Comparative in vitro and in vivo activities of piperacillin combined with the beta-lactamase inhibitors tazobactam, clavulanic acid, and sulbactam

Pharmacokinetics and Pharmacodynamics of High-Dose Piperacillin-Tazobactam in Obese Patients

Background and Objective

Standard piperacillin–tazobactam (P-T) dosing may be suboptimal in obesity, but high-dose regimens have not been studied. We prospectively evaluated the pharmacokinetics and pharmacodynamics of standard- and high-dose P-T in obese adult inpatients.

Methods

Those receiving standard-dose P-T with BMI ≥ 30 kg/m² weighing 105–139 kg or ≥ 140 kg were given up to 6.75 g or 9 g every 6 h, respectively. Patients were monitored closely for safety. Elimination phase blood samples were drawn for 28 patients on standard and high doses to calculate the pharmacokinetic values using a one-compartment model. The likelihood of pharmacodynamic target attainment (100% fT > 16/4 mg/L) on various P-T regimens was calculated using each patient’s own pharmacokinetic values.

Results

Piperacillin and tazobactam half-lives ranged from 0.5–10.6 to 0.9–15.0 h, while volumes of distribution ranged from 13.6–54.8 to 11.5–60.1 L, respectively. Predicted dose requirements for target attainment ranged from 2.25 g every 6 h in hemodialysis patients to a 27 g/24-h continuous infusion in a patient with a short P-T half-life. An amount of 4.5 g every 6 h would have met the target for only 1/12 (8%) patients with creatinine clearance ≥ 80 mL/min and 13/28 (46%) for all enrolled patients. One patient (3%) experienced an adverse event deemed probably related to high-dose P-T.

Conclusion

Some patients required high P-T doses for target attainment, but dosing requirements were highly variable. Doses up to 6.75 g or 9 g every 6 h may be tolerable; however, studies are needed to see if high dosing, prolonged infusions, or real-time therapeutic drug monitoring improves outcomes in obese patients.

Clinical trial registration (clinicaltrials.gov)

NCT01923363.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13318-021-00677-1.

Cefoperazone/sulbactam: New composites against multiresistant gram negative bacteria?

Sulbactam, a class A β-lactamase inhibitor, added to cefoperazone either at a fixed 8 mg/L level of sulbactam or at a level of fixed cefoperazone: sulbactam ratio (2:1) would constitute a combination form of cefoperazone/sulbactam, which has better activities against Enterobacteriaceae, Pseudomonas aeruginosa and Acinetobacter baumannii than cefoperazone alone. Cefoperazone/sulbactam (1:1 or 1:2) has greater in-vitro activity against most multidrug-resistant organisms (ESBL- and AmpC-producing Enterobacteriaceae and carbapenem-resistant A. baumannii except for carbapenem-resistant P. aeruginosa) than a 2:1 ratio. However, increased sulbactam concentration may induce AmpC production. Besides, sulbactam concentration might not be readily achievable in serum if the susceptibility rates were defined by the breakpoints of higher sulbactam composites, such as ≤16/16 (1:1) or 16/32 (1:2) mg/L. Carbapenemases (KPC-, OXA-type enzymes and metallo-β-lactamases) can't be inhibited by sulbactam. Some in-vitro studies showed that increasing sulbactam composites of cefoperazone/sulbactam had no effect on carbapenem-resistant P. aeruginosa, suggesting the presence of carbapenemases or AmpC overproduction that could not be overcome by increasing sulbactam levels to recover cefoperazone activity. Sulbactam alone has good intrinsic activity against carbapenem-resistant Acinetobacter strains sometimes even in the presence of carbapenemase genes, suggesting unsteady levels of carbapenemases. In conclusion, appropriate composites of cefoperazone and β-lactamase inhibitor sulbactam may expand the clinical use if the pharmacokinetic optimization could be achieved in the human serum.

Antibiotic Dosing in Continuous Renal Replacement Therapy

Appropriate antibiotic dosing is critical to improve outcomes in critically ill patients with sepsis. The addition of continuous renal replacement therapy makes achieving appropriate antibiotic dosing more difficult. The lack of continuous renal replacement therapy standardization results in treatment variability between patients and may influence whether appropriate antibiotic exposure is achieved. The aim of this study was to determine if continuous renal replacement therapy effluent flow rate impacts attaining appropriate antibiotic concentrations when conventional continuous renal replacement therapy antibiotic doses were used. This study used Monte Carlo simulations to evaluate the effect of effluent flow rate variance on pharmacodynamic target attainment for cefepime, ceftazidime, levofloxacin, meropenem, piperacillin, and tazobactam. Published demographic and pharmacokinetic parameters for each antibiotic were used to develop a pharmacokinetic model. Monte Carlo simulations of 5000 patients were evaluated for each antibiotic dosing regimen at the extremes of Kidney Disease: Improving Global Outcomes guidelines recommended effluent flow rates (20 and 35 mL/kg/h). The probability of target attainment was calculated using antibiotic-specific pharmacodynamic targets assessed over the first 72 hours of therapy. Most conventional published antibiotic dosing recommendations, except for levofloxacin, reach acceptable probability of target attainment rates when effluent rates of 20 or 35 mL/kg/h are used.

Efficacy, pharmacokinetic and pharmacodynamic profile of ceftolozane + tazobactam in the treatment of complicated urinary tract infections

INTRODUCTION

Urinary tract infections (UTIs) are the second most common nosocomially acquired infections, responsible for approximately 21% of healthcare-associated pyelonephritis and 10.5% of urosepsis. Worldwide trends of increasing resistance resulted in the urgent need for novel antimicrobials that would be active against bacterial resistance mechanisms as an alternative to carbapenems, which are considered last resort antibiotics.

AREAS COVERED

The current review is based on a Medline search of published English language literature and contains summary information regarding the evaluation of pharmacologic properties, efficacy, safety and activity of ceftolozane+tazobactam against common bacterial resistance mechanisms.

EXPERT OPINION

In vivo and vitro studies demonstrated high activity of ceftolozane+tazobactam in the combination of 2:1 against a variety of uropathogens, including ESBL-producers. Phase II and Phase III studies performed in patients with complicated UTIs showed good tolerability and safety of ceftolozane+tazobactam when prescribed intravenously 1.5 g every 8 h for 7 days and at least non-inferiority to a high dose (750 mg) of levofloxacin. The pharmacokinetics of ceftolozane+tazobactam makes it a worthy alternative to carbapenems in cases of complicated UTIs, also caused by multidrug resistant uropathogens.

