PHARMACOLOGY

Pharmacology is the branch of medicine and biology concerned with the study of drug action. More specifically, it is the study of the interactions that occur between a living organism and chemicals that affect normal or abnormal biochemical function. If substances have medicinal properties, they are considered pharmaceuticals. The field encompasses drug composition and properties, interactions, toxicology, therapy, and medical applications and antipathogenic capabilities. The two main areas of pharmacology are pharmacodynamics and pharmacokinetics. The former studies the effects of the drugs on biological systems, and the latter the effects of biological systems on the drugs. In broad terms, pharmacodynamics discusses the interactions of chemicals with biological receptors, and pharmacokinetics discusses the absorption, distribution, metabolism, and excretion of chemicals from the biological systems. Pharmacology is not synonymous with pharmacy and the two terms are frequently confused. Pharmacology deals with how drugs interact within biological systems to affect function. It is the study of drugs, of the reactions of the body and drug on each other, the sources of drugs, their nature, and their properties. In contrast, pharmacy is a biomedical science concerned with application of the principals learned from pharmacology in its clinical settings; whether it is in a dispensing or clinical care role. In either field, the primary contrast between the two is their distinctions between direct-patient care, for pharmacy practice, and the science-oriented field, driven by pharmacology.

Dioscorides' De Materia Medica is often said to be the oldest and most valuable work in the history of pharmacology. The origins of clinical pharmacology date back to the Middle Ages in Avicenna's The Canon of Medicine and Peter of Spain's Commentary on Isaac. Clinical pharmacology owes much of its foundation to the work of William Withering. Pharmacology as a scientific discipline did not further advance until the mid-19th century amid the great biomedical resurgence of that period. Before the second half of the nineteenth century, the remarkable potency and specificity of the actions of drugs such as morphine, quinine and digitalis were explained vaguely and with reference to extraordinary chemical powers and affinities to certain organs or tissues. The first pharmacology department was set up by Rudolf Buchheim in 1847, in recognition of the need to understand how therapeutic drugs and poisons produced their effects.

Early pharmacologists focused on natural substances, mainly plant extracts. Pharmacology developed in the 19th century as a biomedical science that applied the principles of scientific experimentation to therapeutic contexts.

Divisions

• Clinical pharmacology

The medical field of medication effects on humans and animals.

• Neuropharmacology

Effects of medication on nervous system functioning.

• Psychopharmacology

Effects of medication on the brain; observing changed behavior of the body and reading the effect of drugs on the human brain.

• Pharmacogenetics

Clinical testing of genetic variation that gives rise to differing response to drugs.

• Pharmacogenomics

Application of genomic technologies to new drug discovery and further characterization of older drugs.

• Pharmacoepidemiology

Study of effects of drugs in large numbers of people

• Toxicology

Study of toxic or harmful effects of drugs

• Theoretical pharmacology

Study of metrics in pharmacology

• Posology

How medicines are dosed. It also depends upon various factors like age, climate, weight, sex, and so on.

• Pharmacognosy

A branch of pharmacology dealing especially with the composition, use, and development of medicinal substances of biological origin and especially medicinal substances obtained from plants also known as deriving medicines from plants.

Behavioral pharmacology

Behavioral pharmacology, also referred to as 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, methamphetamine, etc.

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 the Environmental science and Medical community in addressing these issues. It is recognized that healthcare can itself be a cause of environmental damage as well as its remediation. Human health and ecology is intimately related. Demand for more pharmaceutical products is destroying countless species of animals and plants, placing the public at risk. 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. The pharmaceutical industry is encouraged to pay greater attention to the environmental impact of its products. More and more biodegradable drugs are needed. It means environment friendly drugs could be designed. General standards for discharge of environment pollutants are implemented strictly and environmental impact assessment is checked frequently by health and other concerned regulators.

Scientific background

The study of chemicals requires intimate knowledge of the biological system affected. With the knowledge of cell biology and biochemistry increasing, the field of pharmacology has also changed substantially. It has become possible, through molecular analysis of receptors, to design chemicals that act on specific cellular signaling or metabolic pathways by affecting sites directly on cell-surface receptors (which modulate and mediate cellular signaling pathways controlling cellular function).

A chemical has, from the pharmacological point-of-view, various properties. Pharmacokinetics describes the effect of the body on the chemical (e.g. half-life and volume of distribution), and pharmacodynamics describes the chemical's effect on the body (desired or toxic).

When describing the pharmacokinetic properties of a chemical, pharmacologists are often interested in LADME:

• Liberation - disintegration (for solid oral forms {breaking down into smaller particles}), dispersal and dissolution

• Absorption - How is the medication absorbed (through the skin, the intestine, the oral mucosa)?

• Distribution - How does it spread through the organism?

• Metabolism - Is the medication converted chemically inside the body, and into which substances? Are these active? Could they be toxic?

• Excretion - How is the medication eliminated (through the bile, urine, breath, skin)?

Medication is said to have a narrow or wide therapeutic index or a therapeutic window. This describes the ratio of desired effect to toxic effect. A compound with a narrow therapeutic index (close to one) exerts its desired effect at a dose close to its toxic dose. A compound with a wide therapeutic index (greater than five) exerts its desired effect at a dose substantially below its toxic dose. Those with a narrow margin are more difficult to dose and administer, and may require therapeutic drug monitoring (examples are warfarin, some antiepileptics, aminoglycoside antibiotics). Most anti-cancer drugs have a narrow therapeutic margin: toxic side-effects are almost always encountered at doses used to kill tumors.

Drug legislation and safety

In the United States, the Food and Drug Administration (FDA) is responsible for creating guidelines for the approval and use of drugs. The FDA requires that all approved drugs fulfill two requirements:

1. The drug must be found to be effective against the disease for which it is seeking approval.

2. The drug must meet safety criteria by being subject to extensive animal and controlled human testing.

Gaining FDA approval usually takes several years to attain. Testing done on animals must be extensive and must include several species to help in the evaluation of both the effectiveness and toxicity of the drug. The dosage of any drug approved for use is intended to fall within a range in which the drug produces a therapeutic effect or desired outcome.

The safety and effectiveness of prescription drugs in the U.S. is regulated by the Federal Prescription Drug Marketing Act of 1987.

The Medicines and Healthcare products Regulatory Agency (MHRA) has a similar role in the UK.

Education

The study of pharmacology is offered in many universities worldwide in programs that differ from pharmacy programs. Students of pharmacology are trained as researchers, studying the effects of substances in order to better understand the mechanisms which might lead to new drug discoveries for example. Whereas a pharmacy student will eventually work in a pharmacy dispensing medications or some other position focused on the patient, a pharmacologist will typically work within a laboratory setting.

Date: 2015-01-29; view: 2339