Methimazole SpotOn 3x1ml. Prescription required. Methimazole SpotOn provides an accurate and stress-free treatment of hyperthyroidism in cats. Hyperthyroidism can be treated. An advanced new treatment option is now available. This involves the once daily application of a medicated gel that is absorbed through the skin of the ear and can be applied easily and painlessly - without the need to struggle with pills, an accurate and stress-free treatment that your cat won't resent. Action: Methimazole is concentrated in the thyroid and interferes with the production of thyroid hormones.  The transdermal formulation allows absorption through the skin barrier when applied to the inner surface of the ear.