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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 to either endogenous or exogenous corticosteroids.
ACTH is primarily used 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 is also used to monitor the response to Mitotane therapy in animals with pituitary dependant 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 2 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 1 hour and at 2 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.
• 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.
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 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.
Dr. Forney is an FEI veterinarian and an active member of the AAEP, AVMA, and AMWA.
You can purchase books by Dr. Forney at www.exclusivelyequine.com
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