Hydroxyzine is a widely prescribed, first-generation antihistamine used to manage anxiety, treat allergic conditions like chronic urticaria, and induce sedation before medical procedures. As a prescription-only drug, it requires a doctor’s authorization due to its potent effects on the central nervous system. Ingesting a quantity significantly greater than the prescribed therapeutic dose can quickly lead to systemic toxicity and a serious medical emergency. Understanding the risks and knowing how to respond to an overdose is important.
Hydroxyzine’s Function and Overdose Definition
Hydroxyzine functions primarily by blocking histamine H1 receptors in the body and the brain, accounting for its anti-allergy and sedative effects. It also possesses considerable anticholinergic properties, interfering with the action of the neurotransmitter acetylcholine. While this combination provides therapeutic benefit, it also contributes to toxicity at high levels. An overdose occurs when a dose overwhelms the body’s ability to metabolize the drug, initiating a toxic cascade.
The toxic threshold is crossed when the drug concentration causes adverse effects in multiple organ systems, particularly the cardiovascular and central nervous systems. Since hydroxyzine must be used under medical guidance, any deviation from the prescribed dosage increases the risk of toxicity. The severity of the overdose relates directly to the amount consumed relative to the patient’s body mass.
Recognizing the Acute Physical Symptoms
Shortly after significant ingestion, initial signs of toxicity often involve the central nervous system (CNS), manifesting as changes in consciousness and behavior. The patient may exhibit profound, rapidly progressing drowsiness, making them difficult to rouse, alongside confusion and disorientation. In more severe cases, excessive CNS stimulation can occur, leading to agitation, restlessness, or visual and auditory hallucinations.
The powerful anticholinergic action also produces a distinct cluster of observable peripheral symptoms. These signs include marked dryness of the mouth and throat, blurred vision, and dilated pupils (mydriasis). The skin may appear flushed or warm to the touch, sometimes with an elevated body temperature. Difficulty urinating, known as urinary retention, is another common sign of peripheral anticholinergic blockade.
The Core Danger: Anticholinergic Toxicity and Cardiac Risk
The observed symptoms are a direct result of the drug’s mechanism of action, which, at toxic levels, triggers a severe anticholinergic crisis. This crisis involves the widespread blockade of muscarinic acetylcholine receptors throughout the body and brain. In the central nervous system, this blockade can rapidly progress from confusion to delirium, seizures, and ultimately, deep coma, posing a risk to respiratory function.
The most life-threatening complication of a hydroxyzine overdose is its cardiotoxicity. Hydroxyzine interferes with the heart’s electrical signaling system by blocking specific potassium channels. This interference leads to a measurable prolongation of the QT interval on an electrocardiogram. A prolonged QT interval destabilizes the heart’s rhythm, which can precipitate a dangerous, rapid, and irregular heart rhythm called Torsades de Pointes.
Torsades de Pointes is a form of ventricular tachycardia that can quickly degenerate into ventricular fibrillation, causing sudden cardiac arrest and death if not immediately treated. This cardiotoxic potential makes hydroxyzine overdose particularly dangerous compared to agents that primarily cause sedation. The risk of these severe cardiac events increases significantly with higher doses and in individuals with pre-existing heart conditions.
Emergency Protocol and Medical Intervention
If an overdose of hydroxyzine is suspected, the immediate priority is to contact emergency medical services or the local Poison Control Center. Providing the emergency operator with the patient’s age, weight, the amount consumed, and the time of ingestion is important for guiding initial care. Do not attempt to induce vomiting, as this practice is ineffective and can be dangerous, potentially leading to aspiration pneumonia.
Upon arrival at a medical facility, the patient will immediately receive supportive care focused on maintaining a stable airway, adequate breathing, and circulation. Continuous cardiac monitoring is instituted to detect any signs of QT prolongation or developing arrhythmias. For patients presenting early after ingestion (typically within one hour), activated charcoal may be administered to bind the remaining drug and prevent further absorption.
Specific interventions target the severe toxic effects. For life-threatening anticholinergic symptoms, such as severe delirium or seizures, the antidote physostigmine may be administered under careful medical supervision. Physostigmine works by temporarily inhibiting the enzyme that breaks down acetylcholine, counteracting the receptor blockade. Detected cardiac arrhythmias, particularly Torsades de Pointes, necessitate immediate treatment with anti-arrhythmic drugs, such as magnesium sulfate, to stabilize the heart’s electrical activity.