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Corticotrophin (ACTH) Gel Injection for Veterinary Use
by Barbara Forney, VMD
Adrenocorticotrophic hormone (ACTH) is a pituitary hormone that stimulates the production and secretion of glucocorticoids by the adrenal gland. The release of ACTH is stimulated by corticotrophin releasing factor and controlled by a negative feedback pathway in response either to endogenous or exogenous corticosteroids.
Dogs and Cats
ACTH is used primarily in dogs and cats for diagnostic testing of hypo- and hyper-adrenocorticism. This test measures cortisol response to exogenous ACTH. The degree of response may help differentiate between primary and secondary hypoadrenocorticism and in cases of suspected hyperadrenocorticism this test may be used to differentiate between iatrogenic and spontaneous causation. ACTH stimulation testing also is used to monitor the response to Trilostane therapy in animals with pituitary dependent hyperadrenocorticism.
Additional information regarding interpretation and protocols for ACTH stimulation testing may be found in many standard veterinary references including the Saunders Manual of Small-Animal Practice
, Current Veterinary Therapy XII
and Plumb's Veterinary Drug Handbook
. One of the published protocols for dogs is a plasma or serum sample before and a second sample two hours after an intramuscular injection of 2.2Units/kg of ACTH gel. A similar protocol for cats is a plasma or serum sample before, at one hour and at two hours following an intramuscular injection of 2.2 Units/kg of ACTH gel. There are other published protocols and reference material should be consulted for interpretation information.
There are no specific circumstances when ACTH is indicated in horses. It is used as a means of stimulating endogenous corticosteroid release.
Corticotrophin (ACTH) Side Effects
When used for testing, ACTH is unlikely to cause significant side effects or toxicity. If used in a long term or daily fashion exogenous ACTH could produce side effects similar to overuse of corticosteroids.
- ACTH gel injection should not be administered IV.
- ACTH will not reverse the effect of long term suppression of the adrenal gland due to overuse of exogenous corticosteroids.
- Fluid and electrolyte disturbances may occur with prolonged use. Some manufacturers recommend potassium supplementation in these circumstances.
- ACTH should not be used in pregnant animals unless the benefits outweigh the potential risks to the fetus.
- Usually this drug is used short term for diagnostic purposes but chronic use of ACTH may result in drug interactions. If a longer course of treatment is contemplated, the following drugs may be involved in drug interactions: ulcerogenic drugs such as NSAIDs, potassium depleting diuretics such as furosemide, barbiturates, phenytoin, rifampin, cyclophosphamide, estrogens and oral anticoagulants.
- Diabetic animals receiving glucocorticoid therapy may undergo a change in their insulin requirements.
A single overdose such as may occur in a testing situation is unlikely to cause significant toxicity. Long term overuse of ACTH may result in toxicity similar to overuse/abuse of corticosteroids.
About the Author
Dr. Barbara Forney is a veterinary practitioner in Chester County, Pennsylvania. She has a master's degree in animal science from the University of Delaware and graduated from the University of Pennsylvania School of Veterinary Medicine in 1982.
She began to develop her interest in client education and medical writing in 1997. Recent publications include portions of The Pill Book Guide to Medication for Your Dog and Cat, and most recently Understanding Equine Medications published by the Bloodhorse.
You can purchase books by Dr. Forney at www.exclusivelyequine.com
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