AMANTADINE - Mar Vista Animal Medical Center

AMANTADINE

(for veterinary information only)

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. (In other words, one nerve sends a chemical message and the other nerve captures and receives it. This is how nerves communicate with each other). The chemical message may be one of stimulation (increased nerve/muscle activity) or one of inhibition (decreased nerve/muscle activity) depending on the type of chemical and type of nerve. 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 which can bind to neurotransmitters such as aspartate (or more specifically to “N-methyl-D-aspartate”) or glutamate to create the on-going sensation of chronic pain. Even worse, when glutamate or aspartate binds to this receptor, a stimulus which is normally not painful actually becomes painful. In short, stimulation of the NMDA receptor creates pain and shutting that receptor off would be very important in the management of chronic pain.

To put this in more common terms, it is this receptor which 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 present state of the wound yet pain continues. (This latter phenomenon of pain persisting despite healing of the original wound is often termed “wind up.”)

Connection (more technically called a "synapse") between two nerve fibers. Granules containing neurotransmitters are shown as round blue-ish dots.

Connection (more technically called a
"synapse") between two nerve fibers.
Granules containing neurotransmitters
are shown as round blue-ish dots.

(original graphic by marvistavet.com)

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 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 special scrutiny for its potential to cause this phenomenon).

Amantadine can be given with or without food. Amantadine is usually given once or twice daily. If a dose is accidentally skipped, do not double up on the next dose but give the dose when it is remembered and time the next dose accordingly.

SIDE EFFECTS

Mild side effects include agitation, gas or diarrhea when the medication is first started. These should resolve with time. Amantadine also has what are called "anticholinergic effects" which include dry mouth (manifested as increased thirst), urinary retention, increased heart rate. These could be problematic in the presence of other medications with similar effects or certain medical conditions.

INTERACTIONS WITH OTHER DRUGS

Trimethoprim/Sulfa (an antibiotic), quinidine (a heart medication), 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 it is recommended to have caution 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.

Amantadine typically takes 2-3 weeks of use before its effectiveness can be judged.

Short version (to help us comply with "Lizzie's Law")

Page posted: 4/16/2008
Page last updated: 7/28/2022