(ăn″tĭ-mĕ-tăb′ō-līt)
[Pronunciation]

1. A substance that opposes the action of or replaces a metabolite and is structurally similar to it.
Certain antibiotics are effective because they act as antimetabolites.
2. A class of antineoplastic drugs used to treat cancer.
Antimetabolites are structurally similar to vitamins, coenzymes, or other substances essential for growth and division of normal and neoplastic cells. These drugs are most effective against rapidly growing tumors. A drug-induced block of DNA synthesis occurs when the cells take in the antimetabolite rather than the necessary nutrient or enzyme.