DETERMINATION OF REMIFENTANIL IN HUMAN AND DOG-BLOOD BY HPLC WITH UV DETECTION

Remifentanil (GI87084) is a phenylaminopiperidine derivative of the fe ntanyl type with a potent analgesic activity and ultra-short half-life . The N-substituted labile methyl propanoate ester group is highly sus ceptible to cleavage by endogenous esterases and by chemical hydrolysi s. The hydrolysis is stopped by addition of 20 mul 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 HC l. 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 w as GI97559 - an ethyl analogue of the drug. The method has been valida ted 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 toxico logical support study. Additionally, it was used to characterize the h ydrolysis of the drug, the enzymes involved in the process, and ex viv o drug interactions.