Abstract
The fact of human body and animal body formed of organs which formed of tissue which its constituents are the cells. The cell enveloped by cell membrane which contain more its content of lipid compounds to protect the cell. Hence when the chemical compounds (drugs) across to the cytoplasm of the cell must have a lipophilic character. Also there is a fact the oily substances not mix with the watery substance, so must be take a cream form (water in oil or oil in water emulsion), so the drugs must be soluble in lipid to across the cell to obtain the desirable effect. The partition co-efficient is a significant expression of lipid solubility. Many of drugs convert to prodrug this prodrug has highly lipid solubility and has long duration of action e.g., testosterone cypionate, rolitetracycline, penicillin procaine, benzylpenicillin G, nandrolone decanoate….etc., on the other hand the water soluble compounds (hydrophilic drugs) e.g., vitamin B complexes which exert its effects and excreted from the kidney quickly this indicate to no long duration of vitamin B complex except the cyanocobalamin (vit.B12) which incorporated to sesame oil to deposit in the body to treatment the inflammation of nerves of diabetic patients which suffering from neuropathy.