Guaifenesin for Veterinary Use
by Barbara Forney, VMD
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Overview
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Therapeutic Class
Muscle relaxant
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Species
Horses
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Commonly Prescribed by Vets for:
Muscle relaxation as an adjunct to anesthesia.
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FDA Status
Approved for use in horses.
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Search for Available Dosage Forms
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Basic Information
Guaifenesin is a centrally acting muscle-relaxant that is used as a part of many anesthetic protocols in the horse. Its mechanism of action is not precisely known but the relaxation of skeletal muscles, mild analgesic and mild sedative properties allows for lower doses of other sedatives and anesthetic agents. Guaifenesin is used for induction before inhalation anesthesia, during inhalation anesthesia and with total intravenous anesthesia (TIVA) for short procedures. Guaifenesin has minimal effects on diaphragmatic function and produces relatively little respiratory depression at normal doses. It is used primarily in horses although it has been studied and is used in other domestic species.
Guaifenesin also was called glyceryl guaiacolate, GG and a number of other similar chemical-names. Guaifenesin is compatible with D-5-W and sterile water. It usually is reconstituted before each use. Warming and agitation will help resolubilize the drug, particularly in cold temperatures.
Horses
Guaifenesin is used in veterinary hospitals as a part of the induction protocol for inhalation anesthesia. It commonly is used after sedation with an alpha agonist drug, followed by ketamine. Other drugs including benzodiazepines, butorphanol, thiopental and other barbiturate drugs may be added at the anesthesiologist's discretion. Induction and recovery generally are smooth.
Guaifenesin also is used in the field or in veterinary hospitals for TIVA for procedures lasting less than an hour. Anesthesia is induced using an alpha agonist such as xylazine, detomidine or romifidine followed by ketamine. Guaifenesin (5%) solution is combined with additional alpha agonist and ketamine to create what commonly is called "Triple Drip." This combination is used to prolong anesthesia up to an hour. The degree of muscle relaxation and quality of recovery generally is good with the Triple-Drip protocols. Further information regarding drug concentrations and dose rates may be found in veterinary anesthesia textbooks.
Guaifenesin within a Triple Drip combination also is administered with inhalant anesthesia as a means of reducing the total amount of inhalant used in a given case. This combination of intravenous and inhalant anesthesia is referred to as "balanced anesthesia." Balanced anesthesia has the advantages of less cardiovascular depression, diminished need for additional drugs to support hemodynamics and improved recoveries.
Guaifenesin Side Effects
- Guaifenesin may cause a mild decrease in blood pressure and an increase in heart rate.
- There are conflicting reports regarding hemolysis and reactions of the vascular endothelium with higher concentration solutions of guaifenesin.
Precautions
- ARCI Class 4 drug.
- Guaifenesin has been shown to cross the placenta. Neonatal levels immediately after delivery were about 30% of the level in the mare. TIVA with Triple Drip has been used successfully in field situations for dystocia. Appropriate ventilation and respiratory support for the foal may be necessary.
- Donkeys and to a lesser extent mules may be more sensitive to guaifenesin. Mules are reported to be intermediate between horses and donkeys.
- Perivascular administration will cause tissue reaction. Guaifenesin should be administered using an intravenous catheter.
Drug Interactions
Anticholinesterase drugs such as physostigmine are contraindicated. (Plumb 2005)
Overdose
Guaifenesin is relatively safe. The margin of safety is reported to be three times the normal dose and cardiovascular side-effects are rare. Signs of overdose include apneustic breathing, nystagmus, hypotension and increased muscle-rigidity. Although there is no specific antidote, Guaifenesin has a relatively short half-life (60 to 85 minutes) (Plumb 2005). Supportive treatment should be instituted while the drug is being cleared.
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
The information contained on this site is general in nature and is intended for use as an informational aid. It does not cover all possible uses, actions, precautions, side effects, or interactions of the products shown, nor is the information intended as medical advice or diagnosis for individual health problems or for making an evaluation as to the risks and benefits of using a particular product. You should consult your doctor about diagnosis and treatment of any health problems. Information and statements have not been evaluated by the Food and Drug Administration ("FDA"), nor has the FDA approved the products to diagnose, cure or prevent disease.
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