Poloxamer and Chitosan-Based In Situ Gels Loaded with Orthosiphon stamineus Benth. Extracts Containing Rosmarinic Acid for the Treatment of Ocular Infections.

Objectives: Orthosiphon stamineus Benth. (OS) is a commonly used medicinal plant for curbing bacterial infections globally. This work aimed to fabricate poloxamer and chitosan-based in situ gels loaded with standardized aqueous-ethanolic OS leaf extracts and investigate their antimicrobial efficacy as a potential remedy against ocular infections.

Materials and methods: In situ gels containing 0.5% w/v OS extract prepared using cold dispersion method were subjected to physicochemical characterization, including in vitro-release studies. Antimicrobial efficacy was tested against Staphylococcus aureus, Micrococcus luteus, Escherichia coli, and Pseudomonas aeruginosa using agar diffusion method.

Results: Thin layer chromatography and high performance liquid chromatography chromatograms confirmed the presence of rosmarinic acid (RA) and sinensitin in OS extracts with same retention factor (0.26 and 0.49) and retention times (12.2 and 20.7 min) against reference standards. A homogenous brown coloured in situ gel exhibited low viscosity as a solution and increased viscosity in gel form at ocular temperature. The optimized formulations, P7 (21% P407/4% P188), P8 (21% P407/5% P188) and F5 (1.5% chitosan and 45% β-glycerophosphate) exhibited ideal ocular pH (7.27-7.46), phase transition at ocular temperature (33-37°C) and prolonged RA release up to 12 h. Formulation F5 showed an inhibition zone of 4.3 mm against M. luteus.

Conclusion: Among all, formulation F5 alone exhibited modest antimicrobial activity against M. luteus. OS extracts at 5% and 10% were most active against tested bacteria however, loading them into in situ gels resulted in sedimentation. Hence, isolation of RA from OS extract is suggested before loading into formulations for a better antimicrobial activity.