A COMPREHENSIVE REVIEW ON STABILITY INDICATING RP-HPLC METHODS AVAILABLE FOR TETRACYCLINES

Tetracyclines are a structurally diverse and therapeutically important class of broad-spectrum antibiotics widely used in human and veterinary medicine. The presence of a polycyclic naphthacene core structure with multiple ionizable functional groups renders these molecules chemically unstable and highly susceptible to epimerization, dehydration, oxidation, hydrolysis, and photolytic degradation.[1,13] Classical tetracyclines such as tetracycline and oxytetracycline, as well as semi-synthetic and synthetic derivatives including doxycycline, minocycline, lymecycline, tigecycline, omadacycline, and eravacycline, exhibit complex degradation behavior that necessitates robust analytical control to ensure quality, safety, and therapeutic efficacy.[2–6,11–18] This review comprehensively evaluates reported approaches for the development and validation of stability-indicating analytical methods for tetracycline-class drugs in bulk substances,pharmaceutical dosage forms, fixed-dose combinations, and biological matrices. Particular emphasis is placed on reversed-phase high-performance liquid chromatography (RP-HPLC), which remains the most widely employed and regulatory-accepted technique for separation of active pharmaceutical ingredients from related substances and degradation products.[3,6,13,17,19] Several studies demonstrate the successful resolution of tetracycline derivatives from impurities generated under acidic, alkaline, oxidative, thermal, and photolytic stress conditions in accordance with ICH stability guidelines.[6,14,17,19] Advanced chromatographic methods have been reported for impurity profiling of oxytetracycline and its epimers and dehydration products using optimized gradient systems and volatile mobile phases compatible with mass spectrometric detection.[13,15] Similarly, validated stability-indicating methods for doxycycline, including its application in pharmaceutical formulations and biological samples, have confirmed adequate specificity, precision, and linearity under forced degradation conditions.[6,19] The emergence of third-generation glycylcycline and fluorocycline derivatives such as tigecycline, omadacycline, and eravacycline has further highlighted analytical challenges due to their enhanced structural complexity and sensitivity to pH-dependent degradation.[11,12,17,18] In addition, simultaneous estimation methods for combination formulations containing tetracyclines—such as tetracycline with hydrocortisone or oxytetracycline with polymyxin B—underscore the importance of chromatographic selectivity and method robustness in multi-component dosage forms.[14,15] Bioanalytical advancements, including LC-MS/MS methods for omadacycline quantification in plasma, further extend the application of stability-indicating principles to pharmacokinetic investigations.[18] Collectively, the reviewed literature demonstrates that successful stability-indicating method development for tetracycline-class drugs requires systematic forced degradation studies, appropriate stationary phase selection, optimized mobile phase composition, pH control, and comprehensive validation of parameters such as specificity, linearity, accuracy, precision, robustness, and sensitivity in accordance with ICH guidelines.[6,17] RP-HPLC, often coupled with diode array or mass spectrometric detection, remains the analytical cornerstone for impurity profiling and quality control of tetracycline derivatives. Continuous methodological refinement is essential to address evolving regulatory requirements and the expanding structural diversity within this antibiotic class.