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THE PET PHARMACY
By Wendy C. Brooks, DVM, DipABVP
Educational Director, VeterinaryPartner.com

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Amantadine

Brand names

Adekin, Amanta, Amantagamma, Amantan, Amantrel, Amixx, Antadine, Antiflu-Des, Atarin, Atenegine, Cerebramed Endantadine, Infectoflu, Influ-A, Lysovir, Mantadine, Mantadix, Mantidan, Padiken, Symadine, Symmetrel, Viroifral and Virucid

Available as 100 mg tablets and oral solution

Background

The nervous system involves millions of branching nerve fibers connecting and communicating with one another. The nerve ending of one fiber releases chemicals called neurotransmitters, which bind to receptors on nearby nerve fibers creating stimulation or inhibition. Different nerve fibers carry different types of signals ultimately sending instructions to muscles or carrying messages of perception.

Amantadine was first used as an antiviral medication against influenza but it is mainly used now for its ability to inhibit something called an NMDA receptor. The NMDA receptor is a nervous system receptor that can bind to neurotransmitters such as aspartate (or more specifically to N-methyl-D-aspartate) or glutamate to create the on-going sensation of pain. Even worse, when glutamate or aspartate binds to this receptor, a stimulus that is normally not painful actually becomes painful. In short, stimulation of the NMDA receptor creates pain and shutting that receptor off would be important in managing chronic pain.

To put this in more common terms, it is this receptor that is involved in the situation where someone who is anxious, stressed, or even angry might be more susceptible to physical pain. Muscle cramps hurt worse, simple irritations are more noticeable. Everything just hurts more when experienced in the context of certain mental states. Another example might be persistent pain that continues long after the original painful wound has healed. There should not be persistent pain if one simply considers the current state of the wound, yet pain continues. (This latter phenomenon of pain persisting despite healing of the original wound is often termed wind up.)

When the NMDA receptor is antagonized or blocked by a medication, such as amantadine, chronic pain may be alleviated. Amantadine alone is not an effective analgesic but when combined with other pain relievers, it adds an extra dimension of pain relief. At this time veterinary experience with this drug is rather limited but it seems to be emerging as a helpful addition to pain relief regimens for dogs and cats.

How this Medication is Used

Typical situations where amantadine might be used:

  • Treatment of arthritis pain.
  • Treatment of neurologic pain (disk disease,etc.)
  • Treatment of pain associated with cancer, especially osteosarcoma.
  • Treatment of chronic pain associated with declaw surgery complications. (Inadequate pain relief after surgery can create the wind up phenomenon described above. The declaw surgery has received scrutiny for its potential to cause this phenomenon.)

Side Effects

Diarrhea, flatulence, and agitation have been described. Humans have reported hallucinations, dizziness, and other forms of mental side effects. Overdose in humans has resulted in heart problems, such as abnormal rhythm and high blood pressure, as well as seizures and respiratory distress.

Interactions with other Drugs

Trimethoprim-sulfa (an antibiotic), quinidine (a heart medication), and thiazide diuretics may decrease the excretion of amantadine, yielding higher blood levels, making amantadine stronger.

Other anticholinergic drugs, such as antihistamines, may enhance the anticholinergic effects of amantadine. These effects include dry mouth (possibly showing as more lip-licking or water consumption), difficulty urinating, increased heart rate.

Other drugs that increase activity/general stimulation may exacerbate the agitation side effect sometimes seen with amantadine. Selegiline, which is frequently used to treat senile cognitive dysfunction, might be an unexpected member of this category of drugs.

Concerns and Cautions

Probably the biggest concern is that this medication is fairly new to veterinary use and a full catalog of what to expect with its use is not yet available. Right now amantadine is growing in popularity for pets and may prove to be an excellent complement to many pain relief regimens.

In human medicine caution is recommended when considering its use in patients with kidney disease, seizure disorders, active psychoses, liver disease, or congestive heart failure. This means that side effects are more likely in these situations.

Amantadine is best used in conjunction with other pain relievers and requires at least a week of use before its effectiveness can be judged.

Amantadine has a narrow therapeutic range, which means accurate dosing is important to avoid toxicity. Use of oral liquid formulations allow for more accurate dosing.

It is our policy not to give dosing information over the Internet.

 

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