influenzae and Moraxella catarrhalis, and penicillin, macrolide and quinolone resistance in Streptococcus pneumoniae. The low propensity of amoxicillin/clavulanate to select resistance mutations as well as a favourable PK/PD profile predictive of high bacteriological efficacy may account for the longevity of this combination in clinical use. However, in certain defined geographical areas, the emergence of S. pneumoniae strains with elevated penicillin MICs has been observed. In order to meet the need to treat drug-resistant S. pneumoniae, two new high-dose amoxicillin/clavulanate formulations have been developed. A pharmacokinetically enhanced tablet dosage form of amoxicillin/clavulanate 2000/125 mg twice daily (available as Augmentin XR in the USA), has been developed for use in adult respiratory tract infection due to drug-resistant pathogens, such as S. pneumoniae with reduced susceptibility to penicillin, as well as beta-lactamase-producing H. influenzae and M. catarrhalis. Amoxicillin/clavulanate 90/6.4 mg/kg/day in two divided doses (Augmentin ES-600) is for paediatric use in persistent or recurrent acute otitis media where there are risk factors for the involvement of beta-lactamase-producing strains or S. pneumoniae with reduced penicillin susceptibility. In addition to high efficacy, amoxicillin/clavulanate has a well known safety and tolerance profile of the two new high-dose formulations are not significantly different from those of conventional formulations. Amoxicillin/clavulanate is included in guidelines and recommendations for the treatment of bacterial sinusitis, acute otitis media, community-acquired pneumonia and acute exacerbations of chronic bronchitis. Amoxicillin/clavulanate continues to be an important agent in the treatment of community-acquired respiratory tract infections, both now and in the future.

Pharmacokinetic and pharmacodynamic issues in the treatment of bacterial infectious diseases

This review outlines some of the many factors a clinician must consider when selecting an antimicrobial dosing regimen for the treatment of infection. Integration of the principles of antimicrobial pharmacology and the pharmacokinetic parameters of an individual patient provides the most comprehensive assessment of the interactions between pathogen, host, and antibiotic. For each class of agent, appreciation of the different approaches to maximize microbial killing will allow for optimal clinical efficacy and reduction in risk of development of resistance while avoiding excessive exposure and minimizing risk of toxicity. Disease states with special considerations for antimicrobial use are reviewed, as are situations in which pathophysiologic changes may alter the pharmacokinetic handling of antimicrobial agents.

Evaluation of a triple-drug combination for treatment of experimental multidrug-resistant pneumococcal meningitis

To evaluate the therapeutic efficacy of ceftriaxone + vancomycin + rifampicin (CVR) in the treatment of pneumococcal meningitis caused by a multidrug-resistant strain, single-drug regimens (ceftriaxone 100 mg/kg, rifampicin 15 mg/kg, or vancomycin 20 mg/kg), double-drug regimens (ceftriaxone + vancomycin [CV] and ceftriaxone + rifampicin [CR]) and a triple-drug combination (CVR) with or without dexamethasone were compared in a rabbit meningitis model. Meningitis was induced by a highly penicillin-resistant (MIC 2 mg/l) and ceftriaxone-resistant (MIC 4 mg/l) pneumococcal strain. Final therapeutic efficacy was evaluated by the bacterial concentration at 24 h, and the bacterial killing rate was also evaluated. All combination regimens were superior to ceftriaxone or vancomycin single-drug regimens with regard to sterilisation of CSF and bacterial killing rate. Rifampicin was as effective as combination regimens. Regardless of dexamethasone, therapeutic efficacy of CVR and CR were superior to that of CV. CVR showed comparable therapeutic efficacy to CR. Data suggested that CVR would not have additional therapeutic benefit over CR during the initial 24 h of treatment.

Bioequivalence evaluation of two brands of amoxicillin/clavulanic acid 250/125 mg combination tablets in healthy human volunteers: Use of replicate design approach

The purpose of this study was to apply a replicate design approach to a bioequivalence study of amoxicillin/clavulanic acid combination following a 250/125 mg oral dose to 23 subjects, and to compare the analysis of individual bioequivalence with average bioequivalence. This was conducted as a 2-treatment 2-sequence 4-period crossover study. Average bioequivalence was shown, while the results from the individual bioequivalence approach had no success in showing bioequivalence. In conclusion, the individual bioequivalence approach is a strong statistical tool to test for intra-subject variances and also subject-by-formulation interaction variance compared with the average bioequivalence approach.

Specific Antibiotics in the Treatment of Periodontitis – A Proposed Strategy

BACKGROUND

The purpose of the present study was to propose a strategy for the selection of antibiotics that specifically target complexes of periodontal pathogens present in patients with periodontitis.

METHODS

Seven hundred seventy-four (774) patients with various forms of periodontitis were included in the study. Subgingival plaque samples were taken from the deepest periodontal pockets in each quadrant using a sterile curet, and pooled. Actinobacillus actinomycetemcomitans, Porphyromonas gingivalis, Eikenella corrodens, Tannerella forsythensis, Prevotella intermedia, and Prevotella nigrescens were identified by polymerase chain reaction, and the prevalence of combinations of these pathogens was determined. To each pathogen complex (PC), i.e., combination of pathogens, those antibiotics were assigned that were most specific according to the published minimum inhibitory concentration (MIC90) values and the gingival crevicular fluid (GCF) concentrations achievable in vivo. Antibiotic GCF concentrations had to be at least 10 times the MIC90 values, and the narrowest spectrum was selected with respect to the assessed periodontal pathogens.

RESULTS

Nine major PCs (each > or = 3% of all patients) were found in 73.4% of all patients, whereas 38 minor PCs (each < 3% of all patients) were distributed in 26.6% of all patients. Ten different antibiotic regimens were found to be specific for the total of 46 PCs; i.e., metronidazole and amoxicillin in 11 PCs (55.0% of all patients), metronidazole and amoxicillin/clavulanic acid or metronidazole and ciprofloxacin in 13 PCs (18.9%), amoxicillin in 4 PCs (8.3%), doxycycline in 2 PCs (6.1%), metronidazole in 8 PCs (4.1%), amoxicillin/clavulanic acid in 3 PCs (2.9%), clindamycin in 2 PCs (1.5%), ciprofloxacin in 2 PCs (0.4%), and tetracycline in 1 PC (0.3%).

