GAS-CHROMATOGRAPHIC ANALYSIS OF BUSULFAN FOR THERAPEUTIC DRUG-MONITORING

The development and validation of a gas chromatographic assay method f or determination of total and free busulfan concentrations in human pl asma for pharmacokinetic studies is reported. 1,6-Bis(methanesulfonylo xy)hexane, the internal standard, and a potential metabolite, 3-hydrox ysulfolane, were synthesized. Plasma and plasma ultrafiltrate samples containing busulfan and internal standard were extracted with ethyl ac etate and derivatized with 2,3,5,6-tetrafluorothiophenol prior to gas chromatographic determination. The Ni-63 electron-capture detector pro vided a limit of detection of 0.0600 mug/ml with a limit of quantitati on of 0.100 mug/ml busulfan in biological samples. Calibration curves were linear from 0.100 to 3.00 mug/ml in plasma (500 mul) and 0.100 to 2.00 mug/ml in plasma ultrafiltrate (100 mul). Extraction and derivat ization yields ranged from 78.4% to 89.6% and 56.0% to 71.3%, respecti vely. Specificity of this assay for busulfan in the presence of its po tential metabolites was demonstrated. Also, plasma samples containing co-administered drugs gave no response under these conditions. Clinica l samples obtained following administration of a 1 mg/kg oral busulfan dose demonstrate the applicability of this method to analysis of tota l and free plasma concentrations.