Guaifenesin
Glyceryl guaiacolate
Also known as: Guailaxin · Mucinex · Robitussin · Humibid · Organidin NR · Liquibid · Anhist · Hist-EQ · Glyceryl guaiacolate · GG · Glycerylguayacolum · Guaiacol glycerol ether · Guaiacyl glyceryl ether · Guaifenesina · Guaifenesinum · Guaiphenesin · Guajacolum glycerolatum
Reviewed by the VetSheet Veterinary TeamUpdated Apr 5, 2026Evidence-based veterinary reference
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Dosing by species
🌎 NA — North America🌍 EU — Europe
Dogs
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Muscle relaxation during certain toxicoses (e.g., strychnine) or tetanus | 110 mg/kg | IV | As needed | — | 🌎 NA |
| Chemical restraint for ventilatory support | Combination of guaifenesin 50 mg/mL, ketamine 1 mg/mL, and xylazine 0.25 mg/mL; give 0.55 mL bolus initially followed by 2.2 mL/kg/hr thereafter | IV | CRI | — | 🌎 NA |
Small Mammals
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Camelids: Using 'GKX' for induction/maintenance | Induce with 2.2 mL/kg IV. Maintain with approximately 2.2 mL/kg/hr IV | IV | CRI | — | 🌎 NA |
- Camelids: Using 'GKX' for induction/maintenance: Mix 1000 mL of 5% (50 mg/mL) guaifenesin with 1000 mg of ketamine ± 200 mg of xylazine.
Horses
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| General anesthesia adjunct | 110 mg/kg | IV | Once | — | 🌎 NA |
| Muscle relaxation in balanced anesthesia | A CRI of ketamine at 0.8-2.3 mg/kg/hr with guaifenesin at 18-60 mg/kg/hr | IV | CRI | — | 🌎 NA |
| Muscle relaxation in balanced anesthesia (alternative) | A CRI of ketamine 1 mg/kg/hr with medetomidine at 0.00125 mg/kg/hr and guaifenesin at 25 mg/kg/hr | IV | CRI | — | 🌎 NA |
| Augment muscle relaxation in field anesthesia | Approximately 25-50 mg/kg (250-500 mL of a 5% solution) | IV | Once | — | 🌎 NA |
| Long-term IV (>30 minutes) anesthesia using 'GKX' or 'triple drip' | Typically the CRI runs at 1.5-2.2 mL/kg/hr depending on the procedure, patient response and ketamine concentration | IV | CRI | — | 🌎 NA |
| Long-term IV anesthesia using 'GKD' | The CRI runs at 0.8 mL/kg/hr for the first hour and 0.6 mL/kg/hour for the final 30 minutes | IV | CRI | — | 🌎 NA |
| Equine intravenous anesthesia (normal healthy patients) | Generally a total dose of 30-50 mg/kg | IV | Rapid infusion | — | 🌎 NA |
| Equine intravenous anesthesia (compromised patients) | Generally a total dose of 30-50 mg/kg | IV | Slow administration | — | 🌎 NA |
| Adjunctive symptomatic treatment of strychnine poisoning | 110 mg/kg | IV | Repeated as necessary | — | 🌎 NA |
- General anesthesia adjunct: Give first 1/3-1/2 of dose until horse falls gently, then give remainder unless respiratory or cardiovascular effects are observed.
- Muscle relaxation in balanced anesthesia: May reduce MAC requirements by 50%.
- Muscle relaxation in balanced anesthesia (alternative): May reduce MAC requirements by 50%.
- Augment muscle relaxation in field anesthesia: For horses that are too light or too tense after alpha-2 agonist + ketamine ± diazepam induction.
- Long-term IV (>30 minutes) anesthesia using 'GKX' or 'triple drip': Guaifenesin (50 mg/mL), ketamine (1-2 mg/mL), and xylazine (0.5 mg/mL).
- Long-term IV anesthesia using 'GKD': Guaifenesin (100 mg/mL), ketamine (4 mg/mL), and detomidine (0.04 mg/mL).
- Equine intravenous anesthesia (normal healthy patients): Administered after xylazine sedation, followed by ketamine.
- Equine intravenous anesthesia (compromised patients): Administered after modest xylazine dose, followed by reduced ketamine dose.
Cattle
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| General | 55-110 mg/kg | IV | Once | — | 🌎 NA |
Sheep
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Using 'GKX' for induction/maintenance | Induce with 2.2 mL/kg IV. Maintain with approximately 2.2 mL/kg/hr IV | IV | CRI | — | 🌎 NA |
| Using 'GKX' | Administer at a rate of 2-4 mL/kg | IV | Once then slowed | — | 🌎 NA |
- Using 'GKX' for induction/maintenance: Mix 1000 mL of 5% (50 mg/mL) guaifenesin with 1000 mg of ketamine ± 0-100 mg of xylazine.
- Using 'GKX': Given rapidly until animal is recumbent and then slowed to maintain desired anesthesia plane.
Goats
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Using 'GKX' for induction/maintenance | Induce with 2.2 mL/kg IV. Maintain with approximately 2.2 mL/kg/hr IV | IV | CRI | — | 🌎 NA |
| Using 'GKX' | Administer at a rate of 2-4 mL/kg | IV | Once then slowed | — | 🌎 NA |
- Using 'GKX' for induction/maintenance: Mix 1000 mL of 5% (50 mg/mL) guaifenesin with 1000 mg of ketamine ± 0-100 mg of xylazine.
- Using 'GKX': Given rapidly until animal is recumbent and then slowed to maintain desired anesthesia plane.
