[Ribamidyl (ribavirin) as a modulator of the biological action of arabinosylcytosine and methotrexate].

Administration of ribamidyl (Rb) prior to Ara-C to intact mice or mice with implanted tumours enhanced Ara-C toxicity. The growth of tumours (plasmacytoma MOPC-21, adenocarcinoma of the small intestine (strain AKATON), mammary adenocarcinoma 755 (Ca 755) resistant to Ara-C or Rb was inhibited after coadministration of these drugs. The augmentation of toxic and antitumour effects of Ara-C by Rb is similar to the described effect of high doses of thymidine. This is in accordance with the enhancement of the intracellular pool of thymidine phosphates under the action of Rb. The toxicity of methotrexate in vivo was increased by coadministration with Rb. This effect may be connected with a decrease in purine precursors pool under the action of Rb.