Efficacy of Combined Rifampicin Formulations Delivered by the Pulmonary Route to Treat Tuberculosis in the Guinea Pig Model

Liposomes, as vehicles alone or in combination with rifampicin (RIF) microparticles (RMs), were evaluated as vehicles to enhance the permeation of RIF into granulomas. RIF liposomes (RLs) were extruded through a 0.1 µm polypropylene membrane. RMs were prepared by the solvent evaporation method. Four weeks after infection, guinea pigs (GPs) were assigned to groups treated with a combination of RM-RLs or RLs alone. RLs were nebulized after extrusion whereas RMs were suspended in saline and nebulized to GPs in a nose-only inhalation chamber. Necropsy was performed after the treatment; the lungs and spleen were resected for bacteriology. RLs had mean diameters of 137.1 ± 33.7 nm whereas RMs had a projected area diameter of 2.48 µm. The volume diameter of RMs was 64 ± 1 µm, indicating that RMs were aggregated. The treatment of TB-infected GPs with RLs significantly reduced their lung bacterial burden and wet spleen weight compared with those treated with blank liposomes. The treatment of TB-infected animals with RM-RLs also reduced their lung bacterial burden and wet spleen weight even though these reductions were not statistically different. Based on these results, the permeation of RIF into granulomas appears to be enhanced when encapsulated into liposomes delivered by the pulmonary route.