β-Lactam/β-Lactamase Inhibitor Combinations

Objective: To review the available evidence regarding the utility of the currently available β-lactam/β-lactamase inhibitor combinations (BLICs) as well as the emerging body of data for the novel agents in the pipeline. Data Sources: A MEDLINE literature search (1960-August 2014) was performed using the search terms β-lactamase, β-lactamase inhibitor, clavulanate, sulbactam, tazobactam, avibactam, NXL104, MK-7655, and RPX7009. Current studies focusing on new agents were obtained from clinicaltrials.gov. Additional references were identified from a review of literature citations and meeting abstracts. Study Selection and Data Extraction: All English-language studies pertaining to BLICs were evaluated. Data Synthesis: Historical clinical and in vitro data focusing on the characteristics of the conventional BLICs are reviewed. Avibactam, relebactam (formerly MK-7655), and RPX7009 are new β-lactamase inhibitors that are being studied in combination with β-lactams. Clinical and in vitro data that provide support for their use for multidrug-resistant organisms are reviewed. β-Lactam antibiotics are a mainstay for the treatment of many infections. The addition of β-lactamase inhibitors enhances their activity against organisms that produce β-lactamases; however, organisms that produce extended-spectrum β-lactamases, AmpC β-lactamases, and carbapenemases are proliferating. The BLICs (amoxicillin/clavulanate, ticarcillin/clavulanate, ampicillin/sulbactam, and piperacillin/tazobactam) lack activity against some of these enzymes, presenting a critical need for new antibiotics. Conclusions: The historical BLICs are useful for many infections; however, evolving resistance limits their use. The new BLICs (combinations with avibactam, relebactam, and RPX7009) may be valuable options for patients infected with multidrug-resistant organisms.

In vitro activity of ceftolozane-tazobactam as determined by broth dilution and agar diffusion assays against recent U.S. Escherichia coli isolates from 2010 to 2011 carrying CTX-M-type extended-spectrum β-lactamases

Ceftolozane MIC(50)/MIC(90)s were 4/8 μg/ml when tested against 26 CTX-M-14-type-producing isolates and 64/>64 μg/ml against 219 CTX-M-15-type-producing isolates. The addition of 4 μg/ml tazobactam lowered the ceftolozane MIC50/MIC9(0)s to ≤ 0.25/0.5 μg/ml by broth microdilution and Etest. The zone diameters for the ceftolozane-tazobactam disks were 23 to 29 mm for 92.2% of the isolates.

Results of a two-center, before and after study of piperacillin-tazobactam versus ampicillin and gentamicin as empiric therapy for suspected sepsis at birth in neonates ≤ 1500 g

OBJECTIVE

We changed from ampicillin and gentamicin (AG) to piperacillin-tazobactam (PT) for routine treatment of suspected early-onset sepsis. The rationale for this change included ototoxic and renal toxic effects of gentamicin, resistance to gentamicin in late-onset infections and emergence of ampicillin resistant Escherichia coli. A before and after study was designed before the start of PT administration to monitor whether PT was associated with altered outcomes within the 501 to 1500 g birth weight (Very Low Birth Weight) population.

METHOD

Both unmatched and matched comparisons of AG (2007 to 2009) and PT (2010 to 2011) exposed infants are reported. Cohorts were evaluated for initial effectiveness for congenital infections, subsequent morbidities and mortality.

RESULTS

Data from 714 patients were collected (499 AG and 215 PT in the unmatched and 301 AG and 183 PT in the matched cohorts). No significant differences in demographics or initial Apgar scores were noted in the unmatched or matched comparisons. There were significant differences in many of the outcomes of interest in both the matched and unmatched comparisons including less necrotizing enterocolitis (NEC) and less diaper rash with PT versus AG. The only adverse finding with PT was a small, but statistically significant elevation in alkaline phosphatase.

CONCLUSIONS

Use of PT as the initial empiric antibiotic for very low birth weight infants was not associated with adverse microbiological outcomes. There was no increase in major morbidities. Although outcomes were superior in ≤ 1500 g infants treated with PT when compared with AG, the study design does not allow us to conclude that others will see a reduction in NEC or diaper rash if they implement this alternative.

Population pharmacokinetics of extended-infusion piperacillin-tazobactam in hospitalized patients with nosocomial infections

While extended infusions of piperacillin-tazobactam (TZP) are increasingly used in practice, the effect of infusion on the pharmacokinetic (PK) profile of TZP has not been widely assessed. To assess its effect on the pharmacokinetic profile of TZP, seven serum samples were collected from 11 hospitalized patients who received 3.375 g TZP intravenously for 4 h every 8 h. Population pharmacokinetic models were fit to the PK data utilizing first-order, Michaelis-Menten (MM), and parallel first-order/MM clearance. A population PK model with first-order clearance was fit to the tazobactam PK data. Monte Carlo simulations (MCSs) were used to determine the most effective administration schedule to ensure that free piperacillin concentrations were above the MIC for at least 50% of the dosing interval (50% fT>MIC) and to quantify the extent of the nonlinear clearance. The model incorporating parallel linear/MM clearance best fit the piperacillin PK data. The MCSs demonstrated that approximately 50% of the administered piperacillin is cleared by the nonlinear clearance mechanism. The results of the MCSs also revealed that more intensive TZP extended infusion dosing schemes (3.375 to 4.5 g intravenously [3-h infusion] every 6 h) than those commonly used in clinical practice were needed to maximize the 50% fT>MIC for MICs of ≥8 mg/liter. This study suggests that extended infusion of TZP is the most effective method of administration for patients with nosocomial infections. Due to the hyperclearance nature of the hospitalized patient populations studied, more intensive TZP dosing regimens may be needed to maximize fT>MIC in certain hospitalized populations.

Beta-lactams and beta-lactamase-inhibitors in current- or potential-clinical practice: a comprehensive update

The use of successive generations of beta-lactams has selected successive generations of beta-lactamases including CTX-M ESBLs, AmpC beta-lactamases, and KPC carbapenamases in Enterobacteriaceae. Moreover, this cephalosporin resistance, along with rising resistance to fluoroquinolones, is now driving the use of carbapenems and unfortunately the carbapenem resistance has emerged markedly, especially in Acinetobacter spp. due to OXA- and metallo-carbapenemases. The industry responded to the challenge of rising resistance and recently developed some novel beta-lactams such as ceftobiprole, ceftaroline etc. and many beta-lactam compounds, including beta-lactamase-inhibitors, such as BMS-247243, S-3578, RWJ-54428, CS-023, SMP-601, NXL 104, BAL 30376, LK 157, and so on are under trials. This review provides the comprehensive accounts of the developments in penicillins, cephalosporins, carbapenems, and beta-lactamase-inhibitors, and the insight about medicinal chemistry, mechanism(s) of action and resistance, potential strategies to overcome resistance due to beta-lactamases, and also the recent advancements in the development of newer beta-lactam compounds; some of which are still under trials and yet to be classified. This review will fill the gap since previously published reviews and will serve as a comprehensive update on the current topic.

Piperacillin-tazobactam: a beta-lactam/beta-lactamase inhibitor combination

Piperacillin-tazobactam is a beta-lactam/beta-lactamase inhibitor combination with a broad spectrum of antibacterial activity that includes Gram-positive and -negative aerobic and anaerobic bacteria. Piperacillin-tazobactam retains its in vitro activity against broad-spectrum beta-lactamase-producing and some extended-spectrum beta-lactamase-producing Enterobacteriaceae, but not against isolates of Gram-negative bacilli harboring AmpC beta-lactamases. Piperacillin-tazobactam has recently been reformulated to include ethylenediaminetetraacetic acid and sodium citrate; this new formulation has been shown to be compatible in vitro with the two aminoglycosides, gentamicin and amikacin, allowing for simultaneous Y-site infusion, but not with tobramycin. Multicenter, randomized, double-blinded clinical trials have demonstrated piperacillin-tazobactam to be as clinically effective as relevant comparator antibiotics. Clinical trials have demonstrated piperacillin-tazobactam to be effective for the treatment of patients with intra-abdominal infections, skin and soft tissue infections, lower respiratory tract infections, complicated urinary tract infections, gynecological infections and more recently, febrile neutropenia. Piperacillin-tazobactam has an excellent safety and tolerability profile and continues to be a reliable option for the empiric treatment of moderate-to-severe infections in hospitalized patients.

