People and their pets are taking more and more antidepressants. These drugs are not benign.
Many drugs can lead to an excess of serotonin in your pet, which can be toxic. This is known as serotonin syndrome.
Serotonin syndrome refers to the multiple and varied signs caused by excess serotonin, either at a therapeutic dose if your pet has an adverse reaction to a drug or at toxic doses.
Drugs and Supplements to Monitor
The list of drugs that can lead to serotonin syndrome is long, but here are the categories of the culprits that can cause excess serotonin levels.
1. SSRI and SNRI antidepressants and MAOIs
These medications are now frequently prescribed for pets, but because so many people are taking them, many animals get into their humans’ meds. Keep them out of your pet’s reach. And remember, child-proof caps do not mean puppy-proof vials. Prozac, Zoloft and Wellbutrin are just a few of the drugs in this category.
2. Veterinary medications prescribed for behavioral modification:
- Mirtazapine (used for appetite stimulation)
3. Over-the-counter (OTC) supplements
- St. John’s wort (Hypericum perforatum)
Just because you bought a supplement without a prescription does not mean it is benign. If your pet was prescribed fluoxetine, for example, and they got into your bottle of St. John’s wort, the combination could induce serotonin syndrome.
4. Miscellaneous drugs
Many drugs, particularly in combination with another drug, can cause SS. Here are just a few:
5. TCAs (tricyclic antidepressants), atypical antipsychotics and illegal drugs
As with all medications, keep any psychiatric and illegal drugs away from pets.
Vets are frequently presented with the family pet who got into their human’s medications or found a teenager’s stash of “recreational” drugs. Once we know the dog is going to be OK, there’s always an element of comedy in these embarrassing family scenarios.
But if the dog is already taking a serotonin-enhancing drug for a problem such as separation anxiety, eating an ounce of the marijuana he found hidden under the porch can put him in more danger than if he just ate the pot by itself. And his teenage buddy will have some explaining to do to Mom.
Be aware that:
- Following the veterinarian’s orders is very important when it comes to these drugs.
- Never give your pet your own medications.
- Do not combine drugs without checking with your vet first.
- Do not give supplements, OTC drugs or previously prescribed drugs to a pet taking an SSRI before checking with your vet first.
Clinical Signs of Serotonin Syndrome
SS can affect multiple body systems. As with all toxicities, the size of the pet, the amount of the drug ingested and individual patient parameters all play a role in the severity of the clinical signs.
At low doses, mild gastrointestinal (GI) and central nervous system (CNS) signs are most common. At higher doses, GI upset, more serious CNS signs and cardiopulmonary signs can occur. Untreated SS can cause death if the heart and the brain are severely affected.
- GI: Nausea, hyper-salivation, vomiting/diarrhea and abdominal pain.
- Nervous system: Signs can vary from sedation and lethargy to hyperexcitability. A pet can be agitated, aggressive, ataxic, exhibit tremors, have seizures or go into a coma.
- Cardiovascular: Fast or slow heart rate, cardiac arrhythmias and high blood pressure.
High fever and changes in respiratory rate can also occur.
As with most toxicities, treatment is supportive rather than specific.
Knowledge of what the pet has ingested and how long ago it was ingested is of great help but isn’t always known. Call your vet if you think there has been accidental ingestion. Don not induce vomiting without calling your vet or poison control center first.
If you know the pet ingested too much of a prescribed drug or the wrong medication and is asymptomatic, it may be safe to monitor them at home after checking with your vet or poison control.
If your pet is symptomatic, they should be admitted to a veterinary hospital. Clinical signs can change abruptly. Intravenous fluids for support, injectable medications, controlling high fevers and controlling neurological signs are all part of the treatment.
Diagnosis and Prevention
There are no simple lab tests to diagnose SS. The pet’s history and clinical signs are the best we have to go on. Toxicology testing of urine or stomach contents is not easily available, timely or practical in most situations.
- Vets should prescribe these drugs carefully and warn their clients of possible side effects. Never be afraid to ask questions if you don’t think something has been explained fully.
- Tell your vet about all supplements and other drugs you are giving your pet.
- Don’t mix medicines without checking it out first. Tramadol, for example, a drug used commonly for pain, or mirtazapine, an appetite stimulant, may have been prescribed for your pet in the past. But if they have now been prescribed an SSRI (like fluoxetine), it is not a good idea to give leftover Tramadol.
- Keep medications out of pet’s reach. If you have a family member who may be on multiple drugs and/or is living with depression or mental instability, make sure the medications are not left out. This occurs all too frequently.
Accidents can happen. Vets sometimes have clients who simply mix up medications or double dose by mistake. If you make the phone call to your veterinarian as soon as you realize the problem, you have the best chance of a happy outcome. This is one scenario where time truly is of the essence.
- Almgren, Colleen M., DVM, PhD, et al. “Serotonin Syndrome.” Clinician’s Brief 11, no. 10 (October 2013).