Development of a rapid method for the simultaneous determination of aminophylline, doxofylline, bromhexine, and ambroxol by HPLC

<b>Introduction:</b> Antitussive and expectorant drugs such as aminophylline (APL), doxofylline (DXL), bromhexine hydrochloride (BXH), and ambroxol hydrochloride (AXH), either individually or in combination, are widely used in the prevention and treatment of respiratory diseases. The study aimed to establish a high-performance liquid chromatography (HPLC) method for the simultaneous determination of these four drugs and to investigate their stability in 0.9% sodium chloride injection or 5% glucose injection over 48 hours. <b>Methods:</b> An InertSustain C₁₈ column (150 mm × 4.6 mm, 5 μm) was used. The mobile phase consisted of acetonitrile and 50 mmol·L^-1 potassium dihydrogen phosphate solution (pH 4.0) with gradient elution. The flow rate was 0.8 mL·min^-1, and the column temperature was maintained at 30°C. The stability of APL, DXL, BXH, and AXH in 0.9% sodium chloride and 5% glucose injections over 48 h was determined using HPLC. <b>Results:</b> APL, DXL, BXH, and AXH showed good linearity within the ranges of 0.01 to 0.20, 0.003-0.06, 0.015-0.30, and 0.016-0.16 mg·mL^-1, respectively (r > 0.999). The intraday and interday relative standard deviations were <2%, with recovery rates between 98.4% and 102.2%. The four drugs remained colorless and clear in infusion mixtures. The pH value fluctuated within ±0.3 over 48 hours, and the relative percentage content of the drugs ranged from 95.0% to 105.0%. <b>Conclusion:</b> The established HPLC method is simple, reliable, and stable, allowing for the simultaneous determination of the four antitussive and expectorant drugs. APL, DXL, BXH, and AXH were stable within 48 hours when mixed with 0.9% sodium chloride and 5% glucose injections.