CONCLUSION

The results of the study indicate that there are at least 46 different combinations of the assessed periodontal pathogens in subjects with periodontitis, and at least 10 different antibiotic regimens might be required to specifically target the various pathogen complexes.

Elements of design: the knowledge on which we build

The time the free drug serum concentration of antibiotic remains above the pathogen MIC (T > MIC) determines bacteriological efficacy and emergence or selection of resistance for penicillin and amoxicillin with or without clavulanate. Multiple studies in animal and in-vitro models now support this conclusion. The size of the T > MIC (the pharmacokinetic/-dynamic target) is > 40-50% to maximise antibacterial effect and pathogen eradication for Streptococcus pneumoniae and probably also Haemophilus influenzae. The size of the T > MIC for optimal antibacterial effect is changed by host immune status but not by bacterial inoculum or mechanism of resistance. There is good animal evidence to support the prediction that, as long as the target T > MIC is achieved, strains of S. pneumoniae with amoxicillin MICs of 0.016 mg/L will respond to amoxicillin in the same way as those with MICs of 1-2 mg/L. Emergence of resistance to amoxicillin/clavulanate in S. pneumoniae is related to low T > MIC (< 20%) and also to the degree of population heterogeneity to amoxicillin. Selection of resistant strains of S. pneumoniae is also related to T > MIC. Monte Carlo simulations based on the pharmacokinetics of amoxicillin with or without clavulanate in humans are needed to best predict the likely efficacy of different amoxicillin dosing regimens. This approach adequately allows the considerable pharmacokinetic variability in amoxicillin handling by infected patients to be accounted for as well as differences in pathogen beta-lactam susceptibility.

Release of gentamicin and vancomycin from temporary human hip spacers in two-stage revision of infected arthroplasty

AIM

Evaluation of the delivery of gentamicin and vancomycin from polymethylmethacrylate (PMMA) spacers before and after implantation for the treatment of total hip replacement infections.

METHODS

Twenty industrially produced spacers containing gentamicin (1.9%) were utilized. Vancomycin (2.5%) mixed with PMMA cement was used to fill holes drilled in the cement of 14 of the 20 spacers immediately before implantation. The spacers were removed from 20 patients 3-6 months after implantation and then immersed in phosphate buffer at 37 degrees C for 10 days. Antibiotic concentrations were determined by fluorescence polarization immunoassay.

RESULTS

Gentamicin and vancomycin were still present in all the spacers removed from the patients. The release of gentamicin alone and in combination with vancomycin was in the range 0.05%-0.4% of the initial amount present, whereas the release of vancomycin was in the range 0.8%-3.3%. The release kinetics showed a similar pattern for both drugs. After a high initial release of drug, a reduced, but constant, elution was observed over the next few days.

CONCLUSIONS

The delivery of gentamicin and vancomycin from PMMA cement was high initially, with sustained release over several months. Incorporation of vancomycin into the surface of the spacers permitted spacers to be prepared with multiple antibiotics present and without adversely affecting the release kinetics of the agents. The gentamicin-vancomycin combination shows potential for the treatment of infection following total hip replacement in specific patients.

Efficacy of ampicillin combined with ceftriaxone and gentamicin in the treatment of experimental endocarditis due to Enterococcus faecalis with no high-level resistance to aminoglycosides

OBJECTIVE

This study tests the usefulness of ceftriaxone combined with ampicillin as an alternative to ampicillin plus gentamicin for the treatment of experimental endocarditis due to Enterococcus faecalis without high-level resistance to aminoglycosides. It also determines whether adding ceftriaxone to ampicillin and gentamicin increases the effectiveness against experimental enterococcal endocarditis resulting from E. faecalis.

METHODS

Animals with catheter-induced endocarditis were infected intravenously with 108 cfu of the EF91 strain of E. faecalis and were treated for 3 days with ampicillin 2 g every 4 h administered as 'human-like' (H-L) pharmacokinetics, plus gentamicin 1 mg/kg every 8 h H-L, or ceftriaxone 2 g every 12 h H-L alone or combined with gentamicin 6 mg/kg every 24 h administered subcutaneously.

RESULTS

The results of therapy for experimental endocarditis resulting from EF91 showed that the combination of ampicillin plus ceftriaxone was as effective as ampicillin plus gentamicin. The triple combination did not improve on the overall efficacies of the two-drug combinations.

CONCLUSIONS

Because of its lower nephrotoxicity, ampicillin plus ceftriaxone may be a useful alternative therapy for E. faecalis endocarditis in selected patients.

Measurement of cefaclor and amoxicillin-clavulanic acid levels in middle-ear fluid in patients with acute otitis media

Concentrations of cefaclor (CFC) or amoxicillin-clavulanic acid (AMX/CA) in middle-ear fluid collected preserving the stability and clearing the cell contents has been compared to those obtained using the traditional method. Sixty-seven children with effusive otitis media were treated orally with CFC (20 mg/kg of body weight) or AMX/CA (20 mg/kg) (4:1 ratio). The concentrations in cell-free fluid (C-) appear higher than those in the total fluid (C+) (as assayed traditionally).

Amoxicillin/clavulanate for infections in infants and children: past, present and future

Chemical synthesis of the penicillin nucleus in the 1950s made introduction of a broad array of new and important antimicrobials, including ampicillin and amoxicillin, possible. Ampicillin was introduced in 1962 in oral and parenteral forms as the first of the semisynthetic penicillins to provide increased activity against Gram-negative bacteria. Amoxicillin replaced oral ampicillin beginning in 1974 because amoxicillin resulted in higher and more prolonged serum concentrations than did equivalent doses of ampicillin. Amoxicillin/clavulanate (Augmentin) was introduced in the United States in 1984 to enhance the activity of amoxicillin by addition of the beta-lactamase inhibitor, clavulanic acid. During the past 20 years, amoxicillin/clavulanate has proven effective for a variety of pediatric infectious diseases, particularly acute otitis media (AOM). In 2001, a new pediatric formulation, high dose amoxicillin/clavulanate (Augmentin ES-600) was approved for use in the United States. The high dose preparation addressed the needs of pediatricians by providing greater amounts of amoxicillin while maintaining the same daily dose of clavulanic acid as the regular strength formulation. Doubling the dose of amoxicillin for management of recurrent and persistent AOM was recommended in 1999 by the Centers for Disease Control and Prevention because of concern about the increased incidence of nonsusceptible strains of Streptococcus pneumoniae. The original formulation combined amoxicillin/clavulanate in a 4:1 ratio and was followed by a 7:1 ratio formulation. The high dose formulation (600 mg of amoxicillin per 5 ml) provides a 14:1 ratio of amoxicillin to clavulanate. Although management of AOM will likely undergo changes in the coming years, amoxicillin is expected to remain first line therapy for AOM. For children who fail initial therapy with amoxicillin, high dose amoxicillin/clavulanate, an oral cephalosporin or parenteral ceftriaxone is recommended.

