[Investigations on the determination of doxycycline concentrations in biological material by high pressure liquid chromatography and the agar diffusion method (author's transl)].

A new high performance liquid chromatographic method for quantitative analysis of doxycycline has been compared with the microbiological assay. Both analytical methods yielded the same results of nearly 100% recovery when doxycycline was incubated with serum, lung-, or liver-homogenate (Table 1). The advantages of the chromatographic method over the microbiological method are i. short and simple way of analysis (Fig. 1), ii. need of only small amounts of biological material. In a pilot study doxycycline - after i.v. application to mice - could be analyzed in good agreement by both methods (Fig. 2). The microbiological analysis yielded in slightly lower serum- or organ-levels what might be due to an inactivation of the antibiotic attached to proteins to some extend.