OBJECTIVE To study the changes in impurity content after exposure to light of lomefloxacin hydrochloride ear drops with different excipients, packaging materials, as well as lomefloxacin and its salts with hydrochloric acid and aspartic acid, the study on the influence of excipients, packaging materials, and salt formation on photostability was conducted.

METHODS Kromasil 100-5 C₁₈(4.6 mm×250 mm, 5 μm) column was used, and the mobile phase A was sodium pentanesulfonate solution(1.5 g of sodium pentanesulfonate, 3.5 g of ammonium dihydrogen phosphate, dissolved in 950 mL of water, adjust the pH value to 3.0 with phosphoric acid, and dilute with water to 1000 mL), while methanol was mobile phase B, gradient elution was used to determine the content of photodegradable impurities in lomefloxacin hydrochloride ear drops. The compatibility of excipients and packaging materials was studied based on influencing factor tests and accelerated tests. GL science inertsil ODS-3V(4.6 mm×250 mm, 5 μm) column was used, the mobile phase A was 10 mmoL·L⁻¹ ammonium formate aqueous solution(adjusted to pH 3.0 with formic acid), and the mobile phase B was acetonitrile, gradient elution was performed to investigate the photodegradation impurities of lomefloxacin, lomefloxacin with hydrochloric acid and aspartic acid salt under light irradiation.

RESULTS The organic matter(glycerol, ethanol, and propylene glycol content) in the formulation was significantly negatively correlated with the content of photodegradable impurities, adding an appropriate amount of organic matter to the formulation could improve the photostability of lomefloxacin hydrochloride ear drops and reduce the occurrence of photodegradation reactions. The transparency of packaging materials for lomefloxacin hydrochloride ear drops was significantly positively correlated with the content of photodegradable impurities, and the use of shading packaging could reduce the occurrence of lomefloxacin hydrochloride photodegradation reaction. The salt formation of lomefloxacin helped to improve the photostability. The photodegradation impurities generated by lomefloxacin hydrochloride were mainly chlorinated impurities, and the chlorinated impurity content in lomefloxacin and lomefloxacin aspartate photodegradation solutions was 1/10 and 1/4 of lomefloxacin hydrochloride, respectively.

CONCLUSION High light shielding inner packaging materials should be used in the production process of lomefloxacin hydrochloride ear drops, and an appropriate amount of organic matter should be added to the formulation to improve the photostability of lomefloxacin hydrochloride ear drops. To improve the photostability of lomefloxacin formulations, appropriate acid groups can be selected to salt lomefloxacin.