Guaifenesin, also called glyceryl guaiacolate, is a centrally acting muscle relaxant used mainly as an adjunct to large-animal anesthesia. It is particularly familiar in equine injectable anesthetic combinations. Oral preparations also have an empirical expectorant role, but that respiratory application has much weaker evidence than its anesthetic use.
Guaifenesin depresses transmission through central interneuronal pathways involved in motor activity, reducing skeletal-muscle tone and facilitating relaxation during anesthesia. Its exact molecular target is incompletely defined. For the separate oral expectorant application, proposed reflex effects increase the volume or hydration of respiratory secretions and support mucociliary clearance, but this mechanism has not been established clinically in veterinary patients.
2.2 mL/kg/hour of a 5% solution, equivalent to 110 mg/kg/hour, administered with an alpha agonist and ketamine in a complete anesthesia protocol.
Cat
Use / stage
Dose
Route
Schedule
Instructions
Expectorant
3–5 mg/kg
PO
Every 8 h
Horse
Use / stage
Dose
Route
Schedule
Instructions
Anesthetic muscle relaxation
110 mg/kg
IV
Equivalent to 2.2 mL/kg of 5% solution before other anesthetic agents.
Muscle relaxation infusion
110 mg/kg/hour
IV
Continuous
Equivalent to 2.2 mL/kg/hour of 5% solution; use with a complete anesthetic plan.
Propofol induction combination
Reference only
IV
Guaifenesin 90 mg/kg over 3 minutes followed by propofol 3 mg/kg IV.
Triple-drip anesthesia
Reference only
IV
One liter of 5% guaifenesin in dextrose combined with xylazine 500 mg and ketamine 2 g: induction 1.1 mL/kg, then 2–4 mL/kg/hour. Final compounded volume and all component delivery rates must be checked. Another source description uses ketamine 1–2 g and 2 mL/kg/hour; keep protocols distinct.
Expectorant
3.5 mg/kg
PO
Every 12 h
Powder mixed with water; clinical evidence is limited.
Sheep
Use / stage
Dose
Route
Schedule
Instructions
Combined injectable anesthesia
Reference only
IV
One protocol combines 1,000 mL of 5% guaifenesin with ketamine 1,000 mg and optional xylazine up to 100 mg; induction approximately 2.2 mL/kg and maintenance approximately 2.2 mL/kg/hour, titrated to effect. Another combines 500 mL of 5% guaifenesin, ketamine 500 mg and xylazine 50 mg, giving 2–4 mL/kg to induction then slowing to maintain anesthesia. Added drug volumes affect final concentration; monitor ventilation and infusion closely.
Goat
Use / stage
Dose
Route
Schedule
Instructions
Combined injectable anesthesia
Reference only
IV
One protocol combines 1,000 mL of 5% guaifenesin with ketamine 1,000 mg and optional xylazine up to 100 mg; induction approximately 2.2 mL/kg and maintenance approximately 2.2 mL/kg/hour, titrated to effect. Another combines 500 mL of 5% guaifenesin, ketamine 500 mg and xylazine 50 mg, giving 2–4 mL/kg to induction then slowing to maintain anesthesia. Added drug volumes affect final concentration; monitor ventilation and infusion closely.
Llama
Use / stage
Dose
Route
Schedule
Instructions
Combined injectable anesthesia
Reference only
IV
Described mixture: 1,000 mL of 5% guaifenesin with ketamine 1,000 mg and optional xylazine 200 mg. Induction approximately 2.2 mL/kg, followed by approximately 2.2 mL/kg/hour titrated to effect. Account for final compounded volume and monitor respiratory and cardiovascular function.
Alpaca
Use / stage
Dose
Route
Schedule
Instructions
Combined injectable anesthesia
Reference only
IV
Described mixture: 1,000 mL of 5% guaifenesin with ketamine 1,000 mg and optional xylazine 200 mg. Induction approximately 2.2 mL/kg, followed by approximately 2.2 mL/kg/hour titrated to effect. Account for final compounded volume and monitor respiratory and cardiovascular function.
Monitor ECG, blood pressure, respiration and anesthetic depth. Guaifenesin provides muscle relaxation and must be part of an adequate anesthetic/analgesic plan.
For a 5% IV solution, prepare 50 g in a final 1 L using an appropriate sterile process. Inspect for precipitation; cool temperatures can reduce solubility.
Expectorant efficacy in animals is not established.
