Mechanism of Action (MOA)

Key facts

Label location

Section 12.1, within Clinical Pharmacology, of prescribing information

Class indexing

FDA mechanism of action terms, openFDA field pharm_class_moa

Relation to EPC

An established pharmacologic class is often, not always, based on MOA

What is a mechanism of action?

A drug's mechanism of action describes what it does at the molecular level: which target it acts on and how. Atorvastatin inhibits the enzyme HMG-CoA reductase, pembrolizumab blocks the PD-1 receptor on immune cells, and omeprazole inhibits the proton pump in stomach cells.

Mechanism of action is narrower than physiologic effect. Lowering cholesterol is a physiologic effect; inhibiting HMG-CoA reductase is the mechanism that causes it. For some long-used drugs the mechanism is still not fully understood, and the label says so.

In contracting and government documents, MOA can also stand for memorandum of agreement, so check the context.

How mechanism of action is described and classified

Mechanism information appears in several regulatory places:

• Prescribing information: in labels using the current format, Section 12.1 describes the mechanism of action, followed by pharmacodynamics in 12.2 and pharmacokinetics in 12.3.
• Class indexing: the FDA indexes drugs with mechanism of action concepts, such as Cyclooxygenase Inhibitors, which appear in openFDA records as pharm_class_moa.
• Established pharmacologic class (EPC): the class named in label Highlights is frequently derived from the mechanism, such as Proton Pump Inhibitor, but can instead rest on physiologic effect or chemical structure.
• Novelty: a drug with a mechanism no approved product has used is often called first in class, a descriptive label rather than a formal FDA designation.

Why mechanism of action matters

Mechanism is one of the most useful ways to organize drug markets:

• Competitive intelligence: grouping marketed and pipeline drugs by mechanism shows how crowded a target is and where a new entrant would compete head to head.
• Pipeline tracking: clinical trial records and company pipelines are often searched by target or mechanism, which surfaces programs before they have trade names.
• Safety review: drugs that share a mechanism often share class-level adverse effects, so adverse event data are frequently reviewed by mechanism class.
• Formulary design: payers compare drugs with the same mechanism when setting step therapy rules and preferred product lists.