Acyclovir can result in tremor, confusion, agitation, hallucination and sedation. Acyclovir is a nucleoside analog that is primarily excreted unchanged (85%) in the urine based on GFR. 15% of acyclovir undergoes metabolism by alcohol dehydrogenase to 9-carboxymethoxymethylguanine (CMMG) that is excreted by the kidney strictly through glomerular filtration. Patients with altered renal function or who are on dialysis, accumulate CMMG leading to neurotoxicity.