Pharmacology: Definition, Branches and Classes

What is Pharmacology?

Pharmacology is the science of drugs (Greek pharmakos, medicine or drug; and logos, study). In actual use, however, its meaning is limited to the study of the actions of drugs. Pharmacology can be defined as the study of substances that interact with living systems through chemical processes, especially by binding to regulatory molecules and activating or inhibiting normal body processes. These substances may be chemicals administered to achieve a beneficial therapeutic effect on some process within the patient or for their toxic effects on regulatory processes in parasites infecting the patient.
Pharmacology is one of the cornerstones of the drug discovery process. The pharmaceutical chemist may create the candidate compound, but the pharmacologist is the one who tests it for physiologic activity.
A promising compound is investigated by many other scientists:

• Toxicologists
• Microbiologists
• Clinicians

but only after the pharmacologist has documented a potential therapeutic effect.
Pharmacology studies the effects of drugs and how they exert their effects. There is a distinction between what a drug does and how it acts. Thus, amoxicillin cures a strep throat, and cimetidine promotes the healing of duodenal ulcers. Pharmacology asks “How”? Amoxicillin inhibits the synthesis of cell wall mucopeptide by the bacteria that cause the infection, and cimetidine inhibits gastric acid secretion by its antagonist action on histamine H2 receptors.

Functions or Roles of Pharmacologists

The main tasks of pharmacologists in the search for and development of new medicines are

• screening for desired activity, 
• determining mode of action, and 
• quantifying drug activity when chemical methods are not available. 

Pharmacology depends largely on experiments conducted in laboratory animals, but even the human animal may be used as a test subject. Friedrich Serturner, the German pharmacist who isolated the first alkaloid from opium in 1805, administered a whopping dose (100 mg) to himself and three friends. All experienced the symptoms of severe opium poisoning for several days. The alkaloid was named morphine, for Morpheus, the Greek god of sleep. Although humans are no longer used as ad hoc laboratory animals, they are essential in clinical pharmacology. When a new drug compound has gone through sufficient preclinical testing to show potential therapeutic action and reasonable safety on short-term administration, and the data have been reviewed by the FDA, the compound is administered to a small number of human volunteers under closely controlled and monitored conditions. These Phase I clinical trials provide information about dosage and the most common side effects to be expected.

Branches or Areas of Pharmacology

The two main areas of pharmacology are

1. Pharmacodynamics: this studies the effects of a drug on biological systems
2. Pharmacokinetics: this studies the effects of biological systems on a drug

 In broad terms, pharmacodynamics discusses the chemicals with biological receptors, and pharmacokinetics discusses the absorption, distribution, metabolism, and excretion (ADME) of chemicals from the biological systems. Pharmacology is not synonymous with pharmacy and the two terms are frequently confused.

Classes or Types of Pharmacology

The discipline of pharmacology can be divided into many sub disciplines each with a specific focus. 

1. Clinical pharmacology: Clinical pharmacology is the basic science of pharmacology with an added focus on the application of pharmacological principles and methods in the medical clinic and towards patient care and outcomes.
2. Neuropharmacology: Neuropharmacology is the study of the effects of medication on central and peripheral nervous system functioning.
3. Psychopharmacology: Psychopharmacology, also known as behavioral pharmacology, is the study of the effects of medication on the psyche (psychology), observing changed behaviors of the body and mind, and how molecular events are manifest in a measurable behavioral form. Psychopharmacology is an interdisciplinary field which studies behavioral effects of psychoactive drugs. It incorporates approaches and techniques from neuropharmacology, animal behavior and behavioral neuroscience, and is interested in the behavioral and neurobiological mechanisms of action of psychoactive drugs. Another goal of behavioral pharmacology is to develop animal behavioral models to screen chemical compounds with therapeutic potentials. People in this field (called behavioral pharmacologists) typically use small animals (e.g. rodents) to study psychotherapeutic drugs such as antipsychotics, antidepressants and anxiolytics, and drugs of abuse such as nicotine, cocaine and methamphetamine.
4. Cardiovascular pharmacology: Cardiovascular pharmacology is the study of the effects of drugs on the entire cardiovascular system, including the heart and blood vessels
5. Pharmacogenetics: Pharmacogenetics is clinical testing of genetic variation that gives rise to differing response to drugs.
6. Pharmacogenomics: Pharmacogenomics is the application of genomic technologies to drug discovery and further characterization of older drugs. the relation of the individual’s genetic makeup to his or her response to specific drugs is close to becoming a practical area of therapy
7. Pharmacoepidemiology: Pharmacoepidemiology is the study of the effects of drugs in large numbers of people.
8. Safety pharmacology:  Safety pharmacology specialises in detecting and investigating potential undesirable pharmacodynamic effects of new chemical entities (NCEs) on physiological functions in relation to exposure in the therapeutic range and above.
9. Systems pharmacology: Systems pharmacology is the coding system principles in the field of pharmacology.
10. Toxicology: Toxicology is the study of the adverse effects, molecular targets, and characterization of drugs or any chemical substance in excess (including those beneficial in lower doses). Toxicology is that branch of pharmacology which deals with the undesirable effects of chemicals on living systems, from individual cells to complex ecosystems.
11. Theoretical pharmacology: Theoretical pharmacology is a relatively new and rapidly expanding field of research activity in which many of the techniques of computational chemistry, in particular computational quantum chemistry and the method of molecular mechanics, are proving to be of great value. Theoretical pharmacologists aim at rationalizing the relation between the activity of a particular drug, as observed experimentally, and its structural features as derived from computer experiments. They aim to find structure—activity relations. Furthermore, on the basis of the structure of a given organic molecule, the theoretical pharmacologist aims at predicting the biological activity of new drugs that are of the same general type as existing drugs. More ambitiously, it aims to predict entirely new classes of drugs, tailor-made for specific purposes.
12. Posology: Posology is the study of how medicines are dosed. This depends upon various factors including age, climate, weight, sex, elimination rate of drug, genetic polymorphism and time of administration.
13. Environmental pharmacology: Environmental pharmacology is a new discipline. Focus is being given to understand gene–environment interaction, drug-environment interaction and toxin-environment interaction. There is a close collaboration between environmental science and medicine in addressing these issues, as healthcare itself can be a cause of environmental damage or remediation. Human health and ecology are intimately related. Demand for more pharmaceutical products may place the public at risk through the destruction of species. The entry of chemicals and drugs into the aquatic ecosystem is a more serious concern today. In addition, the production of some illegal drugs pollutes drinking water supply by releasing carcinogens.This field is intimately linked with Public Health fields.
14. Experimental pharmacology: Experimental pharmacology involves the study of pharmacology through bioassay, to test the efficacy and potency of a drug.

References

1. Microbe Notes: Pharmacology