TOPICS: Acyclovir, valacyclovir, famciclovir, antivirals, guanosine analogs, prodrug, increased bioavailability, shingles, herpes zoster, herpes simplex, HSV-1, HSV-2, chicken pox, thymidine kinase, mono phosphorylation, tri phosphorylation, cellular enzymes, activate the drug, inhibit viral DNA polymerase, terminating growing DNA chain, kidney injury, hydration, nausea, vomiting, resistance, altered viral thymidine kinase