Linezolid and quinupristin/dalfopristin: novel antibiotics for gram-positive infections of the skin

With the continuing development of clinical drug resistance among bacteria, the need for new, effective agents to treat multi-drug-resistant Gram-positive infections remains important. With treatment options limited, it has become critical to identify antibiotics with novel mechanisms of activity. Several new drugs have emerged as possible therapeutic alternatives. This review focuses on agents newly introduced and FDA-approved for the treatment of skin and skin structure infections: linezolid and quinupristin/dalfopristin.

Gastric juice, gastric tissue and blood antibiotic concentrations following omeprazole, amoxicillin and clarithromycin triple therapy

BACKGROUND

Amoxicillin and clarithromycin are key antibiotics in proton pump inhibitor-based Helicobacter pylori eradication therapies.

AIMS

To study gastric mucus and tissue concentrations and collect basic data about optimal antibacterial doses.

METHODS

Plasma, gastric mucosa and gastric juice antibiotic concentrations were measured following either low- or high-dose amoxicillin (750 or 1000 mg b.i.d.) and clarithromycin (400 or 500 mg b.i.d.) given in combination with omeprazole 20 mg bid to 12 male volunteers in an open crossover design. Gastric juice and mucosal biopsy collection was performed either 2 (n=6) or 6 hours (n=6) after dosing.

RESULTS

Amoxicillin concentrations 2 hours after high dosage were gastric juice > gastric body > antral mucosa > plasma. At 6 hours, plasma and gastric juice concentrations were still above the MIC for amoxicillin-susceptible bacteria but no antibiotic was detectable in mucosa samples. Clarithromycin concentrations after high dosage were gastric juice > mucosa > serum; all above the MIC for clarithromycin-susceptible bacteria at both 2 and 6 hours.

CONCLUSIONS

Both dosage regimens provided effective antibiotic concentrations in gastric juice at 2 hours. After dosing, both antibiotics demonstrated high gastric tissue concentrations via local diffusion while clarithromycin also provided sustained delivery (6 hours) via gastric mucosa penetration.

Panipenem/betamipron

Panipenem is a parenteral carbapenem antibacterial agent with a broad spectrum of in vitro activity covering a wide range of Gram-negative and Gram-positive aerobic and anaerobic bacteria, including Streptococcus pneumoniae and species producing beta-lactamases. Panipenem is coadministered with betamipron to inhibit panipenem uptake into the renal tubule and prevent nephrotoxicity. In large, randomised clinical trials, panipenem/betamipron demonstrated good clinical and bacteriological efficacy (similar to that of imipenem/cilastatin) in adults with respiratory tract or urinary tract infections. Panipenem/betamipron was also effective in adults with surgical or gynaecological infections, and in paediatric patients with respiratory tract and urinary tract infections in noncomparative trials. In small trials in elderly patients reported as abstracts, panipenem/betamipron demonstrated clinical efficacy similar to intravenous piperacillin and greater than oral ofloxacin in urinary tract infections. Elderly patients with respiratory tract infections also responded to therapy. Panipenem/betamipron is well tolerated with few adverse events reported in clinical trials, most commonly elevated serum levels of hepatic transaminases and eosinophils, rash and diarrhoea.

Target site bacterial killing of cefpirome and fosfomycin in critically ill patients

We employed an in-vivo pharmacokinetic/in-vitro pharmacodynamic method to simulate bacterial killing in plasma and the interstitium of skeletal muscle tissue after intravenous administration of 2 g of cefpirome and 8 g of fosfomycin alone and in combination to patients with sepsis. Interstitial antimicrobial concentrations were determined by use of in-vivo microdialysis. CFU/ml of Staphylococcus aureus (ATCC 29213) and Pseudomonas aeruginosa (clinical isolate) decreased by approximately 2log(10) for plasma and muscle tissue 6 h after cefpirome and fosfomycin administration compared with the baseline, respectively. The simulation of plasma and tissue pharmacokinetics for the combined administration of these antibiotics resulted in complete eradication of S. aureus within 5 h after drug exposure. No bacterial re-growth occurred in any of the simulations within 6 h. The in-vitro simulation of in-vivo plasma and tissue pharmacokinetics of cefpirome and fosfomycin has shown that both antimicrobial agents kill S. aureus and P. aeruginosa strains effectively after single dose administration. This effect was most pronounced by the combined use of these antimicrobial agents. Therefore, this data corroborates antimicrobial strategies of simultaneous administration of cefpirome and fosfomycin in patients with severe soft tissue infection.

Variable absorption of clavulanic acid after an oral dose of 25 mg/kg of Clavubactin and Synulox in healthy dogs

The aims of this investigation were to calculate the pharmacokinetic parameters and to identify parameters, based on individual plasma concentration-time curves of amoxicillin and clavulanic acid in dogs, that may govern the observed differences in absorption of both drugs. The evaluation was based on the data from plasma concentration-time curves obtained following a single dose in an open, randomized, two-way crossover study involving 24 male Beagle dogs treated with two Amoxi-Clav formulations (A Clavubactin and B Synulox, each with 200/50 mg). Plasma amoxicillin and clavulanic acid concentrations were determined using validated bioassay methods. The half-life of elimination of amoxicillin was 1.5 h (t1/2 = 1.52 +/- 0.19 h, Cmax = 11.4 +/- 2.74 microg/mL), and that of clavulanic acid 0.76 h (t1/2 = 0.71 +/- 0.23 h, Cmax = 2.06 +/- 1.05 microg/mL). There was a fivefold variation in the AUCt of clavulanic acid for both formulations, while the AUCt of amoxicillin varied by a factor of 2. The mean ratio of the AUCt amoxicillin : clavulanic acid was 12.7 +/- 3.65 for formulation A and 11.8 +/- 5.22 for formulation B (P = 0.51).

