Amplification of Antimicrobial Resistance in Gut Flora of Patients Treated with Ceftriaxone

Abstract

Although antibacterial therapy has an impact on human intestinal flora and the emergence of resistant bacteria, its role in the amplification of antimicrobial resistance and the quantitative exposure-effect relationship is not clear. An observational prospective study was conducted to determine whether and how ceftriaxone exposure is related to amplification of resistance in non-intensive care unit (non-ICU) patients. Serial stool samples from 122 extended-spectrum β-lactamase-positive (ESBL+) hospitalized patients were analyzed by quantitative real-time PCR to quantify the resistant gene blaCTX-M Drug exposure was calculated for each patient by using a population pharmacokinetic model. Multi- and univariate regression and classification regression tree (CART) analyses were used to explore relationships between measures of exposure and amplification of blaCTX-M genes. Amplification of blaCTX-M was observed in 0% (0/11) of patients with no treatment and 33% (20/61) of patients treated with ceftriaxone. Stepwise regression analysis showed a significant association between amplification of blaCTX-M and the plasma area under the concentration-time curve from 0 to 24 h for the unbound fraction of the drug (fAUC0-24), the maximum concentration of drug in serum for the unbound fraction of the drug (fCmax), and the duration of ceftriaxone therapy. Using CART analysis, amplification of blaCTX-M was observed in 11/16 (69%) patients treated for >14 days and in 9/40 (23%) patients treated for ≤14 days (P = 0.0019). In the latter group, amplification was observed in 5/7 (71%) patients with an fAUC0-24 of ≥222 mg · h/liter and in 4/33 (12%) patients with lower drug exposures (P = 0.0033). A similar association was found for an fCmax of ≥30 mg/liter (63% versus 13%, P = 0.0079). A significant association was found between the amplification of blaCTX-M resistance genes and exposure to ceftriaxone. Both duration of treatment and degree of ceftriaxone exposure have a significant impact on the amplification of resistance genes. (The project described in this paper has been registered at ClinicalTrials.gov under identifier NCT01208519.).

Keywords: ceftriaxone; pharmacodynamics; pharmacokinetics; resistance.

Copyright © 2017 American Society for Microbiology.

Figures

FIG 1

Time course of quantitative PCR expressed as a percentage of blaCTX-M/16S rRNA ratio in patients without any treatment (A), in patients treated with ceftriaxone alone (B) and in combination with other drugs (C), and in patients treated with other drugs (D) at the time of screening (initial), the time of the maximum (max PCR), and the last sample (final PCR). The % blaCTX-M/16S rRNA ratios are the absolute measurements calculated by dividing blaCTX-M copy numbers by 16S rRNA copy numbers.

FIG 2

Amplification of resistance genes (percent increase calculated as the maximum blaCTX-M/16S rRNA ratio at any time compared to the ratio at the initial screening) in different patient groups. At the top of the graph, the number of patents with a >20% increase in bla/16S ratios relative to the total number of patients per group is shown for each group. Error bars represent the median and interquartile range. For the CFO comb group, P < 0.05 compared to the No Abx group. The horizontal broken lines represent a relative increase of 20% of blaCTX-M/16S rRNA ratios over the ratio at the initial screening.

FIG 3

Amplification of blaCTX-M resistance genes in rectal samples over time for six different patients treated with ceftriaxone for >14.3 days (top graphs) and <14.3 days (bottom graphs) attaining low (right graphs), intermediate (middle graphs), and high (left graphs) fCmaxs. The duration of ceftriaxone therapy and the fCmax together with the fAUC0–24 are shown for each patient. The horizontal line represents the threshold of blaCTX-M gene amplification observed in nontreated patients.