Puls C, Johnson A, et al. J Feline Med Surg. 2018 Oct;20(10):869-874.

Dermatophytosis, commonly called “ringworm,” is a common skin infection in cats. Despite its name, ringworm is not a worm, but rather a fungal infection. Though several types of fungus may cause similar lesions, in cats the vast majority of infections are caused by Microsporum canis.  Though not life-threatening, ringworm can cause significant quality-of-life issues in affected animals. The disease is also contagious to humans, where it causes a classic round, itchy rash. Ringworm is often self-curing, however, this may take very long periods of time, and continual reinfection from the environment, humans, or other cats means that disease often persists for long periods if not treated.

Many therapies exist for ringworm that have various levels of efficacy. The fungus infects hair follicles and shafts, which means that infection is present both above and below the level of the skin. Because of this, treatment of ringworm generally involves both systemic (ie oral) and topical therapies. These may include topical azoles (ie enilconazole), peroxides, chlorhexidine, lime sulfur, or others. Oral therapies include terbinafine, itraconazole, or others. Recently, a feline-approved liquid formulation of itraconazole has entered the market, opening an on-label, more convenient route to treat ringworm. In humans, itraconazole has been shown to be effective in a pulsed-dose regimen (1 week on, 1 week off) due to prolonged residence in the skin.

The purpose of this study was to determine the efficacy of oral liquid itraconazole as a sole agent in the treatment of Microsporum canis in cats.

80 healthy cats 8-9 weeks old were recruited for the study and found to be free of overt clinical disease. The cats were infected with a known strain of M canis on a 3cm area of skin over the flank and allowed to incubate for 4 weeks, during which routine care and feeding were provided.

Cats with a positive fungal culture and Wood’s lamp exam, positive microscopy, and visible skin lesions at the end of the 4 weeks were randomized to a treatment or placebo group. The treatment group received 5mg/kg itraconazole every 24 hours by mouth for 7 days, then spent a week with no medications. This was alternated for three cycles. Placebo cats received an equal volume of sterile water. Groups were blinded to observers.

General health was observed daily and blood analysis was performed at baseline and two points during the study. Fungal cultures were collected weekly during the treatment period, and cats were scored visually and with a Wood’s lamp at each collection point. Clinical cure was based on exam findings, and mycological cure was defined as two consecutive negative fungal cultures.

During the study, treatment cats experienced higher rates of vomiting and diarrhea, as well as several biochemical changes. These bloodwork changes were judged to be clinically insignificant.

Cats treated with itraconazole experienced a statistically higher rate of mycological and clinical cure, and cures occurred more quickly than in the untreated group. By the end of the study, 60% of treated cats attained mycological cure, compared to only 2.5% of placebo cats. The first cats with a negative Wood’s lamp exam were seen at week 1 in the treated cats and week 7 in the control cats.  While this is statistically significant, it is important to note that 40% of treated cats did not experience mycological cure by the end of the study.

This paper demonstrated that oral, pulsed therapy with itraconazole is an effective method for treatment of ringworm infections in cats, though it will not achieve a cure in all animals. This is beneficial information given the difficulty of treating this disease, especially in shelter or high-density population settings. Further work is needed to compare the efficacy of oral-only therapy vs more traditional combinations of topical and oral medications and to investigate the efficacy of itraconazole alone in naturally occurring infections where disease burdens are higher and animals are often immunocompromised. (MRK)