Essential Guide azelaic acid

7. How to formulate with azelaic acid 7.1. How to prepare clear / translucent products

Solubility and bio-availability are prime parameters for working with azelaic acid. The use of azelaic acid in the water phase of emulsions was already described (see: Solubility of azelaic acid), and this also enables the use of azelaic acid in waterborne gels based on carbomers, cellulose ethers or polysaccharides such as xanthan gum or sclerotium gum. However, these gels to be stable and clear enough, are characterized by a pH from neutral (close to 7) to slight alkaline 7.2-7.5) and could have a limited degree of bio-availability. For serum and gel based on high content of organic solvents such as ethanol, glycols, the pH value is not an important parameter as the water content is low.

The solubility of azelaic acid in ethoxydiglycol is 360 g/l. A clear solution will be obtained that will not show crystallisation. Ethoxydiglycol is miscible with water in any proportion, and also soluble in many polar lipids. An example of such an application is given in table 12.

INGREDI Ë NT

CONCENTRATION

ETHOXYDIGLYCOL

61,0 %

AZELAIC ACID

20,0 %

AQUA

11,5 %

PEG-40 HYDROGENATED CASTOR OIL 4,5 %

DIMETHYL ADIPATE

3,0 %

TABLE 12: Clear Azelaic acid solutions

The formulation according to table 12 enables transdermal transport, as ethoxydiglycol is swiftly absorbed through the skin. This results in transport of azelaic acid to the target location, such as in the hair follicles for the treatment of acne vulgaris. The preparation according to table 12 is very low viscous, but can effectively be converted into a transparent transdermal gel using hydroxypropylcellulose (HPC). For serum preparations 1-2% HPC is required, depending on the desired viscosity. For gel preparations 2-4% is needed. As an alternative for ethoxydiglycol butoxydiglycol may also be used although the solubility of azelaic acid is less, estimated at 15%. For personal care & cosmetic products both ethoxydiglycol and butoxydiglycol are limited in use because of their extreme penetration power. According to EU Regulation 1223/2009 the maximum allowed concentration ethoxydiglycol in leave-on products is 2,6% while for butoxydiglycol 9,0% is allowed. These concentration limitations are not applicable for medical devices and pharmaceutical products. Taking the risk of stating the obvious, anti-acne preparations, anti-rosacea preparations and products for the treatment of alopecia areata or hair growth products are not covered by EU Regulation 1223/2009.

Phone : +31 475 20 60 70 • service@azeco-cosmeceuticals.com • www.azeco-cosmeceuticals.com

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