Antidepressant Toxicosis in Cats

Antidepressants are a group of drugs that are used in human medicine to treat clinical depression and other conditions including OCD, PTSD, and anxiety disorders. Antidepressants are divided into different classes, with the main ones being selective serotonin reuptake inhibitors (SSRIs) and tricyclic antidepressants (TCAs).

Antidepressant toxicosis is a rare and severe condition that requires immediate medical attention. Both SSRI and TCA toxicosis can cause life-threatening Serotonin Syndrome (SS).
Seaking early veterinary attention is crucial in improving the animal’s chances of survival. Early treatment allows for decontamination, or removal of the toxic substance, before it is absorbed and causes symptoms.

Symptoms specific to TCA toxicosis generally occur 30 to 60 minutes from ingestion.

Symptoms specific to SSRI toxicosis include:

• Vomiting
• Vocalization
• Slow heart rate

Serotonin syndrome

Overdoses of both TCA and SSRI antidepressants can cause serotonin syndrome (SS). SS is a potentially fatal condition that occurs as the result of repeated use or ingestion of high doses of antidepressant medication and other serotonergic drugs. Symptoms of SS generally occur one to twelve hours from ingestion.

Antidepressant toxicosis is caused by the ingestion of toxic amounts of antidepressant drugs.

Antidepressants encompass several classes of drugs, including:

Selective serotonin reuptake inhibitors (SSRIs): SSRIs are a class of drugs that inhibit serotonin receptors in the brain. These receptors play a role in aggression, depression, sleep, and agitation reactions. SSRI drugs are prescribed in veterinary medicine to treat a number of conditions including OCD, separation anxiety, excessive itchiness, inappropriate urination and defecation (outside litter box).

Tricyclic antidepressants (TCA): TCAs are rapidly absorbed by the GI tract. Once in the system the tricyclic antidepressants affect the animals cardiovascular, GI, CNS, and renal systems, as well as the eyes.

Overdoses of both TCA and SSRI antidepressants can cause serotonin syndrome (SS).

Veterinary formulations of medications may be compounded into flavored chewables or liquids. This eases daily administration, but can increase the likelihood of an overdose if a pet has unsupervised access to the product.

If the ingestion of antidepressant drugs is witnessed, the diagnosis is self-evident. Ingestion may occur without a witness, but it can leave evidence such as missing pills, bite marks on drug containers, or evidence of medication in vomit.

Cats suspected of having ingested antidepressant drugs generally undergo the following diagnostics:

• Physical examination
• Blood test

If possible, the pill container or a photograph of the label should be presented to the veterinarian, as it can help with diagnosis and assist in the indication of proper treatment options.

Once diagnosed, treatment options depend on the kind of antidepressant ingested, timing of ingestion and severity of symptoms.

If the animal receives medical attention prior to the onset of symptoms, gastrointestinal decontamination may be sufficient. Note: Induction of vomiting or administration of activated charcoal should only be performed by a veterinarian. There is no safe way to induce vomiting or administer activated charcoal at home.

• Emesis: induced vomiting can be useful if treatment is sought no longer than 15 minutes after ingestion
• Gastric lavage: gastric lavage is indicated in cases of ingestion of large doses
• Activated charcoal

Subsequent treatment options include:

• Anti-histamines (Cyproheptadine): Cyproheptadine is a serotonin antagonist medication used to reduce toxicity and control hyperactivity
• Benzodiazepines: administered to control seizures caused by the toxicosis
• IV fluid therapy
• Enema: in the case TCA toxicosis if the animals fails to defecate for 12 hours

With proper treatment, prognosis for SSRI antidepressant toxicosis is generally good, with most animals recovering within 24 hours. Animals diagnosed with mild to moderate TCA toxicosis carry a very good prognosis. If the animal presents seizures or cardiovascular symptoms, prognosis is guarded.

Cats that develop severe symptoms of serotonin syndrome carry a guarded to poor prognosis.

Antidepressant toxicosis is not contagious and easily preventable by ensuring that pets do not ingest antidepressant medication and are not accidentally overdosed. Prevention strategies include:

• Never administering human medicine to pets
• Never administering any kind of medication to pets without prior discussion with a veterinarian
• Keeping antidepressant pills out of reach of pets and children
• Keeping medications in original and tightly closed containers

Cats living in households where humans or other pets are prescribed antidepressant medications are at a higher risk of accidental ingestion. Cats being treated with antidepressant medication are more likely to suffer from inadvertent overdose.

IV fluid therapy Emesis Gastric lavage Activated charcoal Anti-histamines Benzodiazepine