ABT492 vs. levofloxacin in an in vitro dynamic model: comparative pharmacodynamics with differentially susceptible Staphylococcus aureus and the relative ability to prevent the selection of resistant mutants
Abstract number: 902_p1025
To compare the kinetics of killing/regrowth of differentially susceptible clinical isolates of Staphylococcus aureus exposed to ABT492 and levofloxacin and to explore their relative abilities to prevent the selection of resistant mutants.
Three clinical isolates of S. aureus including two ciprofloxacin-susceptible S. aureus 201 and 480 and a ciprofloxacin-resistant S. aureus 866 were exposed to clinically achievable ratios of area under the curve (AUC) to MIC in a dynamic model that simulated human pharmacokinetics of ABT492 (400 mg) and levofloxacin (500 mg) as a single dose. In addition, S. aureus 201 was exposed to single and multiple doses of ABT492 and levofloxacin (both q.d. for 3 days) over wide ranges of the 24-h AUC/MIC (AUC24/MIC) including clinically achievable AUC24/MIC ratios.
With each isolate, ABT492 at the clinically achievable AUC/MICs produced greater anti-staphylococcal effects than levofloxacin. Areas between the control growth and the time-kill curves (ABBC in single dose simulations and the sum of ABBCs determined after the first, second and third dosing in multiple dose simulations ABBC1 + 2 + 3) were larger with ABT492 than levofloxacin. Moreover, at comparable AUC/MICs and AUC24/MICs maximal reductions in the starting inoculum of ABT492-exposed S. aureus were more pronounced than with levofloxacin. Loss in the susceptibility of S. aureus 201 exposed to both ABT492 and levofloxacin depended on the simulated AUC24/MIC. Although the maximal increase in MIC (MICfinal) related to its initial value (MICinitial) was seen at the higher AUC24/MIC ratio of ABT492 (120 h) than levofloxacin (50 h), similar AUC24/MICs (240 and 200 h, respectively) were protective against the selection of resistant S. aureus. These threshold values are readily achievable with 400 mg ABT492 (AUC24/MIC 870 h) but not with 500 mg levofloxacin (AUC24/MIC 70 h).
Overall, these findings predict greater efficacy of clinically achievable AUC/MIC (or AUC24/MIC) of ABT492 both in terms of the anti-staphylococcal effect and prevention of the selection of resistant mutants."
|Session name:||XXIst ISTH Congress|
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