 Vancomycin is used mainly for MRSA methicillin-resistant S. aureus infection, and possesses a significant place of therapy in treatment of neurosurgical patients post-operation infection. The serum concentration of vancomycin exhibits a clear relevance to its efficacy and toxicity. From the investigators preliminary research of the disposition of vancomycin in neurosurgical ICU patients, the investigators found that their vancomycin serum concentrations were lower than expected, which can be attributed to their 40 higher mean vancomycin clearances than that of neurosurgical general ward patients. However, no definite mechanism leading to this phenomenon was confirmed. 