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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