Amantadine is a medication that was initially used as an antiviral agent in humans, but it is gaining popularity for its contribution to chronic pain management in both human and veterinary medicine.
You may wonder why you haven’t heard of this medication before, but unless your dog has suffered from long-standing, severe pain, poorly managed by traditional pain relievers, there’s no reason you would have. Amantadine is generally reserved for these situations.
HOW AMANTADINE WORKS FOR DOGS
Amantadine is an N-Methyl-D-aspartate (NMDA) receptor antagonist. NMDA receptors are heavily involved with the transmission of pain impulses from nerve to nerve, especially in chronic pain situations. When a neurotransmitter attaches to NMDA receptors, pain perception is amplified. When the receptors are blocked by amantadine, the neurotransmitter cannot attach and pain perception is diminished. It’s as simple as that.
Amantadine is not useful for acute (sudden) severe pain, such as pain caused by a broken bone or post-operative pain, because the NMDA receptors are not a big player in these situations. Amantadine actually works best when pain is already present, which is why it is used most frequently in chronic pain situations when additional relief is needed.
Amantadine does not work well as a stand-alone pain reliever. A perfect candidate for amantadine might be a dog suffering from arthritis pain who is already being given a nonsteroidal anti-inflammatory drug (NSAID), gabapentin, joint supplements, and maybe even an opioid pain reliever but still needs more relief.
HOW TO USE AMANTADINE
Amantadine works best when dosed twice a day. It takes a couple of weeks to break the chronic pain cycle, so be sure to give it some time before deciding whether it’s helping or not. Amantadine side effects, if they are going to happen, usually occur early on and typically resolve with time. Possible side effects of amantadine for dogs include agitation, restlessness, flatulence, and diarrhea.
Amantadine is excreted by the kidneys, so caution is recommended when given to dogs with kidney disease. Please note that “caution” doesn’t mean you can’t or shouldn’t use it. It just means you and your veterinarian need to be careful and monitor kidney function. Your veterinarian may prescribe a lower dose out of caution.
There are some important drug interactions to consider. Use of amantadine with antihistamines (such as Benadryl) can exacerbate the anticholinergic effects of both drugs, which include dry mouth (expressed with excessive thirst and excessive lip smacking), difficulty urinating, and rapid heart rate. The same goes for clomipramine (Clomicalm), an anti-anxiety medication.
The use of amantadine with tramadol, a common pain medication for dogs, may increase the risk of seizures. If your dog is already on tramadol, be sure to discuss this risk with your veterinarian before adding amantadine.
Amantadine is frequently used in pain management and palliative care protocols for osteosarcoma (bone cancer), an excruciatingly painful condition in dogs. It is not uncommon for these dogs to receive maximum doses of an NSAID, gabapentin or pregabalin, the powerful opioid oxycodone, and amantadine in an effort to maintain a good quality of life for as long as possible.
Hopefully, as the benefits of amantadine become more widely known, we will see it prescribed more for other common, chronic, painful conditions, such as severe arthritis in aging dogs. Better pain management means happier, healthier, longer-lived dogs.