Treating ringworm with oral antifungals and frequent bathing with antifungal shampoos is generally adequate to clear all lesions in three to six weeks. However, in some purebreds, there is little or no success in healing the lesions. In resistant cases, ketoconazole is often used but may have questionable side effects.
Generally, long-term administration of griseofulvin combined with antibacterial shampoos is the traditional approach; this practice may have to be continued for years if the cat has no immune system capability. Consider adding one quarter tablet of echinacea daily for a month to your cat's regimen as a possible immune boost. A ringworm vaccine is also available; ask your veterinarian for advice.