Plasma concentrations of several antiretrovirals drugs were analyzed when administered in presence and absence of valproic acid. Drug concentrations were obtained from the TDM registry of the University Hospital of Torino. A total of 134 individuals receiving concomitantly valproic acid and antiretroviral drugs were identified. No significant effect on plasma exposure was observed for darunavir (n=13). In the presence and absence of valproic acid, median (IQR) boosted darunavir Ctrough was slightly higher in valproic acid recipients 1652 ng/mL (1377-2298) vs 705 ng/mL (435-1183) (P= 0.026). Once daily darunavir Ctrough was 2228 ng/mL (2003-4121) vs 1789 ng/mL (965-1775) (P = 0.182). Twice daily darunavir Ctrough was 4263 ng/mL (2848-5692) vs 3391 ng/mL (2324-5132) (P = 0.659).