Inclusion Criteria:  Patients Admitted to a SSM Health - St. Clare (STL), St. Mary's (STL), Saint Louis University Hospital (STL), St. Anthony's (OKC), St. Mary's Madison (WIS), Rush University Medical Center (RUMC), or Methodist Dallas Medical Center > 18 years old Positive cerebrospinal fluid (CSF) PCR for HSV-1 or HSV-2 BMI > 30 kg/m2 Received guideline-approved, weight-based doses of IV acyclovir for HSV encephalitis for at least 72 hours during the index admission Received appropriately renal dose-adjusted doses of IV acyclovir per package insert recommendations  Exclusion Criteria:  More than one dosing weight strategy utilized for > 24 hours for IV acyclovir dosing during the index admission Patients transferred to the hospital already on IV acyclovir for HSV encephalitis ESRD on admission Concomitant pathogen causing meningitis or encephalitis Oral acyclovir used for treatment