A sensitive assay for the simultaneous measurement of alfentanil and fentanyl in plasma

A reversed-phase high-performance liquid chromatography method for the simultaneous determination of plasma concentrations of the narcotic analgesics alfentanil and fentanyl using papaverine hydrochloride as the internal standard is presented. Chromatographic separations were achieved with an Econosphere CN, 5 mu m, 25 cm x 4.6 mm i.d. column and the effluent was monitored at 195 nm. The assay was linear over the clinically relevant plasma range of 2-2000 ng ml(-1) for alfentanil and 2-100 ng ml(-1) for fentanyl and has the sensitivity and specificity necessary to determine plasma concentrations of these compounds. Inter- and intra-day precision (RSD) for both compounds did not exceed 10% in these ranges. The assay procedure was utilized for pharmacokinetic studies of plasma concentrations in subjects receiving alfentanil and fentanyl during and after cardiac surgery. This will allow better elucidation of pharmacokinetic variables in this populace.