Imidazoline Poisoning in Dogs

Medications containing imidazoline work as a vasoconstrictor in the nose and eyes to help symptoms of congestion due to allergies, colds, or sinusitis; it is even found in the common eye drop known as Visine.  Since these medications can be purchased over the counter, many people do not realize how dangerous they are, not to us but to their dogs.

Imidazoline is found in nasal decongestants and in topical ophthalmic over the counter medications for humans.  If you believe your pet ingested a medicine of this type, it is considered a medical emergency and you need to contact your veterinarian immediately.

The amount of imidazoline your dog ingested will determine the severity of the symptoms and how quickly they manifest.  Symptoms include:

• Vomiting
• Ataxia
• Panting
• Loud breathing sounds
• Shaking
• Hyperactivity
• Nervousness
• Weakness
• Depression
• Gastrointestinal upset
• Agitation
• Lethargy
• Change in blood pressure
• Decreased heart rate (life-threateningly low)
• Abnormal cardiac rhythms
• Death

Symptoms may appear anywhere between 30 minutes to several hours after ingestion.  This medication is absorbed rapidly and you need to seek veterinary attention as soon as possible.  Imidazoline receptors control a lot in the body, hence why so many serious side effects. 

Types

Imidazoline comes in many forms: liquid, solid, and as an aerosol type solution.  These medications can go in the eye, be sprayed up the nose, or taken orally.  The ones that get sprayed up the nose are pretty obvious, but there are less well known ones you have to watch out for too, such as any medication with a decongestant component.

Imidazoline is the component in decongestants that makes many medications so dangerous.  It causes the body to have a response like it would to any other antihistamine but stronger leading to the symptoms listed above.  Be sure to carefully check the medication labels to see if imidazoline is a component.

Your veterinarian will begin with a physical exam to get the basic vitals of your pet.  From there, depending on the symptoms your pet is showing, your veterinarian may want to do blood work.  This will allow her to get an idea of how the internal organs are functioning.  A complete blood count (CBC) and chemistry panel will give them a good broad understanding of what is going on internally.  If your dog’s heart rate and rhythm are being affected by the imidazoline, your dog will be put on monitoring equipment to keep a close eye on the rate and an ECG may be ordered to determine what type of arrhythmia your dog is suffering from.  Whenever possible, bring the bottle of the ingested medication with you so the veterinarian will know exactly what toxin they are dealing with and will know what treatments to begin immediately.

Trying to get your dog to vomit is pointless since imidazoline is too quickly absorbed and might actually do more harm than good.  If your pet is not showing any symptoms of toxicity yet, the veterinarian may give activated charcoal to prevent the absorption of the medication.  Your dog will then be put on fluids to correct any metabolic abnormality and to treat and/or prevent dehydration.  Depending on how the heart is doing, if needed, medications to help heart rate may be administered.  In addition to this, supportive medications to control the shaking and nervousness may or may not be given. Yohimbine can also be administered to cancel out the effect of the antihistamine; it may need to be administered multiple times due to it having a shorter half-life than the imidazoline.  Your dog will need to stay with the veterinarian until all signs of toxicity have disappeared and lab work comes back normal.

Toxicity of imidazoline can be moderate to severe; you need to seek immediate medical attention for your dog if they have gotten into this product.  With proper medical treatment initiated as soon as possible after ingestion, it will increase your pet’s prognosis for a good recovery.  If you wait too long, the outcome is guarded, especially if the heart rate drops too low and isn’t corrected immediately.  Even if you aren’t sure your pet ingested any of the medication but think they may have, contact your veterinarian anyway.  The best way to prevent toxicities from developing in your pet is to keep all of your medications out of their reach; keep them in an area high enough they cannot reach when they are standing on their hind legs.  Many pets are good at getting into things when owners aren’t looking, while they are at work, or running errands.  Prevention of the problem is always better than reaction in toxicity cases.