The researches on drugs are increased due to development in pharmacology and clinical science with the help of chemist that contribute the progress in medical science. The understanding of metabolism in terms biochemical action gave us the pathway and function of drugs as well as the structure of biological compound which can guided a new noble structures. The investigation on human blood and serum bring about the physiochemical properties of drug. The important factor is the interaction between the active pharmaceutical ingredients and excipients present on the desired pharmaceutical formulation products that can be keep in mind so that after taking the medicine does not have any side effects. A description of the classification of drugs based on pharmacological action on human organs is included and finally a brief literature and chemical structures of the four drugs, i.e., metoprolol tartrate, enalapril maleate, labetalol hydrochloride and amiodarone hydrochloride are presented.