Treatment: topical and oral agents
Treatment of tinea infections may rely on antifungal medications singly or in combination. Antifungal agents are classified by their chemical structure—imidazoles, allylamines, benzylamines, and others—and act by different mechanisms to limit the availability of ergosterol, an essential component for normal function of fungal cell membranes.
Most tinea infections may be treated with topical agents alone. Oral therapy is required most often for:
- hyperkeratotic areas as on the palms or soles
- widespread or extensive infection
- immunocompromised patients
- persons intolerant of topical therapy
- failure of topical therapy
- chronic infection
Efforts to educate patients in proper hygiene and infection control may help. Specifically, remind patients that risk of tinea cruris and tinea pedis may be reduced if they wear nonocclusive footwear, use only clean and dry socks and undergarments, wear shower shoes, and apply absorbent powders. Eradication of fungal nail infections may help in controlling tinea pedis and tinea manuum. Caution in making contact with animals or people that have known tinea infections may reduce the incidence of tinea corporis.
Topical therapy
Topical antifungal agents are widely available in both prescription and over-the-counter forms. Preference of a specific agent may be difficult due to the limited number of head-to-head comparisons among these drugs. When recommending or prescribing an agent, consider efficacy, dosing regimen, cost, formulation, and availability. The most important topical antifungal agents are divided into 2 major classes—imidazoles and allylamines—although other agents are also used. Table 3 provides information on commonly used topical antifungal agents.
Imidazoles. Imidazoles are widely available as over-the-counter and prescription forms. Topical members of this class are clotrimazole, miconazole, econazole, ketoconazole, oxiconazole, and sulconazole. Miconazole and clotrimazole are available without a prescription. As a class, imidazoles are primarily fungistatic and are generally well-tolerated.12 Meta-analysis has failed to reveal significant differences in efficacy among members of this class.13 Imidazoles are efficacious with a pooled relative risk of failure to cure of 0.38 at 6 weeks after the initiation of therapy for tinea pedis (level of evidence [LOE]=1a).13
Current guidelines recommend twice-daily application for clotrimazole, miconazole, and econazole; ketoconazole, oxiconazole, and sulconazole may be applied once daily.14 When using imidazoles, usually prescribe a 2-week course for tinea cruris or tinea corporis, and a 4-week course for tinea pedis.15 In cases of inflammatory dermatophytosis, a combination agent containing clotrimazole and the corticosteroid betamethasone dipropionate may be used for a short initial period (LOE=4).16 Many experts recommend that combination steroid agents be used with caution, for no more than a few days, and with a plan for short-term follow-up.
Allylamines. A second, newer group of antifungal agents are the allylamines. Topical allylamines, including terbinafine and naftifine, are generally considered fungicidal. Terbinafine has recently been made available over-the-counter as 1% cream and 1% solution, while naftifine remains a prescription medication. Both agents are efficacious, with cure rates for dermatomycosis greater than 75%.17,18 Naftifine and terbinafine have exhibited long periods of activity in the skin and are therefore administered only once a day.19 Additionally, terbinafine has been shown effective in treating superficial mycoses in much shorter courses than typically required for imidazoles.20
Tinea: A widespread, wide-spreading infection
Tinea infections are among the most common of all skin diseases. They are caused by dermatophytic fungi that digest keratin in the cells of the stratum corneum. Tinea infections are typically named according to the affected anatomic region: tinea corporis for the body, tinea pedis for the feet, tinea cruris for the groin, and so on.
The true prevalence of tinea is difficult to ascertain because many people self-treat or live with chronic infection. Approximately 8.6 million office visits occur each year for tinea infections. Family or general practitioners handle more than 35% of these visits. The estimated cost of office visits plus prescribed medications for cutaneous fungal infections for the 4-year period from 1990 to 1994 is just over $1 billion.1 Tinea infections occur in all age groups and in both genders; however, males have a higher incidence of tinea pedis and tinea cruris.
Dermatophytes affecting humans are from the genera Trichophyton, Microsporum, and Epidermophyton. Dermatophytes, which are ubiquitous in the environment, are categorized as geophilic, zoophilic, or anthropophilic according to their ecologic reservoir. Surveys of dermatophytes isolated from human patients in the United States from 1993 to 1995 indicate T tonsurans (44.9%), T rubrum (41.3%), T mentagrophytes (8.5%), and M canis (3.3%) are the most commonly encountered pathogens.2
The basic pathophysiology of tinea infection is inoculation of keratinized skin by dermatophytic fungi followed by release of keratinases and proteolytic enzymes. Symptoms follow as a result of host immune and epidermal response.3 Host factors, such as immunocompromised state and genetic susceptibility, play a role in infection. Warm temperature, moisture, and occlusion encourage dermatophyte growth.4