Chapter 12 407 used orally for the treatment of multiple mycoses. Several large antidandruff efficacy studies have demonstrated efficacy against pityriasis capitis and seborrheic dermatitis.10,30,64,88 Ketoconazole has been approved for topical over-the-counter use at 1% in shampoos and for prescription use at 2%. Twice-weekly treatments are currently recommended for ketoconazole-containing shampoos. To achieve efficacy, these products are recommended to be left on the scalp for 5 to 10 minutes before rinsing, thereby requiring a change in shampooing habits and practices. As an antifungal, ketoconazole is a member of the imidazole family and blocks fungal synthesis of ergosterol. Ergosterol is an essential constituent of fungal cell membranes. Ketoconazole binds and inhibits cytochrome P450 14-alpha-demethylase. This enzyme is required in fungal thesterol biosynthesis for the formation of ergosterol from lanosterol. Climbazole is another azole antifungal with similar activity and efficacy to ketoconazole. Climbazole is used in antidandruff shampoos in Europe, with high in vitro and in vivo efficacy against Malassezia evaluated for efficacy and safety.89 This shampoo is not marketed in the United States. Coal tar, approved for over-the-counter treatment of dandruff, seborrheic dermatitis and psoriasis at levels of 0.5‑5% (tar equivalent),60,64,77-78 reduces the number and size of epidermal cells, decreases epidermal proliferation and dermal infiltrates. Coal tar may also have slight antifungal activity, which could explain its minimal antidandruff efficacy.60,64-65,77-78 Coal tar-containing shampoo and treatment products have been marketed for decades, mainly for psoriasis. Salicylic acid, approved for over-the-counter treatment of dandruff, seborrheic dermatitis and psoriasis at concentrations of 1.8‑3%,60,64,77-78 is an exfoliant that loosens weakly adherent flakes, enabling them to be washed away. Sulfur is approved for over-the- counter treatment of dandruff at levels of 2‑5%. Combinations of salicylic acid and sulfur have not been approved for over-the counter use in the United States.