The Journey of the drug molecules in the body
Random walk of the molecules and its path!!! It can be easily imagined that the drug molecules are in random movement through out the body। It is carried mainly by blood and only fraction of administered drug is likely to interact with the target sites to evoke a pharmacological response leading to therapeutic effect. Drug reaching its target is like US marines haunting a wanted terrorist in a dessert!!!Human body is machine having its own design to suite its need for input of oxygen and food, and supply of these to each and every cell of the body. The cells in the process of making energy are likely to churn out waste products like carbon dioxide, urea, ketone bodies, uric acid etc., These waste products should be thorn out of the human body as these can cause harmful effects if gets accumulated in the system. The human body has its own systematic control over input and output system.The human body can be viewed as magic box with several compartments inserted one over the others. These compartments may be of one cell membrane thick or many cell layers. There are several semi permeable membranes thought out the body, which makes them to behave as different compartments. The biggest challenges for any drug molecule is to cross these barriers and to reach a remote target site and interact with it to exert its effect in the body. In many cases drugs are given in such a way that in its random journey through out the body, it will interact with its target and exert its action on bio molecules.The drug molecules are likely to undergo various processes like absorption distribution metabolism and excretion [ADME] (see fig.2) details of various Compartmentalization of body and Routes of Drug Administration are depicted in Fig 3.1.Drug Absorption (oral or parenteral): A drug must be absorbed and achieve adequate concentration at its site of action in order to produce its biological effects. Thus, when a drug is applied to a body surface (e.g., gastro intestinal tract, skin, etc.), its rate of absorption will determine the time for its maximal concentration in plasma and at the receptor to produce its peak effect.2.Distribution :The blood, total body water, extra cellular, lymphatic and cerebrospinal fluids are involved in drug movement throughout the body. Depending upon its chemical and physical properties, the drug may be bound to plasma proteins or dissolved in body fat, delaying its progress to its sites of action or excretory mechanism.3.Metabolism: This is how the body in preparation for their elimination handles certain drugs and includes the fate of drugs biotransformation (e.g., hydrolysis, conjugation, oxidation reduction).4. Elimination: The kidney is the most important organ for drug excretion but the liver, lung and skin are also involved in drug elimination. Drugs excreted in feces are mostly derived from unabsorbed, orally ingested drugs or from metabolites excreted in the bile and not reabsorbed by the intestine. The physical and chemical properties, especially the degree of ionization of the drug, are important in the rate of excretion
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