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Overview
Guaifenesin (also known as glyceryl guaiacolate or GG) is a dual-purpose pharmacological agent. In veterinary medicine, it is primarily utilized as a parenteral muscle relaxant to facilitate excitement-free induction and recovery during short anesthetic procedures (30-60 minutes), particularly in large animals.
- Anesthetic Adjunct: Provides skeletal muscle relaxation without compromising diaphragmatic function.
- Oral Expectorant: Used in both human and veterinary medicine to manage respiratory conditions by thinning mucus, though definitive proof of clinical efficacy remains debated.
Clinical Pearl: Guaifenesin is not an anesthetic on its own; it potentiates the activity of preanesthetic and anesthetic agents and must be used in balanced protocols (e.g., "Triple Drip" or GKX). It possesses mild intrinsic analgesic and sedative qualities.
Mechanism of action
- Muscle Relaxation: Acts centrally by depressing or blocking nerve impulse transmission at the internuncial neuron level of the subcortical areas of the brain, brainstem, and spinal cord → selective relaxation of skeletal muscles (including laryngeal and pharyngeal muscles, easing intubation) while sparing respiratory muscles.
- Expectorant Action: Believed to stimulate gastric vagal receptors → triggers efferent parasympathetic reflexes → increases respiratory tract fluid volume and decreases mucus viscosity → facilitates removal of secretions via ciliary action and coughing.
Safety & warnings
Contraindications
- Concurrent use with physostigmine
- Concentrations greater than 5% in ruminants (due to hemolysis risk)
Adverse effects
- Mild hypotensive effect
- Increase in cardiac rate
- Thrombophlebitis (IV administration)
- Perivascular tissue reaction
- Hemolysis (especially in ruminants with >5% solutions)
- Increased gastrointestinal motility
Precautions
Warning: Avoid giving ruminants concentrations of guaifenesin greater than 5% as hemolysis can occur.
- Use of physostigmine is contraindicated.
- May cause transient mild decreases in blood pressure and increases in cardiac rate.
- Perivascular administration may cause tissue reaction; thrombophlebitis has been reported after IV injection.
- Availability of the injectable form is currently an issue; compounding may be required.
Drug interactions
Contraindicated in horses receiving guaifenesin; exact interaction mechanism not elucidated by manufacturer.
Theoretically contraindicated based on the physostigmine interaction.
Monitoring
- Level of muscle relaxation
- Cardiac rate
- Respiratory rate
Pharmacokinetics
Half-life
Absorption
Rapid following IV administration. Recumbency usually occurs within 2 minutes and light restraint persists for about 6 minutes. Muscle relaxation persists for 10-20 minutes after a single dose.
Distribution
Reportedly crosses the placenta, but adverse effects in newborns have not been described.
Metabolism
Conjugated in the liver.
Elimination
Excreted into the urine.
Overdose
- Margin of Safety: Reportedly 3 times the usual dose.
- Clinical Signs: Apneustic breathing, nystagmus, hypotension, and contradictory muscle rigidity are associated with toxic levels.
- Toxicity Reports: In dogs receiving 415-830 mg/kg, signs included hypothermia, mild tremors, ataxia, and vomiting. In cats receiving 132 mg/kg, signs included lethargy and anorexia.
- Treatment: No specific antidote is available. Treatment is entirely supportive until the drug is cleared to sub-toxic levels.
Available products
Formulations
- Injection
- Oral tablets
- Oral granules
- Syrup/Liquid
- Oral powder
Veterinary
- Guaifenesin Injection 50 mg/mL in 500 mL & 1000 mL (Availability may be limited; compounding often required)
- Anhist® Powder (with pyrilamine)
- Hist-EQ® Powder (with pyrilamine)
- Spect-Aid® (with potassium iodide, ammonium chloride)
- Spec-Tuss® (with potassium iodide, ammonium chloride)
Human-labeled
- Guaifenesin Oral Tablets: 200 mg, 400 mg, 600 mg, 1200 mg (Organidin NR®, Liquibid®, Mucinex®, Humibid®)
- Guaifenesin Oral Granules: 50 mg/packet, 100 mg/packet (Mucinex® Mini-Melts)
- Guaifenesin Syrup/Liquid: 100 mg/5mL, 200 mg/5mL (Robitussin®, Mucinex for Kids®, Diabetic Tussin®)
Regulatory status
No regulatory data for: 🇺🇸 US · 🇪🇺 EU · 🇬🇧 UK · 🇭🇰 HK · 🇹🇼 TW · 🇯🇵 JP · 🇰🇷 KR · 🇦🇺 AU
Storage & stability
Stable in light and heat (less than melting point). Store in well-closed containers. Aqueous solutions may precipitate at temperatures <22°C (72°F); slight warming and agitation generally resolubilizes the drug. Fresh preparation is recommended, though a 10% solution in sterile water may be stored at room temperature for up to one week.
Client information
- Anesthesia Use: When used for surgery, this medication is given intravenously by the veterinary team to help your animal relax and recover smoothly from anesthesia.
- Oral Cough/Respiratory Use: If prescribed as an oral expectorant, ensure your pet has access to plenty of fresh water, as hydration is crucial for thinning respiratory secretions.
- Side Effects: Generally very safe when used as directed. Watch for mild lethargy or gastrointestinal upset (like vomiting in dogs) if given orally.
Note: Do not give human over-the-counter cough medications to your pet without explicit veterinary approval, as they often contain toxic additives (like xylitol or decongestants).
VetSheet drug reference is intended for licensed veterinary professionals as a clinical decision-support aid, not a substitute for professional judgement or the manufacturer’s current label.