High-performance liquid chromatographic assay of 6-methylthioguanine, a major metabolite of 6-thioguanine, in urine.

A flow-fluorimetric high-performance liquid chromatographic assay for 6-methylthioguanine in urine has been developed. This compound is a major catabolite of 6-thioguanine, an important drug in cancer chemotherapy. The metabolite was extracted from alkaline urine with ethyl acetate which was injected onto a reversed-phase high-performance liquid chromatographic system for separation and detection. The method is simple, rapid and sensitive to below 500 ng ml-1 which is below the levels encountered following a therapeutic dose of 6-thioguanine. Another metabolite was chromatographically separated from 6-methylthioguanine and partially characterised.