How to Address QTc Prolongation Drug Interactions

Addressing QTc Prolongation drug interactions has always been a challenging topic for me.  These drug interactions are really hard to know what to do.  Problems arising from these interactions rarely happen, but obviously QTc prolongation can increase the risk of incredibly serious events like Torsades de points.  Here’s a few thoughts on this topic:

  1. Assess the risk of the medication being added, started, or changed.  Amiodarone interactions are very notable and medications that can prolong the QT interval being added to amiodarone should be done in a cautious manner.
  2. In patients at risk of QTc prolongation, are other agents appropriate.  Example: In the situation where we are treating an infection with antibiotic therapy, can we avoid quinolones or macrolides?
  3. Minimize dose and/or duration where possible.  As far as minimizing dose, citalopram is the classic example that has numerous QTc prolongation drug interactions.  Looking at minimizing duration of therapy, antibiotics or ondansetron are two good examples where maybe we can get away with shorter treatment durations.
  4. EKG monitoring.  In patients who have known risk factors and must be on medications that can prolong the QT interval, EKG monitoring is an important tool to minimize the risk of potentially dangerous consequences.
  5. Keep an eye out for electrolyte imbalances.  Magnesium and potassium are two big ones that come to mind when we talk about potential cardiac problems.  Assessing that these levels are within the normal range can be an important factor to reduce the risk of potential problems.
  6. Here’s a list (not all inclusive) of some common medications that will come up as potential drug interactions for QTc prolongation:
    • Antiarrhythmics
      • amiodarone, sotalol, quinidine, procainamide, dofetilide
    • TCA’s
      • amitriptyline, nortriptyline, doxepine, imipramine
    • SSRI’s (particularly citalopram)
    • Antibiotics
      • Quinolones (levofloxacin)
      • Macrolides (erythromycin, clarithromycin) – Reference

Here’s a case scenario with levofloxacin and amiodarone.  What other pearls do you think about when assessing for QTc prolongation drug interactions?

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5 Comments

  1. Stacie

    I never received the free 30 questions

    Reply
    • Eric Christianson

      Hey Stacie, sent you an email – let me know if didn’t get it, thanks! Eric

      Reply
  2. Amanda

    I see you didn’t include azithromycin in the list of macrolides. Is this drug considered a “safer” macrolide in terms of QTc prolongation interactions ?

    Reply
  3. Cole

    QTDrugs.org now known as crediblemeds.org (both links will get you there) are a great reference. True incidence is tough to ascertain and the data on a drug like ondansetron is much stronger with higher oncology doses versus 4 or 8mg in the ED

    Reply
  4. Rachael

    What are your thoughts on antipsychotics and Nuedexta combinations in the elderly?

    Reply

Trackbacks/Pingbacks

  1. QT Prolongation for Community Pharmacists: Quick Guide - Med Ed 101 - […] have stepped up and provided education on topics they are passionate about. I’ve touched on QT prolongation in the…
  2. Levofloxacin Risks - Case Study - Med Ed 101 - […] all the many levofloxacin risks, the first one I would look at in this situation is QTc prolongation. We…

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Written By Eric Christianson

August 23, 2017

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