PHYSICO-CHEMICAL MEASUREMENTS

Various measurements on drugs can be made to shed light on the influence of physico-chemical factors on the bio-availability of a drug. Clearly the pK of a drug is going to reflect the extent to which a drug isionized in the stomach and hence the conditions under which it may be absorbed. An oil:water partition co-efficient (octanol or less commonly decanol:water) can reflect transport across lipid barriers while the binding constant to bovine serum albumin can reflect the extent to which a compound is bound to circulatory protein. Measurement of these parameters and their correlation with the variation in biological activity for a series of compounds can be of value in establishing quantitative structure:activity relationships (QSAR) within a related group of compounds. This may be used to predict structural changes, which might then be made to enhance the biological activity.