Guaifenesin

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.

Group

Central muscle relaxant and expectorant

Mechanism of Action

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.

Dose Rates

Dog

Use / stage	Dose	Route	Schedule	Instructions
Expectorant	3–5 mg/kg	PO	Every 8 h
Anesthetic adjunct infusion	Reference only	IV		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.

Indications

Muscle relaxation during induction or maintenance of general anesthesia in horses, usually in combination injectable protocols.
Adjunctive muscle relaxation or restraint during selected procedures in other large-animal species.
Empirical expectorant support in horses with retained respiratory mucus; clinical efficacy evidence is limited.

Contraindications

Do not inject precipitated solution.
Avoid human cough combinations containing unsuitable decongestants or other actives.

Interactions

Anesthetic combinations require adjustment of all components.

Adverse effects

Thrombophlebitis, hypotension and concentration-related hemolysis
Excitement or paddling if used alone for equine induction

Preparations

Preparation	Form	Strength	Route
Guaifenesin immediate-release 100 mg	Tablet	100 mg / tablet	PO
Guaifenesin immediate-release 200 mg	Tablet	200 mg / tablet	PO
Guaifenesin oral liquid 20 mg/mL	Oral Liquid	20 mg / mL	PO
Guaifenesin oral liquid 40 mg/mL	Oral Liquid	40 mg / mL	PO
Guaifenesin sterile 5% solution Prepared sterile solution for anesthesia; inspect for precipitation.	Injection	50 mg / mL	IV

Monitoring and Administration

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.