Reserpine for Veterinary Use
by Barbara Forney, VMD
Reserpine is a naturally occurring drug that has been used for centuries in India. It is extracted from the root of Rauwolfia serpentina
or Rauwolfia vomitoria
plants found in there and in Africa. In traditional herbal medicine, the root was brewed as a tea and used in humans to treat hypertension, insanity, snakebite and cholera. The purified alkaloid, reserpine, was isolated in 1952 and is considered the first modern drug to treat hypertension.
Reserpine irreversibly binds to the storage vesicles of neurotransmitters, particularly norepinephrine, serotonin and dopamine. Eventually, catecholamine depletion occurs because of the body's inability to store these neurotransmitters. It is an unusual drug; it takes many hours or days to reach full effect and continues to have some subtle sedating effects for many days after the last dose.
Reserpine is used as a long-acting tranquilizer in horses. It is used to sedate excitable or difficult horses that are on enforced rest. It sometimes is used illicitly to sedate show horses, sale horses or in other circumstances where a "quieter" horse might be desired. Until relatively recently, reserpine was difficult to test for, but there are now sensitive and accurate tests. Blood testing for reserpine use can be complicated by related herbs and plants found in supplements, pastures and hay, which also can cause a positive drug test. Reserpine once was used in pregnant mares in an attempt to treat fescue toxicosis. Domperidone largely has replaced reserpine for this use.
Reserpine Side Effects
- Different horses vary greatly in their sensitivity to this drug.
- Common side-effects include, colic, gastrointestinal upset and mild diarrhea that may last for days and sweating over the back and hind legs. Signs of sedation include depression, droopy eyes and a dropped penis.
- Reserpine increases gastric secretion in humans and increases the risk of ulcers.
- There is little published information on the clinical use of reserpine in horses. As a consequence, much of the available information is anecdotal and should be considered as such.
- Reserpine causes male horses to drop their penises; penile paralysis in stallions is a possible side-effect.
- Reserpine is a prohibited substance in most sanctioned competition and is a frequent cause of drug violations due to the long and variable withdrawal period. Some herbal products have been implicated in positive tests for reserpine.
- Reserpine may interact with drugs used for general anesthesia.
- Methamphetamine is an antidote to reserpine.
Overdose of reserpine increases the risk and the severity of the above-mentioned side-effects.
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 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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