A pharmacokinetic-pharmacodynamic model characterizing the emergence of resistant Escherichia coli subpopulations during ertapenem exposure.

OBJECTIVES: Resistant subpopulations with reduced expression of outer membrane porins have been observed in ESBL-producing Escherichia coli during exposure to ertapenem. The aim of this work was to develop a pharmacokinetic-pharmacodynamic (PKPD) model to characterize the emergence of resistant E. coli during exposure to ertapenem and to predict bacterial killing following different dosing regimens of ertapenem. METHODS: Data from in vitro time-kill experiments were used to develop a mechanism-based PKPD model for three E. coli strains: a native strain, an ESBL-producing strain, and an ESBL-producing strain with reduced expression of porins OmpF and OmpC. Each strain was exposed to static ertapenem concentrations (1-512 × MIC) for 24 h using starting inocula of ∼10(6) and 10(8) cfu/mL. RESULTS: The developed PKPD model consisted of three bacterial states: susceptible growing, less susceptible non-growing, and non-susceptible non-growing bacteria. A pre-existing bacterial subpopulation was used to describe the emergence of resistance. The PKPD model adequately characterized the data of the three E. coli strains investigated. Results from predictions suggest that the conventional dosage (1 g intravenously once daily) might result in regrowth of resistant subpopulations when used to treat infection caused by ESBL-producing strains. CONCLUSIONS: Resistant subpopulations frequently emerged in E. coli when exposed to ertapenem, supporting that the time course of emergence of resistance should be taken into consideration when selecting dosing regimens.

Dosing regimens of oral ciprofloxacin for children with severe malnutrition: a population pharmacokinetic study with Monte Carlo simulation.

BACKGROUND: Severe malnutrition is frequently complicated by sepsis, leading to high case fatality. Oral ciprofloxacin is a potential alternative to the standard parenteral ampicillin/gentamicin combination, but its pharmacokinetics in malnourished children is unknown. METHODS: Ciprofloxacin (10 mg/kg, 12 hourly) was administered either 2 h before or up to 2 h after feeds to Kenyan children hospitalized with severe malnutrition. Four plasma ciprofloxacin concentrations were measured over 24 h. Population analysis with NONMEM investigated factors affecting the oral clearance (CL) and the oral volume of distribution (V). Monte Carlo simulations investigated dosage regimens to achieve a target AUC(0-24)/MIC ratio of ≥125. RESULTS: Data comprised 202 ciprofloxacin concentration measurements from 52 children aged 8-102 months. Absorption was generally rapid but variable; C(max) ranged from 0.6 to 4.5 mg/L. Data were fitted by a one-compartment model with first-order absorption and lag. The parameters were CL (L/h) = 42.7 (L/h/70 kg) × [weight (kg)/70](0.75) × [1 + 0.0368 (Na(+) - 136)] × [1 - 0.283 (high risk)] and V (L) = 372 × (L/70 kg) × [1 + 0.0291 (Na(+) - 136)]. Estimates of AUC(0-24) ranged from 8 to 61 mg·h/L. The breakpoint for Gram-negative organisms was <0.06 mg/L with doses of 20 mg/kg/day and <0.125 mg/L with doses of 30 or 45 mg/kg/day. The cumulative fraction of response with 30 mg/kg/day was ≥80% for Escherichia coli, Klebsiella pneumoniae and Salmonella species, but <60% for Pseudomonas aeruginosa. CONCLUSIONS: An oral ciprofloxacin dose of 10 mg/kg three times daily (30 mg/kg/day) may be a suitable alternative antibiotic for the management of sepsis in severely malnourished children. Absorption was unaffected by the simultaneous administration of feeds.

Evaluation of automated time-lapse microscopy for assessment of in vitro activity of antibiotics.

This study aimed to evaluate the potential of a new time-lapse microscopy based method (oCelloScope) to efficiently assess the in vitro antibacterial effects of antibiotics. Two E. coli and one P. aeruginosa strain were exposed to ciprofloxacin, colistin, ertapenem and meropenem in 24-h experiments. Background corrected absorption (BCA) derived from the oCelloScope was used to detect bacterial growth. The data obtained with the oCelloScope were compared with those of the automated Bioscreen C method and standard time-kill experiments and a good agreement in results was observed during 6-24h of experiments. Viable counts obtained at 1, 4, 6 and 24h during oCelloScope and Bioscreen C experiments were well correlated with the corresponding BCA and optical density (OD) data. Initial antibacterial effects during the first 6h of experiments were difficult to detect with the automated methods due to their high detection limits (approximately 105CFU/mL for oCelloScope and 107CFU/mL for Bioscreen C), the inability to distinguish between live and dead bacteria and early morphological changes of bacteria during exposure to ciprofloxacin, ertapenem and meropenem. Regrowth was more frequently detected in time-kill experiments, possibly related to the larger working volume with an increased risk of pre-existing or emerging resistance. In comparison with Bioscreen C, the oCelloScope provided additional information on bacterial growth dynamics in the range of 105 to 107CFU/mL and morphological features. In conclusion, the oCelloScope would be suitable for detection of in vitro effects of antibiotics, especially when a large number of regimens need to be tested.