A Comprehensive Review of Analytical Techniques for Doxycycline and Its Metabolites

Doxycycline (DC), a second-generation tetracycline antibiotic, is extensively used in human and veterinary medicine for its broad-spectrum activity, favorable pharmacokinetics, and high bioavailability. This review focuses on analytical methods for detecting and quantifying DC and its metabolites in pharmaceutical, biological, and environmental samples. Spectroscopic, chromatographic, and electroanalytical techniques have been explored, with high-performance liquid chromatography (HPLC) emerging as the most reliable due to its high sensitivity, selectivity, and reproducibility, particularly when coupled with fluorescence or mass spectrometric detectors. Although spectroscopic approaches are simple and economical, they often suffer from matrix interferences. Electroanalytical and voltammetric methods, by contrast, offer rapid and cost-effective alternatives suitable for field applications. Major analytical challenges include DC instability, complex sample matrices, and intricate preparation steps affecting quantification accuracy. Future research should focus on green, miniaturized, and automated analytical platforms that integrate nanomaterials, advanced separation techniques, and artificial intelligence to achieve rapid, accurate, and sustainable monitoring of DC and its metabolites in clinical and environmental settings.