Incorporation of Rifabutin (RB) into GP, a first-line anti-TB drug

GP containing precipitated RB (GP-RB) were made as previously described (Soto et al., 2010[36]), with a slight modification. Briefly, the dry GP were incubated in 0.2 N HCl with stock RB solution (100 mg RB per ml in 0.2 N HCl) for their hydration in a drug to polymer ratio of 1:1. To precipitate and trap RB inside the GP, Tris buffer (1M, pH 8) was added. The samples were then centrifuged twice, to remove the unprecipitated RB and buffer, frozen at -80 °C and lyophilized. The resulting 'GP-RB' formulation had a strong violet-red colored appearance.