General Principles Of Pharmacology/Pharmacology and its Branches

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In general terms, pharmacology is the science of drug action on biological systems. In its entirety, pharmacology embraces knowledge of the sources, chemical properties, and biological effects and therapeutic uses of drugs. It is a science that is basic not only to medicine, but also to pharmacy, nursing, dentistry and veterinary medicine. Pharmacology over years has integrated with other medical and basic sciences like physiology, biochemistry, and pathology that it is very difficult to draw lines among them. Pharmacological studies range from those that examine the effects of chemical agents on sub cellular mechanisms, to those that deal with the potential hazards of pesticides and herbicides, to those that focus on the treatment and prevention of major diseases with drug therapy. Pharmacologists also use molecular modeling and computerized design as drug discovery tools to understand cell function. New pharmacological areas include the genomic and proteomics approaches for therapeutic treatments.

Pharmacology is the study of the nature, actions and uses of drugs. A drug is any substance that is given to humans or animals with the intention of changing the state of body functioning: for example to relieve pain, treat cancer, eliminate infection or improve health in any way or to investigate the functions of the body. However the work of pharmacologists is mainly concerned with mechanisms of drug action. Toxicology is an important component of the Pharmacology discipline like another side of a coin . Toxicology is the study of the harmful effects of chemicals on living organisms. Toxic substances include certain drugs, pesticides, heavy metals, plant and microbial toxins and many organic chemicals. Such substances may have an adverse effect on the health of humans and as well living beings.

The drugs being chemical entities are likely to interact with chemicals (biochemical’s) found in our body. The study of such interaction is called as pharmacodynamics and how the drug molecules are going to be absorbed, distributed, metabolized and eliminated is the domain of pharmacokinetics. We can briefly describe Pharmacodynamics is what the drug does to the body and pharmacokinetics is what body does to the drug.

Other important areas of pharmacology are Pharmacoepdimelogy, Pharmacoeconomics, Biotechnology, Pharmacogenentics and Pharmacogenomic.:

Pharmacoepdimelogy is the study of drugs in populations;

Pharmacoeconomics,a branch of health economics aiming to quantify the cost benefits of therapeutics in economic terms.

Biotechnology contributing to biomedical area mainly by use of recombinant DNA and related technologies for manufacture of therapeutic proteins, diagnosis, genotyping, transgenic animals etc.

Pharmacogenentics refers to the study of inherited differences (variation) in drug metabolism and response.

Pharmacogenomic refers to the general study of all of the many different genes that determine drug behavior.

Thus, among many other things, pharmacologists are involved in the discovery and development of new drugs, their testing, marketing, surveillance and regulation, and in providing information about drugs.

The Journey of the drug molecules in the body?

Fig1.1 Absorption, Metabolism, Distribution and Excretion of Drug

Fig1.2 : Compartmentalization of body and Routes of Drug Administration

Fig 1.3 Barriers Drug Has To Cross Fallowing Oral Administration

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

What is a membrane? And how it is organized in biological systems?

Membranes can be considered as a flexible sheath material or layered that separates two chemically different environments i.e. extra cellular and intra cellular. The cell membrane defines the cell boundary. The cell membranes help the cells to keep all the components together. It has numerous pores through which food and other vital materials of life are exchanged across the membrane. The cell membranes form the barrier between various water rich comportments. For e.g. with in a cell, membranes separate the cell organelles and nucleus.

Chemically bio membranes are bilayer phospholipids in which cholesterols, proteins are embedded. The phospholipids are like surfactants with hydrophilic phosphoric acid moiety and hydrophobic alkyl chains. The hydrophobic portions of the phospholipids are oriented like a sandwich exposing hydrophilic surfaces in the extra cellular and intra cellular surfaces, which are aqueous. The interiors of the cell membrane are hydrophobic. In fact lecithin a phospholipids and cholesterol are like bricks and cements of a wall. The molecules in which electrons are uniformly distributed are hydrophobic which dissolve freely in non-polar solvents e.g. benzene, cholesterol.

Fig.1.4 : Nature of Cell Membrane

The variety of proteins are embedded in the membranes serving different functions. There are many processes, which will be explained, in greater details further. To begin with the, here we mention important functions of transmembrane proteins .The structural glycoprotein, Ion channels, Carrier proteins and Signal transudation proteins [G-Protein Coupled Receptor] and Enzymes [Protein Kinases]

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This is a free Pharmpedia textbook Author Prof.A.N.Nagappa