Rifampicin nanocrystals: Towards an innovative approach to treat tuberculosis

Highlights

• Rif nanosuspensions were developed for tuberculosis treatment by miniaturized wet-bead milling method.

• The validation of the mathematical model was confirmed with two optimized preparations (F1-Rif and F2-Rif).

• The formulations showed the formation of long-term (2 years) stable systems with adequate physical characteristics.

• The formulations presented a significant increase of saturation solubility and increased dissolution of rifampicin.

• The antimicrobial activity and in vitro cytotoxicity assay in HepG2 cells indicated vigorous antimicrobial activity.

Abstract

Tuberculosis (TB) is one of the top ten causes of death worldwide and a leading cause of death in HIV patients. Rifampicin (Rif), a low water-soluble drug, is a critical first-line treatment and the most effective drug substance for therapy of drug-susceptible TB. However, Rif has high interindividual pharmacokinetic variability, mainly due to its highly variable absorption caused by its poor solubility. Drug nanocrystals are a promising technology to overcome this variability by increasing the surface area. This strategy allows for increasing the dissolution rate and improving the bioavailability of this BCS class II drug. In this study, Rif nanocrystals were prepared by a wet-bead milling method. A 3-factor, 3-level Box-Behnken design was used to investigate the independent variables: the concentration of rifampicin, the concentration of the stabilizing agent (Povacoat® type F), and the mass of zirconia beads. Two optimized formulations, F1-Rif and F2-Rif, were characterized by determining their particle size and size distribution, morphology, crystal properties, and antimicrobial activity. Differential scanning calorimetry (DSC) and powder X-ray diffraction (PXRD) revealed that rifampicin's polymorph II crystal structure was unchanged. The reduced particle size of <500 nm (100-fold decrease) increased the saturation solubility and dissolution rate up to 1.74-fold. The novel polymer, Povacoat®, demonstrated to be a suitable stabilizer to maintain the physical stability of nanosuspensions over two years. The Rif nanocrystals showed antimicrobial activity (0.25 μg/mL) not significantly different from standard rifampicin powder. However, the low cytotoxicity of the nanosuspensions in HepG2 cells was determined. When compared to the commercial product, the nanosuspension increased the rifampicin concentration 2-fold. In conclusion, the Rif nanosuspension allows half the needed volume of administration, which might increase compliance among children and elderly patients throughout the long-term treatment of TB.