Definition and scope of Pharmacology
Pharmacology may be defined as the study of drugs. The word pharmacology has been derived from two Greek words- Pharmakon (drugs)and logos (study). This “science of drugs” includes knowledge of all the aspects of drugs.
It includes their origin, source physical and chemical properties preparation, doses, route, of administration pharmacological action, absorption, distribution, biotransformation, excretion.
the rapeutic uses,mode (mechanism) of action,precautions,contraindications,interactions,adverse effects and their treatment.
Drug
The word ‘drug’ is derived from the french word ‘drogue’ meaning a herb. It is defined as any substance used for diagnosis, prevention, relief, or cure of disease in man or animals.
A drug may have useful action as in the treatment of disease (therapeutic effect ) or it may show unwanted reaction (side effects or toxicity)
Branches of Pharmacology
There are two main branches of pharmacology
1 Pharmacokinetics
It is concerned with the absorption, distribution, metabolism (biotransformation), and excretion of drugs (ADME). Pharmacokinetics is what the body does to the drug. This knowledge is essential to obtain the right effect at the right intensity, at the right time, for the right duration, with the least risk of unpleasantness or harm.
2 Pharmacodynamics
It is concerned with the biochemical and physiological effects of drugs and their mode of action, it includes the dose-effect relationship, factors modifying drug e&ects and dosage, and drug toxicity. Pharmacodynamics is what drugs do to the body. This knowledge is essential to choose a drug to obtain the desired effect with proper dosage. Good knowledge of pharmacology (both pharmacokinetics and pharmacodynamics) is, therefore, necessary to use drugs safely and efficiently.
The other terms generally used in pharmacology are
1 Clinical pharmacology It is the study of drug action in human beings.
2 Chemotherapy is concerned with drugs used in the treatment of bacterial, viral, and parasitic diseases. The chemotherapeutic agents destroy the infecting organism without damaging the host tissues.
3 Therapeutics includes any measure which is taken in the treatment of disease; It is a broad term that includes physiotherapy, radiotherapy psychotherapy as well as pharmacotherapy
(therapy with drug)
Pharmacotherapeutics is concerned with the application of drugs to produce the produce the desired effect, whether this is for the treatment of disease or prophylactic purpose
4 Immunopharmacology deals with the study of immunological aspects of drug action. It also includes effects of drugs on immune response
5 Pharmacogenetics is concerned with variations in drug response due to genetic factors e.g. primaquine include hemolysis in G-6PD deficient individuals.
6 Pharmacometrics deals with the identification and comparative evaluation, both qualitative and quantitative of, drug activity
7 Pharmacy is the science and art of preparing a drug or combination. Pharmacy is concerned with the collection, preparation synthesis of new compounds, and standardization.
8 Pharmacognosy ( pharmacon means a drug, gnosis means knowledge ) is the study of the source of drug obtained from plants and animals
9 Drug: World health organization scientific group has defined a drug as any substance or product that is used or intended to be used to modify or explore the physiological system
10 Dose: It is defined as the quantity of a drug that is sufficient to diagnose, prevent or treat a disease.
11 Dosage It is the schedule of dose, frequency, and duration of administration of drugs.
12 Toxicology is the aspect of pharmacology that deals with, the adverse effects of drugs.
13 Drug therapeutic index (margin of safety) indicates the relationship between the dosage that produces an undesirable effect and the dosage that produces a desirable therapeutic effect. The greater the ratio of these dosages, the safer the drugs and the higher its therapeutics index
14 Therapeutic index provides a very crude measurement of the safety of any drug as used in practice
15 Materia Medica deals with the source, description, and preparation of drugs. It is an old branch of Pharmacology.
History of PharmacologyThe earliest known prescription as a record in a Sumerian tablet of 2100 B.C. describes ointments and medicines containing asafoetida, thyme, sodium chloride, and potassium nitrate. The Ebers Papyrus which was written i9n 1550 B.C. contains prescriptions of castor oil, opium, aloes, colchicum, squill, and other drugs which are still in use. This famous document was found drugs that are still in use . This famous document was found in a tomb of a mummy in Thebes and is now preserved at the University of Leipzig. Perhaps, Chinese Medicine was about the earliest, and records dated about 2500 B.C. are available today. Ephedra or Ma huang was used as atonic even in those early days. Ayurveda or Indian medicine is about equal ancients, and it has given some useful remedies to modern medicine.
To the students of history, the names of Hippocrates, Aristotle, Theophrastus, Pliny, Dioscorides, and Galen would be of interest. Hippocrates(460-370B.C.) is referred to as the ‘father of medicine’ and many of his treatises: dealt with anatomy and physiology. The “Hippocratic Oath” of modern-day medicine reflects the high esteem with which this Greek Physician is regarded. It was Hippocrates who first recognized disease as an abnormal reaction of the body rather than as a visitation from the gods.
Aristotle(384-322 B.C. ) a student of Plato, is considered to be the most influential Greek philosopher. He attempted to separate superstition from fact, and his writings were considered authoritative for nearly twenty centuries. Theophrastus (370-287 B.C.), Who studied under Aristotle, utilized his teacher’s scientific reasoning and applied it to the plant kingdom. These works of Aristotle and Theophrastus served as guides to later workers who investigated the plant and animals kingdoms. Wrote his “De Materia Medica” in 78 B.C.