Amoxicillin/clavulanic acid: a review of its use in the management of paediatric patients with acute otitis media

Amoxicillin/clavulanic acid (Augmentin), Augmentin ES-600 is a well established, orally administered combination of amoxicillin (a semisynthetic antibacterial agent) and clavulanic acid (a beta-lactamase inhibitor). Amoxicillin/clavulanic acid shows good activity against the main pathogens associated with acute otitis media (AOM), including penicillin-susceptible and -intermediate strains of Streptococcus pneumoniae, and beta-lactamase producing strains of Haemophilus influenzae and Moraxella catarrhalis. It has moderate activity against penicillin-resistant S. pneumoniae; a high-dose formulation has been developed with the aim of providing better coverage for penicillin-resistant strains. Amoxicillin/clavulanic acid (conventional formulations, mostly 40/10 mg/kg/day in three divided doses) produced clinical response rates similar to those of oral cephalosporin comparators and similar to or significantly greater than those for intramuscular ceftriaxone in randomised trials in paediatric patients with AOM (mean age approximately 2 to 5 years). Clinical response rates were generally similar for amoxicillin/clavulanic acid and macrolide comparators (mean patient age approximately 1 to 6 years), although significantly better clinical and bacteriological responses were seen versus azithromycin in one randomised trial (mean patient age approximately 1 year). The high-dose formulation of amoxicillin/clavulanic acid (90/6.4 mg/kg/day in two divided doses) eradicated a high proportion of penicillin-resistant S. pneumoniae (penicillin MICs 2 or 4 mg/L) in a large noncomparative trial in children with AOM (upper limit of the US indication for S. pneumoniae is 2 mg/L). Amoxicillin/clavulanic acid is generally well tolerated. A low total incidence of adverse events (3.6%) and no serious events were reported from a large paediatric postmarketing study. The most frequently reported adverse events in children are mild gastrointestinal disturbances. Diarrhoea is generally less frequent with twice-daily than with three-times-daily treatment. The new high-dose formulation showed similar tolerability to a conventional twice-daily formulation (45/6.4 mg/kg/day) in a well controlled trial.

CONCLUSIONS

Amoxicillin/clavulanic acid is a well established broad-spectrum antibacterial treatment which is effective and well tolerated in the treatment of AOM in paediatric patients. The high-dose combination should prove valuable in treating AOM caused by penicillin-intermediate and -resistant S. pneumoniae (approved in the US for penicillin MIC < or =2 mg/L). Based on recent recommendations and the available data, high-dose amoxicillin/clavulanic acid can be considered a treatment of choice for recurrent or persistent paediatric AOM (after failure of amoxicillin alone) where involvement of resistant pathogens is suspected.

Stability and compatibility study of cefepime in comparison with ceftazidime for potential administration by continuous infusion under conditions pertinent to ambulatory treatment of cystic fibrosis patients and to administration in intensive care units

Cefepime has been examined for stability, potential liberation of degradation products and compatibility with other drugs under conditions mimicking its potential use by continuous infusion in cystic fibrosis and intensive care patients (5-12% w/v solutions; temperatures from 20 to 37 degrees C; 1 h contact at 25 degrees C with other drugs frequently co-administered by intravenous route to these types of patients). Ceftazidime was used as a comparator based on a previous normative study with this antibiotic for the same indications. Based on a limit of max. 10% degradation, cefepime can be considered stable for a maximum of 24 h at 25 degrees C, but for only approximately 14 h at 30 degrees C, and for <10 h at 37 degrees C. Cefepime released so far unidentified degradation products if maintained at >30 degrees C for >12 h as shown from a marked increase in pH and from the development of a strong red-purple colour. Incompatibilities were observed with erythromycin, propofol, midazolam, phenytoin, piritramide, theophylline, nicardipine, N-acetylcysteine and a concentrated solution of dobutamine. We conclude that: (i) cefepime cannot be used safely by continuous infusion if containers are kept for more than a few hours at 37 degrees C (as will be the case for cystic fibrosis patients if using portable pumps carried under clothes); (ii) caution must be exercised in intensive care patients if the temperature and co-administration of other drugs is not kept under tight control. The nature and safety of the cefepime degradation products need to be studied further.

Identical pattern of highly variable absorption of clavulanic acid from four different oral formulations of co-amoxiclav in healthy subjects

The aims of this investigation were to calculate the pharmacokinetic parameters of amoxicillin and clavulanic acid, and to identify parameters that may affect their observed differences in absorption. Data were obtained from plasma concentration-time curves from four different open, randomized, two-treatment, two-period, two-sequence, crossover Phase I bioequivalence studies, with the following co-amoxiclav formulations: tablets 250/125, 500/125 and 875/125 mg, or 10 mL of an oral suspension 250/62.5 mg per 5 mL. Data from 144 subjects and 288 drug administrations were available for evaluation. After a 125 mg clavulanic acid dose (administered as potassium clavulanate) for all four different formulations, the clavulanic acid AUC(t) data ranged from 1.5 to 8 mg.h/L, varying by a factor of 5. The absorption of clavulanic acid was not related to the absorption of amoxicillin, or demographic factors, and we were unable to identify the reasons for the large variability in the absorption of clavulanic acid. We conclude that the absorption of clavulanic acid, after oral administration, is highly variable and may vary over a five-fold range between patients.

Pharmacological and toxicological aspects of combination of beta-lactam and aminoglycoside antibiotic, prednisolone and procaine hydrochloride on the example of Vetramycin

Vetramycin is an injectable veterinary compound for animal use only. In veterinary medicine, it has been used for a long time as a bactericidal beta-lactam and aminglycoside antibiotics combination, extending the bactericidal spectrum of these substances. This compound, in addition to bactericidal procaine penicillin and dihydrostreptomycin (DHS), contains also prednisolone acetate and procaine hydrochloride, two biologically active substances. Prednisolone, a glucocorticoide, has an antiinflammatory, antiallergic, antiitchical and analgesic effect. Procaine hydrochloride, in turn, has a local anaesthetic effect and attenuates pain caused by irritable properties of antibiotics at the injection sites. The average dosage of, respectively, procaine benzylpenicillin (I.U./kg(-1) b.w.), DHS (microg/kg(-1) b.w.), prednisolone acetate (microg/kg(-1) b.w.) and procaine hydrochloride (mg/kg(-1) b.w.) in horses, cattle, pigs is 6000-15000, 10-11, 0.24-0.6 and 1.2-3.0; s.i.d., in sheep, foals, calves, piglets is 20000-40000, 10, 0.8-1.6 and 4-8; s.i.d., in dogs and cats is 30000-200000, 10, 0.8-1.6 and 4-8; s.i.d.. Intramammary injection dose (Vetramycin antimastitis ointment in syringe) in cows is 1000000 I.U. of procaine benzylpenicillin + 1000000 I.U. of dihydrostreptycin sulphate per quarter of udder, s.i.d., during 3 successive days.

