Quality by design enabled the development of stable and effective oil-in-water emulsions at compounding pharmacy: the case of a sunscreen formulation

Abstract

It is widely accepted that the use of topical sunscreens has medical importance with potential to prevent skin damage by protecting from solar ultraviolet radiation (UVR) effects. Pharmaceutical emulsions require an optimal qualitative and quantitative combination of emollients, emulsifiers and others compounds such as softening agents and, for sunscreens, a combination of chemical and physical UV filters. Herein, we applied the quality by design (QbD) concept to achieve stable and effective compounded sunscreen emulsions. By using the statistical tool of design of experiments, it was possible to identify the influence of emulsifier type (with low and high Hydrophile-Lipophile Balance) and concentrations of emollient and softening agent on the achievement of formulations with suitable organoleptic and physicochemical features. Compounded emulsions with pleasant macroscopic aspects were obtained. Three formulations with physicochemical properties in targeted ranges were selected, namely pH ∼6.0, conductivity > 0.0 µS/cm², spreadability factor ∼1–1.5 g/mm², viscosity ∼12000 mPa.s and sunscreen protection factor ∼30. Freeze-thaw cycle and accelerated stability study under different storage conditions allowed selecting a stable emulsion that ensured photoprotection in biological assays. The QbD approach was essential to select the best, low-cost compounded sunscreen emulsion, with targeted physicochemical parameters.

Keywords:

• Emulsification
• emulsifier Hydrophile-Lipophile Balance
• photoprotection
• compounded sunscreen emulsion

Acknowledgements

The authors are very grateful to pharmacists Camila de Oliveira Melo, Salete Rodrigues, Thayse Silva Medeiros for the help with some technical analysis. We thank Dr. Ana Cláudia Dantas de Medeiros for allowing the use of spectrophotometer and viscosimeter at State University of Paraíba and Dr. Luciana Biagini Lopes for allowing the use of rheometer and dynamic light scattering at University of São Paulo.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This study was supported by National Council of Technological and Scientific Development (CNPq) and CAPES (finance code 001).