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 are interchangeable, i.e. they are pharmaceutically and biologically equivalent, so that a formulation from one source will be absorbed and give the same blood concentrations and have the same therapeutic efficacy as that from another. (Further formal therapeutic trials are not demanded for these well-established drugs.) A prescription for a generic drug formulation may be written for any officially licensed product that the dispensing pharmacy has chosen to purchase (on economic criteria; see ‘generic substitution’ below).4

The proprietary name is a trademark applied to particular formulation(s) of a particular substance by a particular manufacturer. Manufacture is confined to the owner of the trademark or to others licensed by the owner. It is designed to maximise the difference between the names of similar drugs marketed by rivals for obvious commercial reasons. To add confusion, some companies give their proprietary products the same names as their generic products in an attempt to capture the prescription market, both proprietary and generic, and some market lower-priced generics of their own proprietaries. When a prescription is written for a proprietary product, pharmacists under UK law must dispense that product only. But, by agreement with the prescribing doctor, they may substitute an approved generic product (generic substitution). What is not permitted is the substitution of a different molecular structure deemed to be pharmacologically and therapeutically equivalent (therapeutic substitution).

Non-proprietary names

The principal reasons for advocating the habitual use of non-proprietary (generic) names in prescribing are described below.

Clarity

Non-proprietary names give information on the class of drug; for example, nortriptyline and amitriptyline are plainly related, but their proprietary names, Allegron and Triptafen, are not. It is not unknown for prescribers, when one drug has failed, unwittingly to add or substitute another drug of the same group (or even the same drug), thinking that different proprietary names must mean different classes of drugs. Such occurrences underline the wisdom of prescribing generically, so that group similarities are immediately apparent, but highlight the requirement for brand names to be as distinct from one another as possible. Relationships cannot, and should not, be shown by brand names.

Economy

Drugs sold under non-proprietary names are usually, but not always, cheaper than those sold under proprietary names.

Convenience

Pharmacists may supply whatever version they stock,5 whereas if a proprietary name is used they are obliged to supply that preparation alone. They may have to buy in the preparation named even though they have an equivalent in stock. Mixtures of drugs are sometimes given non-proprietary names, having the prefix co– to indicate more than one active ingredient, e.g. co-amoxiclav for Augmentin.6 No prescriber can be expected to write out the ingredients, so proprietary names are used in many cases, there being no alternative. International travellers with chronic illnesses will be grateful for rINNs (see above), as proprietary names often differ from country to country. The reasons are linguistic as well as commercial (see below).

Proprietary names

The principal non-commercial reason for advocating the use of proprietary names in prescribing is consistency of the product, so that problems of quality, especially of bioavailability, are reduced. There is substance in this argument, though it is often exaggerated.

It is reasonable to use proprietary names when dosage, and therefore pharmaceutical bioavailability, is critical, so that small variations in the amount of drug available for absorption may have a big effect on the patient, e.g. drugs with a low therapeutic ratio, digoxin, hormone replacement therapy, adrenocortical steroids (oral), antiepileptics, cardiac antiarrhythmics, warfarin. In addition, with the introduction of complex formulations, e.g. sustained release, it is important clearly to identify these, and the use of proprietary names has a role.

The prescription and provision of proprietary drugs increases profits for the company who first invented the drug, and costs for the purchaser – variably the patient, insurer or national health-care system. There are no absolute rights or wrongs in this. Society rewards the inventer, because it requires inventions, but wishes a healthy generic market in order to restrain costs. The now widespread use of computer programmes for prescribing, which prompt the doctor to use non-proprietary names, has tilted the balance in favour of generics.

Generic names are intentionally longer than trade names to minimise the risk of confusion, but the use of accepted prefixes and stems for generic names works well and the average name length is four syllables, which is manageable. The search for proprietary names is a ‘major problem’ for pharmaceutical companies, increasing, as they are, their output of new preparations. A company may average 30 new preparations (not new chemical entities) a year, another warning of the urgent necessity for the doctor to cultivate a sceptical habit of mind. Names that ‘look and sound medically seductive’ are being picked out. ‘Words that survive scrutiny will go into a stock-pile and await inexorable proliferation of new drugs’.7 One firm (in the USA) commissioned a computer to produce a dictionary of 42 000 nonsense words of an appropriately scientific look and sound.

