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Adrug class is a group ofmedications and other compounds that share similarchemical structures, act through the samemechanism of action (i.e., binding to the samebiological target), have similarmodes of action, and/or are used to treat similar diseases.[1][2] TheFDA has long worked to classify and license new medications. Its Drug Evaluation and Research Center categorizes these medications based on both theirchemical andtherapeutic classes.[3]
In several major drug classification systems, these four types of classifications are organized into a hierarchy.[4] For example,fibrates are a chemical class of drugs (amphipathic carboxylic acids) that share the same mechanism of action (PPAR agonist), the same mode of action (reducing bloodtriglyceride levels), and are used to prevent and treat the same disease (atherosclerosis). However, not all PPAR agonists are fibrates, not all triglyceride-lowering agents are PPAR agonists, and not all drugs used to treat atherosclerosis lower triglycerides.A drug class is typically defined by aprototype drug, the most important, and typically the first developed drug within the class, used as a reference for comparison.
This type of categorisation of drugs is from achemical perspective and categorises them by their chemical structure. Examples of drug classes that are based on chemical structures include:
This type of categorisation is from apharmacological perspective and categorises them by their biological target. Drug classes that share a common molecularmechanism of action modulate the activity of a specificbiological target.[6] The definition of a mechanism of action also includes the type of activity at that biological target. For receptors, these activities includeagonist,antagonist,inverse agonist, ormodulator. Enzyme target mechanisms includeactivator orinhibitor. Ion channel modulators includeopener orblocker. The following are specific examples of drug classes whose definition is based on a specific mechanism of action:
This type of categorisation of drugs is from abiological perspective and categorises them by the anatomical or functional change they induce. Drug classes that are defined by commonmodes of action (i.e. the functional or anatomical change they induce) include:
This type of categorisation of drugs is from amedical perspective and categorises them by the pathology they are used to treat. Drug classes that are defined by theirtherapeutic use (the pathology they are intended to treat) include:
Some drug classes have been amalgamated from these three principles to meet practical needs. The class ofnonsteroidal anti-inflammatory drugs (NSAIDs) is one such example. Strictly speaking, and also historically, the wider class of anti-inflammatory drugs also comprisessteroidal anti-inflammatory drugs. These drugs were in fact the predominant anti-inflammatories during the decade leading up to the introduction of the term "nonsteroidal anti-inflammatory drugs." Because of the disastrous reputation that the corticosteroids had got in the 1950s, the new term, which offered to signal that an anti-inflammatory drug was not a steroid, rapidly gained currency.[7] The drug class of "nonsteroidal anti-inflammatory drugs" (NSAIDs) is thus composed by one element ("anti-inflammatory") that designates the mechanism of action, and one element ("nonsteroidal") that separates it from other drugs with that same mechanism of action. Similarly, one might argue that the class of disease-modifying anti-rheumatic drugs (DMARD) is composed by one element ("disease-modifying") that albeit vaguely designates a mechanism of action, and one element ("anti-rheumatic drug") that indicates its therapeutic use.
Other systems of drug classification exist, for example theBiopharmaceutics Classification System which determines a drugs' attributes by solubility and intestinal permeability.