title: Pharmacodynamics of ceftazidime/avibactam against extracellular and intracellular forms of Pseudomonas aeruginosa.
abstract: When tested in broth, avibactam reverses ceftazidime resistance in many Pseudomonas aeruginosa that express ESBLs. We examined whether similar reversal is observed against intracellular forms of P. aeruginosa .
  
  
  
  Strains: reference strains; two engineered strains with basal non-inducible expression of AmpC and their isogenic mutants with stably derepressed AmpC; and clinical isolates with complete, partial or no resistance to reversion with avibactam. Pharmacodynamic model: 24 h concentration-response to ceftazidime [0.01-200 mg/L alone or with avibactam (4 mg/L)] of bacteria in broth or bacteria phagocytosed by THP-1 monocytes, with calculation of ceftazidime relative potency ( C s : concentration yielding a static effect) and maximal relative effect [ E max : cfu decrease at infinitely large antibiotic concentrations (efficacy in the model)] using the Hill equation. Cellular content of avibactam: quantification by LC-MS/MS.
  
  
  
  For both extracellular and intracellular bacteria, ceftazidime C s was always close to its MIC. For ceftazidime-resistant strains, avibactam addition shifted ceftazidime C s to values close to the MIC of the combination in broth. E max was systematically below the detection limit (-5 log 10 ) for extracellular bacteria, but limited to -1.3 log 10 for intracellular bacteria (except for two isolates) with no effect of avibactam. The cellular concentration of avibactam reflected extracellular concentration and was not influenced by ceftazidime (0-160 mg/L).
  
  
  
  The potential for avibactam to inhibit β-lactamases does not differ for extracellular and intracellular forms of P. aeruginosa , denoting an unhindered access to its target in both situations. The loss of maximal relative efficacy of ceftazidime against intracellular P. aeruginosa was unrelated to resistance via avibactam-inhibitable β-lactamases.
authors.affiliation: Pharmacologie cellulaire et moléculaire, Louvain Drug Research Institute, Université catholique de Louvain, Brussels, Belgium.
authors.forename: J M
authors.initials: JM
authors.lastname: Buyck
authors.affiliation: Pharmacologie cellulaire et moléculaire, Louvain Drug Research Institute, Université catholique de Louvain, Brussels, Belgium.
authors.forename: C
authors.initials: C
authors.lastname: Luyckx
authors.affiliation: MASSMET Platform, Louvain Drug Research Institute, Université catholique de Louvain, Brussels, Belgium.|Bioanalysis and Pharmacology of Bioactive Lipids Research Group, Louvain Drug Research Institute, Université catholique de Louvain, Brussels, Belgium.
authors.forename: G G
authors.initials: GG
authors.lastname: Muccioli
authors.affiliation: Cerexa Inc., Oakland, CA, USA.
authors.forename: K M
authors.initials: KM
authors.lastname: Krause
authors.affiliation: AstraZeneca Pharmaceuticals, Waltham, MA, USA.
authors.forename: W W
authors.initials: WW
authors.lastname: Nichols
authors.affiliation: Pharmacologie cellulaire et moléculaire, Louvain Drug Research Institute, Université catholique de Louvain, Brussels, Belgium.
authors.forename: P M
authors.initials: PM
authors.lastname: Tulkens
authors.affiliation: Pharmacologie cellulaire et moléculaire, Louvain Drug Research Institute, Université catholique de Louvain, Brussels, Belgium.
authors.forename: F
authors.initials: F
authors.lastname: Van Bambeke
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D053961:Azabicyclo Compounds / Q000494:pharmacology*; D002442:Ceftazidime / Q000494:pharmacology*; D003593:Cytoplasm / Q000187:drug effects / Q000382:microbiology; D004338:Drug Combinations; D006801:Humans; D007700:Kinetics; D007963:Leukocytes, Mononuclear / Q000187:drug effects / Q000382:microbiology*; D008826:Microbial Sensitivity Tests; D011550:Pseudomonas aeruginosa / Q000187:drug effects* / Q000235:genetics; D053719:Tandem Mass Spectrometry; D065093:beta-Lactamase Inhibitors / Q000494:pharmacology*
chemical_list: D000900:Anti-Bacterial Agents; D053961:Azabicyclo Compounds; D004338:Drug Combinations; C000595613:avibactam, ceftazidime drug combination; D065093:beta-Lactamase Inhibitors; D002442:Ceftazidime