After 5 days of oral administration of ATV with or without DXM, the concentrations of ATV in plasma and CSF at the same time point were determined. Based on our pharmacokinetics results, drug concentration after oral administration of 24 and 1 h was defined as valley concentration and peak concentration, respectively. As shown in Figure 3, the valley and peak concentrations of ATV in CSF were all below 0.5 ng/mL. However, this was not the same case in plasma. In the ATV group, valley concentration in plasma was distributed from 0.1234 to 0.3476 ng/mL, and peak concentration in plasma was distributed from 2.952 to 23.29 ng/mL. Meanwhile, in the ATV+DXM group, valley concentration in plasma was distributed from 0.0904 to 0.9449 ng/mL, and peak concentration in plasma was distributed from 21.08 to 63.47 ng/mL. However, no matter if it was a valley or peak concentration, the level of ATV in CSF was lower than in plasma (*P < 0.05, **P < 0.01). In addition, comparing the peak concentration of ATV between the ATV group and the ATV+DXM group, DXM significantly increased the ATV level in plasma (*P < 0.05), which was consistent with the pharmacokinetic results. Therefore, these results suggested that ATV cannot cross the blood-brain barrier into CSF.