Pharmacokinetics of intrathecal 1-(4-amino-2-methyl-5-pyrimidinyl) methyl-3-(2-chloroethyl)-3-nitrosourea hydrochloride in rats.

The pharmacokinetics of intrathecal 1-(4-amino-2-methyl-5-pyrimidinyl) methyl-3-(2-chloroethyl)-3-nitrosourea hydrochloride (ACNU) were studied in female Wistar rats by macroscopical autoradiography using 14C labeled ACNU. In normal rats, ACNU rapidly distributed in the subarachnoid space and ventricles after intracisternal administration. Diffusional transport into the brain tissue was limited to a depth of 1 or 2 mm from the cerebrospinal fluid (CSF) surface of the brain. Clearance of ACNU from the CSF space and brain was relatively fast and the half time of ACNU concentration at the cortical or ventricular surface was 10 min. In rats with leptomeningeal tumor induced by intracisternal inoculation of Walker 256 carcinosarcoma cells, the distribution pattern of ACNU after intracisternal administration was essentially the same as in normal rats until the tumor had grown in the subarachnoid space to form more than 10 or 20 layers of tumor cells. ACNU was distributed in the tumor as well. When the tumor had grown to form masses in the subarachnoid space, ACNU failed to penetrate to more than a depth of 1 or 2 mm from the tumor surface. Our results suggest that intrathecal ACNU administration may have no, or minor side effects on the brain and that it can eliminate floating or thin layered tumor cells in the subarachnoid space but not bulky tumors.