Piperacillin–sulbactam versus piperacillin–tazobactam: a multicentre, randomised, single-blind, controlled clinical trial

The objective of this study was to compare the efficacy and safety of piperacillin-sulbactam (PIP-SBT) and piperacillin-tazobactam (PIP-TAZ) in the treatment of bacterial respiratory and urinary tract infections. A randomised, single-blind, controlled clinical trial was performed. Differences in clinical efficacy, bacteriology and safety between the two groups were subjected to statistical analysis, including intent-to-treat (ITT) analysis. A total of 215 cases were enrolled, with 203 complete cases (99 PIP-SBT, 104 PIP-TAZ). A total of 209 cases (103 PIP-SBT, 106 PIP-TAZ) were included in the ITT analysis and a total of 212 cases (104 PIP-SBT, 108 PIP-TAZ) were included in the safety analysis. Overall efficacy rates of PIP-SBT and PIP-TAZ were 93.2% and 93.4%, respectively. Overall bacterial eradication rates of the two groups were 95% and 97.59%, respectively. Among the PIP-SBT group, eight patients (7.69%) had adverse events, including four probable drug-related events. Among the PIP-TAZ group, nine patients (8.33%) had adverse events, including one definitely drug-related and four probable drug-related events. All differences between the two groups were insignificant. PIP-SBT could be a suitable replacement for PIP-TAZ in the therapy of community-acquired respiratory and urinary tract infections caused by beta-lactamase-producing bacterial isolates.

In vitro and in vivo activities of novel 6-methylidene penems as beta-lactamase inhibitors

Novel penem molecules with heterocycle substitutions at the 6 position via a methylidene linkage were investigated for their activities and efficacy as beta-lactamase inhibitors. The concentrations of these molecules that resulted in 50% inhibition of enzyme activity were 0.4 to 3.1 nM for the TEM-1 enzyme, 7.8 to 72 nM for Imi-1, 1.5 to 4.8 nM for AmpC, and 14 to 260 nM for a CcrA metalloenzyme. All the inhibitors were more stable than imipenem against hydrolysis by hog and human dehydropeptidases. Piperacillin was combined with a constant 4-microg/ml concentration of each inhibitor for MIC determinations. The combinations reduced piperacillin MICs by 2- to 32-fold for extended-spectrum beta-lactamase (ESBL)-producing Escherichia coli and Klebsiella pneumoniae strains. The MICs for piperacillin-resistant (MIC of piperacillin, >64 microg/ml) strains of Enterobacter spp., Citrobacter spp., and Serratia spp. were reduced to the level of susceptibility (MIC of piperacillin, < or =16 microg/ml) when the drug was combined with 4, 2, or 1 microg of these penem inhibitors/ml. Protection against acute lethal bacterial infections with class A and C beta-lactamase- and ESBL-producing organisms in mice was also demonstrated with piperacillin plus inhibitor. Median effective doses were reduced by approximately two- to eightfold compared to those of piperacillin alone when the drug was combined with the various inhibitors at a 4:1 ratio. Pharmacokinetic analysis after intravenous administration of the various inhibitors showed mean residence times of 0.1 to 0.5 h, clearance rates of 15 to 81 ml/min/kg, and volumes of distribution between 0.4 and 2.5 liters/kg. The novel methylidene penem molecules inhibit both class A and class C enzymes and warrant further investigation for potential as therapeutic agents when used in combination with a beta-lactam antibiotic.

Steady-state plasma and intrapulmonary concentrations of piperacillin/tazobactam 4 g/0.5 g administered to critically ill patients with severe nosocomial pneumonia

OBJECTIVE

To determine the steady-state plasma and epithelial lining fluid (ELF) concentrations of piperacillin/tazobactam (P/T) administered to critically ill patients with severe bacterial pneumonia.

DESIGN

Prospective, open-label study.

SETTING

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

PATIENTS

Ten adult patients with severe nosocomial bacterial pneumonia on mechanical ventilation.

INTERVENTIONS

All subjects received a 30-min intravenous infusion of P/T 4 g/0.5 g every 8 h. The steady-state plasma and ELF concentrations of P/T were determined by high-performance liquid chromatography.

MEASUREMENTS AND MAIN RESULTS

The mean+/-SD steady-state plasma trough, peak, and intermediate concentrations were 8.5+/-4.6 microg/ml, 55.9+/-21.6 microg/ml, and 24.0+/-13.8 microg/ml for piperacillin, and 2.1+/-1.0 microg/ml, 4.8+/-2.1 microg/ml, and 2.4+/-1.2 microg/ml for tazobactam, respectively. The mean+/-SD steady-state intermediate ELF concentrations were 13.6+/-9.4 microg/ml for piperacillin and 2.1+/-1.1 microg/ml for tazobactam, respectively, showing a mean percentage penetration of piperacillin and tazobactam into ELF of 56.8% and 91.3 %, respectively, with a P/T ratio of 6.5:1.

CONCLUSION

Our results show that during the treatment of severe nosocomial pneumonia, a regimen of P/T 4 g/0.5 g every 8 h might provide insufficient concentrations into lung tissue to exceed the MIC of many causative pathogens. This suggests that higher doses of P/T should be administered in order to maximize the antibiotic concentration at the site of infection, or that a second antimicrobial agent should be used in association.

Comparative in vitro activity of piperacillin, piperacillin–sulbactam and piperacillin-tazobactam against nosocomial pathogens isolated from intensive care patients

We investigated the antimicrobial activity of piperacillin-tazobactam versus piperacillin-sulbactam against common nosocomial pathogens (n = 565) isolated from intensive care patients. For Gram-positive bacteria, antimicrobial susceptibilities to the two piperacillin-beta-lactamase inhibitor combinations were almost identical. For Gram-negative bacteria, piperacillin-tazobactam exhibited greater activity against Escherichia coli and Proteus vulgaris than piperacillin-sulbactam. Both combinations, however, were equally effective against the other Enterobacteriaceae and Pseudomonas aeruginosa isolates. Piperacillin-sulbactam exhibited better antimicrobial activity against Acinetobacter baumannii. Our findings might prove important for the appropriate choice of antibiotic therapy with beta-lactam-beta-lactamase inhibitor combinations.

