Erythromycin ointment cannot cure cat ringworm. Erythromycin ointment is an anti-inflammatory drug, while cat ringworm is a fungal skin disease. The two are not the same. To treat cat ringworm, you need to purchase pet skin medicine and treatment. Fungal Dermatology Spray. During the treatment period, medication must be continued and the cat should be allowed to bask in the sun, so that cat ringworm can heal faster.