Boosting bepotastine fluorescence by switching off intramolecular photoinduced electron transfer: Application to eye drops and aqueous humor.

Bepotastine (BPT), a second-generation antihistamine used for treating allergic rhinitis and pruritus, requires precise dosage calculation and accurate measurement in aqueous humor to ensure therapeutic efficacy and avoid adverse effects. This study presents a highly sensitive, cost-effective, readily-implementable, and ecologically sustainable method to detect BPT by enhancing its weak native fluorescence. This has been achieved by switching off the intramolecular photoinduced electron transfer (PET) process through phosphoric acid-induced protonation of the nitrogen in the piperidinyl ring. Further fluorescence enhancement was achieved by incorporating a solution of sodium dodecyl sulfate (SDS) surfactant thus increasing the quantum yield of BPT up to 10 folds. Fluorescence intensity was measured at 425 nm following excitation at 265 nm. The method, validated according to ICH guidelines, demonstrated linearity over the range of 0.70-6.0 µg/mL with a correlation coefficient of 0.9972 and a low detection limit of 0.046 µg/mL. It was successfully applied to measure BPT in aqueous humor and eye drops with % recoveries between 97.59 % and 102.62 %. Finally, sustainability was assessed using various tools, confirming the method's practicality for routine clinical and pharmaceutical quality control analyses.