Hydroxyzine, sold under brand names like Vistaril and Atarax, is a prescription first-generation antihistamine widely used for its dual properties as a medication to relieve itching and a mild sedative to treat anxiety and tension. It works by blocking histamine receptors in the body and brain, which produces a calming effect and reduces allergic reactions. Ingesting an excessive amount of this medication can lead to a toxic reaction known as an overdose, which is a serious medical emergency requiring immediate professional intervention.
Factors Determining a Toxic Hydroxyzine Dose
Determining a single, universal toxic dose of hydroxyzine is not possible because the threshold for toxicity varies significantly among individuals. The amount that causes a severe reaction in one person may only cause mild sedation in another, making any precise milligram amount difficult to state definitively. A person’s age is a major factor, as both young children and older adults are particularly vulnerable to lower doses. Children metabolize drugs differently, and the elderly often have reduced organ function, which slows the clearance of the drug from the body.
Pre-existing medical conditions, especially those affecting the liver or kidneys, reduce the body’s ability to process and eliminate hydroxyzine, causing it to accumulate to toxic levels more easily. The drug’s half-life, which is about 20 hours, means that poor clearance can lead to a buildup over time, even without a massive single dose. A person’s body weight and metabolic rate also influence the concentration of the drug within the bloodstream.
Toxicity is significantly increased when hydroxyzine is combined with other substances that affect the central nervous system (CNS). Alcohol, opioids, or benzodiazepines are CNS depressants that, when taken with hydroxyzine, can greatly enhance sedation and respiratory risk. This potentiation means that a dose that would be relatively safe on its own becomes dangerous in combination with these substances. The risk of toxicity is also elevated when hydroxyzine is taken with other medications that affect heart rhythm, such as certain antibiotics or antidepressants.
For adults, the maximum prescribed daily dose can range from 100 mg for pruritus to 400 mg for anxiety, depending on the specific formulation and indication. An overdose is generally suspected when someone has ingested an amount significantly exceeding this maximum prescribed range. However, even doses slightly above the therapeutic range can result in severe adverse effects in susceptible individuals due to variability and drug interactions.
Recognizing the Signs of Hydroxyzine Overdose
Recognizing the signs of hydroxyzine overdose is important because symptoms can range from excessive sedation to severe, life-threatening cardiovascular events. The most immediately noticeable effects involve the central nervous system, beginning with profound drowsiness or lethargy that can quickly progress to stupor or unresponsiveness. Confusion, severe dizziness, and disorientation are common; in more severe cases, agitation, delirium, seizures, and hallucinations may occur. Respiratory depression, characterized by slow or shallow breathing, is a serious complication, especially when other CNS depressants are co-ingested.
Hydroxyzine also possesses anticholinergic properties, meaning it blocks the action of the neurotransmitter acetylcholine, leading to a specific set of physical symptoms. These effects include a severely dry mouth, blurred vision, and difficulty urinating (urinary retention). The skin may become flushed and dry, and the pupils may dilate.
The most concerning signs of hydroxyzine toxicity relate to the cardiovascular system. The drug can cause a rapid heart rate (tachycardia) and heart palpitations. More dangerously, hydroxyzine is known to prolong the QT interval, a measurement on an electrocardiogram (ECG) that reflects the time it takes for the heart’s ventricles to recharge between beats.
Excessive QT prolongation creates a risk for a potentially fatal arrhythmia known as Torsades de Pointes. Severe hypotension (dangerously low blood pressure) can also develop, leading to dizziness, fainting, and the risk of shock if not promptly addressed. Any suspicion of an overdose warrants immediate attention due to the potential for these severe cardiac complications.
Immediate Steps and Medical Intervention
If an overdose of hydroxyzine is suspected, the first step is to call for emergency medical help immediately by dialing 911 or the local emergency number. Simultaneously, contacting the national Poison Control Center at 1-800-222-1222 can provide expert guidance while awaiting emergency responders. The caller should be prepared to provide the patient’s age, weight, the name of the medication, the estimated amount taken, and the time of ingestion.
The priority for medical professionals is to stabilize the patient, which involves maintaining a clear airway and supporting breathing and circulation. There is no specific antidote for hydroxyzine toxicity; therefore, treatment focuses on supportive care and managing the symptoms as they arise. This may include administering intravenous fluids to manage low blood pressure and providing respiratory support if breathing becomes dangerously suppressed.
To reduce the amount of the drug absorbed into the body, activated charcoal may be given, but this is only effective if administered soon after ingestion. Continuous cardiac monitoring with an ECG is a necessary part of the intervention due to the risk of rhythm disturbances. Clinicians closely watch for QT prolongation and will manage this with specific medications if the risk of Torsades de Pointes is high. If vasopressors are needed to raise blood pressure, specific agents like levarterenol or metaraminol are used, as hydroxyzine can interfere with the action of other agents, such as epinephrine.