Comparison of four antimicrobial susceptibility testing methods to determine the in vitro activities of piperacillin and piperacillin-tazobactam against clinical isolates of Enterobacteriaceae and Pseudomonas aeruginosa

Susceptibility to piperacillin was similar to that to piperacillin-tazobactam (<1% difference) for 6,938 isolates of Enterobacter aerogenes and 13,954 isolates of Enterobacter cloacae tested using a Vitek system; for the same species, in contrast, susceptibility rates to piperacillin-tazobactam were 5.9 to 13.9% higher than to piperacillin using disk diffusion, MicroScan, and Vitek 2 testing. Unprecedented phenotypes (piperacillin susceptible and piperacillin-tazobactam intermediate; piperacillin intermediate and piperacillin-tazobactam resistant; piperacillin susceptible and piperacillin-tazobactam resistant) accounted for 6.1% of the results for E. aerogenes isolates and 6.0% of the results for E. cloacae isolates tested with the Vitek system.

Antibiotic selection for diabetic foot infections: a review

Foot infections account for about 20% of all hospitalizations in people with diabetes and at least 50% of all nontraumatic lower-limb amputations performed annually in the United States. As many as 25% of all diabetics are expected to develop severe foot problems at some point in their lifetimes. Diabetic foot infections are generally more severe and more difficult to treat than infections in nondiabetics. This is due to impaired microvascular circulation, neuropathy, anatomical alterations, and impaired immune capacity in diabetic patients. Most moderate-to-severe soft-tissue diabetic foot infections are polymicrobial (i.e., due to gram-positive, gram-negative, aerobic, and anaerobic pathogens). Empiric antibiotic therapy should include broad-spectrum antibiotics capable of covering the most common pathogens found in diabetic infections. Other factors to consider in antibiotic selection include the severity of the infection, the presence of peripheral vascular disease, and the possibility of drug-resistant organisms in the infection. This review summarizes the clinical presentation and antimicrobial therapy of diabetic foot infections.

Increasing antimicrobial resistance in gram-negative bacilli isolated from patients in intensive care units

BACKGROUND

We investigated gram-negative bacilli from patients in intensive care units to determine whether antimicrobial resistance was increasing.

METHODS

Minimal inhibitory concentrations were determined by broth microdilution on 334 gram-negative bacilli collected in 1990, 1995, and 1998.

RESULTS

During the 3 study years, the types of gram-negative bacilli encountered in our intensive care units changed with proportional increases of Pseudomonas sp and decreases of inducible enterics. Dramatic increases in resistance for ceftazidime, cefotaxime, and piperacillin were paralleled between respiratory-tract isolates and inducible enterics. By 1998, ticarcillin was more active than piperacillin against most isolates except Escherichia coli and Klebsiella sp, and most isolates became more resistant to gentamicin and tobramycin.

CONCLUSIONS

Continuous changes in the types of gram-negative bacilli and antimicrobial resistance complicate empirical selection of antimicrobials in the intensive care units. These complications will place more emphasis on communication and strategy formations among health care workers (nurses, physicians, laboratorians, and pharmacists) in an effort to treat infections in a timely and effective manner.

In vitro and in vivo activities of Syn2190, a novel beta-lactamase inhibitor

Syn2190, a monobactam derivative containing 1,5-dihydroxy-4-pyridone as the C-3 side chain, is a potent inhibitor of group 1 beta-lactamase. The concentrations of inhibitor needed to reduce the initial rate of hydrolysis of substrate by 50% for Syn2190 against these enzymes were in the range of 0.002 to 0.01 microM. These values were 220- to 850-fold lower than those of tazobactam. Syn2190 showed in vitro synergy with ceftazidime and cefpirome. This synergy was dependent on the concentration of the inhibitor against group 1 beta-lactamase-producing strains, such as Pseudomonas aeruginosa, Enterobacter cloacae, Citrobacter freundii, and Morganella morganii. However, against beta-lactamase-derepressed mutants of P. aeruginosa, the MICs of ceftazidime plus Syn2190 were not affected by the amount of beta-lactamase, and the values were the same for the parent strains. The MICs at which 50% of isolates are inhibited (MIC(50)s) of ceftazidime plus Syn2190 were 2- to 16-fold lower than those of ceftazidime alone for ceftazidime-resistant, clinically isolated gram-negative bacteria. Similarly, the MIC(50)s of cefpirome plus Syn2190 were two- to eightfold lower for cefpirome-resistant clinical isolates. The synergies of Syn2190 plus ceftazidime or cefpirome observed in vitro were also reflected in vivo. Syn2190 improved the efficacies of both cephalosporins in both a murine systemic infection model with cephalosporin-resistant rods and urinary tract infection models with cephalosporin-resistant P. aeruginosa.

Screening and isolation of antibiotic resistance inhibitors from herb materials IV-resistance inhibitors from Anetheum graveolens and Acorus gramineus

The hexane fractions from methanolic extracts of Anetheum graveolens L. (Umbelliferae) and Acorus gramineus Soland. (Araceae), revealed potent inhibitory activities against the resistance of multi-drug resistant Staphylococcus aureus SA2 when combined with ampicillin (Am) or chloramphenicol (Cm). As active principles, carvone and the liquid mixture containing carvone from Anetheum graveolens L. and a liquid mixture mainly consisting of benzoic acid phenylmethyl ester (benzyl benzoate) from Acorus gramineus Soland, were identified. They showed resistance inhibition at the level of 20-50 micrograms/ml when combined with 100 or 50 micrograms/ml of Am or Cm, respectively.

Efficacy, safety, and tolerance of piperacillin/tazobactam compared to co-amoxiclav plus an aminoglycoside in the treatment of severe pneumonia

An open, randomized, multicenter study was conducted to compare the efficacy and safety of piperacillin/tazobactam and co-amoxiclav plus aminoglycoside in the treatment of hospitalized patients with severe community-acquired or nosocomial pneumonia. Of the 89 patients who entered the study, 84 (94%) were clinically evaluable. A favorable clinical response was observed in 90% of the piperacillin/ tazobactam group and in 84% of the co-amoxiclav/aminoglycoside group (not significant). The bacteriological efficacy was comparable in both groups (96% vs. 92%; not significant). There was only one fatal outcome in the piperacillin/tazobactam group compared to six in the co-amoxiclav/aminoglycoside group regimen (P=0.058). The adverse event rate was non-significantly lower in the piperacillin/ tazobactam group compared to the co-amoxiclav/aminoglycoside group (2% vs. 7%; P=0.32). Piperacillin/tazobactam is safe and highly efficacious in the treatment of serious pneumonia in hospitalized patients. It compares favorably with the combination of co-amoxiclav/aminoglycoside.

