Hydroxyzine is a prescription medication used to manage anxiety, treat allergic conditions like chronic hives and itching, and serve as a mild sedative or sleep aid. It belongs to a class of first-generation antihistamines, generally considered safe when taken as directed. Ingesting a dose significantly higher than prescribed constitutes an overdose, which is a serious medical emergency. Hydroxyzine toxicity disrupts normal bodily functions through its powerful effects on the central nervous system and heart, potentially leading to life-threatening complications.
Signs of Hydroxyzine Toxicity
Hydroxyzine overdose manifests across multiple body systems, beginning with severe central nervous system (CNS) depression. Individuals experience profound drowsiness that progresses to stupor and disorientation. Toxic amounts can cause mental disturbances such as agitation, confusion, and visual or auditory hallucinations, a state known as anticholinergic delirium. Severe overdose may lead to uncoordinated movements, seizures, and a dangerously decreased level of consciousness, potentially resulting in coma.
Cardiovascular Effects
Cardiovascular symptoms are a major concern due to the drug’s effect on the heart’s electrical system. The most common sign is a rapid heartbeat, or tachycardia, along with heart palpitations. Hydroxyzine can prolong the QT interval, increasing the risk of a severe, life-threatening irregular heart rhythm called Torsade de Pointes. This cardiac risk is exacerbated by low blood pressure, or hypotension, which can lead to dizziness, fainting, or shock.
Peripheral Symptoms
The drug’s effects on peripheral systems create a classic set of symptoms. These include a severely dry mouth, blurred vision, and dilated pupils. Overdose can also impair the body’s ability to regulate temperature, resulting in flushed skin and fever. Difficulty or inability to urinate, known as urinary retention, may also occur. Any combination of these symptoms, especially severe sedation or changes in heart rhythm, demands immediate medical attention.
The Anticholinergic Mechanism of Action
The severe symptoms of hydroxyzine toxicity are explained by its anticholinergic properties. While hydroxyzine is primarily an antihistamine blocking histamine H1 receptors, its structure also allows it to block muscarinic acetylcholine receptors throughout the body and brain. Acetylcholine is a neurotransmitter regulating essential functions, including muscle contraction, glandular secretions, and cognitive processes.
Overdose causes excessive blockade of these acetylcholine receptors, leading directly to the classic signs of toxicity. For example, blocking receptors in the salivary glands causes dry mouth, and blockade in the eyes leads to pupil dilation and blurred vision. In the brain, high drug concentration results in the confusion, delirium, and hallucinations characteristic of anticholinergic toxicity. This disruption to the nervous system’s communication pathways causes the systemic breakdown observed during an overdose.
Factors That Increase Overdose Severity
The severity of a hydroxyzine overdose is significantly worsened by co-ingested substances or underlying health issues. Combining hydroxyzine with other central nervous system (CNS) depressants dramatically amplifies sedative effects, increasing the risk of respiratory depression and coma. This includes substances like alcohol, opioids, and benzodiazepines, which compound the sedation already caused by hydroxyzine.
A serious risk factor is co-ingestion with medications known to prolong the QT interval. Hydroxyzine inhibits the heart’s potassium ion channels, so combining it with other QT-prolonging drugs, such as certain antipsychotics or antibiotics, significantly increases the likelihood of a fatal heart arrhythmia. Individuals with pre-existing heart conditions, such as prolonged QT syndrome, heart failure, or electrolyte imbalances, are at a much higher risk for a catastrophic cardiac event, even at lower toxic doses.
Emergency Response and Treatment
If a hydroxyzine overdose is suspected, the immediate step is to contact emergency services or a local poison control center. Obtaining professional help is time-sensitive; do not wait for severe symptoms like loss of consciousness or seizures to begin. When relaying information, provide details about the amount of drug taken, the time of ingestion, and any other substances consumed.
In the hospital setting, treatment focuses on supportive care and stabilizing vital functions. Medical professionals closely monitor heart rhythm using an electrocardiogram (ECG) to watch for QT prolongation or dangerous arrhythmias. Interventions include administering intravenous fluids to manage low blood pressure and using activated charcoal if ingestion occurred recently to prevent further absorption. For severe anticholinergic toxicity, physostigmine may be administered, which temporarily increases acetylcholine levels to counteract the drug’s blocking effects, often reversing delirium and other CNS symptoms.