Mycobacterium tuberculosis
(Mtb) has acquired resistance and consequently the antibiotic therapeutic options available
against this microorganism are limited. In this scenario, the use of usnic acid (UA), a natural compound, encapsulated
into liposomes is proposed as a new approach in multidrug-resistant tuberculosis (MDR-TB) therapy. Thus the aim of this
study was to evaluate the effect of the encapsulation of UA into liposomes, as well as its combination with antituberculous
agents such as rifampicin (RIF) and isoniazid (INH) against MDR-TB clinical isolates. The in vitro antimycobacterial
activity of UA-loaded liposomes (UA-Lipo) against MDR-TB was assessed by the microdilution method. The in vitro
interaction of UA with antituberculous agents was carried out using checkerboard method. Minimal inhibitory concentration
values were 31.25 and 0.98 μg/mL for UA and UA-Lipo, respectively. The results exhibited a synergistic interaction
between RIF and UA [fractional inhibitory concentration index (FICI) = 0.31] or UA-Lipo (FICI = 0.28). Regarding INH,
the combination of UA or UA-Lipo revealed no marked effect (FICI = 1.30-2.50). The UA-Lipo may be used as a dosage
form to improve the antimycobacterial activity of RIF, a first-line drug for the treatment of infections caused by Mtb.
