DOXYCYCLINE DETERMINATION IN HUMAN-SERUM AND URINE BY HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY

A reversed‐phase high‐performance liquid chromatographic method for quantitative doxycycline determination in human serum and urine is described. The drug was extracted from buffered (pH 6.1) serum or urine into ethyl acetate. A structural analog, demeclocycline, was added as the internal standard. A 10‐cm × 2‐mm i.d., 5‐μm Lichrosorb RP8 column with acetonitrile‐0.1 M citric acid as the eluent was used. The effluent was monitored at 350 nm. The extraction recovery from spiked serum was 87.8 ± 4.3% (mean ± SD, n = 11); for urine, a value of 92.2 ± 2.0% (mean ± SD, n = 10) was found. Within‐run and within‐day relative standard deviations averaged 1.80% (x = 2.5 μg/ml, n = 10) and 4.75% (x = 2.6 μg/ml, n = 9), respectively. The detection limit was estimated at 50 ng/ml of serum. No significant extra peaks were observed in chromatograms obtained on serum or urine extracts, suggesting the probable absence of metabolic processes in vivo. Copyright © 1979 Wiley‐Liss, Inc., A Wiley Company