[Optimized preparation of dry powder inhalation of Rehmannia glutinosa oligosaccharides by central composite design and response surface method].

OBJECTIVE: To optimize the formulation of dry powder inhalation of Rehmannia glutinosa oligosaccharides (RGOS-DPI) extracted from traditional Chinese medicinal herbs.

METHOD: RGOS-DPI was prepared by spray drying technique. Dependent variables such as yield, moisture absorption rate, emptying rate and mean diameter of micropowder were transformed into desirabilities mathematically by Hassan's method. Overall desirability was calculated from the geometric mean of the four desirabilities of each formulation. The effects of influence factors such as the inlet temperature, the contents of mannitol in the total amount of adjuvant and solution density were investigated using central composite design and response surface method. The data of overall desirability were analyzed using multi-linear equation and second-order polynomial equation for selecting the optimal conditions for DPI preparation.

RESULT: The method of second-order polynomial equation was superior to multi-linear equation method in view of the correlation coefficients. Under the optimal conditions, the yield, moisture absorption rate, emptying rate and mean diameter of the RGOS-DPI were 78.60%, 5.93%, 94.20% and 2.537 microm, respectively.

CONCLUSION: The central composite design can be used to optimize preparation. The optimized process for RGOS-DPI preparation is stable and feasible. The diameter of micropowder is suitable which can meet the demands of pulmonary delivery.