In it, he described several plants of medicinal value. Later, Pliny (23-70 A.D.) compiled 37 volumes of natural history, and these books were employed as reference data for many years. The Hippocratic concept of disease was then lost and did not reappear until the Renaissance. During this dark period, the concept of Galen (131-201 A.D.) and his dogmatic system of polypharmacy prevailed. Galen was a Greek pharmacist physician who lived in Rome and described many methods for preparing formulae containing plants and animals drugs. He compiled this knowledge into twenty books. Galen’s name is retained in the term “galenical” pharmacy, which includes the preparation of crude vegetable drugs.
One of the outstanding leaders of the Renaissance, who reintroduced free through and critical inquiry, was Paracelsus (1493-1541A.D.). He attacked the Galenic system of Polymacy and introduced the use of simple chemicals rather than the complex and mixed vegetable preparation of Gakuen.
Paracelsus introduced mercurials in the treatment of syphilis. During his lifetime the first official pharmacopeia was printed at Florence in 1497. . Virchow, the German physiology in 1855 propounded the concept of “all cells from cells”. With advances in the knowledge of the physiology of circulation, central nervous system, the hormones, and enzymes in the body, the study of pharmacology and therapeutics was stabilized,
In reality, pharmacology originated as a branch of physiology. but The application of the scientific method to studies on drugs was generated in France by Francois Megendie(1783-1855), and was expanded by Claude Bernard (1813-1878), who came to be known as the “father of experimental medicine” The name of Oswald Schmiedeberg(1838-1921)is associated with the development of experimental pharmacology in Germany, and Jonh Jacob Abel (1857-1938)played a similar role in the united state of India,
In India Sir Ram Nath Chopra(1882-1973) was responsible for the development of pharmacology as a well-defined discipline. He laid the foundation of scientific investigation on Indian indigenous drugs and was the Founder Director of the Drug Research Laboratory, of the Council of Scientific and Industrial Research located at Jammu-Tawi. Sir Chopra was an outstanding luminary in the field of medical education and research and has been widely acclaimed as the Father of Indian Pharmacology,
The growth of pharmacology was further greatly stimulated by the development of synthetic organic chemistry which has provided many new therapeutic agents some of the greatest changes in therapeutics have occurred during the last four decades. Today we live in an era of a “drug explosion “ due to the introduction of a large number of drugs, and the knowledge of clinical pharmacology aims at the rational and safe use of drugs in man, avoiding the hazards of drugs, drug interactions, and polypharmacy.
Source of Drugs
The following are the source of drugs :
1 Naturally occurring compound
These are extracted from plants and animals and are probably the oldest types of drugs. Examples of drugs from plant or vegetable sources are atropine, digitalis, morphine, reserpine, ephedrine, emetine, etc. The drugs obtained from animals sources are heparins, insulin, thyroxine, etc
2 Modified natural drugs
Some natural drugs can be modified in order to produce better and more efficacious drugs, e.g. porcine insulin can be modified so that it is closer to human insulin, and semisynthetic penicillins are an important group of drugs in the treatment of infections.
3 Mineral source
Iron, iodine, sulfur, calcium, aluminum, and magnesium salts are obtained from mineral sources.
4 Microbial sources
Antibiotics are derive from microbial sources.
5 Synthetic sources
Drugs produced purely by synthetic means have many advantages over natural drugs and have become one of the principal sources of drugs. They are cheaper and more certain in supply. It is impossible to synthesize ‘tailor-make drugs by using structure-activity relationships.
6 Human source
Immunoglobulins from blood, growth hormone from the anterior pituitary, chorionic gonadotropin from the urine of pregnant women.
7 Generic engineering
This is the newest and most modern by which drugs can be made. Human insulin can be made by incorporating the necessary gene into Escherichia coli, a gram-negative rod.
Essential Drug Concept
Essential medicines are those that satisfy the priority health care needs of the population. They are selected with due regard to public health relevance, evidence on efficacy and safety, and comparative cost-effectiveness.
but Essential medicines are intended to be available within the context of a functioning health system at all times in adequate amounts, in the appropriate dosage forms, with assured quality and adequate information, and at a price, the individual and the community can afford.
The implementation of the concept of essential medicines is intended to be flexible and adaptable to many different situations. The list of essential medicines relates closely to guidelines for clinical health care practice, which are used for the training and supervision of health professionals.
Lists of essential medicines also guide the procurement and supply of medicines in the public sector, schemes that reimburse medicine coast, medicine donations, and local medicine production
so The Essential Medicines List aims to identify cost-effective medicines for priority conditions, together with the reason for their inclusion linked to evidence-based clinical guidelines and with special emphasis on public health.
The complementary list presents essential medicines for priority diseases, for which specialized diagnostic or monitoring facilities, and /or specialist medical care, and /or specialist training are needed. In case of doubt, medicines may also be listed as complementary on the basis of consistent higher costs or less attractive cost-effectiveness in a variety of settings.