Topical dermatological products allow direct treatment of a skin condition with fewer side effects than those associated with systemic agents. These products have a key component in addition to the active ingredient: the vehicle. The dermatological vehicle houses and supports the active ingredient.
The vehicle also has properties of its own. Namely, it must direct or “drive” the active medication either past the stratum corneum or into the dermis to take therapeutic effect. Not only does the vehicle drive the active ingredient into the skin, it also enhances patient tolerance, which ultimately affects patient adherence. There are many types of dermatological vehicles and choosing the right one is both an art and a science.
An ideal vehicle is odorless, non-greasy, easy to apply, inexpensive, non-irritating, stable and leaves little to no residue. Does the perfect vehicle exist? Not yet. However, choosing the right vehicle for the appropriate anatomy and skin condition is imperative for the practicing physician.
Ointments. These are either petrolatum- or propylene glycol–based ointments. Petrolatum-based ointments are occlusive and retard evaporation, creating an oily residue on the skin. This greasy residue may be a deterrent for some patients to use consistently but it allows greater absorption of the active drug into the skin by increasing the hydration of the stratum corneum. Ointments are well suited to glabrous areas of skin.
Creams. As emulsions, creams can either be oil-in-water or water-in-oil formulations that leave a slight oily residue on the skin. Creams are easily washed off and generally more cosmetically elegant than ointments. Cosmetic elegance refers to the ability of a topical medication to dry quickly and leave little to no residue on the skin, thus giving the illusion that the patient has used no medication.
Lotions. Lotions are one liquid (oil) surrounded by another liquid (water), which creates an emulsion or topical suspension. Lotions are typically less moisturizing than creams. These are easy to spread (i.e., cover the entire leg) and cool the skin as the water in the preparation evaporates.
Gels. These are either alcohol-based or water-based. Alcohol-based gels tend to sting more than the water-based gels but both are in use for their rapid drying and excellent penetration properties. Gels are also excellent for hair bearing areas and work well in intertriginous areas and areas that tend to stay moist (i.e., interdigital spaces).
Sprays. Sprays are metered (pre-measured) pumps of emulsions that dry quickly. Patients can spread them easily over large surface areas.
Foams. Since they are a dispersion of gas in small amounts of liquid, foams are cosmetically elegant and easy to use.
Tapes. These are strips of an occlusive adhesive with the active ingredient impregnated and often formulated to release the active ingredient in a time-controlled manner.
Lacquers. Lacquers are organic materials with an evaporable solvent that leaves a film on the skin or nail.
Powders. As solids that are ground up or pulverized ingredients, powders generally have a drying effect.
Over the last few years, older active ingredients (such as some topical corticosteroids) with reformulated vehicles have flooded the market. When choosing such a drug, it is important to consider the following: anatomical location, patient adherence and the type of dermatological issue you are treating.
The above table is a guide of the types of vehicles available, their brand names and an example of the anatomical location and/or dermatologic condition, which one could treat with the vehicle.