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Aim: To evaluate (i) the in vitro activity of eugenol (EUG) and three derivatives against Mycobacterium tuberculosis (Mtb), nontuberculous mycobacteria (NTM) and other bacteria, (ii) the EUG and antituberculosis drugs combinatory effect and (iii) the EUG and its derivatives cytotoxicity. Materials & methods: Minimum inhibitory concentration of the compounds were determined by resazurin microtiter or broth microdilution assay and the drug interaction between EUG and antituberculosis drugs by resazurin drug combination microtiter. The cytotoxicity was carried out in macrophages, HeLa and VERO cells. Results: EUG and derivatives displayed activity and synergic effect of EUG combined with rifampicin, isoniazid, ethambutol, and pyrazinamide in Mtb including multidrug-resistant isolates, with more selectivity to bacillus than macrophages, HeLa and VERO cells (selective index from 0.65 to 31.4). EUG derivatives (4-allyl-2-methoxyphenyl acetate, 4-allyl-2-methoxyphenyl benzoate, and 4-allyl-2-methoxyphenyl 4-nitrobenzoate) were more active against nontuberculous mycobacteria than EUG. EUG and derivatives exhibited low activity in other Gram-positive and -negative bacteria. Conclusion: EUG and its derivatives show activity against Mycobacterium spp. and synergic effect of EUG combined with antituberculosis drugs against Mtb.

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