Pharmacokinetics of intravenous azithromycin and ceftriaxone when administered alone and concurrently to healthy volunteers

This study was conducted to identify whether or not a pharmacokinetic interaction existed when azithromycin and ceftriaxone were administered concurrently. This randomized, open-label, three-way crossover study in 12 healthy volunteers characterized the plasma pharmacokinetic parameter profiles of both drugs, as well as the white blood cell uptake and exposure to azithromycin, when the drugs were administered alone and together. The plasma pharmacokinetic parameters for azithromycin and ceftriaxone did not differ significantly either after a single dose or at steady state when the two were co-administered as opposed to being administered alone. Moreover, the neutrophil and monocyte/lymphocyte peak azithromycin concentrations and sampling period exposures also did not differ significantly between the study arm and the control arm. This study confirms that there is no interaction between azithromycin and ceftriaxone when they are administered concurrently.

Pharmacokinetics of lansoprazole, amoxicillin and clarithromycin after simultaneous and single administration

In a randomized, double-blind, placebo-controlled, four-way crossover study, possible influences of the triple therapy with amoxicillin, clarithromycin and the proton pump inhibitor lansoprazole on the pharmacokinetics of each of the drugs and the active 14-OH-clarithromycin metabolite were assessed. Twelve Helicobacter pylori-negative healthy male volunteers (age 27 +/- 4.3 years; creatinine clearance 7.0 +/- 2.0 L/h) were given lansoprazole 30 mg, amoxicillin 1 g and clarithromycin 500 mg, alone and in triple combination. Drug elimination intervals were at least 9 days between the dosing periods. The study medication was administered twice daily for 4 days. On the fifth day of each period, drugs were only given once in the morning, and blood and urine samples were collected for 12 h. The concentrations of the three substances administered, and 14-OH-clarithromycin, were determined by validated HPLC methods. Alterations in the serum kinetics were found for lansoprazole and the active 14-OH-clarithromycin metabolite (all data expressed as mean +/- S.D.). For lansoprazole, the elimination half-life (t(1/2)) was significantly prolonged (1.46 versus 1.7 h, P < 0.05) and the area under the concentration-time curve from 0 to 8 h (AUC(0-8)) was significantly increased (3.65 versus 4.59 mg.h/L, P < 0.05) by combination of the drugs. For 14-OH-clarithromycin, the peak concentration (C(max)) was 0.95 versus 1.18 mg/L and the AUC from 0 to 12 h (AUC(0-12)) was 8.3 versus 10.5 mg.h/L (augmented significantly, P < 0.05). The amoxicillin concentrations were slightly elevated by concomitant administration of lansoprazole and clarithromycin but without statistical significance (11.1 versus 12.6 mg/L). For clarithromycin, the time to maximum concentration of drug in serum (T(max)) was increased (2.73 versus 3.31 h, P < 0.05), whereas AUC and C(max) remained unchanged. Simultaneous administration of lansoprazole, amoxicillin and clarithromycin increases the serum concentrations of lansoprazole and the active 14-OH-clarithromycin metabolite significantly. These effects were not so pronounced as to have any therapeutic influence, making dosage adjustment unnecessary.

[Sinusal penetration of amoxicillin-clavulanic acid. Formulation 1 g./125 mg., twice daily versus formulation 500 mg./125 mg., three times daily]

INTRODUCTION

In order to meet the evolution of pneumococcus resistance to beta-lactam antibiotics, a new formulation of amoxicillin (AMX) and clavulanic acid (CA), with twice as much AMX (1 g/125 mg vs. 500 mg/125 mg) was developed for the treatment of acute pneumonia in patients at risk. This formulation can also be used in the treatment of acute maxillary sinusitis using a 1 g/125 mg regimen twice-daily.

OBJECTIVES

Compare the sinusal penetration of AMX and CA (1 g/125 mg twice-daily vs. 500 mg/125 mg three times a day) when administered at both regimens to demonstrate equivalent pharmacokinetic and pharmacodynamic behaviour of the former when compared to the latter.

METHODS

Concentrations of AMX and CA were measured in the anterior ethmoid, maxillary, posterior ethmoid sinus and in the middle nasa concha in 62 patients undergoing surgery for nasosinusal polyps. Patients randomised in two groups corresponding to 2 oral regimens, received either 1 g/125 mg twice a day or 500 mg/125 mg three times a day for 4 days. The last dose in both groups was administered 1 h 30, 3, 5 or 8 hrs prior to surgery. Serum samples were taken simultaneously to tissue samples. AMX and CA were measured by high performance liquid chromatography. Exogenous and above all endogenous blood contamination were taken into account with the hematocrit as well as blood and tissue haemoglobin concentrations. Comparisons of tissue concentrations were made for each sampling time, according to values obtained for a specific tissue with both doses on one hand, and on the other to values obtained with a specific dose in different tissues. The calculated pharmacodynamic parameters, which are considered to be predictive for bacteriological and clinical efficacy, result directly from tissue concentrations of AMX. tissue inhibitory quotients (IQtissue = Tissue concentration/MIC). time above MICs for serum and tissue concentrations (T > MIC).

