Category: Formulation and Quality
Purpose: Bedaquiline (BD) was approved by the FDA in 2012 and was the first new medication for tuberculosis (TB) in more than 40 years. BD is primarily used, along with a combination of other drugs, for the treatment of pulmonary multidrug-resistant tuberculosis (MDR-TB). BD is a member of diarylquinoline class of drugs. It inhibits mycobacterial ATP synthase, thereby disrupting the energy metabolism in actively replicating and non-replicating drug-sensitive and drug-resistant strains of MDR-TB. However, BD has multiple limitations such as poor solubility, low bioavailability, cardiac and hepatic toxicity that limit its clinical applications. BD is a known substrate of efflux transporter, p-glycoprotein (p-gp) that is present significantly in intestinal epithelium, and as such limits BD absorption into systemic circulation. Further, the efflux mechanism increases possibility for development of antimicrobial drug resistance. In this study, we synthesized cyclodextrin-based inclusion complex using sulfobutyl ether derivative of β-cyclodextrin, as a potential approach to improve the solubility and bypass p-gp mediated efflux, therefore enhancing BD antimicrobial activity and mitigating the chances of antimicrobial resistance.
Methods: Sulfobutyl ether derivative of β-cyclodextrin (SBE-β-CD, Dexolve™) was investigated to prepare inclusion complex with BD. Phase solubility studies were carried out wherein excess amount of BD was added to aqueous solution of CD having different concentrations (0-200 mM). Suspensions were bath sonicated for 30 min and left for 24 hours under continuous stirring for equilibration. After 24 hours, un-complexed BD was separated by filtering the suspension through 0.22 µm polyvinylidene fluoride (PVDF) syringe filter. Filtered solutions were quantified for BD using UV absorbance method at 285 nm. Job’s plot analysis to check the stoichiometry of BD and CD during complex formation was performed. Characterization with Differential Scanning Calorimetry (DSC), Fourier Transform Infrared (FT-IR) Spectroscopy, Proton (1H) Nuclear Magnetic Resonance (NMR) Spectroscopy, and Thermogravimetric Analysis (TGA) were performed to confirm the formation of inclusion complex.
Results: Resulted (AN) phase solubility diagram (Figure 1) indicated significant increase in solubility of BD with increasing concentration of sulfobutyl ether derivative of β-cyclodextrin (SBE-β-CD, Dexolve™). Upon formation of BD/SBE-β-CD inclusion complexes, apparent solubility of BD increased from 0.4 µM to 6.9 mM, a >1,600 fold solubility enhancement. Job’s plot curve revealed that 1:1 stoichiometry between BD and SBE-β-CD is optimum for formation of inclusion complexes. The stability constant (Ks) for SBE-βCD based inclusion complex was found to be 406.5 M-1, which is well in the range (100-1000 M-1) required for appropriate stability of inclusion complexes and required to improve oral bioavailability of therapeutics. DSC, FTIR and 1H NMR confirmed complexation of selected cyclodextrin with BD. Further studies involve significant characterization of the optimized inclusion complex and in-vitro studies to support the efficacy of complexation.
Conclusion: Development of BD /SBE-β-CD complex is instrumental not only in enhancing its aqueous solubility but will also provide protection against p-gp mediated efflux, suppress development of drug resistance, improve systemic bioavailability and in turn increase concentration at the target tissue.