Rapid and simple determination of doxycycline in serum by high-performance liquid chromatography. Application to particulate drug delivery systems.

A simple, rapid and sensitive reversed-phase high-performance liquid chromatographic (HPLC) method for the measurement of doxycycline concentrations in both drug delivery systems (DDS) and serum extracted from mice after intraperitoneal (free drug) and intravenous (doxycycline administered in DDS) administration, has been developed. For the analysis of doxycycline in DDS, a known amount of particles was dissolved in chloroform and, after precipitating the polymer with methanol, the drug was assessed in the supernatant. For doxycycline quantification in microsamples of serum, proteins were precipitated with acetonitrile before chromatographic analysis. After centrifugation, the supernatant was mixed with a mixture of methanol and acetic acid (1:1) for analysis. The samples were chromatographed on a narrow-bore C18 column (Alltech Alltima 150 mm x 2.1 mm) using a mobile phase with 55% acetic acid (5%), 25% acetonitrile and 20% methanol. Doxycycline was detected 347 nm and the run time was 10 min. Linearity was confirmed in the concentration range 0.4-80 microg/ml for doxycycline quantification in serum and from 1 to 800 microg/ml for doxycycline extracted from DDS samples.