Assay methods for sufentanil in plasma. Radioimmunoassay versus gas chromatography-mass spectrometry

The terminal pharmacokinetic parameters of sufentanil have, until now, been poorly characterized. This is probably because of the poor sensitivity or unreliability of the assay methods used. Radioimmunoassay (RIA) can be a very helpful assay method for sufentanil. However, before application to key pharmacokinetic studies, it requires adequate validation, e.g., by comparison with a method of proven sensitivity and specificity, such as gas chromatography-mass spectrometry (GC-MS).

Spiked control plasma samples and 135 plasma samples obtained from five patients receiving intravenous doses of 500 or 750 micrograms sufentanil, as a 10-20-min infusion, were analyzed by an improved, sensitive RIA and capillary GC-MS.

Both techniques had comparable limits of quantitation (0.02 ng/ml). Between-day coefficients of variation in the 0.05-10-ng/ml concentration range were 8.5-10.5% for the RIA and less than 10% for the GC-MS method. The patient plasma concentrations determined by RIA (y) and GC-MS (x) showed a good agreement (y = 1.016x + 0.002) and a correlation coefficient of 0.97.

The results demonstrate the validity of the improved RIA method for the determination of sufentanil plasma concentrations.