Pharmacokinetics and pharmacodynamics of two multiple-dose piperacillin-tazobactam regimens

The pharmacokinetics and pharmacodynamics of two multiple-dose regimens of piperacillin-tazobactam (3.375 g every 6 h and 4.5 g every 8 h) were evaluated at steady state for 12 healthy adult volunteers. Inhibitory and bactericidal activities for the two regimens were determined with five American Type Culture Collection (ATCC) organisms (Escherichia coli, Staphylococcus aureus, Klebsiella pneumoniae, Pseudomonas aeruginosa, and Bacteroides fragilis). The percentage of time that plasma concentrations remained above the MIC (T > MIC) for each organism and dosage regimen was calculated. Areas under the inhibitory (AUIC0-24) and bactericidal activity (AUBC0-24) curves were calculated with the trapezoidal rule by using the reciprocal of the inhibitory and bactericidal titers determined for each dosage regimen. In order to assess the validity of predicted measures of bactericidal (AUC0-24/MBC) and inhibitory (AUC0-24/MIC) activity to determine bacteriological response to beta-lactam antimicrobial agents, AUC0-24/MBC and AUC0-24/MIC values were compared with measured AUBC0-24 and AUIC0-24 values. Total body clearance values were equivalent for piperacillin (183.96 +/- 22.66 versus 181.72 +/- 19.54 ml/min/1.73 m2, P > 0.05) and tazobactam (184.71 +/- 19.89 versus 184.87 +/- 18.35 ml/min/1.73 m2, P > 0.05) following the administration of the 3.375-g-every-6-h and 4.5-g-every-8-h dosages, respectively. Comparison of area under the plasma concentration-time curve (AUC0-24) for piperacillin (967.74 +/- 135.56 microg x h/ml versus 978.88 +/- 140.96 microg x h/ml) and tazobactam (120.14 +/- 15.78 microg x h/ml versus 120.01 +/- 16.22 microg x h/ml) revealed no significant differences (P > 0.05) between the 3.375-g-every-6-h and 4.5-g-every-8-h regimens, respectively. Both regimens provided T > MIC values of > 60% for all organisms tested. Measured values of bactericidal (AUBC) and inhibitory (AUIC) activity were significantly different (P < 0.05) from predicted values (AUC0-24/MBC and AUC0-24/MIC) for all organisms studied with the exception of the bactericidal activity for P. aeruginosa and S. aureus. Additionally, ATCC organisms possessing the same MICs and MBCs exhibited great differences in measured AUBC0-24 and AUIC0-24 values. Reasons for this difference may be inherent differences in organism specific susceptibility.

Assessment of two penicillins plus beta-lactamase inhibitors versus cefotaxime in treatment of murine Klebsiella pneumoniae infections

The in vivo efficacies of piperacillin, piperacillin plus tazobactam, ticarcillin, ticarcillin plus clavulanic acid, piperacillin plus clavulanic acid, and cefotaxime were compared in a mouse model of pneumonia induced by the SHV-1 beta-lactamase-producer Klebsiella pneumoniae. Each antibiotic was injected either once intraperitoneally at 24 h postinfection or at repeated times during 24 h. The efficacies of the drugs and therapeutic protocols were assessed by counting viable bacteria recovered from the lungs of mice sacrificed at selected times. No emergence of beta-lactam-resistant organisms was detected. Ticarcillin at 300 mg/kg was ineffective. Repeated injections of piperacillin at 300 mg/kg, either alone or in combination with tazobactam (8:1), led to a significant decrease in bacterial counts, but this was followed by bacterial regrowth. The pharmacokinetic analysis demonstrated that this short-lasting antibacterial effect was not due to a failure of piperacillin and/or tazobactam to penetrate the lungs. The combinations of ticarcillin at 300 mg/kg plus clavulanic acid (15:1) and piperacillin at 300 mg/kg plus tazobactam (4:1) were proven to be effective in that they decreased the bacterial burden in the lungs from 10(5) to < 10(3) CFU. This dose effect of tazobactam can be explained by its dose-dependent penetration in the lungs. Cefotaxime at 100 mg/kg and the combination of piperacillin (slightly hydrolyzed by SHV-1) at 300 mg/kg plus clavulanic acid (15:1) led to the best efficacy. Both of these treatments induced a decrease in bacterial counts of nearly 4 log10 units. The survival rates correlated with the quantitative measurements of in vivo bacterial killing. These experimental results obtained from the restricted animal model used here may help in the design of further protocols for clinical trials.

Beta-lactam resistance in anaerobic bacteria: a review

The majority of the human microflora consists of anaerobic bacteria. Normally these bacteria have low pathogenicity, but under certain conditions, such as destruction of tissues and poor circulation or impaired host defense, they may cause serious infections. Bacteroides species are the most frequently isolated microorganisms from suppurative anaerobic infections and they have the broadest spectrum of resistance to the commonly used antimicrobial agents. Resistance to antimicrobial agents is an increasing problem, especially to beta-lactam compounds. Multiresistant clinical isolates, resistant to beta-lactam antibiotics as well as other antimicrobial agents used in the treatment and prophylaxis of anaerobic infections are now occurring. Resistance to beta-lactam antibiotics is usually mediated by beta-lactamase production. A few isolates of Bacteroides fragilis are producing metallo-beta-lactamases which are capable of hydrolyzing beta-lactamase stable compounds such as cefoxitin and imipenem. The enzyme activity in metallo-beta-lactamases is not affected by the clinically used beta-lactamase inhibitors clavulanic acid, sulbactam and tazobactam. Other resistance mechanisms are alterations in the penicillin-binding proteins (PBPs) or a decreased permeability through the outer membrane. Beta-lactam resistance and beta-lactamase production have also been detected in some species of clostridia, fusobacteria, Prevotella, Porphyromonas and in some other anaerobic bacteria.

Activity of beta-lactamase inhibitor combinations on Escherichia coli isolates exhibiting various patterns of resistance to beta-lactam agents

The efficacy of the clinically available beta-lactam/beta-lactamase inhibitor combinations (amoxicillin/clavulanic acid (CA), ticarcillin/CA, amoxicillin/sulbactam, and piperacillin/tazobactam) was evaluated on 300 amoxicillin-resistant Escherichia coli isolates having the main patterns of beta-lactam resistance. The patterns, which reflect the production of various beta-lactamase enzymes, were analyzed by a principal component analysis of susceptibility to 11 beta-lactam antibiotics or beta-lactam/beta-lactamase inhibitor combinations. Sixty-two percent of strains were not very susceptible to penicillins, cephalothin, or any beta-lactam/beta-lactamase inhibitor combinations except for piperacillin/tazobactam; these strains may represent high-level broad-spectrum beta-lactamase (so-called penicillinase) production phenotype or inhibitor-resistant TEM-like enzyme production phenotype. Of the strains, 14.7% were resistant to amoxicillin and ticarcillin compatible with low-level broad-spectrum beta-lactamase production phenotype; 5.7% were cefoxitin resistant and were postulated to present a high-level cephalosporinase production phenotype; and 2.6% were resistant to cephalothin only, attributable to a low-level cephalosporinase production phenotype. Three percent of strains were intermediate or resistant to cefotaxime and may produce an extended-spectrum beta-lactamase, and the remaining strains (12 %), resistant to all tested antibiotics except for cefotaxime and piperacillin/tazobactam, were hypothesized to produce both broad-spectrum beta-lactamase plus cephalosporinase. The minimal inhibitory concentration (MIC) for these phenotype patterns indicated that combinations of CA plus amoxicillin or ticarcillin, or sulbactam plus amoxicillin, restored the activity of penicillins against phenotype 1 strains, whereas these combinations remained inactive against the other phenotype strains. Piperacillin plus tazobactam showed the best in vitro effect against the strains of all resistance phenotypes.

beta-Lactamases in laboratory and clinical resistance

beta-Lactamases are the commonest single cause of bacterial resistance to beta-lactam antibiotics. Numerous chromosomal and plasmid-mediated types are known and may be classified by their sequences or phenotypic properties. The ability of a beta-lactamase to cause resistance varies with its activity, quantity, and cellular location and, for gram-negative organisms, the permeability of the producer strain. beta-Lactamases sometimes cause obvious resistance to substrate drugs in routine tests; often, however, these enzymes reduce susceptibility without causing resistance at current, pharmacologically chosen breakpoints. This review considers the ability of the prevalent beta-lactamases to cause resistance to widely used beta-lactams, whether resistance is accurately reflected in routine tests, and the extent to which the antibiogram for an organism can be used to predict the type of beta-lactamase that it produces.

