: a substance (as a sulfa drug) that replaces or inhibits the utilization of a metabolite
Substance that competes with, replaces, or inhibits a specific compound within a cell, whose functioning is thereby disrupted. Because its structure resembles the compound's, it is taken up by the cell, but it does not react in the same way with the enzyme that acts on the usual compound. It may inhibit the enzyme or be converted into an aberrant chemical. Many antimetabolites are useful in treating disease, including sulfa drugs, which disrupt bacterial but not human metabolism for bacterial diseases, and others (e.g., methotrexate, 5-fluorouracil) for various cancers.