Any FDA-approved drug has both a generic name and a brand name. In the United States, the United States Adopted Names (USAN) Council assigns the generic name. You can think of the relationship like this: the generic name relates to the drug’s “chemical name” the way a brand name relates to a “trade name.”

Generic name: The generic name is built from a stem and sometimes a substem, usually found at the end of the name. Stems can indicate a drug’s chemical structure, its clinical use (indication), or its action at a specific receptor. Drugs that share the same stem are typically related.

A generic name also includes a one- or two-syllable prefix that helps distinguish one drug from others in the same class.

For example, “sildenafil” and “tadalafil” share the stem “-afil” because they belong to the same class of medications: PDE5 (phosphodiesterase 5) inhibitors. Their prefixes are “sil-” and “tadal-.” The “den” in sildenafil is an infix, which may be used to further classify certain medications.

Brand name: A brand name is a specific name chosen by a drug company or manufacturer and protected by a patent.

For example, “Tylenol” is the brand name for “acetaminophen.”

Examples of brand names and generic names of common drugs

Brand name	Generic name
Protonix	Pantoprazole
Benadryl	Diphenhydramine
Tums	Calcium carbonate
Nasonex	Mometasone
Allegra	Fexofenadine
Ventolin	Albuterol

A generic medication may be sold under its generic name or under one or more brand names. For example, ibuprofen (generic) is sold under various brand names, such as Advil and Motrin.

Sidenote

Bioequivalence:

Generic versions of brand name drugs must be bioequivalent to the original drug. This means the two drugs should release the active ingredient into the bloodstream:

• at the same amount
• at the same rate
• with the same quality

Common drug name stems

Stem	Drug class or classification	Example
-stat	Anti-hyperlipidemics or HMG CoA reductase inhibitors	Atorvastatin
-prazole	Proton pump inhibitors or PPI for acid reflux/GERD	Omeprazole
-lukast	Leukotriene receptor blockers	Montelukast
-grel	Platelet aggregation inhibitors	Clopidogrel
-faxine	Antidepressants; serotonin and norepinephrine reuptake inhibitors (SNRI)	Venlafaxine
-oxetine	Antidepressants; selective serotonin reuptake inhibitors (SSRI)	Duloxetine
-sartan	Angiotensin II receptor blockers	Valsartan
-floxacin	Antibiotics; quinolone derivatives	Levofloxacin
-vir	Antivirals (avir, ovir, ivir)	Valacyclovir
-mab	Monoclonal antibodies	Daclizumab
-alol	Combined alpha and beta blockers	Labetalol
-ilol	Combined alpha and beta blockers	Carvedilol
-olol	Beta blockers	Metoprolol
-olone	Non-prednisone steroids	Minaxolone
-cillin	Penicillins	Penicillin
-ase	Enzymes	Dornase alfa
-caine	Local anesthetics	Lidocaine, bupivacaine, prilocaine
-conazole	Azole antifungals	Fluconazole

Commonly used drug prefixes

Prefix and meaning	Example
Cef- (related to cephalosporins)	Cefazolin
Ceph- (related to cephalosporins)	Cephalexin
Chlor- (chlorine-containing compound)	Chlorpromazine
Flu- (fluorinated compounds)	Fluoxetine
Sulfa- (sulfonamides)	Sulfamethoxazole, sulfasalazine
Thio- (Sulfur-containing compounds)	Thiopental
Meth- (methylated compounds)	Methotrexate
Pred- (type of corticosteroid)	Prednisone, prednisolone

Prefix “Peg” indicates that a biologic substance (such as a peptide) is pegylated. Infix -io- may be added to suggest a high iodine content (e.g. amiodarone). When -fos- appears anywhere in a drug name, the element phosphorus is present (e.g. ifosfamide).

Sidenote

Therapeutic equivalence:

• Therapeutic equivalence = Bioequivalence + Pharmaceutical equivalence*

• Therapeutically equivalent drugs are expected to have the same clinical effect and safety profile and contain identical amounts of the identical active drug ingredient in the identical dosage form and route of administration.

• Therapeutically equivalent drugs can be substituted for each other.

• Therapeutically equivalent drugs can still differ in shape, color, flavor, inactive ingredients etc.

*Pharmaceutical equivalence means drugs with identical active ingredients in identical amounts (strength), forms, and routes of administration.

Orange Book

To help pharmacists determine whether a generic drug can be substituted for a brand-name drug, the FDA maintains a reference called the Orange Book.

The Orange Book, formally titled Approved Drug Products with Therapeutic Equivalence Evaluations, lists medications approved by the FDA for safety and effectiveness in the United States.

Pharmacists and pharmacy technicians use the Orange Book to check whether generic drugs are therapeutically equivalent to brand-name drugs and can be substituted.

The FDA maintains an online Orange Book database that allows users to search approved drugs by active ingredient, brand name, generic name, or patent information.

The Orange Book also includes a coding system that indicates therapeutic equivalence:

• A codes: Products considered therapeutically equivalent to other pharmaceutically equivalent drugs and generally acceptable for substitution.
• B codes: Products that require further investigation or review to determine therapeutic equivalence.