Introduction
Topical medication is a staple in the treatment of mild to moderate acne vulgaris. Not only is it an efficient way to deliver therapy to the source of the disease, but it also involves a decreased risk of systemic exposure to ingredients such as antibiotics and retinoids. However, local cutaneous irritation from the vehicle or the medication itself can lead to non-adherence and poor outcomes. Thus, choosing the right formulation that will be effective and well tolerated is essential. This can be challenging as the topical drug formulations for acne are numerous and complex. This article will review the goals of topical therapy for the treatment of acne, common therapies and their challenges, and newer therapies on the forefront.Topical drugs are absorbed primarily by passive diffusion. There are three main methods of permeation of topical drugs through the stratum corneum: transappendageal, transcellular, and intercellular. Transappendageal transport occurs at the sweat glands or hair follicles and their associated sebaceous glands. This delivery system may be preferred for diseases of the pilosebaceous unit, such as acne or folliculitis, because it can be used to create a reservoir effect.1,2 Diffusion via the transcellular and intercellular pathways differ because they depend more on the active molecule’s characteristics. The transcellular route is the most common path, where drugs pass through corneocytes by repeated partitioning between lipophilic and hydrophilic compartments. In the intercellular pathway, drugs pass around the corneocytes via the lipid rich extracellular domains.3 There are several challenges to formulating topical drugs. As the active molecule passes through the epidermis, it may go through chemical changes that alter its efficacy at the target site. The active molecule may also be altered in the vehicle itself as it is applied to the skin.3 Several methods can be utilized to improve drug delivery through the epidermis. For example, using an evaporating, volatile component in the vehicle will help to increase the concentration of the active drug on the skin surface when applied.3 Vehicles usually include ingredients that disrupt the skin barrier, fluidize the lipid channels between corneocytes and alter partitioning of the drug into the cutaneous structures. Detergents, emulsifiers, and solubilizing agents can all be used as drug mediums to help disrupt the barrier and improve penetration of the active ingredient through the epidermis.3When developing a vehicle delivery system for a drug, it is important to consider that it accommodates the drug being formulated and that it is suitable for application to the body site requiring treatment. The FDA recognizes the following topical dosage forms: solution, suspension, lotion, paste, gel, ointment, cream and “other” category including novel formulations such as aerosol, powders, and patches.4In clinical practice, the optimal formulation needs to be effective and well tolerated. These are both features that help contribute to patient adherence with therapy, which can lead to better outcomes and lower long-term treatment costs. Poorer
