Time-kill kinetics of anti-tuberculosis drugs, and emergence of resistance, in relation to metabolic activity of Mycobacterium tuberculosis.
OBJECTIVE
The pharmacodynamics of tuberculosis (TB) treatment should be further explored, to prevent emergence of resistance, treatment failure and relapse of infection. The diagnostic drug susceptibility tests guiding TB therapy investigate metabolically active Mycobacterium tuberculosis (Mtb) isolates under static conditions and as such are not informative with respect to the time-kill kinetics of anti-TB drugs and the emergence of resistance in metabolically lowly active or even dormant mycobacterial cells.


METHODS
In vitro, the killing capacity of rifampicin, isoniazid, ethambutol and amikacin regarding the degree of killing, killing rate and selection of resistant mutants was investigated in metabolically highly active versus metabolically lowly active Mtb cells.


RESULTS
Isoniazid showed rapid and high killing capacity towards highly active mycobacteria, but due to the emergence of resistance could not eliminate the Mtb. Efflux pump-mediated isoniazid resistance was predominant. Rifampicin revealed a relatively slow and time-dependent killing capacity, but achieved elimination of all mycobacteria. Ethambutol was not bactericidal. Amikacin showed a high and extremely rapid killing activity that was not time dependent and could eliminate all mycobacteria. Exposure of lowly active Mtb populations to isoniazid, rifampicin or amikacin led to the emergence of resistant mutants. Compared with the highly active mycobacteria, elimination of the susceptible lowly active mycobacteria required a 64-fold increased isoniazid concentration and a 4-fold increased rifampicin concentration, whereas amikacin was equally effective irrespective of the metabolic state of the mycobacteria.


CONCLUSIONS
The anti-TB drugs differ significantly regarding their time-kill kinetics. In addition, the metabolic state of Mtb significantly affects its susceptibility to antimicrobials, with the exception of amikacin. Optimization of dosage of anti-TB drugs is required to achieve maximum drug concentrations at the site of infection in order to maximize reduction in Mtb load and to minimize the emergence and selection of resistance.
de Steenwinkel
Jurriaan E M
JE
Department of Medical Microbiology and Infectious Diseases, Erasmus MC, University Medical Centre Rotterdam, Rotterdam, The Netherlands. j.desteenwinkel@erasmusmc.nl
de Knegt
Gerjo J
GJ
ten Kate
Marian T
MT
van Belkum
Alex
A
Verbrugh
Henri A
HA
Kremer
Kristin
K
van Soolingen
Dick
D
Bakker-Woudenberg
Irma A J M
IA
D000995:Antitubercular Agents / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D024881:Drug Resistance, Bacterial / Q000235:genetics*; D006801:Humans; D007700:Kinetics; D008826:Microbial Sensitivity Tests; D009154:Mutation; D009169:Mycobacterium tuberculosis / Q000187:drug effects* / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D013997:Time Factors
D000995:Antitubercular Agents