Formulation and optimisation of bedaquiline nanoemulsions for the potential treatment of multi drug resistant tuberculosis in paediatrics using quality by design
Bedaquiline is a drug used for the treatment of multidrug-resistant TB in adults and children that is currently only commercially available in tablet form. The present study was aimed at preparing nanoemulsion (NE) of BDQ using natural vegetable oils to deliver BDQ. The optimisation of surfactant mixtures was undertaken using Design of Experiments (DoE), specifically an optimal mixture design. The NEs were optimised while monitoring droplet size (DS), zeta potential (ZP), polydispersity index (PDI) and drug content (DC). The optimised NEs were further characterised using transmission electron microscopy, electrical conductivity, viscosity, pH and in vitro release studies. The optimised NE showed values of 191.6 nm±2.38 nm, 0.1176±1.69, -25.9 mV±3.00 mV and 3.14±0.82 mg/ml for DS, PDI, ZP and DC respectively. Furthermore, the TEM studies demonstrated the spherical shape of the optimised globules. The nanoemulsion was characterised by measuring its electrical conductivity, viscosity and pH which were determined as 53.1 µS/cm, 327±3.05 cP and 5.63±1.78, respectively. In conclusion, these NEs have great potential for improving solubility, drug delivery, and administration of BDQ. However, further studies are required to maximise the drug content and to demonstrate to what extent these NE have effect against MDR-TB.
Globally, it was estimated that 410,000 people developed Multidrug-resistant tuberculosis (MDR-TB) in 20221 . According to the most recent report on MDR-TB in children, an estimated 25,000–32,000 children were diagnosed with MDR-TB in 20211 . MDR-TB refers to tuberculosis (TB) caused by microorganisms that exhibit significant resistance to both isoniazid and rifampicin, either independently or in combination with resistance to other anti-TB medications2 . In March 2022, the WHO released updated guidelines for the management of MDRTB in children and adolescents. These guidelines recommended the use of bedaquiline (BDQ) and delamanid (DMD) in all age groups, along with revised dosing instructions for all tuberculosis medications3 . The recommended regimen includes seven drugs, with an initial phase lasting 4–6 months (depending on smear conversion within four months of treatment) consisting of BDQ, moxifloxacin (or levofloxacin), clofazimine, ethambutol, ethionamide, high-dose isoniazid, and pyrazinamide. The continuation phase which lasts 5–6 months comprises the use of clofazimine, moxifloxacin/levofloxacin, ethambutol, and pyrazinamide4 . BDQ is an oral diarylquinoline medication that was approved by the Food and Drug Administration (FDA) for treating MDR-TB5 . BDQ exerts its effects by inhibiting adenosine triphosphate (ATP), thereby impeding the energy production and metabolism of mycobacterium cells. The recommended dosage is an initial 400 mg daily for 2 weeks, followed by 200 mg three times a week for 22 weeks, totalling a 24-week treatment duration6 . However, for paediatric patients, the dose is administered based on weight, necessitating the breaking or crushing of tablets to achieve a safe dosage, which poses challenges for administration7 . Improper tablet manipulation could result in either sub-therapeutic or toxic blood concentrations8 . Moreover, many TB medications have unpleasant tastes and may induce vomiting, potentially affecting drug absorption and bioavailability9 .
Materials and methods: Materials BDQ was purchased from Iffect Chemphar Co. Ltd (Hong Kong, China). Tween 80 and Span 20 were donated by BASF (Johannesburg, Gauteng, South Africa). Ethanol was purchased from Fisher Scientific (Massachusetts, United States). Olive oil was purchased from Escentia Products (Johannesburg, Gauteng, South Africa).
Methods: Preparation of nanoemulsion NEs of BDQ were prepared by the spontaneous emulsification method as described previously22. Briefly, 30 mg of BDQ was weighed using a Radwag AS 220.R2 Plus Analytical balance (Toruήska, Poland) and added to olive oil and stirred using a magnetic stirring hot plate (Lasec, Cape Town, South Africa) at 200 rpm for 10 min. Appropriate amounts of the surfactant mix (Smix) according to the runs suggested by optimal design were subsequently added. Distilled water was then added dropwise with continuous stirring using a magnetic stirring hot plate (Lasec, Cape Town, South Africa) at 200 rpm. The nano-emulsions were centrifuged at 3000 rpm for 15 min using a Rotafix 32 A centrifuge (Hettich, Tuttlingen, Germany) to separate excess BDQ from the nanoemulsion23. Experimental design A three-factor optimal mixture design was used to assess the effects of 3 critical materials attributes (CMA) on the CQA of the NE24. In these experiments, we monitored Tween 80 (A); Span 20 (B); and Ethanol (C), on the response variables, namely DS and PDI, ZP and DC on the formulated NE. The design set the levels of Span 20 (A) and Tween 80 (B) at a minimum of 37.5 mg and a maximum of 675 mg with ethanol (C) content set to a maximum of 150 mg. The amounts of olive oil and water were kept constant at 100 mg and 150 mg, respectively to make a total of approximately 1 g of NE. Each design was assessed independently to observe the influence of the composition of each variable on the four responses. The constraints of the independent variables are presented in Table 1. The optimisation function was used to estimate the levels for each component of the surfactant mixture, taking into account the criteria and specific constraints outlined in Table 2. These criteria and constraints subsequently produced composition solutions according to the desirability function. The summary of the experiments conducted in the optimisation process are provided in Table 3.
