DETERMINATION OF DOXYCYCLINE IN SMALL SERUM SAMPLES BY LIQUID-CHROMATOGRAPHY - APPLICATION TO PHARMACOKINETIC STUDIES ON SMALL LABORATORY-ANIMALS

Several methods have been described for the analysis of doxycycline in serum which require at least 0.5 mL sample. The assay presented here requires small amounts of serum (0.1 mL) and shows good sensitivity. A Ultrabase C-18 column and mobile phase consisting of acetonitrile-bid istilled water (28 : 72) were used, flow rate 1 mL min-1 and monitored at 350 nm. Linearity proved satisfactory between 0.025 and 2.5 mug mL -1 of serum. This assay for doxycycline showed good precision (coeffic ient of variation < 6 %) and allowed quantitation of serum levels as l ow as 25 ng mL-1 using 100 muL samples.