Drug nanosizing using microfluidic reactors. Development, characterisation and evaluation of corticosteroids nano-sized particles for optimised drug delivery.

Abstract

Over recent years the delivery of nanosized drug particles has shown potential in improving bioavailability. Drug nanosizing is achieved by ¿top-down¿ and by ¿bottom-up¿ approaches. Owing to limitations associated with the top-down techniques, such as high energy input, electrostatic effects, broad particle size distributions and contamination issues, great interest has been directed to alternative bottom up technologies. In this study, the hypothesis that microreactors can be used as a simple and cost-effective technique to generate organic nanosized products is tested using three steroids (hydrocortisone, prednisolone and budesonide). Arrested antisolvent nanoprecipitation using ethanol (solvent) and water (antisolvent) was conducted within the microreactors. To enable experimental design for the microreactor studies, solubility profiles in different ethanol-water combinations at 25 °C were explored. All three drugs¿ solubility increased with increasing ethanol concentration showing maxima at 80-90 % v/v ethanol-water mixtures. Because of the complex multivariate microfluidic process, artificial neural network modelling was then employed to identify the dominant relationships between the variables affecting nanoprecipitation (as inputs) and the drug particle size (as output). The antisolvent flow rate was found to have the major role in directing drug particle size. Based on these successful findings, the potential of preparing pharmaceutical nanosuspensions using microfluidic reactors was researched. A hydrocortisone (HC) nanosuspension (NS) was prepared by introducing the generated drug particles into an aqueous solution of stabilizers stirred at high speed with a propeller mixer. A tangential flow filtration system was then used to concentrate the prepared NS. Results showed that a stable narrow sized HC NS of amorphous spherical particles 500 ± 64 nm diameter and zeta potential ¿18 ± 2.84 mV could be produced. The ocular bioavailability of a microfluidic precipitated HC NS (300 nm) was assessed and compared to a similar sized, milled HC NS and HC solution as a control. The precipitated and the milled NS achieved comparable AUC0-9h of 28.06 ± 4.08 and 30.95 ± 2.2, respectively, significantly (P < 0.01) higher than HC solution (15.86 ± 2.7). These results illustrate the opportunity to design sustained release ophthalmic formulations. Going nano via microfluidic precipitation was also exploited to tailor budesonide (BD) NS for pulmonary administration. The in vitro aerosolization by nebulization of a BD NS was studied in comparison with a commercial BD microsuspension. Overall, the fine particle fraction generated from BD NS (56.88 ± 3.37) was significantly (P < 0.05) higher than the marketed BD (38.04 ± 7.81). The mean mass aerodynamic diameter of BD NS aerosol (3.9 ± 0.48 ¿m) was significantly smaller (P < 0.05) than the microsuspension (6.2 ± 1.09 ¿m) indicating improved performance for BD NS. In conclusion, findings of this study support the hypothesis of using microfluidic nanoprecipitation as a promising and economical technique of drug nanosizing.