5. Limitation
In this study, we have evaluated CSF-to-serum ratio of TGC at steady-state trough concentration based on bio-samples from 12 patients with CNSI. For lots of drugs, previous studies has demonstrated that the peak time and clearance time in brain were longer than that in plasma[19, 20]. This might lead to the difference of CSF-to-serum ratio at different periods [8]. Therefore, the evaluation of penetration ability of TGC through BBB based on CSF-to-serum ratio at single period might be influenced by above factors. Increasing of the sample collection points would made the study more potent. And in our study, we compared our results with the data of 6 healthy adults reported by Rodvold [8]. We should not ignore the possible influence of different dosage scheme and sample time occurred in these two studies. However, collection of CSF samples was quite invasive, which makes CSF samples from health human and multipoint collection could not be achieved.