wherein each of R<1>, R<2>, R<3>, R<4>, R<5>, R<6>, R<7>, R<8>, R<9> and A has the same meaning as given in the specification. The present invention relates to a method for exhibiting a virus growth-inhibiting effect and/or a virucidal effect, in which pyrazine nucleotide analog Ä2Ü and pyrazine nucleoside analog Ä3zÜ are subjected to biotransformation, decomposed and then phosphorylated, so that they become a pyrazine nucleotide analog Ä1bÜ exhibiting the aforementioned effect. This method is useful as a method for treating virus infections. Moreover, the pyrazine carboxamide analog or a salt thereof of the present invention is useful as an agent for preventing or treating virus infections.