Tinea capitis: Fungal isolates highly susceptible to terbinafine

July 1, 2008

Fungal isolates from patients with tinea capitis participating in international clinical trials were tested for in vitro susceptibility to terbinafine. The results showed terbinafine had potent activity against all 301 dermatophytes tested. There was no difference in MIC values comparing U.S. and non-U.S. isolates of the same organism.

Key Points

National report - Results of an in vitro susceptibility study demonstrate terbinafine (Lamisil, Novartis) has consistently potent antifungal activity against dermatophytes isolated from tinea capitis patients around the world, according to Mahmoud Ghannoum, M.S., M.B.A., Ph.D.

Dr. Ghannoum and colleagues conducted laboratory tests to determine the minimum inhibitory concentration (MIC) of terbinafine against clinical isolates from patients participating in two international clinical trials of tinea capitis treatment.

A total of 301 dermatophytes were randomly selected from a total sample of almost 1,000 baseline isolates.

Trichophyton tonsurans was the most common organism isolated from patients in the United States (63 of 97 isolates), but equal numbers of T. tonsurans, Microsporum canis and Trichophyton violaceum were represented in the non-U.S. isolates, and there were also 19 isolates of Microsporum audouinii from non-U.S. patients.

Results

The results showed terbinafine had potent antifungal activity against all isolates tested, with an MIC range between 0.001 and 0.25 mcg/ml.

"In the United States, we know that T. tonsurans accounts for almost all cases of tinea capitis, but the etiology of these infections differs in other countries.

"As our sample shows, Microsporum spp. and other Trichophyton spp. may be more common causes of tinea capitis in countries outside of the U.S.," says Dr. Ghannoum, professor, department of dermatology and director of the center for medical mycology, Case Western Reserve University, Cleveland.

"The results of this study indicate that terbinafine is an excellent empiric choice for treating tinea capitis, regardless of the pathogenic cause and the patient's nation of origin," Dr. Ghannoum tells Dermatology Times.

The susceptibility testing was performed according to the CLSI M38A2 standard. For the various fungal species evaluated, the MIC50 values ranged from 0.002 to 0.125 mcg/ml and the MIC90 values ranged from 0.03 to 0.25 mcg/ml.

Differences were identified in MIC50 and MIC90 values between species, but not within the same species comparing U.S. and non-U.S. isolates.

Dr. Ghannoum says there is little published information on potential geographic variability of the activity of antifungal agents.

"To our knowledge, this is the first study to evaluate the activity of terbinafine against dermatophyte isolates obtained from different countries around the world and using a standardized assay method," he says.

Dr. Ghannoum also says tinea capitis continues to be an important public health problem, especially among blacks.

While the infection occurs primarily in children, it is becoming increasingly common to see adult household contacts who are asymptomatic carriers and a reservoir for disseminating infection.

"When a physician sees a child with tinea capitis, it is very important that all family members be evaluated for infection or a carrier state, and treated as appropriate," Dr. Ghannoum says.