Simplified Determination of Antipyrine Clearance by Liquid Chromatography of a Microsample of Saliva or Plasma

We describe a simplified and rapid liquid chromatographic determination of antipyrine clearance (CLAP) calculated from peak height ratios of drug/internal standard. Saliva or plasma was collected 24 hr after the oral administration of 1 g of antipyrine to the subject. A 25-µl aliquot of the sample is deproteinized with acetonitrile containing 3-nitrophenol (internal standard) and injected into a radial compression module equipped with a 10-µm, 8 mm × 10-cm C18 cartridge, using a 0.025 M aqueous solution of sodium acetate and acetonitrile (88.5:11.5). The minimum measurable concentration was 0.2 µg/ml. The obtained CLAP values in five healthy subjects and five patients with chronic liver disease coincided well (r > 0.9994) with those generated by the use of an established method. The antipyrine clearance in the healthy subjects ranged from 2.203 to 5.721 liters/hr, while in patients with chronic liver disease it was significantly (P < 0.0027) less (range, 0.544 to 1.103 liter/hr). We also determined antipyrine clearance in two of these subjects given lower doses of this drug and found that the dose has no significant impact on this parameter.