Methadone

What is this medication for?

• Analgesia, drowsiness, anesthetic adjunct

How is it given?

Give exactly as your veterinarian prescribed — never change the dose or stop on your own unless your veterinarian has told you to.

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

• Panting, drowsiness, defecation, constipation, unusually slow heart rate (Common, generally milder than morphine)
• Less excitation/vomiting than other mu-agonists (Comparatively favorable profile)
• CNS excitement at into a vein ≥0.1 mg/kg (Dose-related)

Worth a phone call to your veterinarian

• Any new symptom that worries you.

⚠️ 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: Hypersensitivity
• has or has had: Heart failure, high blood pressure, head injury/↑ICP, geriatric/debilitated patients

• is pregnant, nursing, or used for breeding
• is taking any other medications, supplements, or flea/tick products, including:
  • Chloramphenicol
  • Alpha-2 agonists (medetomidine, xylazine)
  • MAO inhibitors (amitraz, selegiline)
  • Azole antifungals, macrolides
  • SSRIs
  • Class I/III antiarrhythmics, calcium channel blockers

Storage and handling

Room temperature, protect from light. Schedule II. Incompatible with pentobarbital, phenobarbital, amobarbital, or thiopental in same syringe.

Good to know

• Causes less histamine release, drowsiness, and vomiting than morphine — often preferred where available.
• Oral bioavailability in dogs is too poor for oral dosing; buccal route is a cat-specific option, not a dog one.