(…) The ideal solution is a new patented galenic solvent based on Water, Low Ethyl Alcohol, Isopropyl Alcohol, PEG 400, Transcutol, Glycerol and Lactic Acid.
Water and ethyl alcohol are obviously the starting point, as these are solvents needed in most topical galenic preparations.
One should, however, use an alcohol concentration that is between 50 and 60 percent, so as to avoid the undesirable hygroscopicity problems that arise in high alcohol solutions.
Isopropyl alcohol is needed as a back-up to ethyl alcohol to best solubilize substances that are less polar, such as most of the actives of dermatological interest, and which would therefore find it difficult to be dissolved in simple hydroalcoholic ethanol solutions.
PEG400 is already in very wide use in cosmetics because it is an excellent emulsifier and a very hydrophilic solvent, but it is also extremely versatile, and is capable of solvating both polar and nonpolar molecules: it is miscible with water, all alcohols, benzene, and aromatic hydrocarbons, showing limitations only in the solvation of paraffins. These chemical properties make it the ideal solvent for galenic solutions, greatly increasing its ability to solubilize a great many active ingredients without compromising patient comfort.

On the other hand,adding propylene glycol would lose this advantage as it is an irritant and known to be very viscous .

The Transcutol, which is in common use in dermatology, serves to maximize the ability of actives to penetrate the stratum corneum: being an amphiphilic molecule (di-ether between one molecule of ethanol and two of propylene glycol that has a free hydroxyl group at one end of the carbonaceous chain) it is able to coordinate with skin lipids, altering their organization and creating more permeable interstices and through which even the most polar substances can diffuse and penetrate.

The Transcutol is, in addition, also useful for increasing the solubility of less polar actives.

The Glycerol is present for the purpose of moisturizing the skin by virtue of its humectant properties, but also because, due to its small molecular size, it is able to perform transdermal enhancer action like Transcutol, resulting in changes to the three-dimensional arrangement of skin lipids.

Finally, lactic acid is present for the purpose of forming, together with its sodium salt, a buffer solution, so as to keep the pH of the solution as stable as possible and close to the physiological pH of the scalp (pH approximately 4.5-5.5).

Such a solvent has been shown to solubilize Minoxidil up to 5,5% in cumulative association with all active ingredients of trichological interest such as hydrocortisone butyrate, finasteride, progesterone, 17-alpha estradiol, etc.

In addition, the tests of stability at six months, have shown that the solutions remain clear and crystalline without any kind of precipitate. In vivo tests have also been carried out so that this solvent can boast of being “dermatologically tested.” 

The new patented solvent DryDil simplifies and speeds up the preparation of dermatological master preparations, ensures an optimal cosmetological result, and guarantees greater satisfaction and adherence to therapy even by very difficult patients, such as those with seborrheic dermatitis of the scalp.