RESULTS

As regards AMX, whatever the dose, at 1 h 30 and at 3 hrs, tissue concentrations did not differ significantly whatever the tissue studied (from 1.1 to 2.5 micrograms/g). Conversely, at 5 and 8 hrs, they were greater than after the 1 g/125 mg regimen given twice-daily (0.06-0.7 vs. 0.7-1.8 micrograms/g). If we consider a given dose, the comparison between the various tissues showed identical concentrations in the four tissues studied at each sampling time, except in two cases with the dose of 500 mg/125 mg 3 times a day. T > MIC for serum and tissue showed higher values than those required for AMX/pneumococcus association (40-50%) with, nevertheless, greater tissue values for the 1 g/125 mg dose given twice-daily when MIC was of 1 microgram/ml (40-52% vs. 50-66%). The maximum tissue inhibitory quotients were also greater with the twice-daily 1 g/125 mg dose, when calculated with MIC 50 or 90 of S. Pneumoniae, H. influenzae, M. catarrhalis or S. pyogenes. As for CA, concentrations were equivalent for both doses at each sampling time and greater than those required in vitro during respectively 4 and 5 hours for beta-lactamases H. influenzae and M. catarrhalis.

DISCUSSION-CONCLUSION

A least an equivalence between both dose regimens was observed, with occasionally a superiority of the twice-daily 1 g/125 mg dose, in terms of pharmacokinetics, tissue penetration and pharmacodynamics for both AMX and CA. This new regimen therefore appears more appropriate for the treatment of acute maxillary sinusitis in adults.

Treatment of life-threatening multiresistant staphylococcal and enterococcal infections in patients with end-stage renal failure with quinupristin/dalfopristin: preliminary report

BACKGROUND

Life-threatening infections with multiresistant gram-positive bacteria are increasing. Treatment with quinupristin/dalfopristin (Q-D) has turned out to be effective against such resistant pathogens.

PATIENTS AND METHODS

We report on treatment of six patients on dialysis (four with additional liver injury) and of one renal graft recipient with normal renal function who had severe infections caused by multiresistant Staphylococus epidermidis (1/7), methicillin-resistant Staphylococcus aureus (4/7) and vancomycin-resistant Enterococcus faecium (2/7).

RESULTS

Six out of seven patients were cured by therapy with Q-D in adjusted doses lasting for 10 to 34 days. Pharmacokinetics of Q-D and its metabolites were determined and remained within the therapeutic range, despite a modest increase of all compounds at the presumed steady state. The concentrations of the metabolites of Q-D were clearly lower than the parent drugs, including those of quinupristin-conjugated derivatives, which has not been reported previously.

CONCLUSION

These preliminary results suggest that: a) neither quinupristin nor dalfopristin or its metabolites accumulated despite the long duration of treatment; b) no adjustment of the standard dosage regimen (three times 7.5 mg/kg/day) is necessary in end-stage renal disease.

Pharmacodynamic profiling of continuously infused piperacillin/tazobactam against Pseudomonas aeruginosa using Monte Carlo analysis

Standard doses of piperacillin/tazobactam (9-13.5 g over 24 h) administered by continuous infusion (CI) routinely provide serum concentrations in excess of the susceptibility breakpoint (< or =16/4 micro g/ml) for most Enterobacteriaceae. Since the breakpoint of this agent for Pseudomonas aeruginosa is considerably higher (< or=64/4 micro g/ml), the likelihood of obtaining adequate drug exposures with these doses against this bacterium is currently unknown. Monte Carlo simulation was utilized to determine the probability of obtaining adequate piperacillin concentrations above its MICs for P. aeruginosa in patients receiving CI. MICs of 557 P. aeruginosa isolates were determined by E-test and a distribution was constructed for the 496 susceptible isolates. Using a previously validated population pharmacokinetic equation, steady-state serum concentrations were estimated for 210 patients who received piperacillin/tazobactam via CI. A Monte Carlo simulation was performed to predict the probability of obtaining concentrations at the MIC, 2 x MIC, 4 x MIC, 5 x MIC, and 6 x MIC for patients infected with susceptible P. aeruginosa isolates. MICs ranged from 0.09 to 64 micro g/ml with modal and median values of 3 and 4 micro g/ml, respectively. Steady-state concentrations of 51.14 +/- 17.52 micro g/ml were estimated in our patient population. The simulation resulted in a median level of exposure 12.62 times the MIC. The level of certainty of obtaining concentrations at the MIC, 2 x MIC, 4 x MIC, 5 x MIC, and 6 x MIC for piperacillin administered by CI was 97, 93, 85, 81, and 77%, respectively. Despite concern for the place of CI piperacillin/tazobactam in the management of P. aeruginosa infections due to the higher established breakpoint, these data suggest a high probability of achieving adequate drug exposure against susceptible isolates with this dosing regimen.

The in vitro elution characteristics of vancomycin combined with imipenem-cilastatin in acrylic bone-cements: a pharmacokinetic study

The aim of this in vitro study was to compare the elution characteristics of vancomycin alone and in combination with imipenem-cilastatin from 3 acrylic bone-cements (CMW1 [DePuy International, Blackpool, UK], Palacos R [Schering-Plough, Wehrheim, Germany], and Simplex P [Howmedica International, London, UK]). Six groups of 3 antibiotic-loaded cement disks were prepared, incorporating 2 g of vancomycin (3 groups) and 2 g of vancomycin plus 2 g of imipenem-cilastatin (3 groups). The disks were placed in saline baths for 5 weeks, with the baths being sampled periodically and the elution rates calculated. The total amount of vancomycin released by the cements treated with vancomycin alone was 7.98 mg for CMW1, 7.74 mg for Palacos R, and 6.76 mg for Simplex P; with the addition of imipenem-cilastatin, the total amount of vancomycin released by the 3 cements increased by 30.58%, 50.52%, and 50.15%. CMW1 had better elution characteristics than the other cements when treated with vancomycin alone; the elution of Palacos R and Simplex P was better than that of CMW1 when vancomycin was combined with imipenem-cilastatin.

