Kinetics of low-dose intravenous antipyrine: use of liquid chromatography.

Rapid and sensitive quantitation of antipyrine in plasma is achieved by high-pressure liquid chromatography. Antipyrine and phenacetin, the internal standard, are readily extracted from alkalinized plasma into ethyl acetate. After evaporation of the organic solvent, the redissolved residue is chromatographed using a reverse-phase C-18 column. The sensitivity limit is approximately 0.25 micrograms antipyrine per ml plasma, with a coefficient of variation for identical samples not exceeding 3%. Using the automated sampling system, one person can analyze up to 100 samples per day. The method is reliable and sensitive enough to allow human pharmacokinetic studies of antipyrine using doses considerably less than utilized in previous studies. The disposition kinetics of a single i.v. dose of antipyrine in four human volunteers were essentially identical over a 5-fold range of doses.