A drug like aspirin that covalently binds to or reacts with an enzyme to permanently inactivate it is classified as a(n):

Aspirin is classified as an irreversible inhibitor because it covalently modifies an enzyme, leading to permanent inactivation. This process typically occurs when the drug forms a stable bond with an amino acid residue in the enzyme’s active site, preventing the enzyme from functioning.

The nature of irreversible inhibitors contrasts with reversible inhibitors, which bind to enzymes non-covalently and can dissociate from the enzyme, allowing the enzyme to regain its function. Competitive inhibitors, a subset of reversible inhibitors, specifically compete with the substrate for access to the active site but do not permanently affect the enzyme. Allosteric modulators act by binding to sites other than the active site, inducing conformational changes that affect enzyme activity but do not involve covalent modifications. Thus, the definition of an irreversible inhibitor precisely captures the mechanism by which aspirin operates.