Stability indicating high‐performance liquid chromatography method for determining doxycycline hyclate and related substances in their various dosage forms: Utilizing Six Sigma tools, uniformity testing, and in‐vitro dissolution approaches

Abstract Doxycycline hyclate (DOXH) is very important to treat acne and prevent infections caused by bacteria, so quantifying doxycycline hyclate and its related substances is crucial. In this work, All analytes of doxycycline and its related substances, including methacycline, 4‐epi doxycycline, 6‐epi doxycycline, and 2‐acetyl‐2‐carbamoyl doxycycline, were successfully separated at low concentrations in a single run utilizing the suggested isocratic high‐performance liquid chromatography method with a mobile phase comprising water:acetonitrile:perchloric acid (75:25:0.2, v/v), Phenomenex Luna C18 column (50 × 4.6 mm, 3 μm i.d.) maintained at 30°C with a flow rate of 0.7 mL/min, injection volume of 25 μL, and photodiode array detector at 269 nm. DOXH and its related substances were linear in the range of 0.25–50, 0.1–30, 0.2–35, 0.5–50, and 0.6–20 μg/mL, respectively, with correlation coefficients greater than 0.999 and good accuracy results between 98% and 102%. The method has been successfully used to determine the drug's comparative study in both generic and reference products, demonstrating the similarity between the two products. According to the International Council for Harmonization requirements, the proposed approach was validated. Additionally, the technique has effectively studied in vitro dissolution, Six Sigma, and content uniformity.