Objective: The E. ulmoides and G. jasminoides (EG) tablets containing 67 mg E. ulmoides spray-dried extract (ESE) and 173 mg G. jasminoides spray-dried extract (GSE) were prepared by employing the direct compression method. Due to the poor flowability and compressibility of the two spray-dried extracts, various excipients were added at different ratios so that the blends can be compressed into tablets with the required standards. This study aimed at the cause-effect relations and optimization of the EG tablet formulation.Methods: Different diluents including dibasic calcium phosphate anhydrous (DCPA), silicified microcrystalline cellulose (SMCC), spray-dried lactose (SDL) and the active ingredients (blend of ESE and GSE at the ratio of 67:173, w/w) were separately investigated their own physical properties. The binary mixtures of the active ingredients with different ratios of DCPA, SMCC, and SDL were evaluated their flowability. D-optimal design based on three independent variables (% DCPA, % croscarmellose sodium (CCS) and % SMCC) was applied to evaluate the cause-effect relations and optimize the EG tablet formulation. The weight variation, disintegration time, hardness and friability were investigated as four dependent variables.Results: The flowability of the powders was found to be affected by the particle size distribution, particle shape and density. The three diluents could significantly improve the flowability of the active ingredients. All independent variables had significant effects on the dependent variables. An increase in % SMCC reduced the weight variation, hardness and increased the friability of tablets. Disintegration time was found to be in the negative relations with % CCS. The tablet hardness was in positive relations with % DCPA. The optimized EG tablet formulation composed of 9 % DCPA (w/w), 35 % SMCC (w/w), and 14 % CCS (w/w) of the excipient blend. The weight variation, disintegration time, hardness and friability of the optimized EG tablets were found to be 1.8 %, 11.7 min, 61.4 N, and 0.5 %, respectively.Conclusion: The ESE and GSE could be formulated into tablet by using direct compression method. The cause-effect relations and optimization of EG tablet formulation were studied and reported for the first time
