Topics covered in this snack-sized chapter:
A pharmaceutical drug, also referred to as medicine, medication or medicament, can be loosely defined as any chemical substance intended for use in the medical diagnosis, cure, treatment, or prevention of disease.
Drugs can be classified according to various criteria including:
The preferred classification is the one which may be divided into main groups as follows:
- Chemotherapeutic agents - used to cure infectious diseases and cancer (Sulfa drugs, Antibiotics).
- Pharmacodynamic agents - used in non-infectious diseases (Cholinergic, Adrenergic, Hallucinogenic, Sedatives).
- Miscellaneous agents (Narcotic Analgesics, Local Anesthetics).
Drugs have three or more names including:
- Chemical name: The chemical name is assigned according to rules of nomenclature of chemical compounds.
- Brand or trade name: The brand name is always capitalized and is selected by the manufacturer.
- Generic or common name: The generic name refers to a common established name irrespective of its manufacturer.
A very broad definition of a drug would include "all chemicals other than food that affect living processes”.
If the affect helps the body, the drug is a medicine. However, if a drug causes a harmful effect on the body, the drug is a poison.
The same chemical can be a medicine and a poison depending on conditions of use and the person using it.
Another definition would be "medicinal agents used for diagnosis, prevention, treatment of symptoms, and cure of diseases."
Contraceptives would be outside of this definition unless pregnancy was considered a disease.
Drugs act within the cell by modifying normal biochemical reactions.
Enzyme inhibition may be reversible or non-reversible; competitive or non-competitive.
Antimetabolites may be used which mimic natural metabolites. Gene functions may be suppressed.
Drug-Receptor Interaction
Drugs act on the cell membrane by physical and/or chemical interactions.
This is usually through specific drug receptor sites known to be located on the membrane.
A receptor is a specific chemical constituent of the cell with which a drug interacts to produce its pharmacological effects.
Some receptor sites have been identified with specific parts of proteins and nucleic acids.
In most cases, the chemical nature of the receptor site remains obscure.
Non-specific Interactions
Drugs act exclusively by physical means outside of cells.
These sites include external surfaces of skin and gastrointestinal tract.
Drugs also act outside of cell membranes by chemical interactions.
Neutralization of stomach acid by antacids is a good example.
A disease is a condition of impaired health resulting from a disturbance in the structure or function of the body.
Diseases may be classified into the following major categories:
- Infections caused by viruses, rickettsia, bacteria, fungi, protozoa and worms.
- Allergic diseases caused by antigens and foreign substances.
- Metabolic disorders caused by defects in the body's ability to carry out normal reactions - these may be hereditary, deficiency, and congenital defects.
- Toxic diseases caused by poisons
- Psychosomatic and mental diseases
It is important to distinguish between actions of drugs and their effects.
Actions of drugs are the biochemical physiological mechanisms by which the chemical produces a response in living organisms.
The effect is the observable consequence of a drug action.
For example, the action of penicillin is to interfere with cell wall synthesis in bacteria and the effect is the death of the bacteria.
Drugs are chosen to exploit differences between normal metabolic processes and any abnormalities which may be present.
The biological effects observed after a drug has been administered are the result of an interaction between that chemical and some part of the organism.
Mechanisms of drug action can be viewed from different perspectives, namely, the site of action and the general nature of the drug-cell interaction.
