Author Tanya M. Barnes, Dalibor Mijaljica, Joshua P. Townley, Fabrizio Spada and Ian P. Harrison
Many dermatological conditions, such as eczema and psoriasis, are treated with topical therapeutic products. Instead of applying the active drug directly onto the skin, it is combined with a vehicle to aid in its delivery across the stratum corneum (SC) and into deeper regions of the skin, namely the epidermis and dermis. Absorption into the systemic circulation is minimized. Topical vehicles are also used as cosmetic moisturizers (often termed emollient therapy) to ameliorate dry skin, which is a cornerstone of the management of various dermatological conditions, including xerosis, eczema, psoriasis, and aging. The most common topical vehicles include ointments, creams, gels, and lotions, among others. It is crucial that topical vehicles are chosen based upon the size and properties (wet/dry, mucous/non-mucous, healthy/diseased) of the skin to be treated in order to optimize application and contact of the product with the skin, as this can have profound impacts on potency, efficacy, and patient compliance. This review examines common topical vehicles used for drug delivery and cosmetic moisturizers, including their formulation, advantages and disadvantages, and effects on the skin. ointment, cream, gel, excipient, humectant, emollient, occludent, drug delivery, dermatitis, regulatory, skin is the outermost defensive barrier, which protects the human body from physical, chemical and microbial insults, and prevents the uncontrolled loss of water, the barrier function of the skin resides in the stratum corneum (SC), which is composed of protein enriched corneocyte layers and intercellular membrane lipids, such as ceramides, cholesterol, and free fatty acids, corneocytes are rapidly and continually replaced to maintain skin hydration, flexibility and structural integrity, and repair any skin damage, a dysfunctional skin barrier leads to skin dryness, and may be due to a genetic predisposition [5]; pathological causes such as eczema, psoriasis or xerosis, environmental insults from the sun, wind or air conditioning, frequent exposure to chemicals such as harsh soaps or detergents, medications such as statins, diuretics or retinoids ; and other causes such as aging, dry skin exhibits a defective desquamation process, where corneocytes are shed as visible scales, causing a cosmetically unattractive rough texture and excessive transepidermal water loss (TEWL), dry skin is unable to efficiently bind and hold water, and favors the penetration of irritants, allergens, and microorganisms, provoking discomfort and itchiness, as well as visible irritation or redness, Thus, there is a need to protect both healthy and dry, compromised skin from a plethora of insults, and to preserve or restore its functional and structural integrity, Topical vehicles are used as carrier systems, which aid in the delivery of an active drug (e.g., corticosteroid, calcineurins, vitamin D derivatives, retinoids) across the SC and into deeper regions of the skin, namely the epidermis and dermis, whilst minimizing absorption into the systemic circulation. These formulations are often used to treat dermatological conditions, such as eczema and psoriasis, to restore the skin barrier, however, topical vehicles may also be used on their own as cosmetic moisturizers (often termed emollient therapy) to ameliorate dry skin, including conditions such as eczema and psoriasis where the use of moisturizers has become pivotal as first-line treatment strategies, the most common topical vehicles include ointments, creams, gels, and lotions, among others. Topical vehicles are chosen based upon the nature (wet/dry, mucous/non-mucous, healthy/diseased) and size of the skin area to be treated to optimize application and contact of the product with the skin, Topical Drug Delivery, Transepidermal Route, Transappendageal Route, The Role of the Vehicle, Delivering drug molecules to and through the skin involves the complex interplay between the active drug, the type of topical carrier system or vehicle, the choice of excipients, skin type and location, and skin condition. The topical carrier system, or vehicle, is defined as the substance that carries the chosen active drug into contact with and through the skin at an appropriate level to provide a therapeutic effect, the challenge to topical drug delivery is the transport across the SC. To overcome this barrier, a vehicle must: maintain the solubility and stability of the active drug; release the active drug, depositing it on the skin with even distribution; enable penetration into and permeation through the SC skin barrier; facilitate partitioning from the SC into and diffusion through the viable epidermis; sustain the active drug at the target site for a sufficient duration to provide a therapeutic effect; and limit systemic absorption, furthermore, a vehicle should be soothing and comfortable, spread easily and be aesthetically pleasant, which aids in patient compliance, these important attributes of a topical vehicle are dependent on the selection of the right excipients, topical vehicles can be classified based on their physical state, including semisolids (e.g., ointments, creams, gels) and liquids (e.g., lotions, solutions, foams, sprays) , lotions, gels and solutions are monophasic, ointments and creams are biphasic, whilst foams are triphasic
