Hydroxyzine is a prescription, first-generation antihistamine (piperazine class) known by brand names like Atarax and Vistaril. It is prescribed for its effects on the central nervous system. The medication crosses the blood-brain barrier, allowing it to relieve symptoms by interfering with the body’s natural chemical messengers.
Primary Uses of Hydroxyzine
The medication’s utility is based on its strong antihistamine and depressant properties.
Anxiolytic
One primary role is acting as an anxiolytic, managing anxiety and tension associated with psychoneuroses or generalized anxiety disorder. This calming effect stems from its ability to depress activity in certain subcortical regions of the central nervous system.
Sedation
A second main application is for sedation, often utilized to calm patients before medical procedures or as a short-term aid for sleep. The drug’s sedative action results from its potent blockade of histamine H1 receptors in the brain, reducing the activity of histamine, a neurotransmitter that promotes wakefulness.
Pruritus Treatment
The third significant use is treating pruritus, or severe itching, typically caused by allergic conditions like hives, eczema, or contact dermatitis. Hydroxyzine prevents histamine from binding to H1 receptors on peripheral cells, mitigating allergic response symptoms.
How Hydroxyzine Affects the Heart Rate
Whether hydroxyzine lowers the heart rate is nuanced, relating more to its secondary and indirect effects. The drug’s primary action is to induce sedation and relaxation, which often results in a mild, indirect slowing of the heart rate, known as bradycardia. This effect is not a direct action on the heart muscle but rather a reflection of the reduced physiological stress and anxiety in the patient.
A reduction in anxiety leads to a decrease in sympathetic nervous system activity, which in turn can lower the overall heart rate and blood pressure. This mild heart rate slowing is generally dose-dependent and typically occurs within the normal therapeutic range as the patient becomes more relaxed. This indirect mechanism contrasts sharply with dedicated cardiac medications, such as beta-blockers, which slow the heart rate through direct action on specific cardiac receptors.
Hydroxyzine can also cause a mild hypotensive effect, or a slight drop in blood pressure. When blood pressure drops, the body’s baroreceptor reflex usually triggers a compensatory increase in heart rate to maintain adequate circulation. However, because of the medication’s central depressant effects, this compensatory increase is often blunted, contributing to the overall calming profile.
While mild heart rate slowing is a common indirect effect, hydroxyzine is not a primary medication for treating high heart rate conditions. In some cases, the drug’s weak anticholinergic activity can paradoxically lead to a slight increase in heart rate (tachycardia). Significant or dangerous heart rate reduction is rare when the drug is taken as prescribed.
Recognizing Serious Cardiac Side Effects
While mild heart rate changes are common, a serious, though rare, cardiovascular risk associated with hydroxyzine is QTc interval prolongation. The QTc interval represents the time it takes for the heart’s ventricles to electrically recharge between beats, and its prolongation indicates a delay in this critical cycle. An excessively long QTc interval can destabilize the heart’s electrical rhythm.
This delay can lead to a specific, life-threatening heart rhythm disorder called Torsades de Pointes (TdP), which is a rapid, irregular ventricular tachycardia. The mechanism involves hydroxyzine’s ability to inhibit the hERG potassium channels in the heart, which are responsible for the electrical repolarization phase. This risk is primarily associated with high doses or in patients who already have specific risk factors.
Several factors significantly increase the chance of this serious side effect:
- A pre-existing history of heart disease, uncompensated heart failure, or a history of congenital long QT syndrome.
- Electrolyte imbalances, particularly low levels of potassium (hypokalemia) or magnesium (hypomagnesemia), also heighten the susceptibility to QTc prolongation.
- The most common factor that increases risk is a drug-drug interaction with other medications that also prolong the QT interval.
These include certain antiarrhythmic drugs like amiodarone or quinidine, specific antibiotics such as azithromycin, and certain antifungal medications. Using hydroxyzine concurrently with these agents can push the heart’s repolarization delay into a dangerous range.
Patients must seek immediate medical attention if they experience symptoms that may indicate a serious heart rhythm issue. These symptoms include severe dizziness, fainting or syncope, sudden shortness of breath, or noticeable palpitations. These signs warrant an immediate medical evaluation to assess the heart’s electrical activity.