Sensitive gas liquid chromatography method for the determination of fentanyl concentrations in blood

A method for the determination of fentanyl blood concentrations using gas liquid chromatography coupled to a nitrogen phosphorus detector (NPD) is presented. A highly inert fused-silica, megabore column coated with a methyl silicone stationary phase was used for the analysis. The mean coefficient of variation for the range of fentanyl concentrations tested (0.25-10 ng/ml) was 4.65%, ranging from 0.85% at 10 ng/ml to 10.8% at 0.25 ng/ml. The assay was used to quantify blood fentanyl concentrations collected from a 56-year-old woman who was administered fentanyl postoperatively via a patient-controlled on-demand analgesic computer (ODAC). The mean hourly fentanyl dose rate over the 44 hr study period was 41.8 micrograms/hr (range 20-120). The sixfold variation in hourly dose rate was not mirrored by similar fluctuations in the fentanyl blood concentration (mean 0.45 ng/ml, range 0.3-0.7 ng/ml). The patient thus titrated herself to a perceived minimum effective concentration (MEC) of fentanyl.