Prediction of Molecular State of Therapeutic Agents in Biological Fluids from Theoretical Partition Coefficients Determined from Retention Factors ‎

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Biological fluids (extracellular and intracellular) help maintain body homeostasis and therefore are very important for life. The n-octanol-water partition coefficients, (usually given as log P values), are used as a measure of lipophilicity. Lipophilicity of a therapeutic agent (drug) is one of the parameters, which influences its biological activity.  The objective of this study was to investigate the ability of thin layer chromatography to provide reliable information on the lipophilic behaviors of drugs when exposed to ions in biological fluids. The chromatographic separation of the drugs was carried out on plain silica gel F254 plates as well as silica gel F254 plates impregnated with a sodium ion, potassium ion, and calcium ion respectively. The spots were visualized with UV254 light and iodine vapor respectively. All the ions decreased the retardation factor values (Rf values) of the fourteen drugs investigated.  A linear relationship occurred when experimental retention factor values (Rm values) were plotted against known (literature) log P values of the drugs. In general, log P values of all the drugs studied increased as the concentration of the ions increased except for piroxicam (with Na+ and Ca2+ ions respectively), loratadine (with Na+ and K+ ions respectively). The study suggests that retention factor values (Rm values) obtained from the thin-layer chromatographic analysis, could be used to predict the lipophilicity (invariably the cell membrane permeability) of the investigated drugs in biological fluids