The EE of X drug in the NLCs was assessed indirectly by measuring the concentration of free drug in the aqueous phase of the nanoparticles suspension. Free drug was separated from X‑NLCs using Sephadex‑G50 column . In brief, approximately 0.5  mL of NLCs suspension was added into a Sephadex G‑50 gel column and eluted with distilled water at the rate of 1 mL/min. The free drug was separated and collected, and its concentration was determined by HPLC. Finally, the %EE of X‑NLCs was calculated using the following equation: EE% = Wtotal ‑ Wfree/Wtotal ×100 where Wtotal and Wfree are the total amount of X drug present in X‑NLCs suspension and the amount of untrapped X drug, respectively.