Antimetabolites call the substances close on chemical structure to natural metabolic products (metabolites) and the inhibiting transformations and physiological activity of these endogenous connections.
A number of the drugs which are structural analogs of folic acid (methotrexate), purines (Mercaptopurinum, thioguanine, etc.), pyrimidines belongs to the antimetabolites applied as antineoplastic means (ftoruratsit, Phthorafurum, Cytarabinum).
Cytostatic effect of all these drugs is connected with disturbance of synthesis of nucleic acids (DNA and RNA).
Action of a methotrexate is connected with inhibition of activity of enzyme of the folatreduktaza causing transformation of folic acid into its active form - the tetrahydrofolic acid participating in biosynthesis of nucleic acids.
Analogs of purines (Mercaptopurinum, etc.) break biosynthesis of purine nucleotides.
The antineoplastic activity ftoruratsit and its analogs is caused by their transformation in tumor cells into active inhibitors of the enzyme of a tinidinsintetaza participating in synthesis of nucleic acids.