A more recent cause for confusion for patients (consumers) in purchasing proprietary medicines is the use by manufacturers of a well-established ‘brand’ name that is associated in the mind of the purchaser with a particular therapeutic effect, e.g. analgesia, when in fact the product may contain a quite different pharmacological entity. By a subtle change or addition to the brand name of the original medicine, the manufacturer aims to establish ‘brand loyalty’. This unsavoury practice is called ‘umbrella branding’. It is also important to doctors to be aware of what over-the-counter (OTC) medicines their patients are taking, as proprietary products that were at one time familiar to them may contain other ingredients, with the increased risk of adverse events and drug interactions.

For the practising doctor (in the UK) the British National Formulary provides a regularly updated and comprehensive list of drugs in their non-proprietary (generic) and proprietary names. ‘The range of drugs prescribed by any individual is remarkably narrow, and once the decision is taken to “think generic” surely the effort required is small’.8 And, we would add, worthwhile.

Confusing names

The need for both clear thought and clear handwriting is shown by medicines of totally different class that have similar names. Serious events have occurred as a result of the confusion of names and dispensing the wrong drug, e.g. Lasix (furosemide) for Losec (omeprazole) (death); AZT (intending zidovudine) was misinterpreted in the pharmacy and azathioprine was dispensed (do not use abbreviations for drug names); Daonil (glibenclamide) for De-nol (bismuth chelate) and for Danol (danazol). It will be noted that non-proprietary names are less likely to be confused with other classes of drugs.

Guide to further reading

Aronson J.K. Where name and image meet – the argument for adrenaline. Br. Med. J.. 2000;320:506–509.

Chief Medical Officer, Department of Health, Medicines and Healthcare products Regulatory Agency. Change in names of certain medicinal substances. Professional letter of 17 March 2004, pp. 1–6 (available to download as PL CMO (2004)1: change in names of certain medicinal substances from http://www.dh.gov.uk, 2004. (accessed 20.10.11.)

Furberg C.D., Herrington D.M., Psaty B.M. Are drugs within a class interchangeable? Lancet: .1999;354:1201–1204.(and correspondence: are drugs interchangeable?. Lancet. 2000;355:316–317.

George C.F. Naming of drugs: pass the epinephrine please. Br. Med. J: .1996;312:1315.(and correspondence in. Br. Med. J.. 1996;313:688–689.

Jack D.B., Soppitt A.L. Give a drug a bad name. Br. Med. J.. 1991;303:1606–1608.

1 The ATC classification system developed by the Nordic countries and widely used in Europe meets most classification requirements. Drugs are classified according to their anatomical, therapeutic and chemical characteristics into five levels of specificity, the fifth being that for the single chemical substance.

2 The generic name is now widely accepted as being synonymous with the non-proprietary name. Strictly ‘generic’ (L. genus, race, a class of objects) should refer to a group or class of drug, e.g. benzodiazepines, but by common usage the word is now taken to mean the non-proprietary name of individual members of a group, e.g. diazepam.

3 Trigg R B 1998 Chemical nomenclature. Kluwer Academic, Dordrecht, pp. 208–234.

4 European Medicines Agency and US Food and Drug Agency guidelines are available and give pharmacokinetic limits that must be met.

5 This can result in supply of a formulation of appearance different from that previously used. Patients naturally find this disturbing.

6 This is a practice confined largely to the UK. It is unknown in Europe, and not widely practised in the USA.

7 Pharmaceutical companies increasingly operate worldwide and are liable to find themselves embarrassed by unanticipated verbal associations. For example, names marketed (in some countries), such as Bumaflex, Kriplex, Nokhel and Snootie, conjure up in the minds of native English speakers associations that may inhibit both doctors and patients from using them (see Jack & Soppitt 1991 in Guide to further reading).

8 Editorial 1977 British Medical Journal 4:980 (and subsequent correspondence).

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