Immunosuppressive Drugs: What’s NEW?
By: Dr. Jamie Etish, DVM, DACVIM
Board-Certified Internal Medicine Specialist
Veterinary Specialty & Emergency Center
Unfortunately, immune-mediated diseases are all too common in veterinary medicine. Today, there are many new medications that have shown promise in the treatment of these conditions. These medications include Leflunomide, Mycophenolate Mofetil and intravenous Immunoglobulin.
Leflunomide is an immunosuppressant drug that has been used in human medicine for years and is becoming more popular in veterinary medicine more recently. The drug inhibits pyrimidine synthesis in the S phase of the lymphocyte cell cycle. This action reduces production of T and B cells, decreases production of immunoglobulins, and interferes with leukocyte adhesion. The activity of the drug is focused on lymphocytes because non-lymphoid cells are able to synthesize pyrimidine through alternate pathways. Leflunomide can be used as an initial therapy (most often in combination with prednisone) for the treatment of immune mediated polyarthritis (IMPA). It may also be used for treatment of immune-mediated thrombocytopenia (ITP) or immune-mediated hemolytic anemia (IMHA).
The recommended starting dosages in dogs are 2-4 mg/kg once a day. In cats, we use 2 mg/kg once a day as the initial dose.
Potential side effects include decreased appetite, vomiting, and diarrhea. A cutaneous, ulcerative drug eruption can also be seen with this drug, which should resolve if leflunomide therapy is discontinued. Liver enzyme elevations may be seen in some patients. These are typically reversed with dose reduction or discontinuation of the medication. Additionally, decreases in leukocytes, red blood cells, and platelets can be seen. Monitoring of CBCs on a monthly basis is recommended.
Another new immunosuppressant is Mycophenolate Mofetil.
This drug inhibits purine biosynthesis in lymphocytes. This inhibits antibody formation by B cells and inhibits cell-mediated responses by T cells. Mycophenolate may be used in the treatment of immune mediated hemolytic anemia and thrombocytopenia, polyarthropathies, glomerulonephropathies, and possibly autoimmune skin disease. Mycophenolate may cause gastrointestinal side effects, which consist mostly of anorexia and diarrhea. Dose reductions may help to decrease side effects. The recommended starting dose is approximately 10-15mg/kg BID. This drug is absorbed better on an empty stomach.
Intravenous immunoglobulin (IVIG) is a fractionated sample of human plasma that contains primarily IgG. The mechanisms of action include: Fc receptor blockade on phagocytes which decreases phagocytosis by mononuclear cells, interference with complement-mediated damage, increase in anti-inflammatory cytokines, increase in clearance of IgG, and modulation of B and T cell function. IVIG has been used in treatment of IMHA and ITP in dogs.
Previous studies have shown improved platelet recovery time and duration of hospitalization when a single injection of IVIG is given in patients with ITP.
IVIG can be quite an expensive drug, however, so use of this drug may be limited in certain cases. Side effects of IVIG may include an increased risk of thromboembolism, facial swelling, and pruritus. This medication should be given under close hospital supervision given the possible side effects.
Despite the many different treatment options that are now available, immune-mediated diseases are often quite difficult to treat, and appropriate medications should be chosen based on individual patient needs. If you have any questions about immune-related diseases, and possible treatments, please feel free to contact the VSEC Internal Medicine service at any time.
Dr. Jamie Etish is a Board-Certified Internal Medicine Specialist at the Veterinary Specialty & Emergency Center. The Veterinary Specialty & Emergency Center operates state-of the-art emergency and specialty veterinary hospitals that are open 24/7/365 in both Levittown PA and Philadelphia PA. For more information about our world-class emergency and specialty care, please visit VSEC on the web at www.VSECVET.com.