Low surface tension, non-greasy touch, high permeability to drugs and persistence of action in various controlled release pharmaceutical devices, make silicones ideal as excipients in topical pharmaceutical products.
Drug developers are increasingly realising the value of excipients in providing enhanced functionality to products at lower costs and Frost & Sullivan expect the total excipient market in Europe to grow 5.3 per cent between 2004 and 2008.
Silicones are not new to the medical and pharmaceutical industry, having been used since the 1950s. They are now used in more than half of all consumer skin care products.
Until recently, their use as topical drug-delivery excipients has been rare, however, this has been changing, with the emergence of pharmaceutical-grade silicones.
Silicone polymers, such as gums, elastomers, waxes or emulsifiers are now bringing additional and complementary benefits as excipients for topical pharmaceutical applications.
Silicon excipients can improve penetration of the API through the skin, and improve drug bioavailability because of their unique physicochemical properties.
Studies, published in the October 2005 issue of PharmaChem, also indicate that silicones can improve the aesthetics of topical formulations through improved spreadability, emolliency and lubrication, while imparting a silky, non-oily and tack-free feel compared with non-silicone products.
Thus, silicones can improve treatment compliance, which is often hindered by poor aesthetics of topical formulations that reduce patient comfort. This is particularly the case for treatments of chronic illnesses that require repetitive use.
In light of these benefits, silicone polymers are increasingly providing an efficient vehicle for drug delivery in topical formulations - a major need within the industry.
>Dow Corning has already been actively pursuing various applications for silicon excipients for topical pharmaceuticals over the past few years, and has since commercialised a broad range of silicon polymers for this purpose.
The range includes two volatile silicones, three special silicone blends, a more hydrophilic silicone fluid, two silicone waxes and one emulsifier.
More recently, >Galderma has been looking to combine hexamethyldisiloxane (HMDS) with silicone gums to provide sprayable silicone-based formulations containing APIs such as vitamin D derivative or clobetasol 17-propinoate (a steroid used to treat dermatological conditions).
Good aesthetic results have been observed for these and many other silicone-based formulations that are under development, when compared to a petrolatum-based commercial product.
In addition to being used as excipients, advanced analytical techniques are also allowing the development of silicone pressure sensitive adhesives for use in transdermal drug delivery systems.
The advantage of these silicone pressure adhesives is that they are silyated to reduce the overall concentration of residual sinols that can otherwise lead to excess crosslinking within the adhesive during storage and loss of adhesive properties.
Furthermore, silicones are also increasingly being used to improve various pharmaceutical-manufacturing processes, because of their purity profiles and high stability during sterilisation.