Amantadine HCl

What is this medication for?

• Adjunctive treatment of chronic pain (osteoarthritis, neuropathic pain, osteosarcoma pain, "wind-up") when NSAIDs/opioids alone are insufficient; reduces opioid tolerance
• Antiviral (influenza A) — human label; FDA banned extra-label use in chickens/turkeys/ducks (2006)

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.

• Amantadine is not an analgesic on its own — always pair with an NSAID or opioid. Its value is NMDA blockade: reducing central sensitization/wind-up and opioid tolerance.

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

• Agitation/restlessness, loose stools, flatulence, diarrhea (Mainly early in therapy)
• Anxiety states, dry mouth (Occasional)

Worth a phone call to your veterinarian

• Narrow safety margin (Toxicity appears only at ≥2× doses, but margin described as fairly narrow)

⚠️ 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; untreated angle-closure glaucoma; pregnancy
• has or has had: Renal or hepatic disease (reduce dose), CHF, seizure disorders, psychoses, eczematoid dermatitis — caution until more safety data

• is pregnant, nursing, or used for breeding
• is taking any other medications, supplements, or flea/tick products, including:
  • Selegiline / dopamine-increasing drugs
  • Other CNS stimulants
  • Anticholinergics

Storage and handling

Room temperature. Available as 100 mg capsules/tablets and 10 mg/mL syrup; small-animal doses usually require compounding.

Good to know

• Amantadine is not an analgesic on its own — always pair with an NSAID or opioid. Its value is NMDA blockade: reducing central sensitization/wind-up and opioid tolerance.
• Effect is delayed — give at least a week before judging efficacy.
• Overdoses are potentially very serious in dogs and cats (narrow index) — counsel owners on storage.
• Plumb notes no dog/cat PK studies; Papich gives t½ ~5–6 h — data quality overall is thin, consistent with "adjunct, not primary" positioning.