The aim of the study was to analyze the effect of the active pharmaceutical ingredient on the flowability of the powder and properties of tablets prepared using direct compression method. Each analyzed formulation contained one model active pharmaceutical ingredient, diphenhydramine, ketoprofen or loratadine. Granulometric properties of the powder formulations were determined based on bulk density prior and after compression, Hausner ratio, Carr index and angle of repose values. The analysis of manufactured tablets included determination of their hardness, thickness, mass, disintegration time, wettability, contact angle and swelling index values. The preformulation study confirmed that characteristics of the active pharmaceutical ingredient might have modified physicochemical properties... of both powder formulations and tablets.