Piperacillin/tazobactam: a new beta-lactam/beta-lactamase inhibitor combination

OBJECTIVE

To discuss the antimicrobial activity, pharmacokinetics, clinical efficacy, and adverse effect profile of piperacillin/tazobactam, a new beta-lactan/beta-lactamase inhibitor combination.

DATA SOURCES

Literature was identified by MEDLINE search of the medical literature, review of selected references, and data provided by the manufacturer.

STUDY SELECTION

In vitro susceptibility data were surveyed from studies following the methods of the National Committee for Clinical Laboratory Standards. Data evaluating clinical efficacy were selected from all published trials and abstracts. Additional information concerning safety, chemistry, and pharmacokinetics was reviewed.

DATA SYNTHESIS

The antimicrobial activity of piperacillin is enhanced by addition of tazobactam against gram-positive, gram-negative, and anaerobic bacteria. Tazobactam is active against a broad spectrum of plasmid and chromosomally mediated enzymes and has minimal ability to induce class I chromosomally mediated beta-lactamase enzymes. Piperacillin/tazobactam's expanded activity appears encouraging in the treatment of mixed aerobic and anaerobic infections. Direct comparisons of ticarcillin/clavulanate and piperacillin/tazobactam for the treatment of lower respiratory tract infections showed piperacillin/tazobactam to be clinically superior, and in the treatment of skin and soft tissue infections the 2 agents were comparable. For the treatment of intraabdominal infections, piperacillin/tazobactam was at least as effective as imipenem/cilastatin and clindamycin plus gentamicin.

CONCLUSIONS

The combination of tazobactam with piperacillin results in an antimicrobial agent with enhanced activity against most beta-lactamase-producing organisms. Preliminary data indicate that piperacillin/tazobactam has proven clinical efficacy in the treatment of a variety of infections, especially polymicrobic infections.

National survey of the in vitro spectrum of piperacillin-tazobactam tested against more than 40,000 aerobic clinical isolates from 236 medical centers

Hospital microbiology laboratories from 41 states participated in a bacterial antimicrobial susceptibility study comparing in vitro results generated by the standardized disk diffusion method. Over 41,000 freshly isolated aerobic and facultative strains, representing all specimen types (except stools and urines), were tested for their susceptibility to piperacillin-tazobactam and 21 other antimicrobial agents. Enterococcus spp. was the second or third most common isolate from intraabdominal, gynecologic, and cutaneous infections, confirming its growing importance as a nosocomial pathogen. Escherichia coli was the most frequent isolate overall, despite the exclusion of urinary tract specimens from the study. Pseudomonas aeruginosa was the second most prevalent species, ranking first in frequency of recovery from lower-respiratory-tract specimens. Piperacillin-tazobactam was the most active beta-lactamase inhibitor combination tested against Gram-negative bacteria. Its activity against Gram-positive bacteria and Haemophilus influenzae was similar to that of ampicillin-sulbactam (95-97% susceptible). Imipenem and piperacillin-tazobactam displayed similar spectrums of activity against Gram-positive organisms and Haemophilus influenzae. Against Enterobacteriaceae, piperacillin-tazobactam and ceftazidime exhibited similarly wide spectrums of activity, but with some gaps, particularly among Enterobacter spp. and Citrobacter freundii. In this large-scale in vitro study, piperacillin-tazobactam and imipenem displayed the widest antimicrobial spectrums, inhibiting > 90% of all isolates tested.

Comparative antimicrobial activity of piperacillin-tazobactam tested against more than 5000 recent clinical isolates from five medical centers. A reevaluation after five years

Piperacillin combined with tazobactam at a fixed concentration (4 micrograms/ml) and a ratio (8:1) was tested against 5,029 aerobic isolates and 447 fastidious organisms, including anaerobes. Among the Enterobacteriaceae, > 95% inhibition was shared only by imipenem (99.1% at < or = 4 micrograms/ml), and some newer cephalosporins (95.1% - 99.8% at < or = 8 micrograms/ml), and piperacillin-tazobactam (95.8% at < or = 16/4 micrograms/ml). Piperacillin-tazobactam was the most active agent tested against nonenteric Gram-negative bacilli (93.5% at < or = 8 micrograms/ml). Ampicillin-sulbactam was the most active agent against staphylococci (95.0% at < or = 8 micrograms/ml), followed by imipenem (91.8%), piperacillin-tazobactam (89.3% at < or = 8/4 micrograms/ml), and cefepime (86.2% at < or = 8 micrograms/ml). Against the enterococci, only ampicillin (93.0% at < or = 8 micrograms/ml) with or without sulbactam, piperacillin (91.0% at < or = 16 micrograms/ml) with or without tazobactam, and imipenem (91.0%) had acceptable activity. Piperacillin-tazobactam and imipenem were the most active drugs tested against all aerobic isolates, inhibiting 93.5% of isolates each. Piperacillin-tazobactam inhibited all fastidious isolates tested, including Haemophilus influenzae (MIC90, 0.094/4 micrograms/ml), Moraxella catarrhalis (MIC90, 0.064/4 micrograms/ml), Neisseira gonorrhoeae (MIC90, < or = 0.016/4 micrograms/ml), and Streptococcus pneumoniae (all MICs, < or = 4/4 micrograms/ml). Against the anaerobic isolates, the most broad-spectrum antimicrobial agents tested were imipenem (100.0%), piperacillin-tazobactam (99.5% at < or = 32/4 micrograms/ml), metronidazole (98.4% at < or = 8 micrograms/ml), and ticarcillin-clavulanic acid (95.1% at < or = 32/2 micrograms/ml). These results are nearly identical to a previous study involving the same five medical centers in 1989. Piperacillin-tazobactam appears to remain a highly effective beta-lactamase inhibitor combination with a wide empiric spectrum and potency in teaching hospitals.

