T-705 can be converted to T-705RMP and T-705RTP by cellular kinases; Host cell enzymes can differentiate T-705, T-705RMP, and T-705RTP from the natural nucleotides. The level of inhibition of IMPDH by T-705RMP is about 150-fold weaker than that by Ribavirin monophosphate, and it became apparent that the antiviral effect of T-705 is not a result of the inhibition of the cellular enzyme[1].