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Health Canada is sending out a warning about a life-threatening side effect caused by a commonly used antihistamine called hydroxyzine. According to the health agency, patients taking hydroxyzine (Atarax®) are at risk of abnormal heart activity called “QT prolongation”. This type of warning comes after two antihistamines -terfenadine and astemizole- were previously removed from the market in the late 1990’s for causing QT prolongation.

Here are some key points for patients taking hydroxyzine.

About Hydroxyzine

Hydroxyzine has been on the Canadian market since 1956! It belongs to a family of sedating antihistamines that are used for allergic conditions such as swelling, and itching. It can also be used to help manage anxiety and as a sleep aid, thanks to its sedating effects.

In Canada, hydroxyzine is available as capsules, a syrup, and an injection. Its therapeutic effect lasts up to 24 hours, which means you often only need to take a dose once per day at bedtime. However, it can be taken up to four times per day if needed.

The Problem – QT Prolongation

Our heart contractions are coordinated by electrical activity in our heart cells. When this activity is out of sync it can result in dangerous abnormal heart rhythms. Drugs can often impact something called the QT interval, which refers to a specific measurement on the electrocardiogram.

A prolonged QT interval can result in a life-threatening abnormal heart rhythm called torsade de pointes. Signs and symptoms of this abnormal heart rhythm include feeling your heart beat rapidly (palpitations), fainting, dizziness, or sudden cardiac death.

Who is at risk of QT prolongation?

In addition to certain drugs, numerous factors can increase your risk of QT prolongation:

  • Female sex
  • Older age
  • Electrolyte changes (low potassium, low magnesium, low calcium)
  • Drug-drug or drug-herb interactions
  • Heart disease (e.g., heart failure, heart attack)
  • Congenital long-QT syndrome
  • Low thyroid

What Should I Do If I’m Taking Hydroxyzine?

Work with your clinical pharmacist to ensure you are on the lowest effective dose for your specific health condition. Health Canada now states that hydroxyzine should be given for as short a duration as possible, and that doses should not exceed 100 mg per day for adults and 50 mg per day for the elderly.

Make sure you routinely monitor your electrolyte levels and your electrocardiogram, especially if your health changes or you start taking a new medication that prolongs the QT interval.

Potential Drug Interactions

Hydroxyzine’s impact on prolonging QT may be worsened if you are on other drugs that have a similar effect. Some common medications that prolong QT interval include:

  • Antidepressants
  • Antipsychotics
  • Antiarrhythmics
  • Antifungals
  • Antibiotics

It is best that you review your entire medication list with your clinical pharmacist to see if you’re at risk of a severe drug-drug interaction. Not every health professional is capable of a drug interaction review, so speaking to a clinical pharmacist is critical.

Leave a comment below or contact me today if you have questions about hydroxyzine or any of your medications.