Determining β-lactam exposure threshold to suppress resistance development in Gram-negative bacteria.
β-Lactams are commonly used for nosocomial infections and resistance to these agents among Gram-negative bacteria is increasing rapidly. Optimized dosing is expected to reduce the likelihood of resistance development during antimicrobial therapy, but the target for clinical dose adjustment is not well established. We examined the likelihood that various dosing exposures would suppress resistance development in an in vitro hollow-fibre infection model.



Two strains of Klebsiella pneumoniae and two strains of Pseudomonas aeruginosa (baseline inocula of ∼10 8  cfu/mL) were examined. Various dosing exposures of cefepime, ceftazidime and meropenem were simulated in the hollow-fibre infection model. Serial samples were obtained to ascertain the pharmacokinetic simulations and viable bacterial burden for up to 120 h. Drug concentrations were determined by a validated LC-MS/MS assay and the simulated exposures were expressed as C min /MIC ratios. Resistance development was detected by quantitative culture on drug-supplemented media plates (at 3× the corresponding baseline MIC). The C min /MIC breakpoint threshold to prevent bacterial regrowth was identified by classification and regression tree (CART) analysis.



For all strains, the bacterial burden declined initially with the simulated exposures, but regrowth was observed in 9 out of 31 experiments. CART analysis revealed that a C min /MIC ratio ≥3.8 was significantly associated with regrowth prevention (100% versus 44%, P  = 0.001).



The development of β-lactam resistance during therapy could be suppressed by an optimized dosing exposure. Validation of the proposed target in a well-designed clinical study is warranted.
University of Houston, Houston, TX, USA.
Vincent H
VH
Tam
University of Houston, Houston, TX, USA.
Kai-Tai
KT
Chang
University of Houston, Houston, TX, USA.
Jian
J
Zhou
University of Houston, Houston, TX, USA.
Kimberly R
KR
Ledesma
University of Houston, Houston, TX, USA.
Kady
K
Phe
University of Houston, Houston, TX, USA.
Song
S
Gao
Pharmacologie Cellulaire et Moléculaire & Louvain Drug Research Institute, Université Catholique de Louvain, Brussels, Belgium.
Françoise
F
Van Bambeke
Servicio de Microbiología, Hospital Universitario Ramón y Cajal and Instituto Ramón y Cajal de Investigación Sanitaria (IRYCIS), Madrid, Spain.
Ana María
AM
Sánchez-Díaz
University Hospital Son Espases, Instituto de Investigación Sanitaria de Palma, Palma de Mallorca, Spain.
Laura
L
Zamorano
University Hospital Son Espases, Instituto de Investigación Sanitaria de Palma, Palma de Mallorca, Spain.
Antonio
A
Oliver
Servicio de Microbiología, Hospital Universitario Ramón y Cajal and Instituto Ramón y Cajal de Investigación Sanitaria (IRYCIS), Madrid, Spain.
Rafael
R
Cantón
D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D000077723:Cefepime; D002442:Ceftazidime / Q000494:pharmacology; D002511:Cephalosporins / Q000494:pharmacology; D006801:Humans; D007700:Kinetics; D007711:Klebsiella pneumoniae / Q000187:drug effects* / Q000254:growth & development; D000077731:Meropenem; D008826:Microbial Sensitivity Tests / Q000379:methods; D011550:Pseudomonas aeruginosa / Q000187:drug effects* / Q000254:growth & development; D053719:Tandem Mass Spectrometry; D013845:Thienamycins / Q000494:pharmacology; D018440:beta-Lactam Resistance; D047090:beta-Lactams / Q000494:pharmacology*
D000900:Anti-Bacterial Agents; D002511:Cephalosporins; D013845:Thienamycins; D047090:beta-Lactams; D000077723:Cefepime; D002442:Ceftazidime; D000077731:Meropenem