An international nonproprietary name (INN) is an official generic and nonproprietary name given to a pharmaceutical drug or an active ingredient. INNs are intended to make communication more precise by providing a unique standard name for each active ingredient, to avoid prescribing errors. The INN system has been coordinated by the World Health Organization (WHO) since 1953.
Having unambiguous standard names for each drug (standardization of drug nomenclature) is important because a drug may be sold by many different brand names, or a branded medication may contain more than one drug. For example, the branded medications Celexa, Celapram and Citrol all contain the same active ingredient: citalopram; and the antibiotic widely known by the brand name Bactrim contains two active ingredients: trimethoprim and sulfamethoxazole. This combination of two antibiotic agents in one tablet has been available as a generic for decades, but the brand names Bactrim and Septra are still in common use.
Each drug's INN is unique but may contain a word stem that is shared with other drugs of the same class; for example, the beta blocker drugs propranolol and atenolol share the -olol suffix, and the benzodiazepine drugs lorazepam and diazepam share the -azepam suffix.
The WHO issues INNs in English, Latin, French, Russian, Spanish, Arabic, and Chinese, and a drug's INNs are often cognate across most or all of the languages, with minor spelling or pronunciation differences, for example: paracetamol (en) (la), (fr) and (ru). An established INN is known as a recommended INN (rINN), while a name that is still being considered is called a proposed INN (pINN).
Name stems
Drugs from the same therapeutic or chemical class are usually given names with the same stem. Stems are mostly placed word-finally, but in some cases word-initial stems are used. They are collected in a publication informally known as the Stem Book.
Examples are: -anib for angiogenesis inhibitors (e.g. pazopanib) -anserin for serotonin receptor antagonists, especially 5-HT2 antagonists (e.g. ritanserin and mianserin) -ant for various receptors antagonists (e.g. aticaprant and rimonabant) -arit for antiarthritic agents (e.g. lobenzarit) -ase for enzymes (e.g. alteplase) -azepam or -azolam for benzodiazepines (e.g. diazepam and alprazolam) -caine for local anaesthetics (e.g. procaine or cocaine) -cain- for class I antiarrhythmics (e.g. procainamide) -coxib for COX-2 inhibitors, a type of anti-inflammatory drugs (e.g. celecoxib) -mab for monoclonal antibodies (e.g. infliximab); see Nomenclature of monoclonal antibodies -- for cannabinoid receptor agonists (e.g. cannabidiol, dronabinol) for cannabinoid receptor antagonists -olol for beta blockers (e.g. atenolol) -pril for ACE inhibitors (e.g. captopril) -sartan for angiotensin II receptor antagonists (e.g. losartan) -tinib for tyrosine kinase inhibitors (e.g. imatinib) -vastatin for HMG-CoA reductase inhibitors, a group of cholesterol-lowering agents (e.g. simvastatin) -vir for antivirals (e.g. aciclovir or ritonavir) for antiretroviral protease inhibitors (e.g. darunavir) arte- for artemisinin antimalarials (e.g. artemether) cef- for cephalosporins (e.g. cefalexin) io- for iodine-containing radiopharmaceuticals (e.g. iobenguane) -vec for gene therapy vectors (e.g. alipogene tiparvovec) -meran for messenger RNA products (e.g. tozinameran)
Linguistic discussion
Stems and roots
The term stem is not used consistently in linguistics. It has been defined as a form to which affixes (of any type) can be attached. Under a different and apparently more common view, this is the definition of a root, while a stem consists of the root plus optional derivational affixes, meaning that it is the part of a word to which inflectional affixes are added. INN stems employ the first definition, while under the more common alternative they would be described as roots.