Naming convention for chemical substances

General guidelines for naming chemical substances (including antibiotics)

The International Non-proprietary Name (INN) is the preferred reference for chemical substances, see Supporting references for approved ingredient names. 

If there is no INN (or other preferred reference) available for your chemical substance you can propose a new name. 

Use the following rules when proposing a new name:

• use International Union of Pure and Applied Chemistry (IUPAC)- external site naming conventions, for example 1-[3,3-dimethylcyclohexyl]-4-penten-1-one
• unless the name includes a salt, ester or glycol suffix, form names by joining elements of the name together to form a single word for example, ethylcellulose rather than ethyl cellulose
• capital letters are not generally used in chemical names except in the circumstances detailed below:
  • include the designator 'N-' in the name to indicate a constituent group attached to a nitrogen
  • where relevant, include stereochemical descriptors, such as 'R-' and 'S-'; 'd-', 'l-' and 'dl-'; and/or 'cis-' and 'trans-', in ingredient names, in accordance with IUPAC nomenclature. This increases the amount of information provided by the name and reduces ambiguity.
• use the designators 2-, 3-, 4-, for chemicals that include aromatic rings rather than o-, m-, p-, or ortho-, meta-, para-
• use the designators n-, iso-, sec- and tert- to describe the branching of alkyl groups
• use Table 4 to identify the acceptable approach for these chemical groups.

Naming of specific types of chemical ingredients

Polymeric substances

Polymeric substances are frequently identified by a name part and a number that indicates the grade of polymer by:

• chain length or molecular weight
• viscosity.

Some common examples are in Table 5.

Macrogols (polyethylene glycols - PEGs)

The term macrogol is generally used by the pharmaceutical industry, whereas PEG is used in the chemical and cosmetics industries. 'Macrogol' is used in ingredients for polyethylene glycols (and their simple esters and ethers), rather than polyoxyl, polyoxyethylene, polyethylene glycol or PEG. This is consistent with International Non-proprietary Names (INN) terminology.

'Macrogol' is the INN for polymeric substances with the following general formula:

HOCH₂(CH₂OCH₂)_mCH₂OH

INNs have also been assigned to simple esters and some simple ethers of macrogols. Examples are macrogol stearate and lauromacrogol.

International Non-proprietary Names (INN) definitions

The INN definitions state that each name is followed by a number indicating the average molecular weight of the:

• macrogol
• macrogol portion of an ester or ether.

For example, macrogol 300 has an average molecular weight of about 300 (m = 5 or 6, giving a molecular weight of 282.3 or 326.4).

Average molecular weights

To prevent the creation of numerous macrogol names where only minor differences exist, such as macrogol 1500 and macrogol 1540, we will use average molecular weights in the ingredient name, rounded in the following manner:

Molecular weight for macrogols with shorter chain lengths is averaged to the nearest 50, up to a weight of 800. Following 800, the molecular weight is averaged to the nearest 100 up to 1500; then to the nearest 500 up to 8000 and so on.

Size of the polymer molecule

In chemical ingredients, the size of the polymer molecule will be based on the average molecular weight of the polymer chain, not the chain length. (Chain length, based on the approximate number of oxyethylene units, is generally used for PEG-based nomenclature.)

Where names are converted to macrogol from PEG, the chain length designating number will also be appropriately amended, and the reference will be shown as 'modified' for example, International Cosmetic Ingredient Dictionary (modified). The name listed in the reference is included as a synonym.

For example, all pure macrogols (macrogol 2000, etc.) will have references as 'modified', because the reference does not usually list the number.

Complex polymers with polyethylene glycol components

Where there are no INNs for more complex polymers with polyethylene glycol components, these are named according to the best available reference.

For example, macrogol poly(vinylalcohol) grafted copolymer is named using the British Pharmacopoeia, whereas acrylates/PEG-10 maleate/styrene copolymer is named using the International Cosmetic Ingredient Dictionary.

Carbomers

When giving different names to carbomers, we follow the conventions of the United States Pharmacopoeia (USP). This approach relies on whether or not they are manufactured using benzene.

Ensure that you refer to the synonyms in the Ingredients Table, and/or the relevant USP references, to help determine the correct name for the substance.

Derivatives

Derivatives each have individual names to identify the salt or ester and distinguish the substances from the base.

For example, 'ibuprofen' and 'ibuprofen sodium' are two separate chemical ingredients.

If a derivative has an INN

The INN will be the approved name.

If there is no INN (or other common reference)

Ensure you name derivatives in accordance with the conventions described in the WHO document International Non-proprietary Names Modified, which you can find on the WHO INN Publications page- external site.

Salts

There is no need to specify the molar ratio of the salt if:

• there is no INN or other common reference, and
• the salt can exist in only one form.

For example, if an ingredient can only exist as a monosodium salt, use 'sodium' in the name (for example sodium benzoate).

Monohydrochloride would be stated as hydrochloride, whereas dihydrochloride would be stated as is.

Please note

If there is no preferred reference, and there is more than one possible stoichiometry for the salt (and the stoichiometry is not specified), the ratio is assumed to be 1:1.

