Objective: Bemotrizinol (BEMT) is the most efficient broad-spectrum UV-absorber having a dual mechanism of action in absorbing and reflecting photons. The main objective of this work was to develop successful oil in water (o/w) nanoemulsion for improving the solubility of BEMT and its protective characteristics.

Methods: Pseudo-ternary phase diagrams were constructed using labrafac PG and isopropyl myristate as oil phase, tween 80 as surfactant (S) and cremophor EL as cosurfactant (CoS) the ratio of S/CoS was determined according to highest percent of water incorporation to the system. Full factorial study design (24) using Design-Expert® software was adopted to study the effect of four independent variables namely: oil type, oil concentration, S/CoSmix (3:1) concentrations and BEMT concentration on the particle size and the in vitro release at 2 h (Q2h) of the prepared nanoemulsion formulae. Two systems each of eight formulae were developed and evaluated through droplet size analysis, zeta potential measurement, refractive index, in vitro drug release and according to the desirability value two formulae (F6 and F14) were used for further evaluations including in vitro sun protection factor (SPF), ex-vivo deposition by tape stripping technique, permeation test and photostability study.

Results: Formula (F14) was chosen as the optimum formula having an in vitro SPF of 16.08±0.39, lowest permeation of 140±0.06 μg/cm2after six h and highest photostability (t90% = 168.02) after 120 min.

Conclusion: Despite the poor solubility of bemotrizinol, it could be enhanced by novel drug delivery systems with good SPF value while maintaining its photostability.
Keywords: Bemotrizinol, Nanoemulsion, In-vitro SPF, Ex-vivo deposition, Tape stripping technique, Photostability