Pharmacology is the science of drugs.
It is the study of chemical substances that interact with the living
things by chemical processes, especially by binding to regulatory molecules, i.e. receptors.
In 1847, Rudolph established the first institute of pharmacology.
Drug:
The word drug comes from a French word ‘Drogue’ meaning a dry herb. It can be defined as:
drug“Substance or material that is used or intended to be used to modify or explore physiological
processes or pathological states, for the benefit of the recipient.”
Branches of Pharmacology:
Following are the important branches of Pharmacology:
1. Pharmacokinetics
2. Pharmacodynamics
3. Therapeutics
4. Chemotherapy
5. Toxicology
6. Clinical Pharmacology
7. Pharmacy
8. Pharmacognesy
9. Pharmacogenetics
10. Pharmacoeconomics
11. Pharmacoepidemiology
12. Comparative Pharmacology
13. Animal Pharmacology
14. Pharmacoeconomics
15. Posology
1. Pharmacokinetics:
The word Pharmacokinetics is derived from two words, Pharmacon meaning drug and kinetics meaning
putting in motion. It can be defined as:
“The branch of pharmacology that deals with the absorption, distribution, metabolism and excretion of
drugs and their relationship with the onset, duration and intensity of the drug effect.”
What the body does to the drug is pharmacokinetics. For example, the absorption, distribution,
metabolism and excretion of Paracetamol is included in Pharmacokinetics.
2. Pharmacodynamics:
Pharmacodynamics is the branch of Pharmacology that deals with the mechanism of action of drug and
the relation between the drug concentration and its effect.
It is the study of physical and chemical effects of drugs on body, parasites and microorganisms.
What the drug does to the body is pharmacodynamics. For example, adrenaline acts on adrenal
receptors, stimulates adenyl cyclase system producing effects such as cardiac stimulation and
hyperglycemia is studied in Pharmacodynamics.
3. Therapeutics:
The branch of pharmacology that deals with the art and science of treatment of disease. It is the
application of pharmacological information together with the knowledge of disease, for the prevention
and cure of the disease.
4. Chemotherapy:
Chemotherapy refers to the treatment of diseases by chemicals that kill the cells, specially those of
microorganisms and neoplastic cells. It is classified into two divisions:
a. Antibiotics
Includes the choice of drugs most potent against the organism or least toxic. Examples include
Erythromycin given for gram positive organisms and Aminoglycans for gram negative organisms.
b. Antineoplastics
Examples include:
Methotrexate, which is anticancer drug. It inhibits the dihydrofolate reductase and interferes with the
DNA synthesis and repair.
Vinca alkaloids, which bind tubulin of microtubules and arrest mitosis in metaphase.
5. Toxicology:
Toxicology is the branch of pharmacology which includes the study of adverse effects of drugs on the
body. It deals with the symptoms, mechanisms, treatment and detection of poisoning caused by
different chemical substances.
The main criterion is the dose. Essential medicines are poisons in high doses and some poisons are
essential medicines in low doses.
6. Clinical Pharmacology:
Clinical pharmacology is the scientific study of drugs in man. It includes pharmacokinetic and
pharmacodynamic investigations in healthy or diseased individuals. It also includes the comparison with
placebos, drugs in the market and surveillance programmes.
The main objectives are:
1. Maximize the effect of drug
2. Minimize the adverse effects
3. Promote safety of prescription
Aims include:
1. Generate optimum data for use of drug.
2. Promote usage of evidence based medicine.
7. Pharmacy:
Pharmacy is the branch of Pharmacology and is the art and science of compounding by dispensing drugs,
preparing suitable dosage form for administration to man and animals. The health profession blends
health science with chemical science and effective use of drugs.
8. Pharmacognosy:
Pharmacognosy is the identification of drugs by just seeing or smelling them. It is a crude method no
longer used. Basically it deals with the drugs in crude or unprepared form and study of properties of
drugs form natural sources or identification of new drugs obtained from natural sources.
9. Pharmacoeconomics:
Pharmacoeconomics deals with the cost of drugs. In this discipline the cost of one drug is compared with
another for same use. The cheap drugs are preferred.
10. Pharmacogenetics:
Branch of pharmacology dealing with the genetic variations that cause difference in drug response
among individuals or population.
Example includes succinyl choline which is a skeletal muscle relaxant used in general anasthesia. It is
metabolized by pseudocholine esterase and has short duration of action. The presence of enzyme is
determined by the gene and lack of this is recessively inherited. This may lead to respiratory paralysis,
apnea and death.
11. Pharamcogenomics:
Pharmacogenomics is the broader application of genomic technologies to new drug discovery and
further characterization of older drugs.
Recombinant DNA technology involves the artificial joining of DNA of one specie to another. E. coli is
mostly used. In this way we can get huge amounts of drug in purified form which is less antigenic.
Examples include GH, interferon and vaccines.
12. Pharmacoepidemiology:
Pharmacoepidemiology deals with the effects of drugs on a large population. The effects may be good or
harmful. It is conducted in three ways:
a. Observational cohort studies
b. Case control studies
c. Phase trials
a. Cohort studies:
Patients receiving drugs are collected and followed up to determine the outcomes. It is prospective
(forward looking) research, however, is time consuming and lengthy.
b. Case Control Studies:
These are retrospective studies. They reverse the direction of scientific logic from forward looking to
backward looking.
c. Phase Trials:
These include different phases:
i. Human pharmacology (20 to 50 subjects), pharmacokinetics and pharmacodynamics of the drug are
observed
ii. Therapeutic exploration (50 to 300 subjects), drugs are compared with plessabos
iii. Therapeutic confirmation (250 to 1000 subjects), safety, efficacy of drugs is compared with the drugs
already present
iv. Therapeutic use (2000 to 10000 subjects), the opinion of physicians prescribing the drugs is collected
regarding dosage and efficacy. Surveillance programmes are lengthy when conducted outside hospitals.
13. Comparative Pharmacology:
Branch of pharmacology dealing with the comparison of one drug to another belonging to the same or
another group.
14. Posology:
Posology deals with the dosage of drugs. Example includes paracetamol given as one tablet of 500mg
thrice a day.
15. Animal Pharmacology:
Animal pharmacology deals with the different properties of drugs in animals. A vast variety of animals
are utilized including rabbits, mice guinea pigs, etc. Drugs are given to the animals and all parameters
(their behavior, activites, vital signs, etc.) are recorded. Any change is noted down. If found to be useful
in animals, then the drug is tested on humans.
