Inclusion complexation of the sunscreen agent 2-ethylhexyl-p-dimethylaminobenzoate with hydroxypropyl-beta-cyclodextrin: Effect on photostability

The interaction between the UV filter, 2-ethylhexyl-p-dimethylaminobenzoate , and unmodified and modified alpha-, beta- or gamma-cyclodextrins was stud ied in water by phase-solubility analysis, Of the cyclodextrins available, only hydroxypropyl-beta-cyclodextrin caused a marked increase in the aqueous solubility of 2-ethylhexyl-p-dimethylamin obenzoate. The data from the solubility study indicated the formation of a 1:1 (sunscreen-cyclodextrin) complex. The inclusion of the sunscreen agent into the hydroxypropyl-beta-cyclodextrin cavity was confirmed by thermal an alysis and by nuclear magnetic resonance spectroscopy. Irradiation-induced degradation of 2-ethylhexyl-p-dimethylaminobenzoate was reduced by complexa tion with hydroxypropyl-beta-cyclodextrin, this effect being more pronounce d in solution (the extent of degradation was 25.5% for the complex compared with 54.6% for free 2-ethylhexyl-p-dimethylaminobenzoate) than in the emul sion vehicle (the extent of degradation was 25.1% for the complex compared with 33.4% for free 2-ethylhexyl-p- dimethylaminobenzoate). Although photodegradation of the sunscreen agent is significantly reduced b y formation of the inclusion complex it is important to design a suitable v ehicle, Inclusion of 2-ethylhexyl-p-dimethylaminobenzoate-DMAB into the hyd roxypropyl-beta-cyclodextrin cavity limits interaction of the UV filter wit h the skin reducing the side-effects of the formulation.