Do not use nystatin to treat any tinea infection because dermatophytes are resistant to nystatin. (However, nystatin is often effective for cutaneous Candida infections.)

Do not use oral ketoconazole to treat any tinea infection because of the U.S. Food and Drug Administration boxed warnings about hepatic toxicity and the availability of safer agents.

Do not use griseofulvin to treat onychomycosis because terbinafine (Lamisil) is usually a better option based on its tolerability, high cure rate, and low cost.

Do not use combination products such as betamethasone/clotrimazole because they can aggravate fungal infections.

Do not use topical clotrimazole or miconazole to treat tinea because topical butenafine (Lotrimin Ultra) and terbinafine have better effectiveness and similar cost (Table 4).

Do not, in general, treat tinea capitis or onychomycosis without first confirming the diagnosis with a potassium hydroxide preparation, culture, or, for onychomycosis, a periodic acid–Schiff stain. However, kerion should be treated aggressively while awaiting test results, and it may be reasonable to treat a child with typical lesions of tinea capitis involving pruritus, scale, alopecia, and posterior auricular lymphadenopathy without confirmatory testing.2,7,8 If there is no lymphadenopathy, a confirmatory test is recommended.2

Do not treat tinea capitis solely with topical agents, but do combine oral therapy with sporicidal shampoos, such as selenium sulfide (Selsun) or ketoconazole.

Do not perform potassium hydroxide preparations or cultures on asymptomatic household members of children with tinea capitis, but do consider empiric treatment with a sporicidal shampoo.2