by George Taniwaki

Modern medical therapies often include the use of drugs, many of which have strange-sounding names. I noticed that various drugs used by kidney transplant patents have similar sounding names like tacrolimus and sirolimus or daclizumab and basiliximab. All four drugs are used to reduce the incidence and severity of acute organ rejection. Just from the sound/spelling of their names, I assumed the first two were similar to each other, the last two are similar to each other and that each pair is different from the other.

Similarly, if you read articles about advances in healthcare, you will often come across the name of a new drug. For instance, I recently saw a Reuters article mentioning ichorcumab, an experimental anticoagulant that may start clinical trials soon. The name of this drug ends in -mab. I wondered if it was related to the kidney transplant drugs I was familiar with and how.

Generic drug names

These sometimes difficult to pronounce words are called generic drug names. Unlike the names of simple chemical compounds like titanium dioxide (TiO2), drug names do not describe the arrangement of atoms in the molecule. Instead, they describe the pharmaceutical origins or uses of the molecules.

There is a single organization called the United States Adopted Names Council (USAN) that reviews and approves all generic drug names used in the U.S. The USAN includes representatives from the American Medical Association (AMA), the United States Pharmacopeial Convention (USP), and the American Pharmacists Association (APhA). A liaison from the U.S. Food and Drug Administration (FDA) also participates.

Whenever a pharmaceutical company develops a new biologic agent, it submits an application to the USAN for a generic name for it. The company can suggest a name. The USAN will approve it, or if it rejects it, will suggest an alternative. The process usually moves quite smoothly, though on occasion there is a disagreement that can lead to a court case (C&EN Jan 2012).

Separately, the company that has developed the drug is free to create a brand name for it and register the brand name as a trademark. This is a completely different process. There need not be any connection between the generic name and the brand name. In fact, the FDA will reject any brand names that are too close to the generic name. An article with some details appeared in the J. Am. Pharm Assoc. 2004.

The USAN works with the International Nonproprietary Name (INN) program of the World Health Organization (WHO) to ensure that generic drug names are standardized worldwide. About 60 percent of all new drugs are developed by U.S. pharmaceutical companies, so the USAN heavily influences the INN program.

Specific naming rules

The USAN follows specific nomenclature rules. The USAN’s guidelines for naming new drugs are available here. Summarizing them, a new generic drug name should be:

  1. Unique – reducing confusion and enhancing safety when prescribing
  2. Nonproprietary – can be referred to without violating intellectual property rights or being specific to the product of a single company or source
  3. Informative – Useful for healthcare practitioners and medical education
  4. Short and easy to pronounce – can be used worldwide, a single word with preferably no more than 4 syllables with up to one modifier, also with no more than 4 syllables

Names are based on prefixes and stems. Prefixes are the unique identifiers for a drug. The stems are letter sequences common to a group of drugs that share pharmacologic actions. A complete list of rules for creating new prefixes and stems is available here. Some general naming rules are listed in the table below.

Rule Reason
Do not begin with rac, dex. lev-, ar-, and es These are reserved for racemic mixture, dextro- [R(+)] or levo- [S(-)] rotating enantiomers, and for R(-) and S(+) isomers of the levorotatory and dextrorotatory forms respectively
Do not begin with h, j, k, or w These letters either do not exist in some of the 130 countries that use USANs, or have different sounds in various languages
Do not begin with x or z X and z often sound alike at the start of words
Do not use ph, th, ae, oe, or y Different sounds in different languages, use f, t, e, and i instead
Avoid prefixes and stems like brev, vel, mal, or mor These stems imply other things (brevity, velocity, bad, or death, respectively)
Avoid stem name based on a drug or agent’s target indication Indications often change; mechanism of action is a better basis for names

There are hundreds of approved stem names under the USAN and new ones are added regularly. A complete list is provided here. A few common stems and their meanings are shown in the table below.

Stem Meaning
-anib angiogenesis inhibitors
-ase enzymes
-bufen non-steroidal anti-inflammatory agents, fenbufen derivative
-caine local anesthetics
-cept receptor molecules, native or modified (a preceding infix should designate the target)
-coxib selective cyclooxygenase-2 inhibitors
-erg ergot alkaloids
-imus immunosuppressives
subgroup: –rol-imus immunosuppressant, rapamycin derivatives
-kin interleukins
-mab monoclonal antibodies or fragments
-stat enzyme inhibitors
-tide peptides
-a-, -e-, -i-, -o-, -u-, -xi-, -zu- animal source, rat = a; hamster = e; primate = i; mouse = o; human = u; chimera (from proteins or genes of two different species) = xi; humanized = zu
-vir-,bac-, -li- or –lim-, les-, –cir-, tu target disease or condition: viral = vir; bacterial = bac; immunomodulator = li or lim; infectious lesion = les; cardiovascular or circulatory = cir; tumor = tu

To assist those unfamiliar with drug names, a guide to pronouncing generic drug names is available here.

Examples of generic names

Going back to our example of antirejection drugs prescribed to kidney transplant patients, one common drug is sold under the brand name Prograf by Astellas, a name that is intended to sound like it supports organ grafts. The generic name for this drug is tacrolimus. The prefix or unique identifier of the name is tac-. The stem –rol-imus means it is a rapamycin (a type of fungus) derivative immunosuppressant. This drug reduces the activity of T-cells and thus reduces the chance of acute rejection of the grafted kidney.

A similar drug is Rapamune sold by Pfizer and has the generic name sirolimus. As you may guess by looking at both its commercial name and generic name, it is also a rapamycin derivative immunosuppressant.

Another immunosuppressant drug often prescribed just prior and after surgery is  Zenapax, sold by Roche. The generic name is daclizumab. The identifier prefix is dac-. The stem –li-zu-mab indicates this is a humanized monoclonal antibody targeted at the immune system. Monoclonal antibodies are highly specific. Daclizumab will only bind with the CD25 receptors of T-cells. It does not suppress other T-cell activity and so does not increase the incidence of opportunistic infections like other immunosuppression medications.

A similarly prescribed drug is basiliximab, sold as Simulect by Novartis. The identifier prefix is basi-. The stem -li-xi-mab indicates this is a chimeral (meaning it made by combining bits from two different species, in this case mouse and human) monoclonal antibody. It also binds to the CD25 receptor of T-cells.

Some more examples are shown below.


Drug naming convention. Image from C&EN

As a final case, let’s look at the new anticoagulant drug, ichorcumab mentioned earlier. The prefix is ichorc-. The stem –u-mab indicates this is a human derived monoclonal antibody. In Greek mythology, ichor is the golden ethereal fluid in the blood of the gods and other immortals. A nice description of the discovery of a patient who naturally produced the antigen that resulted in the development of ichorcumab is described in Fierce Biotech Jun 2013.

To learn more about drug naming conventions, there is an online app at Quizlet that includes flash card training, a scatter game, and a race game.