Reversed-phase liquid-chromatographic simultaneous analysis for thiopental and pentobarbital in serum

We describe a reversed-phase liquid-chromatographic assay suitable for therapeutic monitoring of thiopental and pentobarbital simultaneously in human serum. The drugs are extracted from serum at pH 6.6 into n-butyl chloride containing thiamylal and barbital as the respective internal standards. The compounds are back-extracted into dilute sodium hydroxide, an aliquot of which is submitted to chromatography. The lowest measurable concentrations are 1.0 mg/L for thiopental and 2.0 mg/L for pentobarbital. The standard curve is linear from 0 to 100 mg/L for both. Between-run CVs are: at 25 mg/L, 4.1% (thiopental) and 3.2% (pentobarbital); at 50 mg/L, 2.8% (thiopental) and 3.4% (pentobarbital). Data on patients receiving thiopental and pentobarbital illustrate use of the method.