Study of 
Antiherpetic Efficiency of Phosphite of Acycloguanosine Ableto Over come the Barrier of Resistance to Acyclovir

It's excellent to have a backup plan for when drug resistance arises. Phosphite
 of acycloguanosine (Hp-ACG) isn't as effective in vivo as the current standard for treating herpes simplex virus (HSV), acyclovir, but it's antiviral activity is effective where acyclovir's is not. In this paper by Andronova et al. are continuing the testing of Hp-ACG on a mouse model, and found it able to successfully treat acyclovir-resistant strains of HSV-1.

Read more here: