Immunosuppressive therapy is used to treat immune-mediated, also known as autoimmune, diseases in small animals. These diseases occur when the animal’s immune system fails to differentiate between the body’s own tissues and foreign bodies. Autoimmune diseases cause the immune system to attack the body’s tissues and blood cells. Immunosuppressive therapy, as the name suggests, suppresses the immune system’s reaction. 

While some cases of autoimmune disease can be attributed to a specific cause, roughly 70% of autoimmune diseases are idiopathic, or do not have an identifiable cause. Autoimmune diseases are not fully understood by veterinary professionals. However, certain viral, bacterial, and parasitic infections have been known to cause autoimmune disease, in addition to genetics and certain types of cancer.

Because immunosuppressive drugs are typically administered orally, there is no surgical procedure involved. However, cats diagnosed with IMHA and IMTP may be hospitalized if they are in critical condition. Severe cases of IMHA may require blood transfusion. Idiopathic IMHA is treated with immunosuppressive drugs. For allergic bronchitis and asthma, immunosuppressive drugs may be administered via an inhaler.

The most popular immunosuppressive drugs include, but may not be limited to:

The ultimate aim of treatment is to put the condition into remission. Glucocorticoids are generally the drug of choice for most autoimmune diseases in small animals.

The efficacy of this therapy will depend on the cause of the underlying condition, the efficacy of additional treatments, and the overall health of the cat. However, most cats respond well to immunosuppressive therapy, especially those diagnosed with IMTP. Cats diagnosed with IMHA which is caused by cancer or viral disease do not respond as well to immunosuppressive therapy as cats with idiopathic IMHA or IMHA caused by bacterial infection. Although there are some complications associated with immunosuppressive drugs, this treatment method is less invasive and more cost effective compared to surgery.

The recovery process will vary based on the underlying condition and the recommended treatments. Owners should follow their veterinarian’s recovery instructions carefully. Regular follow-up examinations will be scheduled as needed to evaluate the cat’s condition and determine whether immunosuppressive therapy should continue. If the condition appears to be in remission during any of these appointments, the veterinarian will gradually decrease the dosage of the immunosuppressive drug(s). Following the decrease, the cat will be evaluated again in another three weeks. If the condition is still in remission, the veterinarian will decrease the dosage again. Some cats may no longer require immunosuppressive therapy after the condition is in remission, while others will require lifelong therapy at a low dosage.

The cost of immunosuppressive therapy will vary based on the drug(s) prescribed, the duration of administration, and concurrent treatment methods. The cost of immunosuppressive therapy may range from $30 to $100 or more each month.

Most medications have side effects, and immunosuppressive drugs are no exception. Side effects of immunosuppressive drugs may include, but are not limited to:

However, it should be noted that cats do not tend to suffer from side effects of immunosuppressive therapies compared to dogs. Many of these complications are also treatable. Cats who  experience side effects will be examined by a veterinarian, who will treat the side effect(s) and decide whether or not to continue administering the drug(s). Veterinarians will discuss the side effects of the specific recommended immunosuppressive drug(s) with the owner before any drugs are prescribed.

Because they are not fully understood by veterinary professionals, autoimmune diseases are difficult to prevent. However, some professionals have linked autoimmune disease to environmental pollutants, hormone production, stress, food additives, and vaccines. Owners should feed their cats an appropriate and complete diet, and decrease stress-inducing factors as much as possible. Cats diagnosed and treated for autoimmune disease should not be bred.