Lime sulfur has been used since the 1900s to treat various fungal infections and ectoparasite infestations. Several new products have recently entered the market; the goal of this study was
to test the in vitro antifungal efficacy of 8 commercially available lime sulfur formulations. Microsporum canis spores (from infected untreated cats) were isolated, placed in suspension, and incubated for 5 minutes with 7 various lime sulfur concentrations (at manufacturer’s concentration, twice label concentration, or half label concentration). A single prediluted product was tested at the label and half label recommendations. Distilled water and bleach were used as negative controls. Colony forming units (CFU) were counted for 21 days total. The test spore suspension (positive control) yielded > 300 CFU per plate. Each dilution was tested 5 times (on 5 replicate plates). The investigators identified complete growth inhibition of M canis spores by all products at all tested dilutions. The investigators concluded that the products were equivalent.

Commentary: The fungicide lime sulfur was first used by the ancient Greeks to control rust on wheat. It is still regularly used in home horticulture as a fungicide. Lime sulfur is 1 of several topical antifungal solutions used as adjunct topical therapy for the treatment of dermatophytosis. In this study, 8 formulations of lime sulfur (a garden product, research grade formulation, and 6 veterinary products) were equally fungicidal in vitro. In this model, physical barriers (organic debris, hair cuticle, oils) were removed to allow maximum contact of antifungal solution. In the author’s experience, lime sulfur is most effective when the haircoat and skin are thoroughly soaked. Topical therapy is recommended because it helps prevent spread to other susceptible animals and people and limits spread of spores into the environment.—Karen A. Moriello, DVM, Diplomate ACVD

Efficacy of eight commercial formulations of lime sulfur on in vitro growth inhibition of Microsporum canis. Diesel A, Verbrugge M, Moriello K. VET DERMATOL doi: 10.1111/j.1365-3164.2010.00928.x