Capillary Gas Chromatography and Thermionic N-P-specific Detection of 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) or 1-(2-chloroethyl)-3-cyclohexyl-1-nitrosourea (CCNU) in Stability and Pharmacokinetic Studies

An expedient, rapid, and sensitive capillary gas chromatographic method for the analysis of 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) or 1-(2-chloroethyl)-3-cyclohexyl-1-nitrosourea (CCNU) in plasma is described. Separation of the underivatized nitrosourea compounds was performed on a 0.33-mm-i.d., 25-m fused-silica, SE-30 capillary column, and detection was carried out using a thermionic N-P-specific detector. The compounds were extracted from plasma with benzene with a yield of greater than 87%. The assay was linear in the ranges of 0.001 to 0.5 and 0.5 to 25 micrograms/ml for CCNU or 0.003 to 0.50 and 0.5 to 25 micrograms/ml for BCNU, with correlation coefficients from 0.9914 to 0.9999 and coefficients of variation (CV) of less than 3.3%. Other antineoplastic agents did not interfere in the assay. The method was employed to study the pharmacokinetics of BCNU in rabbits. The plasma concentration-time curves were fit to a two-compartment model with a mean (SE) alpha, beta, and total-body clearance of 2.898 (0.913) hr-1, 0.1228 (0.0179) hr-1, and 7.211 (2.862) liters/hr.kg, respectively. Further, the stability of BCNU and CCNU in solution was examined at different temperatures. Both compounds were stable in benzene or acetone (4 to 37 degrees C) but labile in plasma even if refrigerated. The apparent rate constants for degradation of BCNU and CCNU were 0.09921 and 0.02853 hr-1 at 4 degrees C and 5.998 and 2.553 hr-1 at 37 degrees C, respectively.