Effects Of Overdosing On Hydroxyzine

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Hydroxyzine is a 'first-generation' antihistamine and is used for a variety of indications, including:

• Symptomatic relief of anxiety and tension.
• Management of pruritus (itching) and chronic urticaria (hives).
• As a mild sedative.

First-generation antihistamines, like hydroxyzine and diphenhydramine (Benadryl) work by blocking H₁ receptors in the body, preventing the binding of histamine.

They also possess relatively strong sedative and anticholinergic properties. For this reason, 'first-generation' antihistamines are often used as mild sedatives and sleep aids.

Can You Overdose On Hydroxyzine?

Like all medications, it is possible to overdose on hydroxyzine.

According to the prescribing information (and toxicology information) for hydroxyzine, the most common potential symptoms of over-dosage include:

• Somnolence
• Pupil dilation
• Flushing
• Fever
• Dry mouth
• Constipation
• Increased heart rate
• Mild hypertension
• Nausea and vomiting

Moderate to severe symptoms include:

• Agitation
• Confusion
• Hallucinations
• Agitated delirium
• Psychosis
• Seizures
• Coma
• Low blood pressure
• Cardiac arrhythmia
• Rhabdomyolysis
• Renal failure

Overdose Care

There is no set standard for care when it comes to hydroxyzine over-dosage.

In most cases, monitoring of vital signs and general supportive care is recommended. According to the prescribing information for the drug:

"If vomiting has not occurred spontaneously, it should be induced. Immediate gastric lavage is also recommended. General supportive care, including frequent monitoring of the vital signs and close observation of the patient, is indicated. Hypotension, though unlikely, may be controlled with intravenous fluids and vasopressors (do not use epinephrine as hydroxyzine counteracts its pressor action.) Caffeine and Sodium Benzoate Injection, USP, may be used to counteract central nervous system depressant effects."

According to the National Institute of Health Toxicology Data Network:

"The majority of antihistamine overdoses requires only supportive care; give activated charcoal if patient presents shortly after ingestion; sedate with benzodiazepines for agitation and delirium. Hypertension and tachycardia are generally mild and well tolerated, and do not require specific treatment."

Are Hydroxyzine Overdoses Lethal?

Reports of a hydroxyzine overdose causing death are extremely rare.

Nevertheless, there are published case reports of hydroxyzine playing a factor in accidental deaths but there are often additional contributing factors, such as concomitant drugs or alcohol.

Animal studies indicate that only extremely high doses of hydroxyzine are associated with lethality.

The LD₅₀ (amount of an ingested substance that kills 50 percent of a test population) in rats has been reported to be 840 mg/kg. In mice, it is reported to be 480 mg/kg. Translating this to a 100-pound human amounts to over 20,000 milligrams!

How Long Do Symptoms Of Overdose Last?

The reported half-life (the time it takes to metabolize and eliminate 50% of a drug from the body) of hydroxyzine is between 14 to 25 hours.

However, the medication has a duration of action of only 4 to 8 hours for most individuals and is therefore dosed 3 to 4 times daily.

Nevertheless, certain effects of hydroxyzine can last significantly longer than 4 to 8 hours. Suppression of our body's inflammatory response and anti-itch effects are known to last up to 3-4 days after a dose of hydroxyzine.

In cases of overdose, how long symptoms last will depend on a variety of factors, including:

• Dose taken
• Age
• Liver function
• Kidney function
• Concomitant medications
• Whether or not medical/supportive care was received

In most reported cases, symptoms of overdose (described above) can be resolved within a few hours after receiving medical care (e.g. administration of a benzodiazepine for seizures/muscle spasms). Other cases report full resolution of symptoms within 72 hours after receiving supportive care.

Final Words

If you suspect an overdose of hydroxyzine, or any medication, it is important to seek medical care or at the very least contact the Poison Control Center at 1-800-222-1222.

In addition, for resources on suicide prevention, you can contact the National Suicide Prevention Lifeline at 1-800-273-8255.

There do not appear to be reports of long-lasting adverse effects after an overdose of hydroxyzine (whether it was accidental or intentional).

In every case, even if emergency care wasn't received, it is important to be evaluated by your doctor. If you believe there are residual symptoms, medical attention should be sought.