Does hydroxyzine (an antihistamine) lower heart rate, specifically in cases of tachycardia?

Hydroxyzine's Effect on Heart Rate

Hydroxyzine can cause tachycardia rather than lowering heart rate, and should be used with caution in patients with cardiac concerns due to its potential to prolong QT interval and trigger arrhythmias.

Mechanism and Cardiovascular Effects

Hydroxyzine is a first-generation H1 antihistamine with anticholinergic properties that is commonly used for various conditions including pruritus, anxiety, and as a sedative. Its cardiovascular effects include:

• Primarily associated with tachycardia rather than bradycardia
• Potential to prolong QT interval, especially at higher doses
• Risk of triggering arrhythmias in susceptible individuals

The 2019 AAAAI Mast Cell Disorders Committee guidelines specifically mention that hydroxyzine can reduce tachycardia in patients with mast cell activation syndrome (MCAS) 1. However, this effect is in the context of treating histamine-mediated tachycardia, not as a general heart rate-lowering medication.

Evidence from Case Reports and Studies

There is evidence contradicting the notion that hydroxyzine lowers heart rate:

• A case report documented supraventricular tachycardia in a 9-year-old child taking clinical doses of hydroxyzine for pruritus 2
• Another case report described hydroxyzine-induced Torsade de Pointes in an 82-year-old patient with complete atrioventricular block after receiving just 12.5 mg of hydroxyzine 3
• A study comparing midazolam and hydroxyzine premedication found that hydroxyzine was associated with greater increases in heart rate after intubation 4

Clinical Considerations

When considering hydroxyzine in patients with tachycardia:

1. Assess underlying cause: If tachycardia is histamine-mediated (as in MCAS), hydroxyzine may help reduce heart rate by blocking histamine effects 1

2. Cardiac risk factors: Use with extreme caution in patients with:

   • Pre-existing cardiac disease
   • QT prolongation
   • Bradycardia
   • Electrolyte abnormalities
   • Concomitant QT-prolonging medications

3. Alternative options: For patients with tachycardia requiring management:

   • Beta blockers are first-line agents for inappropriate sinus tachycardia 1
   • Calcium channel blockers like diltiazem or verapamil are alternatives 1
   • Ivabradine may be considered for symptomatic inappropriate sinus tachycardia 1

Safety Concerns

The European Society of Cardiology Task Force on Sudden Cardiac Death notes that some cardiac deaths have been associated with older antihistamines 1. First-generation H1 antihistamines like hydroxyzine have anticholinergic effects that can be associated with cognitive decline, particularly in elderly patients, and there is concern about their use in patients prone to cardiovascular events 1.

Conclusion

For patients with tachycardia, hydroxyzine should not be considered a heart rate-lowering medication except in specific cases where the tachycardia is histamine-mediated. In most clinical scenarios, standard rate-control agents like beta blockers or calcium channel blockers would be more appropriate choices for managing tachycardia.