Nomenclature of Drugs and Rules applied

Nomenclature of Drugs and Rules applied

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Drugs have three or more names. These names are the following: a) code number or code designation; b) chemical name; c) proprietary, trivial, brand or trade name; d) nonproprietary, generic, official, or common name; and e) synonym and other names.

The code number is usually formed with the initials of the laboratory or the chemist or the research team that prepared or tested the drug the first time, following by a number. It does not identify the chemical nature or structure of the drug. Its use is discontinued as soon as an adequate name is chosen.

The chemical name is the only one that describes unambiguously the chemical structure of a drug, identifying it fully and exactly. It is given according to rules of nomenclature of chemical compounds. Since the chemical name is sometimes very elaborate, it is not suitable for routine usage.

The proprietary name is the individual name selected and used by manufacturers. If a drug is manufactured by more than one company, as frequently happens, each firm assigns its own proprietary name. Sometimes the proprietary name denotes a drug combination not a single drug. A proprietary name is written with the first letter of each word of the name capitalized.

The nonproprietary name refers to the common, established name by which a drug is known as an isolated substance, irrespective of its manufacturer. It is chosen by official agencies, such as the U.S. Adopted Names (USAN) Council, the American Pharmaceutical Association, and other. On a worldwide scale, however, the World Health Organization is the official agency that selects, approves, and disseminates the generic names of drugs.


Chemical name: N-(4-hydroxyphenyl) acetamide   

Generic name: Acetaminophen    

Trade name: Tylenol.


Chemical name: 7-chloro-1,3-dihydro-1-methyl-5-phenyl-2H-1,4-benzodiazepin-2-one

Generic name: Diazepam

Trade name: Valium

Synonyms are names given by different manufacturers to the same drug or old nonproprietary names. Some drugs may have several names. It is usually assumed that a drug bearing a generic name is equivalent to the same drug with a brand name.

However, this is not always true. Although chemically equivalent, drugs having the same nonproprietary name but different proprietary names, because they are manufactured by different laboratories, can differ markedly in their pharmacological action. Several factors – mainly of formulation and manufacture – account for this difference.


Rules of Drug Nomenclature

The World Health Organization has advised its member states to adopt the following general principles in devising international nonproprietary names (INN) for pharmaceutical substances:

1. INN should be distinctive in sound and spelling. They should not be inconveniently long and should be liable to confusion with names in common use.

2. The INN for substances belonging to a group of pharmacologically related substances should, where appropriate, show this relationship. Names that are likely to convey to a patient an anatomical, physiological, pathological or therapeutic suggestion should be avoided.

3. In devising the INN of the first substance in a new pharmacological group, consideration should be given to the possibility of devising suitable INN for related substances, belonging to the new group.

4. In devising INN for acids, one-word names are preferred; their salts should be named without modifying the acid names, e.g. “oxacillin” and “oxacillin sodium”, “ibufenac” and “ibufenac sodium”.

5. INN for substances which are used as salts should in general apply to the active base or the active acid. Names for different salts or esters of the same active substances should differ only in respect of the name of the inactive acid or the inactive base.

6. The use of an isolated letter or number should be avoided; hyphenated construction is also undesirable.

7. To facilitate the translation and pronunciation of INN, “f” should be used instead of “ph”, “t” instead of “th”, “e” instead of “ae” or “oe”, and “i” instead of “y”; the use of the letters “h” and “k” should be avoided.

8. Provided that the names suggested are in accordance with these principles, names proposed by the person discovering or first developing and marketing a pharmaceutical preparation. Or names already officially in use in any country, should receive preferential consideration.

9. Group relationship in INN should if possible be shown by using a common stem. Where a stem is shown without any hyphens it may be used anywhere in the name.

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