Which immunomodulatory drug is widely used in dogs for ADDE/KCS?

• A. Cyclosporine
• B. Tacrolimus
• C. Sirolimus
• D. Pimecrolimus

Answer: (A)

The key idea is that immune-mediated damage to the lacrimal glands drives aqueous-deficient dry eye in dogs, so an immunomodulatory approach that calms T-cell driven inflammation can restore tear production. Cyclosporine is a calcineurin inhibitor chosen for this purpose. It binds to cyclophilin inside T cells and blocks calcineurin, which prevents transcription of interleukin-2 and other cytokines. With T-cell activation suppressed, the inflammatory attack on the lacrimal gland subsides, allowing tear production to improve and the ocular surface to heal. In dogs, topical cyclosporine A is the standard therapy for this condition because it directly targets the immune-mediated component and has robust clinical support for increasing tear production.

Other options also affect T cells but are used less frequently for canine KCS. Tacrolimus is a potent calcineurin inhibitor like cyclosporine but is less commonly employed for this indication in dogs due to formulation availability, cost, and long-term data. Sirolimus and pimecrolimus target related pathways but are not as widely established or studied for canine ADDE/KCS, and thus are not standard choices for this purpose.