The efficacy and safety of oral pharmacokinetically enhanced amoxycillin–clavulanate 2000/125 mg, twice daily, versus oral amoxycillin–clavulanate 1000/125 mg, three times daily, for the treatment of bacterial community-acquired pneumonia in adults

This double-blind, double-dummy, parallel-group study was designed to show that a pharmacokinetically enhanced formulation of oral amoxycillin-clavulanate (16:1, 2000/125 mg), twice daily, is at least as effective clinically and microbiologically as oral amoxycillin-clavulanate 1000/125 mg, three times daily, in the 10 day treatment of community-acquired pneumonia (CAP) in adults. The pharmacokinetically enhanced formulation is designed to provide higher serum concentrations of amoxycillin for a longer period than standard dosing to achieve coverage of Streptococcus pneumoniae isolates with amoxycillin-clavulanic acid minimum inhibitory concentrations (MICs) up to and including 4 mg/l. A total of 344 patients with CAP from 77 centres received amoxycillin-clavulanate 2000/125 mg twice daily for 10 days (169 patients) or amoxycillin-clavulanate 1000/125 mg three times daily for 10 days (175 patients). The most common pathogen isolated was S. pneumoniae (52.3% of patients, amoxycillin-clavulanate 2000/125 mg group; 46.8% of patients, amoxycillin-clavulanate 1000/125 mg group). In the clinical per-protocol (PP) population at test of cure (days 18-39), the clinical success rate in the amoxycillin-clavulanate 2000/125 mg group was at least as good as in the amoxycillin-clavulanate 1000/125 mg group (91.5 and 93.0%, respectively; 95% CI, -8.3, 5.4). The radiological and bacteriological success rates at test of cure for the PP populations were 92.4 and 90.6% in the amoxycillin-clavulanate 2000/125 mg group and 93.9 and 84.4% in the amoxycillin-clavulanate 1000/125 mg group, respectively. The clinical, bacteriological and radiological success rates at the end of therapy (days 11-17) for the PP populations were all over 85%. Both regimens were well tolerated, with no differences in adverse events between the groups. Amoxycillin-clavulanate 2000/125 mg, twice daily, is well tolerated and at least as effective clinically as amoxycillin-clavulanate 1000/125 mg, three times daily, in patients with CAP and may also be appropriate for the treatment of infections due to S. pneumoniae strains with high-level penicillin resistance.

Pharmacokinetics of an ampicillin/sulbactam (2:1) combination in rabbits

The pharmacokinetics of a 2:1 ampicillin-sulbactam combination in six rabbits, after intravenous and intramuscular injection at a single dosage of 20 mg/kg bodyweight (13.33 mg/kg of sodium ampicillin and 6.67 mg/kg of sodium sulbactam) were investigated by using a high performance liquid chromatographic method for determining plasma concentrations. The plasma concentration-time curves were analysed by compartmental pharmacokinetic and noncompartmental methods. The disposition curves for both drugs were best described by an open two-compartment model after intravenous administration and a one-compartment model with first order absorption after intramuscular administration. The apparent volumes of distribution calculated by the area method for ampicillin and sulbactam were 0.62 +/- 0.09 and 0.45 +/- 0.05 L/kg, respectively, and the total body clearances were 0.65 +/- 0.04 and 0.42 +/- 0.05 L/kg h, respectively. The elimination half-lives of ampicillin after intravenous and intramuscular administration were 0.64 +/- 0.11 and 0.63 +/- 0.16 h, respectively, whereas for sulbactam the half-lives were 0.74 +/- 0.12 and 0.77 +/- 0.17 h, respectively. The bioavailability after intramuscular injection was high and similar in both drugs (73.34 +/- 10.08% for ampicillin and 83.20 +/- 7.41% for sulbactam). The mean peak plasma concentrations of ampicillin and sulbactam were reached at similar times (0.20 +/- 0.09 and 0.34 +/- 0.15 h, respectively) and peak concentrations were also similar but nonproportional to the dose of both products administered (13.07 +/- 3.64 mg/L of ampicillin and 8.42 +/- 1.74 mg/L of sulbactam). Both drugs had similar pharmacokinetic behaviour after intramuscular administration in rabbits.

Pharmacokinetics and pharmacodynamics of piperacillin/tazobactam when administered by continuous infusion and intermittent dosing

BACKGROUND

Although intermittent bolus dosing is currently the standard of practice for many antimicrobial agents, beta-lactams exhibit time-dependent bacterial killing. Maximizing the time above the minimum inhibitory concentration (MIC) for a pathogen is the best pharmacodynamic predictor of efficacy. Use of a continuous infusion has been advocated for maximizing the time above the MIC compared with intermittent bolus dosing.

OBJECTIVE

This study compared the pharmacokinetics and pharmacodynamics of piperacillin/tazobactam when administered as an intermittent bolus versus a continuous infusion against clinical isolates of Pseudomonas aeruginosa and Klebsiella pneumoniae.

METHODS

Healthy volunteers were randomly assigned to receive piperacillin 3 g/ tazobactam 0.375 g q6h for 24 hours, piperacillin 6 g/tazobactam 0.75 g continuous infusion over 24 hours, and piperacillin 12 g/tazobactam 1.5 g continuous infusion over 24 hours. Five clinical isolates each of P aeruginosa and K pneumoniae were used for pharmacodynamic analyses.

RESULTS

Eleven healthy subjects (7 men, 4 women; mean +/- SD age, 28 +/- 4.7 years) were enrolled. Mean steady-state serum concentrations of piperacillin were 16.0 +/- 5.0 and 37.2 +/- 6.8 microg/mL with piperacillin 6 and 12 g, respectively. Piperacillin/tazobactam 13.5 g continuous infusion (piperacillin 12 g/tazobactam 1.5 g) was significantly more likely to produce a serum inhibitory titer > or = 1:2 against P aeruginosa at 24 hours than either the 6.75 g continuous infusion (piperacillin 6 g/tazobactam 0.75 g) or 3.375 g q6h (piperacillin 3 g/ tazobactam 0.375 g). There were no statistical differences against K pneumoniae between regimens. The median area under the inhibitory activity-time curve (AUIC) for the 13.5 g continuous infusion was higher than that for 3.375 g q6h and the 6.75 g continuous infusion against both P aeruginosa and Kpneumoniae (P < or = 0.007, 13.5 g continuous infusion and 3.375 g q6h vs 6.75 g continuous infusion against K pneumoniae). The percentage of subjects with an AUIC > or = 125 was higher with both 3.375 g q6h and the 13.5 g continuous infusion than with the 6.75 g continuous infusion against P aeruginosa and K pneumoniae (both, P < 0.001 vs 6.75 g continuous infusion against K pneumoniae).

CONCLUSIONS

Piperacillin 12 g/tazobactam 1.5 g continuous infusion consistently resulted in serum concentrations above the breakpoint for Enterobacteriaceae and many of the susceptible strains of P aeruginosa in this study in 11 healthy subjects. Randomized controlled clinical trials are warranted to determine the appropriate dose of piperacillin/tazobactam.

