196 - Assessing the Clinical Impact of Intravenous Acyclovir Dosing in Obese Patients: Should We Be Using Ideal, Adjusted, or Total Body Weight?

Background: Obesity impacts the pharmacokinetics and pharmacodynamics of medications. Pharmacokinetic studies of intravenous (IV) acyclovir have demonstrated that dosing obese patients according to their ideal body weight (IBW) may provide a sub-therapeutic dose, while dosing based on total body weight (TBW) may increase adverse effects. This has led to the use of adjusted body weight (AdjBW) for dosing in this population; however, this has not been evaluated clinically. The purpose of this study is to assess the impact of different dosing strategies of IV acyclovir in obese patients.

Methods: This retrospective observational chart review evaluated adult patients admitted to Long Island Jewish Medical Center with a body mass index greater than or equal to 30 kg/m² who received at least 48 hours of high-dose IV acyclovir therapy during the study period of January 2014 to August 2019. Patients were stratified to IBW, AdjBW, and TBW for analysis. The primary statistical tests utilized include descriptive statistics and logistic regression. The primary endpoint was the outcome of infection. The secondary endpoints included duration of therapy, length of stay, and adverse effects.

Results: 51 patients were included in the efficacy analysis and 84 patients were included in the safety analysis. Treatment failure occurred in 3 out of 51 patients (1 patient in IBW group, 2 patients in AdjBW group, p=0.445). There was no significant difference in median length of stay (p=0.977) or median duration of IV therapy (p=0.78). Nephrotoxicity occurred in 22.2%, 19.2%, and 22.7% of patients in the IBW, AdjBW, and TBW groups respectively (p=1).

Conclusion: When comparing different dosing modalities, there was no significant difference in the outcome of infection, duration of therapy, or length of stay. The results of this study were limited by small sample size. However, dosing patients according to AdjBW led to smaller doses of acyclovir, and therefore less drug exposure.