Introduction to Pharmacology

Definition

• Pharmacos- Medicine/ drug & logos- Study
• Pharmacology is a science of medicine that deals with the study of drugs and their action on the body where the drug exerts a physiological & biochemical reaction in the cell, tissues or organisms.
• It is the study of the drugs and their interaction with the living Organisms.

Sources of Drugs

The sources of drugs are being derived mainly from natural sources in the early centuries to semi-synthetic & are being synthetically manufactured today.

The sources are mainly classified as

• Natural sources: Drugs obtained from plant, animal, microbiological, marine, mineral, geographical origins constitute the natural sources.
• Semi-synthetic Sources: Semi-synthetic drugs generally made by converting starting materials from natural sources into final products via chemical reactions.
• Synthetic Sources: Synthetic drugs are also called as designer drugs manufactured using man made chemicals in the laboratories and they mimic many illicit drugs that pose a severe adverse effect on health & can cause addiction or abuse.

·         Bio-synthetic sources: These are genetically engineered drugs developed by mixing discoveries from molecular biology, recombinant DNA technology, DNA alteration, gene splicing, immunology, and immune pharmacology.

Natural sources of Drugs

• Plant sources: The entire plant, plant parts, secretion, and exudate of plants are the sources of plant drugs.
•  Ergot, ephedra, and datura are entire plants, Senna leaf and pod, leaf of Digitalis, bark of Chinhona, capsule of Opium, seeds of Nux vomica, rhizome of Ginger function as sources of a number of drugs useful against different diseases.
• Animal sources:  Drugs obtained from animals sources are whole animals, glandular products (thyroid organ), liver extract, polypeptide venoms, non-peptide toxins, etc.
•  Fish liver oil, musk, beeswax, hormones, enzymes, and antitoxins sera are the products obtained from animal sources.
•  A large number of other natural products from animal sources are used as pharmaceutics ingredients and are also used as important drugs or as nutritional supplements.
• Microbial sources: Many life-saving drugs are obtained from microbes such as penicillin from Penicillium notatum, chloramphenicol from Streptomyces venezuelace, anti-fungal drug grisofulvin from Penicillium griseofullivum, neomycin from Streptomyces fradiae and streptomycin from actinobacterium Streptomyces griseus. Aminoglycosides such as gentamicin and tobramycin are obtained from Micromonospora sp. and Streptomyces tenebrarius, respectively.
• Marine Sources: Coral, sponges, fish, and marine microorganisms have large biologically potent chemicals with interesting inflammatory, anti-viral, and anticancer activity. For example, curacin A, lipid constituent, from a marine cyanobacterium Lyngbya majuscule shows potent anti tumor activity.
• Mineral sources: Drugs from mineral source are kaolin, chalk, diatomite, borax, flourine & Radioactive Isotopes. Minerals or their salts are useful pharmacotherapeutic agents. For example, ferrous sulfate (FeSO4) is used in iron deficiency anemia, magnesium sulfate (MgSO4) is employed as purgative, magnesium trisilicate, aluminium hydroxide {Al(OH)3} and sodium bicarbonate (NaHCO3) are used as antacids.
• Geographical sources: Geographical source or habitat gives us information about the country or place where the drug is produced. Zingiber officinale is indigenous to southern China and was spread eventually to  other parts of Asia and subsequently to West Africa and the Caribbean and Cannabis indica, Tamarinds indica, Strychnosnux-vomica and Plantago ispaghula in the Indian subcontinent.

Semi-Synthetic Sources

• In Semi-synthetic drugs, the nucleus of drug obtained from natural source is retained but the chemical structure is altered.
• semi-synthetic processes are used to prepare drugs when the natural sources may yield impure compounds or when the synthesis of drugs (complex molecules) may be difficult, expensive, and commercially unviable.
• Some examples are semi-synthetic human insulin and 6-aminopenicillanic acid derivatives. Prepared by chemically modifying substances that are available from natural source to improve its potency, efficacy and also reduce side effects.
• Semisynthetic drugs from plant sources include heroine from morphine, bromoscopolamine from scopolamine, homoatropine from atropine.
• And from animal sources are animal insulin changed to be like human insulin and 6-aminopenicillanic acid derivatives.
• Other examples include apomorphine, diacetyl morphine, ethinyl estradiol, homatropine, ampicillin and methyl testosterone.

Synthetic Sources

• In Recent years, majority of drugs used in clinical practice are prepared synthetically, such as aspirin, oral anti-diabetics, antihistamines, amphetamine, chloroquine, chlorpromazine, general and local anaesthetics, paracetamol, phenytoin, synthetic corticosteroids, sulphonamides, and thiazide diuretics.
•  Most of the synthetic drugs are prepared synthetically, i.e., by chemical process (reaction) with the help of the knowledge of phytochemical investigation.
• Advantages of synthetic drugs are their chemical purity, simple and cost-effective method of preparation and high quality. Since the pharmacological activity of a drug depends on its chemical structure and physical properties, more effective & can be prepared by modifying the chemical structure of the prototype drug.
• Disadvantage is that many synthetic drugs are used as designer drugs prepared chemically to mimic ilicit drugs like cannabis which can pose adverse health reactions & addiction or abuse.

Biosynthetic Sources

• These are the recent developments where drugs are obtained from the desired gene is coupled to rapidly replicating DNA (viral, bacterial, or plasmid). The new genetic combination is inserted into the bacterial cultures which allow production of vast amount of genetic material & by this process huge amount of drugs are produced.
• Egs Include genetically engineered novel vaccines (Recombivax HB—a hepatitis-B vaccine),
• Recombinant DNA engineered insulin (Humulin–human insulin) for diabetes and interferon-alpha-2a,
• Interferon-alpha-2b for hairy cell leukemia. Recombinant DNA technology involves cleavage of DNA by enzyme restriction endonucleases.
• The advantage is drug can be obtained in pure form, and it is less antigenic.
• The disadvantage is well-equipped.