Analysis and quantitation of a metabolite of doxycycline in mice, rats, and humans by high-performance liquid chromatography

A metabolite of doxycycline has not previously been isolated. In this paper it is demonstrated that doxycycline is metabolized in mice, rats, and humans. By means of high-performance liquid chromatography and consecutive gel chromatography one metabolite of doxycycline was isolated from animal organs and human urine. The metabolite was tentatively identified as N-monodemethyldoxycycline by mass spectral and spectrophotometric analyses. The rate of metabolism could be enhanced by pretreatment of the animals with phenobarbital, an inducing agent of the drug-metabolizing enzymes.