Simultaneous high-performance liquid chromatographic assay of droperidol and flunitrazepam in human plasma. Application to haemodilution blood samples collected during clinical anaesthesia.

A simultaneous assay for droperidol and flunitrazepam by high-performance liquid chromatography has been developed and applied to blood samples collected during an acute normovolemic haemodilution under general anaesthesia. Haemodilution blood samples were stored at +4 degrees C to be transfused, if required, to a patient during the post-surgical phase. A C18 Supelclean cartridge was used for solid-phase extraction, and the recoveries were 74% and 89%, respectively, for droperidol and flunitrazepam. Compounds were chromatographed on a C18 Novapak column at 250 nm, with a mobile phase of acetonitrile-10 mM ammonium acetate buffer (pH 6.7) (45:55, v/v). Nitrazepam was used as the internal standard. For both drugs, the assay was linear up to 500 micrograms/l, and the detection limits were 20 and 10 micrograms/l for droperidol and flunitrazepam, respectively, and their observed levels in haemodilution samples were 93 +/- 82 micrograms/l and 76 +/- 107 micrograms/l, respectively. Some of the values for flunitrazepam were higher than the minimal efficient concentration, defined as the plasma level observed at the time of the patient wakening from anaesthesia (12 +/- 4 micrograms/l). According to our results, haemodilution sampling can be performed before induction of anaesthesia. When the blood is collected after the anaesthetic induction, it seems necessary to determine levels of the two drugs in haemodilution samples to avoid side-effects.