Natural Surfactant-Based Emulsion Vehicles: A Correlation Between Colloidal Structure and In Vitro Release of Diclofenac Diethylamine

Abstract

The need for an official pharmaceutical vehicle or carrier of drug based on natural sugar emulsifiers that protect and regenerate natural barriers of the skin lipid layer is constantly increasing. This article studies the specific structures of emulsions and two manners of water binding that provide prolonged skin moisturization and delayed or prolonged release of drugs insoluble in water. Natural emulsifiers of an alkylpolyglucoside (cetearyl alcohol and cetearyl glycoside) and estar-type (sorbitan stearate and sucrose cocoate) are used for manufacturing vehicle/carriers of drugs (diclofenac diethylamine). Specific hydrofilic groups in emulsifiers, such as glycozide and ester, are capable of binding in different manners and variable quantities of water by hydrogen bonds within the cream, which is responsible for water distribution and prolonged skin moisturization. This lyotropic potential of natural emulsifiers—alkylpolyglucoside and estar type—may affect the physical stability of topical vehicles by determining the colloidal structure, further reflecting the drug delivery from the pharmaceutical excipient to the skin. The aim of this article is to evaluate whether the type of emulsifier influences the structural characteristics of emulsion systems and how the content and availability of water within the cream reflects the delivery of diclofenac diethylamine (1.16%) from the topical vehicles. Freeze-fracture transmission electron microscopy, wide-angle x-ray diffraction, thermogravimetric analysis, and continual and oscilatory rheological measurements are employed for characterization of emulsion system colloidal structure. Diclofenac diethylamine release profiles from investigated emulsion systems were evaluated using the rotation paddle apparatus, modified by addition of diffusion cells (enhancer cell). There is an important difference in water distribution within the creams with emulsifiers of different chemical types. In the sample with ester-type sugar emulsifiers, the quantity of interlamellar-bound water is four times less than bulk and secondary water, while in the sample with alkylpolyglucoside emulsifier, approximately two thirds of total water are bound inside the system and one third is poorly bound, that is, bulk water. It can also be seen that diclofenac diethylamine is gradually released from the vehicle during 6 hours of testing. Formulation of topical vehicle as dermopharmaceutical drug carrier system, with natural emulsifier, like cetearyl alcohol, cetearyl glucoside, sorbitan stearate, and sucrose cocoate, is recommended.

Keywords:

• Cetearyl alcohol and cetearyl glycoside
• diclophenac diethylamine release
• emulsion water distribution
• natural surfactants
• sorbitan stearate and sucrose cocoate