FIG. 1.

Schematic diagram depicting viramidine as a prodrug and as a catabolic inhibitor for ribavirin. Ribavirin is subject to either 5′ phosphorylation by nucleoside and nucleotide kinases or degradation to nucleobase by purine nucleoside phosphorylase. In addition to functioning as a prodrug of ribavirin, viramidine could directly inhibit nucleoside phosphorylase and prevent or slow down the catabolism of the newly converted ribavirin, thereby providing more ribavirin for phosphorylation.