Classification and naming of drugs

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Chapter 7 Classification and naming of drugs

Morris Brown

Synopsis

In any science there are two basic requirements, classification and nomenclature (names):

• Classification – drugs cannot be classified and named according to a single rational system because the requirements of chemists, pharmacologists and doctors differ.

• Nomenclature – nor is it practicable always to present each drug under a single name because the formulations in which they are presented as prescribable medicines may vary widely and be influenced by commercial considerations.

Generic (non-proprietary) names should be used as far as possible when prescribing except where pharmaceutical bioavailability differences have overriding importance.

The wider availability of proprietary medicines through pharmacy sale and direct to the public has the potential for greater confusion to consumers (patients) and doctors.

Classification

It is evident from the way this book is organised that there is no homogeneous system for classifying drugs that suits the purpose of every user. Drugs are commonly categorised according to the convenience of whoever is discussing them: clinicians, pharmacologists or medicinal chemists. Drugs may be classified by:

• Body system, e.g. alimentary, cardiovascular.

• Therapeutic use, e.g. receptor blockers, enzyme inhibitors, carrier molecules, ion channels.

• Mode or site of action:

image molecular interaction, e.g. glucoside, alkaloid, steroid
image cellular site, e.g. loop diuretic, catecholamine uptake inhibitor (imipramine).

• Molecular structure, e.g. glycoside, alkaloid, steroid.1

Nomenclature (names)

Any drug may have names in all three of the following classes:

1. The full chemical name.

2. A non-proprietary (official, approved, generic) name used in pharmacopoeias and chosen by official bodies; the World Health Organization (WHO) chooses recommended International Non-proprietary Names (rINNs). The harmonisation of names began 50 years ago, and most countries have used rINNs for many years. The USA is an exception, but even here most US National Names are the same as their rINN counterparts. In the UK, there are two exceptions to the policy: adrenaline (rINN epinephrine) and noradrenaline (rINN norepinephrine). Manufacturers are advised to use both names on the product packaging and information literature.

In general we use rINNs in this book and aim to minimise some unavoidable differences with, where appropriate, alternative names in the text and index (in brackets).

3. A proprietary (brand) name that is the commercial property of a pharmaceutical company or companies. In this book proprietary names are distinguished by an initial capital letter.

Example: one drug – three names

1. 3-(10,11-dihydro-5H-dibenz[b.f]-azepin-5-yl) propyldimethylamine

2. imipramine

3. Tofranil (UK), Melipramine, Novopramine, Pryleugan, Surplix, etc. (various countries).

The full chemical name describes the compound for chemists. It is obviously unsuitable for prescribing.

A non-proprietary (generic,2 approved) name is given by an official (pharmacopoeia) agency, e.g. WHO.

Three principles remain supreme and unchallenged in importance: the need for distinction in sound and spelling, especially when the name is handwritten; the need for freedom from confusion with existing names, both non-proprietary and proprietary, and the desirability of indicating relationships between similar substances.3

The generic names diazepam, nitrazepam and flurazepam are all of benzodiazepines. Their proprietary names are Valium, Mogadon and Dalmane respectively. Names ending in –olol are adrenoceptor blockers; those ending in –pril are angiotensin-converting enzyme (ACE) inhibitors; and those in –floxacin are quinolone antimicrobials. Any pharmaceutical company may manufacture a drug that has a well-established use and is no longer under patent restriction, in accordance with official pharmacopoeial quality criteria, and may apply to the regulatory authority for a licence to market. The task of authority is to ensure that these generic or multi-source pharmaceuticals

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