Tuberculosis (TB) is a major cause of morbidity and mortality worldwide for people living with HIV. Rifabutin (RFB) is an anti-TB drug with potent anti-bactericidal activity, low minimum inhibitory concentration (MIC, 64 ng/ml), long terminal half-life, higher tissue uptake and reduced potential for drug-drug interactions compared to other TB drugs from the rifamycin family. Successful TB treatment requires strict adherence to drug regimens for prolonged periods of time. Long-acting (LA) injectable drug formulations can potentially simplify TB treatment by reducing drug dosing intervals, improving adherence to treatment regimens. We developed LA injectable RFB formulations (LA-RFB) made of biodegradable polymers, that solidify after subcutaneous injection that can efficiently deliver drug for 4 months.
Twenty-one LA-RFB formulations with various composition were first evaluated for release properties in vitro. Then, RFB plasma concentration was assessed for 4 months in BALB/c mice (n=4) administered a single subcutaneous injection of optimized LA-RFB (15 mg RFB/dose). RFB tissue penetration (lung, liver, spleen, kidney, and lymph nodes) was analyzed at 2-and 6-weeks post administration. The efficacy of the LA-RFB formulation was evaluated in BALB/c mice (n=6) after pre- or post-exposure to Mtb via aerosol (~200 CFU). Bacterial burden was quantitated in lung, liver, and spleen (CFU/g of tissue) and lung pathology was evaluated by immunohistochemistry.
The selected LA-RFB formulation provided RFB plasma concentrations above the MIC for 16 weeks post administration. Mean tissue RFB concentrations six-weeks post injection were: 6.7 ± 1.6 ?g/g lung, 7.8 ± 2.1 ?g/g liver, 9.0 ± 2.1 ?g/g spleen, 8.3 ± 1.7 µg/g kidney, 14.0 ± 3.2 µg/g lymph nodes (mean ± S.E.M.). A high tissue to plasma ratio of drug was observed in lung 15.4 (median, range 12.4-23.7). BALB/c mice treated with LA-RFB pre- Mtb exposure were fully protected from the infection. Post exposure treatment resulted in clearance of existing Mtb infection in lung, prevention of Mtb dissemination to distal organs (Figure 1a) and no lung pathology (Figure 1b).
The LA-RFB formulation can deliver drug for four months after a single subcutaneous injection, efficiently prevents Mtb infection, treats existing Mtb infection, and prevent Mtb dissemination to distal organs. LA-RFB provides a proof of concept for the further development of multiple LA formulations of anti-TB drugs.