SENSITIVE HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHIC FLUORESCENCE ASSAY FOR THE QUANTITATION OF TOPOTECAN (SKF 104864-A) AND ITS LACTONE RING-OPENED PRODUCT (HYDROXY ACID) IN HUMAN PLASMA AND URINE

A sensitive reversed-phase high-performance liquid chromatographic flu orescence method is described for the simultaneous determination of to potecan (I) and the hydrolysed lactone ring-opened product hydroxy aci d (II) in plasma and for the determination of I in urine. To 250 mu l of plasma, a 750-mu l volume of cold methanol was added to stabilize t he pH-dependent conversion of I into II. In plasma, the lower limit of quantitation (LLQ) for both compounds was 0.10 ng/ml. The between-day variation for I at the LLQ was 7.1% and for II was 5.5%. Prior to inj ection, urine samples were acidified with orthophosphoric acid and dil uted with phosphate-buffered saline (PBS). In urine, the calibration c urve for I was linear in the range of 10 to 250 ng/ml and the LLQ was 10 ng/ml. The assay was developed to enable pharmacological analysis o f I, in on-going phase I and II studies, in patients with solid tumors .