Section 1
General Pharmacology
HISTORICAL ASPECTS
Pharmacology is the science that deals with the study of drugs and their interaction with the living systems.
The useful and toxic effects of many plant and animal products were known to man in ancient times. The earliest writings on drugs are the Egyptian Medical Papyrus (1600 BC). The largest of them, Ebers Papyrus lists some 800 preparations.
In early days there was a close relationship between religion and treatment of diseases. The knowledge of the use of drugs often rested with the priest or holyman. Drugs were thought to be magical in their actions.
Several cultures like the Chinese, Greek, Indian, Roman, Persian, European and many others contributed a great deal to the development of medicine in early times. The drug prescriptions included preparations from herbs, plants, animals and minerals. In the middle ages many herbal gardens were cultivated particularly by monasteries.
Though medicine developed simulta-neously in several countries, the spread of knowledge was limited because of poorly developed communication across the world.
India's earliest pharmacological writings are from the ‘Vedas’. An ancient Indian physician Charaka and then, Sushruta and Vagbhata, described many herbal preparations included in ‘Ayurveda’ (meaning ‘the science of life’). Indians practiced vaccination as early as 550 BC.
Various other traditional systems of medicine were practiced in different parts of the world – like Homeopathy, Unani, Siddha system and Allopathy.
Allopathy means ‘the other suffering’. This word still being used for the modern system of medicine, is a misnomer. Homoeopathy meaning ‘similar suffering’ was introduced by Hanneman. The principles of this system include ‘like cures like’ and ‘dilution enhances the potency of drugs’.
Thus several systems of medicine were introduced, of which only a few survived. The basic reason for the failure of many systems is that man's concepts about diseases were incorrect and baseless in those days. By the end of the 17th century the importance of experimentation, observation and scientific methods of study became clear. Francois Magendie and Claude Bernard popularised the use of animal experiments to understand the effects of drugs. Simultaneous development of other branches of science viz, botany, zoology, chemistry and physiology helped in the better understanding of pharmacology.
The last century has seen a rapid growth of the subject with several new drugs, new concepts and techniques being introduced. We now know much more about receptors and molecular mechanisms of action of many drugs. Several diseases, which were considered incurable and fatal, can now be completely cured with just a few tablets.2
DEFINITIONS
The word pharmacology is derived from the Greek word—Pharmacon meaning an active principle and logos meaning a study (discourse).
Drug (Drogue—a dry herb in French) is a substance used in the diagnosis, prevention or treatment of a disease. WHO definition—“A drug is any substance or product that is used or intended to be used to modify or explore physiological systems or pathological states for the benefit of the recipient.”
Pharmacodynamics is the study of the effects of the drugs on the body and their mechanisms of action, i.e. what the drug does to the body.
Pharmacokinetics is the study of the absorption, distribution, metabolism and excretion of drugs, i.e. what the body does to the drug (in Greek Kinesis = movement).
Therapeutics deals with the use of drugs in the prevention and treatment of disease.
Pharmacoeconomics deals with the cost, i.e. economic aspects of drugs used therapeutically.
Pharmacogenomics is a branch of pharmaco-genetics which deals with the use of genetic information in selecting drugs for a person.
Pharmacoepidemiology is the study of both the useful and adverse effects of drugs on large numbers of people. Pharmacovigilance is a branch of pharmacoepidemiology which deals with the epidemiologic study of adverse drug effects.
Toxicology deals with the adverse effects of drugs and also the study of poisons, i.e detection, prevention and treatment of poiso-nings (Toxicon=poison in Greek).
Chemotherapy is the use of chemicals for the treatment of infections. The term now also includes the use of chemical compounds to treat malignancies.
Pharmacopoeia (in Greek Pharmacon = drug; poeia=to make) is the official publication containing a list of drugs and medicinal preparations approved for use, their formulae and other information needed to prepare a drug; their physical properties, tests for their identity, purity and potency. Each country may follow its own pharmacopoeia to guide its physicians and pharmacists. We thus have the Indian Pharmacopoeia (IP), the British Pharmacopoeia (BP) and the United States Pharmacopoeia (USP). The list is revised at regular periods to delete obsolete drugs and to include newly introduced ones.
Pharmacy is the science of identification, compounding and dispensing of drugs. It also includes collection, isolation, purification, synthesis and standardisation of medicinal substances.
SOURCES OF DRUGS
The sources of drugs could be natural or synthetic.
Natural sources Drugs can be obtained from:
- Plants, e.g. atropine, morphine, quinine, and digoxin.
- Animals, e.g. insulin, heparin, gonad-otrophins and antitoxic sera.
- Minerals, e.g. magnesium sulphate, aluminium hydroxide, iron, sulphur and radioactive isotopes.
- Microorganisms—antibacterial agents are obtained from some bacteria and fungi. We thus have penicillin, cephalosporins, tetracyclines and other antibiotics.
- Human—some drugs are obtained from human beings, e.g. immunoglobulins from blood, growth hormone from anterior pituitary and chorionic gonadotrophins from the urine of pregnant women.
Synthetic Most drugs used now are synthetic, e.g. quinolones, omeprazole, neostigmine, sulfonamides.
Many drugs are obtained by cell cultures, e.g. urokinase from cultured human kidney cells. Some are now produced by recombinant DNA technology, e.g. human insulin, tissue plasminogen activator, haematopoietic growth factors like erythropoietin and some others by hybridoma technique eg. monoclonal antibiodies.