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Initial concentration-time profile of gentamicin determines efficacy against Enterobacter cloacae ATCC 13047
C R Rayner1, L L Ioannides-Demos, J A Brien
1Department of Pharmacy, Alfred Healthcare Group, Prahran, Victoria, Australia.
Abstract:
In vitro studies were designed to investigate the influence of peak drug concentration (Cmax), the area under the concentration-time curve (AUC), and, consequently, the trough concentration on the bactericidal effects of gentamicin against Enterobacter cloacae (MIC, 0.5 mg/liter) by simulating bolus versus infusion administration and bolus dosing with altered drug clearance. Bacteria in the lag phase were exposed to gentamicin concentration-time profiles modelling either bolus or infusion dosing (AUC constant, Cmax changing) with 30-min postdose peak concentrations (Cpeak30) of 4, 6, 8, and 10 mg/liter or bolus dosing with normal and double drug clearance (Cmax constant, AUC changing) corresponding to normal clearance profiles with Cpeak30 of 6 and 8 mg/liter. Exposure to gentamicin caused early bactericidal effects apparent by 2 h, followed by variable bacteriostatic and recovery phases. Exposure to bolus profiles resulted in greater bactericidal activity than the corresponding infusion profile up to a Cpeak30 of 8 mg/liter. At a Cpeak30 of 10 mg/liter, there were no differences in bactericidal effect. Double clearance profiles had a reduced bactericidal effect at 6 mg/liter compared to the corresponding normal clearance profile, but no differences in bactericidal effect were observed for 8-mg/liter double and normal clearance profiles. These results suggest that the initial exposure (i.e., 0 to 30 min) is a more important determinant for bacterial killing than the AUC or trough concentration for this bacterium. Subject to confirmation of these findings with other gram-negative bacteria, to optimize aminoglycoside efficacy the initial exposure (Cmax) should be maximized by giving higher doses or bolus administration at intervals which may not produce detectable trough concentrations. Clinical trials with a broad range of patients, especially those with higher clearance, would confirm these in vitro observations and define optimal dosing recommendations.
Insights
Maximizing initial gentamicin exposure (Cmax) via bolus dosing is key for killing Enterobacter cloacae, more so than total drug exposure (AUC) or trough levels. This suggests optimizing peak concentrations for improved aminoglycoside efficacy.
Area of Science:
- Pharmacology
- Microbiology
- Infectious Diseases
Background:
- Gentamicin efficacy depends on drug concentration over time.
- Understanding the impact of peak (Cmax), area under the curve (AUC), and trough concentrations is crucial for optimizing antibiotic therapy.
- Enterobacter cloacae is a significant Gram-negative pathogen.
Purpose of the Study:
- To investigate the in vitro bactericidal effects of gentamicin against Enterobacter cloacae.
- To determine the influence of Cmax, AUC, and trough concentrations on gentamicin's killing activity.
- To compare the effects of bolus versus infusion administration and altered drug clearance.
Main Methods:
- In vitro simulation of gentamicin concentration-time profiles.
- Modeling bolus vs. infusion dosing with constant AUC and varying Cmax.
- Modeling bolus dosing with constant Cmax and altered drug clearance (normal vs. double).
- Exposure of bacteria in lag phase to various gentamicin Cpeak30 levels (4-10 mg/liter).
Main Results:
- Gentamicin demonstrated early bactericidal effects within 2 hours.
- Bolus administration showed greater bactericidal activity than infusion up to Cpeak30 of 8 mg/liter.
- Altered clearance affected bactericidal activity, with reduced effect at 6 mg/liter for double clearance.
- Initial drug exposure (0-30 min) appeared more critical for bacterial killing than AUC or trough concentration.
Conclusions:
- Initial gentamicin exposure (Cmax) is a primary determinant of bactericidal effect against Enterobacter cloacae.
- Maximizing Cmax through higher doses or bolus administration may optimize aminoglycoside efficacy.
- Further clinical studies are needed to confirm these findings and establish optimal dosing strategies, especially in patients with high drug clearance.