Common examples are sodium, potassium, magnesium, calcium, hydrochloride and hydrobromide.

Starches

Unmodified, naturally occurring starches are classified as herbal ingredients and have herbal names, for example maize starch*.

*Note: 'maize' is used to identify ingredients derived from corn.

Some starches (such as soluble potato starch) have been chemically modified, and are therefore classified as chemical substances.

Alcohols, aldehydes, acids, esters and acyl groups

Alcohols, aldehydes, acids, esters and acyl groups should be named in accordance with references commonly used in the pharmaceutical industry, for example the British Pharmacopoeia (BP), Merck Index.

If there is no suitable reference in the Reference Codes list on the Code Tables:

• use the currently accepted International Union of Pure and Applied Chemistry (IUPAC)- external site nomenclature.

Where numbers are included in the name:

• place them in the middle of the name rather than at the start, e.g. butan-1-ol.

Ethanol

The Ingredients Table has two entries relating to ethanol, both of which use the British Pharmacopoeia as a naming reference. However, both have other default standards that sponsors can choose to comply with:

• 'ethanol absolute' (BPM) which is subject to either:
  • 'ethanol' (absolute alcohol) as described in the BP monograph of that title
  • 'dehydrated alcohol', as described in the USP monograph of that title
• 'ethanol' (BPM) which is subject to either:
  • 'ethanol (96 per cent)', as described in the BP monograph of that title
  • 'alcohol', as described in the USP monograph of that title.

Anions and cations

The quantities of individual ions (or ion equivalents) may need to be stated on a medicine label, in addition to the statement of strength for ingredients. The medicine labelling Orders include these requirements for:

• intravenous infusions (large-volume injections)
• concentrated haemodialysis solutions.

All approved anions and cations have AANs and are available in the Ingredients Table.

Amino acids, sugars and other chiral ingredients

Many chiral substances, such as amino acids, can exist as either:

• a single optical isomer (enantiomer) or
• a mixture of isomers.

The reference quoted for the name defines the isomer or mixture.

Some substances of biological origin exist in nature exclusively as a single enantiomer. These include amino acids, sugars and lactic acid. For these substances the:

• stereochemistry of the naturally occurring isomer isn't identified in the ingredient name, e.g. 'lysine' and 'glucose' are AANs, NOT 'l-lysine' or 'd-glucose'
• designators, 'dl-' and 'd-' should be included in the names of amino acids that occur naturally in these forms, to distinguish them from the 'l' form. This is consistent with INN naming conventions and reduces ambiguity
• designators 'R', 'RS' and 'S' are not used for chiral molecules, unless they are in the reference title or are required to distinguish between different approved names.

Metals

Use the common name for metals when naming metal salts or complexes. For example, use 'copper' and 'iron', rather than 'cuprous' or 'cupric', and 'ferrous' or 'ferric' as they are more readily understood by consumers.

• If a single oxidation state occurs, include it in the name, e.g. copper (I), copper (II), iron (II), iron (III))
• Where mixed oxidation states occur, use the names copper, iron, and so on; for example, iron phosphate.

Colour names

Do not include the Colour Index (CI) number for new ingredients that are colours.

Each colour and its lakes will have separate names.

For example, erythrosine and erythrosine aluminium lake are both approved names.

Radioactive pharmaceuticals

Use the INN format for radioactive ingredients, e.g. Iometin (131I); iometopane (123I)) noting that mass numbers in chemical substances are not in superscript format.

Stearates

The term 'stearate' in the name of a salt or ester refers to mixtures of fatty acids that have as their major component(s) either:

• stearic (octadecanoic) acid, or
• palmitic (hexadecanoic) and stearic acids in varying proportions.

The term 'palmitostearate' is sometimes used where the mixture of fatty acids contains approximately equal quantities of palmitic and stearic acids.

Vitamin E substances

There are no INNs for vitamin E substances - that is, alpha-tocopherol and its derivatives. The USP and BP systems for naming vitamin E substances are different.

The chemical ingredient names are essentially the same as the names specified in the USP monograph 'Vitamin E', with an additional hyphen, as demonstrated in Table 6.

Waters of hydration

Use the following approach for identifying waters of hydration, for example the waters of crystallisation of a substance:

• if a hydration state is not included in the name, the ingredient is anhydrous. This policy is used even if the 'normal' state of the ingredient is hydrated.

Note: In a small number of cases, the term 'anhydrous' is retained in the ingredient name to avoid confusion, for example 'colloidal anhydrous silica' and 'hydrophobic colloidal anhydrous silica'.

• there are separate names for each hydration state in which the substance occurs.
• substances that occur with a mixed hydration state are called 'substance hydrate'.

This approach to ingredient naming is consistent with INN naming conventions. The objective is to provide an unambiguous name, without users needing to refer to other documents to determine which state of hydration is defined.

Exceptions to this approach

If the water is not part of the crystal structure then some substances may include the word 'dried' as part of their name, e.g. 'dried magnesium sulfate'.

Use on labels

Waters of hydration may be expressed differently on labels.

For information on how an ingredient is expressed on a medicine label, see Medicine labels: Guidance on TGO 91 and 92.