A simple method for determining thiopental in plasma.

A simple rapid HPLC method for the measurement of thiopental is described. Plasma was deproteinised with 50% (v/v) acetonitrile in methanol containing flufenamic acid as an internal standard. Chromatography was carried out on a C-18 mu Bondapak reverse phase column using 220 mL of buffer (1.79 g of ammonium dihydrogen phosphate and 1.75 g of sodium sulfate adjusted to pH 7.9 with ammonium hydroxide) in 300 mL of methanol. Detection at 280 nm was near the absorption maxima of both thiopental and flufenamic acid. The method is linear up to 75 micrograms/mL and is therefore suitable for the measurement of thiopental in plasma from patients sedated by thiopental infusion. The sensitivity can be increased such that single dose studies can be investigated.