Ceftazidime-avibactam: a novel cephalosporin/ß-lactamase inhibitor combination.

Avibactam (formerly NXL104, AVE1330A) is a synthetic non-ß-lactam, ß-lactamase inhibitor that inhibits the activities of Ambler class A and C ß-lactamases and some Ambler class D enzymes. This review summarizes the existing data published for ceftazidime-avibactam, including relevant chemistry, mechanisms of action and resistance, microbiology, pharmacokinetics, pharmacodynamics, and efficacy and safety data from animal and human trials. Although not a ß-lactam, the chemical structure of avibactam closely resembles portions of the cephem bicyclic ring system, and avibactam has been shown to bond covalently to ß-lactamases. Very little is known about the potential for avibactam to select for resistance. The addition of avibactam greatly (4-1024-fold minimum inhibitory concentration [MIC] reduction) improves the activity of ceftazidime versus most species of Enterobacteriaceae depending on the presence or absence of ß-lactamase enzyme(s). Against Pseudomonas aeruginosa, the addition of avibactam also improves the activity of ceftazidime (~fourfold MIC reduction). Limited data suggest that the addition of avibactam does not improve the activity of ceftazidime versus Acinetobacter species or most anaerobic bacteria (exceptions: Bacteroides fragilis, Clostridium perfringens, Prevotella spp. and Porphyromonas spp.). The pharmacokinetics of avibactam follow a two-compartment model and do not appear to be altered by the co-administration of ceftazidime. The maximum plasma drug concentration (C(max)) and area under the plasma concentration-time curve (AUC) of avibactam increase linearly with doses ranging from 50 mg to 2,000 mg. The mean volume of distribution and half-life of 22 L (~0.3 L/kg) and ~2 hours, respectively, are similar to ceftazidime. Like ceftazidime, avibactam is primarily renally excreted, and clearance correlates with creatinine clearance. Pharmacodynamic data suggest that ceftazidime-avibactam is rapidly bactericidal versus ß-lactamase-producing Gram-negative bacilli that are not inhibited by ceftazidime alone.Clinical trials to date have reported that ceftazidime-avibactam is as effective as standard carbapenem therapy in complicated intra-abdominal infection and complicated urinary tract infection, including infection caused by cephalosporin-resistant Gram-negative isolates. The safety and tolerability of ceftazidime-avibactam has been reported in three phase I pharmacokinetic studies and two phase II clinical studies. Ceftazidime-avibactam appears to be well tolerated in healthy subjects and hospitalized patients, with few serious drug-related treatment-emergent adverse events reported to date.In conclusion, avibactam serves to broaden the spectrum of ceftazidime versus ß-lactamase-producing Gram-negative bacilli. The exact roles for ceftazidime-avibactam will be defined by efficacy and safety data from further clinical trials. Potential future roles for ceftazidime-avibactam include the treatment of suspected or documented infections caused by resistant Gram-negative-bacilli producing extended-spectrum ß-lactamase (ESBL), Klebsiella pneumoniae carbapenemases (KPCs) and/or AmpC ß-lactamases. In addition, ceftazidime-avibactam may be used in combination (with metronidazole) for suspected polymicrobial infections. Finally, the increased activity of ceftazidime-avibactam versus P. aeruginosa may be of clinical benefit in patients with suspected or documented P. aeruginosa infections.

Comparison of the next-generation aminoglycoside plazomicin to gentamicin, tobramycin and amikacin.

Plazomicin (formerly ACHN-490) is a next-generation aminoglycoside that was synthetically derived from sisomicin by appending a hydroxy-aminobutyric acid substituent at position 1 and a hydroxyethyl substituent at position 6'. Plazomicin inhibits bacterial protein synthesis and exhibits dose-dependent bactericidal activity. Plazomicin demonstrates activity against both Gram-negative and Gram-positive bacterial pathogens, including isolates harboring any of the clinically relevant aminoglycoside-modifying enzymes. However, like older parenteral aminoglycosides, plazomicin is not active against bacterial isolates expressing ribosomal methyltransferases conferring aminoglycoside resistance. Plazomicin has been reported to demonstrate in vitro synergistic activity when combined with daptomycin or ceftobiprole versus methicillin-resistant Staphylococcus aureus, heteroresistant vancomycin-intermediate S. aureus, vancomycin-intermediate S. aureus, and vancomycin-resistant S. aureus and against Pseudomonas aeruginosa when combined with cefepime, doripenem, imipenem or piperacillin-tazobactam. After intravenous administration of plazomicin to humans at a dose of 15 mg/ kg, the maximum concentraration was 113 µg/ml, the area under the curve(0-24) was 239 h·µg/ml, the half-life was 4.0 h and the steady-state volume of distribution was 0.24 L/kg. Results from a Phase II randomized, double-blind study in patients with complicated urinary tract infection and acute pyelonephritis including cases with concurrent bacteremia comparing plazomicin 15 mg/kg intravenously once daily for 5 days with levofloxacin 750 mg intravenously. for 5 days are anticipated in 2012. Human studies to date have not reported nephrotoxicity or ototoxicity, and lack of ototoxicity has been reported in the guinea pig model. Given reported increases in bacterial resistance to current antimicrobial agents and the lack of availability of new agents with novel mechanisms, plazomicin may become a welcomed addition to the antibacterial armamentarium pending positive results from large-scale clinical trials and other required clinical studies.