Single-dose pharmacokinetics of piperacillin and tazobactam in infants and children

The pharmacokinetics of piperacillin and tazobactam were assessed after single-dose administration to 47 infants and children. Study subjects ranging in age from 2 months to 12 years were randomized to receive one of two different doses of a piperacillin-tazobactam combination (8:1): a low dose (n = 23) of 50 and 6.25 mg of piperacillin and tazobactam per kg of body weight, respectively, or a high dose (n = 24) of 100 and 12.5 mg, respectively. The pharmacokinetic behavior of tazobactam was very similar to that observed for piperacillin, supporting the use of these two agents in a fixed-dose combination. No differences in the pharmacokinetics of piperacillin or tazobactam were observed between the two doses administered. The elimination parameters half-life and total body clearance decreased and increased, respectively, with increasing age, whereas volume parameters (volume of distribution and steady-state volume of distribution) remained relatively constant for both compounds. The primary metabolite of tazobactam, metabolite M1, was measurable in the plasma of 18 of the 47 study subjects; 17 of these 18 subjects received the high doses. More than 70% of the administered piperacillin and tazobactam doses were excreted unchanged in the urine over a 6-h collection period. These data combined with the known in vitro susceptibilities of a broad range of pediatric bacterial pathogens indicate that a dose of 100 mg of piperacillin and 12.5 of mg tazobactam per kg of body weight administered as a fixed-dose combination every 6 to 8 h would be appropriate to initiate clinical efficacy studies in infants and children for the treatment of systemic infections arising outside of the central nervous system.

Pharmacodynamics of piperacillin alone and in combination with tazobactam against piperacillin-resistant and -susceptible organisms in an in vitro model of infection

The pharmacodynamics of dosage regimens of piperacillin alone or in combination with tazobactam against piperacillin-resistant or -susceptible bacteria were studied in an in vitro model of infection. Experiments were conducted by using a fixed daily exposure of 12 g of piperacillin, given as 3 g alone or in combination with tazobactam at 0.375 g every 6 h, or the same total dose of the combination given as 4 g of piperacillin plus 0.5 g of tazobactam every 8 h. The addition of tazobactam to piperacillin, irrespective of the dosing interval, did not alter the killing of piperacillin-susceptible organisms (Escherichia coli J53 and Pseudomonas aeruginosa ATCC 27853). In contrast, experiments with an isogenic TEM-3-containing transconjugant of E. coli J53 (E. coli J53.2-TEM-3) that was resistant to piperacillin (MIC, 128 micrograms/ml) showed that the addition of tazobactam resulted in bacterial killing similar to that observed with the wild-type strain. Although tazobactam concentrations fell to less than 4 mg/liter (the concentration associated with a reduction in the piperacillin MIC from 128 to 2 mg/liter) 2 to 3 h after a dose, a similar degree of bacterial killing was observed when the same total 24-h dose of piperacillin-tazobactam was fractionated into dosing intervals of every 6 or 8 h. Investigations with Staphylococcus aureus 7176 (piperacillin MIC, 128 micrograms/ml) showed that the addition of tazobactam, again irrespective of dosing interval, also resulted in net bacterial killing which was not seen with piperacillin alone. These data support the use of extended dosing intervals (every 8 h) of piperacillin-tazobactam in the treatment of infections caused by piperacillin-resistant bacteria.

Piperacillin/tazobactam in the treatment of community-acquired and nosocomial respiratory tract infections: a review

Investigators assessed the efficacy and safety of piperacillin/tazobactam therapy in a study of patients with community-acquired lower respiratory tract infections and a study of patients with nosocomial, severe lower respiratory tract infections. Piperacillin 4 g/tazobactam 500 mg was given intravenously every 8 h to 193 hospitalized lower respiratory tract infection patients for a minimum of 5 days. There was a favorable response rate of 97% and eradication of the causative pathogen was documented or presumed in 93% of patients. There was a low incidence of adverse experiences and the combination was well tolerated. Seventy-one intensive care patients with severe lung disease received 4 g piperacillin/500 mg tazobactam intravenously every 6 h; afterward they were given amikacin 7.5 mg/kg every 12 h. Minimum duration of treatment was 5 days. Therapy with piperacillin/tazobactam plus amikacin was well-tolerated, produced a 74% favorable clinical response rate, and eradicated the responsible pathogen in 70% of patients.

Piperacillin/tazobactam in complicated urinary tract infections

Piperacillin/tazobactam, at a dosage of 4 g/500 mg every 8 h, was administered intravenously to 217 patients with complicated urinary tract infections. The most common diagnosis was pyelonephritis. The most common pathogen was Escherichia coli (47%) followed by Pseudomonas aeruginosa (13%), and enterococci (8%). Among clinically evaluable patients, 86% (115/134) were cured or improved at the study endpoint and 14% (19/134) were clinical failures or relapsed. Among bacteriologically evaluable patients, 85% (95/112) had a favorable clinical response at endpoint. The bacteriological response rate was 73% (82/112) at endpoint. Overall, 82% of all pathogens were eradicated. Therapy was associated with a low incidence of side effects, and adverse experience were mild and of short duration.

Review of piperacillin/tazobactam in the treatment of bacteremic infections and summary of clinical efficacy

One method of resistance to beta-lactam antimicrobials involves production of beta-lactamases, enzymes that render the beta-lactam ineffective. Beta-lactamase inhibitors have been combined with beta-lactam antibiotics to combat beta-lactamase producing organisms. One such agent, piperacillin/tazobactam, has been shown to be safe and effective therapy for infections usually treated with a combination of antibiotics such as polymicrobial and nosocomial infection, and has been used for empiric therapy in cases of serious infection. A survey of the literature shows that piperacillin/tazobactam is a safe and efficacious therapy for bacteremia as well as soft tissue, intra-abdominal, and lower respiratory tract infections. When combined with an aminoglycoside, it is also useful in the treatment of severe nosocomial respiratory infections.

Piperacillin/tazobactam. A review of its antibacterial activity, pharmacokinetic properties and therapeutic potential

Combining tazobactam, a beta-lactamase inhibitor, with the ureidopenicillin, piperacillin, successfully restores the activity of piperacillin against beta-lactamase-producing bacteria. Tazobactam has inhibitory activity, and therefore protects piperacillin against Richmond and Sykes types II, III, IV and V beta-lactamases, staphylococcal penicillinase and extended-spectrum beta-lactamases. However, tazobactam has only species-specific activity against class I chromosomally-mediated enzymes. Resistant organisms include some Citrobacter spp., Enterobacter spp., Serratia spp., Xanthomonas maltophilia and Enterococcus faecium. Consistent with its in vitro activity, preliminary clinical data indicate that the fixed combination of piperacillin/tazobactam (dose ratio 8:1) is effective in the treatment of moderate to severe polymicrobial infections, including intra-abdominal, skin and soft-tissue and lower respiratory tract infections. In limited comparative trials, piperacillin/tazobactam demonstrated equivalent or better efficacy than standard comparator regimens in these infections. Piperacillin/tazobactam in combination with an aminoglycoside was effective in the empirical treatment of fever in patients with neutropenia and compared favourably with ceftazidime in combination with an aminoglycoside, although second-line therapy with a glycopeptide antibiotic may be indicated in unresponsive episodes. Data from phase III trials indicate that piperacillin/tazobactam has a tolerability profile typical of a penicillin agent. Piperacillin/tazobactam provides a broad spectrum of antibacterial activity in a convenient single formulation suitable for use in the treatment of polymicrobial infections. Possible limitations concern its restricted activity against class I beta-lactamases, enzymes that are becoming increasingly important in the nosocomial environment. Combined therapy with an aminoglycoside may be necessary in more serious infections.

