Studies reporting on the sporicidal activity of antifungal products are often conducted on the fungal culture plate form, but this is not the naturally infective state of fungal pathogens. By using a previously published model, isolated infective spores from cats with naturally occurring Microsporum canis infections were harvested from infected hairs and used to compare the efficacy of two commercially available topical antifungal rinses. The 2 products were lime sulfur (LymDyp, IVX) and miconazole base 5.2%/chlorhexidine gluconate 5.9% (Malaseb Rinse Concentrate, DVM Pharmaceuticals. Spores were incubated for 5 minutes and 4 hours in dilutions of lime sulfur varying from 1:8 to 1:28 and in dilutions of miconazole/chlorhexidine varying from 1:2 to 1:128. Water and bleach were used as controls. Lime sulfur was 100% sporicidal at all test dilutions at both 5 minutes and 4 hours. The miconazole/chlorhexidine gluconate was 100% sporicidal at all dilutions except for 1:28 after 5 minutes, but after 4 hours it was 100% sporicidal. This study showed that both commercial products were equally sporicidal at the manufacturer's recommended dilutions of 1:4 or 1:8 (lime sulfur) or 4 oz/gal (miconazole/chlorhexidine gluconate).

COMMENTARY: Use of sporicidal topical rinses in the treatment of M canis dermatophytosis may be particularly useful in decreasing environmental contamination and promoting the fastest clinical resolution in affected patients. This study demonstrates that two popular topical rinses (Malaseb and LymDyp) are sporicidal in vitro at manufacturer recommended dilutions, with the caution that multiple factors may alter the efficacy in individual patients.  In all, topical rinses are safe when used in accordance with label directions, and are valuable adjunctive therapy for this often frustrating dermatologic disease in our small animal patients.

Use of isolated infected spores to determine the sporicidal efficacy of two commercial antifungal rinses against Microsporum canis. Moriello KA, Verbrugge M. VET DERMATOL 18:55-58, 2007.