Canine NMDA Receptor Blockers

The NMDA receptor blockers belong to a group of anesthetics that inhibit the N methyl d aspartate receptors (NMDAR). The NMDA receptor blockers are used in dogs when anesthesia is needed. These blockers are also effective in reducing coughing. The NMDA receptor blockers cause dissociative anesthesia, which can efficiently eliminate pain.

Types of NMDA Receptors and Blockers

There are a lot of NMDA receptors which are ionotropic receptors which bind to glutamate and glycine and will facilitate the transfer of signals between the brain and the spinal cord. The NMDA receptor blockers will stop the transmission of these signals. The most commonly used NMDA receptor blocker is ketamine, but there are also other NMDA receptor blockers that may be used in dogs:

  • Dextromethrophan
  • Phencyclidine
  • Nitrous oxide

The NMDA receptor antagonists are metabolized in the liver and dogs don’t usually have difficulties metabolizing these drugs. However, if the dog receives NMDA receptors on a regular basis, the liver may not be able to metabolize the drugs and these may stay in the dog’s system, causing toxicity.

The NMDA receptor blockers or antagonists may be divided in:

  • Competitive blockers such as the 2-amino-7-phosphonoheptanoic acid, which block the glutamate, which is a neurotransmitter
  • Glycine antagonists, which block the glycine (i.e. 1-Aminocyclopropanecarboxylic acid or ACPC or 5,7-dichlorokynurenic acid)
  • Uncompetitive channel blockers (i.e. ketamine or Dextromethrophan).
  • Non competitive antagonists such as Cerestat, which  block the ion channel

Ethanol is also an uncompetitive channel blocker, but shouldn’t be applied in dogs as it is toxic and may be fatal if administered in high amounts.

Effects of NMDA Receptor Blockers

The effects of the NMDA receptors will include anesthesia and analgesia. The NMDA receptors are used when the dog requires anesthesia, case in which a higher amount of the drugs are used.

If the NMDA receptors are used as analgesics, these will be administered in lower amounts. The NMDA receptors may be used in conjunction with other pain medication.

Dextromethrophan may be used as a cough suppressant in dogs.

NMDA Receptor Blockers Side Effects

The NMDA receptor blockers may have some side effects such as:

  • Respiratory problems
  • Sedation
  • Depression
  • Hallucinations
  • Lack of coordination
  • Confusion
  • Agitation and aggressiveness
  • Frequent mood swings

These side effects are only temporary and should go away a few days after the administration of the NMDA receptor blockers.

In rare cases, the NMDA receptor blockers can cause brain damage and neurotoxicity. If neurotoxicity occurs, the dog should receive alpha 2 blockers (i.e. clonidine or guanfacine). Other drugs that may be efficient for neurotoxicty caused by NMDA receptor blockers include diazepam, ethanol and serotonin agents.

The vet will establish the best course of action, should any of the above mentioned side effects occur.

If the side effects are severe, the vet will look for alternative drugs that have similar effects on canines.