Intra- and Extracellular Activities of Trimethoprim-Sulfamethoxazole against Susceptible and Multidrug-Resistant Mycobacterium tuberculosis

Abstract

We investigated the activity of trimethoprim-sulfamethoxazole (SXT) against Mycobacterium tuberculosis, the pathogen that causes tuberculosis (TB). The MIC distribution of SXT was 0.125/2.4 to 2/38 mg/liter for the 100 isolates tested, including multiand extensively drug-resistant isolates (MDR/XDR-TB), whereas the intracellular MIC 90 of sulfamethoxazole (SMX) for the pansusceptible strain H37Rv was 76 mg/liter. In an exploratory analysis using a ratio of the unbound area under the concentrationtime curve from 0 to 24 h over MIC (fAUC 0 -24 /MIC) using >25 as a potential target, the cumulative fraction response was >90% at doses of >2,400 mg of SMX. SXT is a potential treatment option for MDR/XDR-TB. Due to the global increase in multidrug-resistant tuberculosis (MDR-TB) and extensively drug-resistant tuberculosis (XDR-TB) (1), already approved drugs, such as trimethoprim-sulfamethoxazole (SXT), have been reinvestigated with favorable results (2, 3). However, very few highly drug-resistant isolates have been tested, despite the main potential of SXT being in the treatment of XDR-TB. The active component of SXT regarding Mycobacterium tuberculosis is sulfamethoxazole (SMX) (3-9), although it is unknown whether its effect is mainly extra-or intracellular. Therefore, the objective of this study was to determine the extra-and intracellular activities of SMX against both MDR-and XDR-TB isolates and to explore a ratio of the unbound area under the concentration-time curve from 0 to 24 h over MIC (fAUC 0 -24 / MIC) using Ն25 as a potential target and the associated cumulative fraction response values (10) at different doses of SMX.In this study, 100 M. tuberculosis isolates with unique restriction fragment length polymorphism (RFLP) patterns were included, comprising 14 consecutive fully susceptible wild-type isolates, 48 MDR-TB isolates, 13 XDR-TB isolates, and the remainder with mixed resistance patterns, referred to as non-MDR/XDR-TB isolates. The pansusceptible strain H37Rv (ATCC 27294) was used as a control.A stock solution of trimethoprim (TMP) and SMX diluted in dimethyl sulfoxide (DMSO) and 1 M NaOH, respectively, was prepared in serial two-step dilutions, reaching a final concentration range of 0.008 to 8/0.15 to 152 of TMP and SMX, respectively (ratio of 1:19). The MICs were determined using Middlebrook 7H10 (7H10) medium (n ϭ 84), as previously described (11). In Bactec 960 MGIT (MGIT; Becton, Dickinson, Franklin Lakes, NJ, USA) tubes, 17 isolates were included (14 fully susceptible wildtype isolates, two isoniazid-resistant isolates, and one MDR-TB isolate).The MIC distribution of the 84 drug-resistant M. tuberculosis isolates in 7H10 ranged from 2.4 to 38 mg/liter of sulfamethoxazole (0.125/2.4 to 2/38 mg/liter of trimethoprim-sulfamethoxazole, i.e., SXT) (Fig. 1a). No significant differences in the MIC distributions between MDR-TB, XDR-TB, or isolates with other resistance patterns were observed. All isolates had MICs of Յ38 mg/liter of SMX, including the susceptible consecutive wild-type strains (n ϭ 14...

Minimum inhibitory concentration distributions for Mycobacterium avium complex—towards evidence-based susceptibility breakpoints

“…1,3,5,[7][8][9] Although no breakpoint has been established for amikacin, a similar rate of isolates below 16 mg/l (80.8%) was found, in agreement with a previous study (85.9%). 7 For the remaining drugs, and in particular for rifampicin, ethambutol, linezolid, and moxifloxacin, most isolates had MICs beyond the reach of therapeutic doses based on what is suggested by PK/PD, clinical outcome, and MIC distribution data for MAC, 5,6,8 even if synergy is taken into account. The evidence on which such drugs are recommended for the initial treatment of MAC is unclear and this has been based in part on clinical trials involving HIV patients in the pre-antiretroviral therapy era.…”

Mycobacterium tuberculosis Folate Metabolism and the Mechanistic Basis for para -Aminosalicylic Acid Susceptibility and Resistance

“…The need for novel therapeutic agents to meet the challenge of MDR and XDR TB has renewed interest in these and other antifolates. Several reports indicate that the vast majority of clinical isolates of M. tuberculosis, including MDR and XDR strains, are susceptible to a combination of sulfamethoxazole and the diaminopyrimidine trimethoprim (29)(30)(31)(32)(33). In addition, PAS has recently been shown to be an antifolate prodrug (34)(35)(36).…”

“…A recent structural study suggested that the Tyr100 residue in M. tuberculosis DHFR may be responsible for the weak binding of trimethoprim to M. tuberculosis DHFR and showed that a variant, Y100F, had increased affinity for trimethoprim (59). Despite this limited antitubercular activity of trimethoprim, several studies have demonstrated that combinations of trimethoprim and sulfamethoxazole are effective against drug-susceptible and MDR strains of M. tuberculosis (29)(30)(31)(32)(33)). An evaluation of synergy between these drugs showed that subinhibitory concentrations of sulfamethoxazole conferred a significant reduction of the MIC of trimethoprim (fractional inhibitory concentration index of 0.5) (31).…”

Meropenem-Clavulanic Acid Has High In Vitro Activity against Multidrug-Resistant Mycobacterium tuberculosis

“…As MDR/XDR-TB is notoriously difficult to treat, already approved drugs, such as trimethoprim-sulfamethoxazole, are being investigated as treatment options (1). The activity of penicillin against Mycobacterium tuberculosis was investigated in the 1940s (2), but ␤-lactams were deemed ineffective.…”