Guaifenesin (GG)

What is this medication for?

• Muscle relaxation adjunct for induction/maintenance anesthesia (with α2 + ketamine); field anesthesia rescue for "too light/too tense"
• Expectorant (mucolytic-lite) in cough formulas

How is it given?

This medication is normally given by your veterinary team (in clinic or hospital).

What if I miss a dose?

• Give it as soon as you remember — unless it is almost time for the next dose (then skip the missed one; never double up).
• Call your clinic if you miss more than one dose in a row.

Side effects — what should I watch for?

Effects listed as common in this handout

• Mild low blood pressure + ↑HR (Usual-dose physiology)
• Thrombophlebitis / perivascular reaction (into a vein-discipline related)
• Hemolysis (>5% in ruminants) (Concentration error)

Worth a phone call to your veterinarian

• Apnea at overdose (toxic: dog 415–830 mg/kg — hypothermia/tremors/wobbliness/unsteadiness) (Massive overdose)

⚠️ Contact your veterinarian or an emergency clinic IMMEDIATELY if you notice

• Trouble breathing, collapse, seizures, severe vomiting or diarrhea, facial swelling, or pale gums

Before starting (or refilling), tell your veterinarian if your pet:

• has or has had: Physostigmine co-use (manufacturer — the listed contraindication)
• has or has had: Ruminant 5% ceiling; not a solo anesthetic (relaxation ≠ sleep ≠ analgesia)

• is pregnant, nursing, or used for breeding
• is taking any other medications, supplements, or flea/tick products, including:
  • Physostigmine
  • Ketamine/α2 (deliberate)
  • Other depressants

Storage and handling

Thrombophlebitis with into a vein + perivascular tissue reaction — clean catheter, avoid extravasation; 5%-rule for ruminants.

Good to know

• "Triple drip" is the drug's identity: GG + ketamine + xylazine (or detomidine) = field anesthesia for horses where inhalant machines don't exist — GG contributes ONLY relaxation.
• The 5%-ruminant hemolysis rule and the physostigmine contraindication are the two quirky must-knows.
• The Jekyll-Hyde molecule: same drug is an OTC human expectorant (Mucinex) and an into a vein anesthetic adjunct — route and dose define the drug.