Ex vivo pharmacodynamic study of piperacillin alone and in combination with tazobactam, compared with ticarcillin plus clavulanic acid

Ten volunteers received piperacillin (4 g), piperacillin (4 g) plus tazobactam (0.5 g) (Tazocin), and ticarcillin (3 g) plus clavulanic acid (0.2 g) (Timentin) intravenously over 30 min in a cross-over blinded scheme. Blood samples were obtained 0.5 and 3 h after the end of infusion to measure by (high-pressure liquid chromatography) the concentration and bactericidal titers against 70 gram-negative bacilli. Serum time-kill curves were done against 35 strains to measure killing rates and area under the time-kill curve. Using the measure of serum bactericidal activity, ticarcillin-clavulanic acid and piperacillin-tazobactam were equally effective against Pseudomonas aeruginosa, Escherichia coli, Enterobacter cloacae, Serratia marcescens, and Bacteroides fragilis. Piperacillin-tazobactam was superior to ticarcillin-clavulanic acid against piperacillin-resistant Klebsiella pneumoniae (4 to 16 times) and S. marcescens (2 to 4 times). By using the area under the time-kill curve, piperacillin-tazobactam was equivalent to ticarcillin-clavulanic acid against piperacillin-susceptible strains; piperacillin-tazobactam was significantly more active than piperacillin against piperacillin-resistant strains and was more active than ticarcillin-clavulanic acid when the sample obtained 3 h after the end of infusion to volunteers was considered. Serum piperacillin concentrations (mean +/- standard error of the mean; in mg/liter) were 115 +/- 13 at 0.5 h and 7.4 +/- 1.4 at 3 h after the administration of piperacillin alone and 105.5 +/- 12.6 (0.5 h) and 7.7 +/- 1.6 after the administration of piperacillin-tazobactam. Serum tazobactam concentrations (in milligram per liter) were 13.1 +/- 1.4 at 0.5 h and 1.2 +/- 0.2 at 3 h. The piperacillin-tazobactam ratio was 8 +/- 0.3 at 0.5 h and 6.2 +/- 0.5 at 3 h. Piperacillin-tazobactam appears promising against beta-lactamase-producing gram-negative bacilli.

Kinetic interactions of tazobactam with beta-lactamases from all major structural classes

Tazobactam was shown to be a potent inhibitor of group 1, 2a, 2b, and 2b' beta-lactamases. Extended kinetic studies with class A and C serine beta-lactamases showed that the PC1, TEM-2, and P99 enzymes all were reversibly inhibited prior to inactivation of the enzymes. The CcrA metallo-beta-lactamase was less well inhibited, with a 50% inhibitory concentration at least 3 orders of magnitude less favorable than those for most serine beta-lactamases. The numbers of hydrolytic turnovers of tazobactam before inactivation were 2 for PC1, 125 for TEM-2, 50 for P99, and 4,000 for the CcrA enzyme. In spectral studies, transient intermediates were formed after reaction of tazobactam with the PC1, TEM-2, and CcrA beta-lactamases, corresponding to enzyme-associated intermediates responsible for hydrolysis of tazobactam. Chromophores absorbing at 270 nm (CcrA) and 288 nm (TEM-2 and PC1) were observed for these reaction intermediates. The P99 cephalosporinase formed a stable complex with a UV maximum at 295 nm. Incubation of tazobactam with all of the enzymes resulted in accumulation of a tazobactam reaction product with a short-wavelength absorbance. This product has characteristics similar to those of the major eucaryotic metabolite of tazobactam. Possible reaction mechanisms are presented to explain the findings. In conclusion, both serine-based and metallo-beta-lactamases were irreversibly inactivated by tazobactam following an initial transient inhibition phase.

Relative efficacy of tazobactam, sulbactam and clavulanic acid in enhancing the potency of ampicillin against clinical isolates of Enterobacteriaceae

Three beta-lactamase inhibitors were combined with ampicillin in a fixed 2:1 ratio. The activity of ampicillin was enhanced by tazobactam and by clavulanic acid, and to a lesser extent by sulbactam when tested against fresh clinical isolates of Enterobacteriaceae. At a concentration of 8 micrograms/ml, ampicillin alone inhibited 49.6% of 2,434 consecutive isolates of enteric bacilli compared to 81% inhibited by ampicillin combined with tazobactam or clavulanic acid and 69.3% inhibited by the sulbactam/ampicillin combination. A four-fold or greater reduction in ampicillin MICs was observed in comparable numbers of isolates with all three combinations, but the most marked effects were seen with strains that were highly resistant to ampicillin.

Piperacillin/tazobactam/amikacin versus piperacillin/amikacin/teicoplanin in the empirical treatment of neutropenic patients

A prospective randomized trial was performed to compare the efficacy of a regimen containing a glycopeptide versus one containing a beta-lactamase inhibitor in the treatment of febrile episodes in neutropenic patients. Fifty-eight patients received piperacillin/amikacin/teicoplanin (group 1) and 56 received piperacillin/amikacin/tazobactam (group 2). In the case of persistence of fever without microbiological documentation of the cause, teicoplanin was also given empirically in group 2 on day 4, and amphotericin B in both groups on day 6. In 114 evaluable febrile episodes, the rate of success without modification of therapy was 60% in patients on piperacillin/amikacin/teicoplanin and 41% in patients on piperacillin/amikacin/tazobactam (p < 0.03). Eleven of 34 patients in the latter group who failed to improve eventually responded upon addition of teicoplanin. Ten and nine patients in group 1 and group 2 respectively required the addition of amphotericin B for definite improvement. There were 14 episodes of gram-positive septicemia in each group: the response rate was 100% in group 1 and 43% in group 2. Three episodes of gram-negative breakthrough septicemia occurred in group 1 versus no cases in group 2 (p = 0.1). Three deaths occurred in each group. Piperacillin/amikacin/tazobactam may be as efficacious as piperacillin/amikacin/teicoplanin in the treatment of febrile neutropenic patients provided the regimen is modified (usually by addition of teicoplanin) in unresponsive cases.

Current antimicrobial therapy of anaerobic infections

The treatment of many anaerobic infections involves antimicrobial therapy, appropriate surgical drainage of abscesses, and debridement of devitalized tissue. Most anaerobic infections are polymicrobial and require treatment with agents active against an array of aerobic and anaerobic bacteria. Bacterial resistance, especially to penicillins and tetracyclines, but also to newer agents of other classes, continues to increase. As a result, treatment with more than one drug is often required. Combination therapy is often necessary in serious infection, and is indicated for empiric treatment before receiving culture results. In the past combination therapy has been the mainstay of antimicrobial therapy, but more recent studies suggest that monotherapy for anaerobic infections may dominate the future. Selection of an agent requires consideration of the site of infection and the most likely etiologic agents. In vitro susceptibility is important, but it is not the only determinant of antimicrobial effectiveness. The pharmacology of the drug--absorption, distribution, concentrations in body fluids and tissues, excretion and metabolism--also plays an important role. The nature and severity of the underlying illness are important factors in selecting empiric therapy. Although it is a clinical judgement, in patients considered to have mild to moderate infections, several factors in selecting antimicrobial agents may be considered, including cost, whereas in patients judged to have severe or life-threatening infections, the most potent agents should be chosen as initial therapy, regardless of cost. Finally, the toxicities of the agent must also be considered.