Variable absorption of clavulanic acid after an oral dose of 25 mg/kg of Clavubactin and Synulox in healthy cats

The aims of this investigation were to calculate the pharmacokinetic parameters and to identify parameters, based on individual plasma concentration-time curves of amoxicillin and clavulanic acid in cats, that may govern the observed differences in absorption of both drugs. The evaluation was based on the data from plasma concentration-time curves obtained following a single-dose, open, randomised, two-way crossover phase-I study, each involving 24 female cats treated with two Amoxi-Clav formulations (formulation A was Clavubactin and formulation was B Synulox; 80/20 mg, 24 animals, 48 drug administrations). Plasma amoxicillin and clavulanic acid concentrations were determined using validated bioassay methods. The half-life of elimination of amoxicillin is 1.2 h (t1/2 = 1.24 +/- 0.28 h, Cmax = 12.8 +/- 2.12 microg/ml), and that of clavulanic acid 0.6 h (t1/2 = 0.63 +/- 0.16 h, Cmax = 4.60 +/- 1.68 microg/ml). There is a ninefold variation in the AUCt of clavulanic acid for both formulations, while the AUCt of amoxicillin varies by a factor of two. The highest clavulanic acid AUCt values indicate the best absorption; all other data indicate less absorption. Taking into account that the amoxicillin-to-clavulanic acid dose ratio in the two products tested was 4:1, the blood concentration ratios may actually vary much more, apparently without compromising the products" high efficacy against susceptible microorganisms.

[Novel compounds active on staphylococci]

Research efforts to discover new compounds active against staphylococci are more than ever justified today. The incidence of methicillin-resistant staphylococci remains very high in hospitals, and the solution provided by glycopeptides is far from being satisfactory. These compounds exhibit mediocre pharmacokinetic and pharmacodynamic properties. Their ease and safety of use are poor. Finally, strains with diminished sensitivity to these antibiotics are beginning to appear. This article examines the opportunities offered by two new anti-staphylococcal agents: quinupristine-dalfopristine (Synercid) and linezolide (not marketed in France).

Comparative pharmacokinetic and pharmacodynamic profile of piperacillin/tazobactam 3.375G Q4H and 4.5G Q6H

When piperacillin/tazobactam has been used to treat hospitalized patients with serious infections, including nosocomial pneumonia caused by Pseudomonas aeruginosa, it has usually been dosed at 3.375 g q4h to provide serum concentrations above commonly encountered organisms' MICs (T > MIC) for at least 40-50% of the dosing interval. Pharmacodynamic principles suggest that a similar efficacy can be realized with extended dosing intervals when a larger dose (e.g. 4.5 g q6h) is administered, which was the objective of this study. Twelve healthy volunteers, 29.4 +/- 8.9 years of age, were enrolled in this multiple-dose, open-labeled, randomized, two-period crossover study. Blood samples were collected after the third dose and concentrations of piperacillin/tazobactam were determined with a validated HPLC method. Pharmacokinetic profiles were determined by noncompartment analysis. T > MIC of piperacillin was calculated for a range of MIC values. Piperacillin/tazobactam was well tolerated in 11 subjects who completed both regimens. The C(max), T(1/2), K, and AUC of P were significantly different according to a paired t test (p < 0.05) between two study regimens. Significant differences (p < 0.05) in tazobactam regimens were noted for C(max), and AUC. The piperacillin/tazobactam regimen of 4.5 g q6h achieved a 44% T > MIC for MIC values of < or = 16 microg/ml, while the 3.375-gram q4h regimen achieved 42% T > MIC, for MIC values of < or = 32 microg/ml. Dosage regimens for treating serious infections can be extended safely and effectively to 4.5 g q6h and obtain at least 40-50% T > MIC in the coverage of pathogens implicated with serious infections, including P. aeruginosa.

Pharmacokinetics of piperacillin-tazobactam in anuric intensive care patients during continuous venovenous hemodialysis

The pharmacokinetics of piperacillin-tazobactam were investigated in eight anuric intensive care patients treated by continuous venovenous hemodialysis (CVVHD). The elimination half-life of piperacillin was 4.3 +/- 1.2 h, and that of tazobactam was 5.6 +/- 1.3 h. The contribution of CVVHD to the overall elimination was relevant (>25%) for both drugs.

Pharmacokinetic and pharmacodynamic evaluation of two dosing regimens for piperacillin-tazobactam

STUDY OBJECTIVE

To compare the pharmacokinetic and pharmacodynamic profiles of two dosing regimens for piperacillin-tazobactam against commonly encountered pathogens. The regimens compared were piperacillin 4.0 g-tazobactam 0.5 g administered every 8 hours, and piperacillin 3.0 g-tazobactam 0.375 g administered every 6 hours.

DESIGN

Multiple-dose, open-label, randomized, crossover study.

SETTING

Clinical research center at Hartford Hospital.

SUBJECTS

Twelve healthy volunteers.

INTERVENTION

The two dosing regimens for piperacillin-tazobactam were administered intravenously in crossover design. Blood was sampled after the third dose.

MEASUREMENTS AND MAIN RESULTS

Drug concentrations were determined by a validated high-performance liquid chromatography assay. The percentage of time above minimum inhibitory concentration (%T>MIC) for piperacillin was calculated for a range of MIC values. The maximum concentration (Cmax), area under the concentration-time curve (AUC0-tau), and total clearance of piperacillin differed significantly between the two study regimens, as did the Cmax, AUC0-tau, volume of distribution, and total clearance of tazobactam (p<0.05). The piperacillin 4.0 g-tazobactam 0.5 g regimen provided 40-50% T>MIC for MIC values 8-16 microg/ml; a similar value for the piperacillin 3.0 g-tazobactam 0.375 g regimen was 16-32 microg/ml.

CONCLUSION

Although statistically significant differences in the pharmacodynamic profile were noted for the regimens, both provide adequate T>MIC against commonly encountered pathogens considered susceptible to piperacillin-tazobactam. However, for treatment of Pseudomonas aeruginosa infection, combination therapy or higher-dosage regimens (e.g., piperacillin 3.0 g-tazobactam 0.375 g every 4 hours, piperacillin 4.0 g-tazobactam 0.5 g every 6 hours, or continuous-infusion piperacillin 12 g-tazobactam 1.5 g/day) may be a prudent option when full MIC data are unavailable.