Summation, drug interactions

Richardson T, Foster J, Mawer GE. Enhancement by sodium salicylate of tiie blood glucose lowering effect of chlorpropamide - drug interaction or summation of similar effects BrJ Clin Pharmacol (1986) 22, 43-48. 

Above are major principles guiding the formation of Chinese medical prescription, Fang-Ji. Thus, multiple drug composition and mechanism is the most unique character in TCM. The mechanisms of TCM which produce therapeutic effects are 1). summation effect of one active component on different parts of the body, 2). summation effect of various active components acting on the same or a different part of the body, and 3). drug interactions in the body. 

XRD is an excellent technique to study drug-excipient interactions, provided the drug and the excipients are crystalline. In a solid mixture, the powder pattern of each crystalline phase is produced independently of the other constituents. Thus the diffraction pattern of a powder mixture will be the summation of the diffraction patterns of the individual constituents. If the drug-excipient interaction results in a crystalline product, this will be characterized by the appearance of new peaks in the powder pattern. However, if the interaction results in an amorphous product, this will become evident from the broad halos in the pattern. 

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