The immunosuppressive activity of azathioprine in serum and cerebrospinal fluid

Azathioprine and its active metabolites can be detected in the cerebrospinal fluid (after i.v. injection). At a single dose of azathioprine maximum immunosuppressive activity occurs in the serum after 1 h and in the cerebrospinal fluid after about 4 h. Maximum immunosuppressive activity in human cerebrospinal fluid is about 12.5% of the equivalent serum level. A certain amount of time is needed for azathioprine and its metabolites to reach the cerebrospinal fluid where they remain for some time before passing into the serum, from where they are broken down. The findings are clinically important for the treatment of inflammatory nervous diseases, for example, multiple sclerosis, which are assumed to be of immunopathological origin.