PMEG (9-[2-(phosphonomethoxy)ethyl] guanine) is an acyclic nucleoside phosphonate.

Acyclic nucleoside phosphonates can have significant antiviral, cytostatic and antiproliferative activities.

GS-9191 and GS-9219 prodrugs are just two of the next generation PMEG compounds being evaluated for antiviral and anticancer activities.

[citation needed] Acyclic nucleoside phosphonates prodrugs require further phosphorylation in the cell in order to become the active metabolite.

Since it is an acyclic nucleoside, lacking a 3'-OH moiety, to further extension of the DNA strand occurs.