Calcineurin inhibitors are a class of medications that suppress the immune system by inhibiting the activity of the enzyme calcineurin. This action helps prevent the activation of T-cells, which are crucial for the immune response. They are commonly used in organ transplantation to reduce the risk of rejection and in autoimmune diseases to manage inflammation. Examples of calcineurin inhibitors include cyclosporine and tacrolimus. These drugs are typically administered orally or intravenously and require careful monitoring due to potential side effects, such as kidney damage and increased risk of infections. Regular blood tests are often necessary to ensure safe and effective dosing.