Determination of remifentanil in human and dog blood by HPLC with UV detection

Abstract

Remifentanil (G187084) is a phenylaminopiperidine derivative of the fentanyl type with a potent analgesic activity and ultra-short half-life. The N-substituted labile methyl propanoate ester group is highly susceptible to cleavage by endogenous esterases and by chemical hydrolysis. The hydrolysis is stopped by addition of 20 μl of 50% citric acid per 1 ml of blood. The method involves a liquid extraction of chilled blood at pH 7.4 with butyl chloride and back-extraction into 0.01 M HCI. The chromatographic conditions are: column — Zorbax SB-CN 4.6 x 250 mm; mobile phase — 7% acetonitrile-14% methanol in phosphate buffer (0.03 M; pH 3.0); detection — UV at 210 nm. The internal standard used was G197559 — an ethyl analogue of the drug. The method has been validated in human blood over the range of 1–200 ng ml −1 and in dog over the range 10–60, 135 ng ml −1 with the latter assay being used in a toxicological support study. Additionally, it was used to characterize the hydrolysis of the drug, the enzymes involved in the process, and ex vivo drug interactions.