As a hospital pharmacist, you will get questions about which medications or combos can "tip the balance" and lead to problems with QT prolongation. Many commonly used medications can prolong the QT interval. But it rarely leads to torsades and sudden death in low-risk patients on one QT drug.
Watch for the highest-risk patients, where torsades is more likely. This includes patients with a history of QT prolongation, bradycardia, acute MI, low ejection fraction, etc. Also look for hypokalemia, hypomagnesemia, especially with new diuretic use, vomiting, etc. Females are also at higher risk due to a longer QT at baseline.
Stay alert for medications known to prolong the QT (see table 1), especially those also associated with torsades. For example, think of methadone and amiodarone (Cordarone) as red flags, particularly in a high-risk patient. Limit QT risk by using lower doses of some medications, such as no more than 40 mg/day of citalopram (Cipram) or 20 mg/day for patients over age 60.
| Table (1) List of some drugs that can cause QT prolongation. | |
|---|---|
| CLASS | EXAMPLES |
| Antiarrhythmic drugs | Antiarrhythmic drugs
|
| Others |
|
| Antibiotics |
|
| Antifungal | Azole group |
| Antimotility Agents | Cisapride |
| Methadone | |
| Information from, Ther Adv Drug Saf. 2012 Oct; 3(5): 241–253. | |
Continue to watch for quinolones (moxifloxacin, etc), macrolides (clarithromycin, etc), antipsychotics (haloperidol, etc), fluconazole, or ondansetron. Torsades is very rare, but possible in some settings. Try to avoid high-risk combos, such as two or more QT medications, or adding a medication that interacts and increases levels of a QT medication. These situations can create the perfect setting for a "QT storm", such as an elderly woman prescribed ciprofloxacin (Ciprobay) for bacterial gastroenteritis, with hypokalemia, also given ondansetron (Zofran) for vomiting.
Check a baseline ECG and monitor closely if you need to use a risky drug in a high-risk patient. Be aware that the corrected QT can be falsely elevated. If it's higher than expected, use the manually calculated QT for monitoring. Weigh risks of adding a QT-prolonging medication when the baseline QTc is above 450 ms, or especially above 470 ms for men or 480 ms for women. Stop QT-prolonging medications if the QTc rises above 500 ms. These patients are at the highest risk of death when taking a QT-prolonging medication.
REFERENCES
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Schwartz PJ, Woosley RL. Predicting the Unpredictable: Drug-Induced QT Prolongation and Torsades de Pointes. J Am Coll Cardiol. 2016 Apr 5;67(13):1639-1650. Available at: https://www.sciencedirect.com/science/article/pii/S0735109716003387?via%3Dihub#sec6
CredibleMeds. [online] Available at: https://www.crediblemeds.org
Georgia, J.L.T., PharmD Clinical Pharmacist Columbus Regional Healthcare System Columbus , Georgia Ryan R. Crossman, PharmD Pharmacy Practice Resident Columbus Regional Healthcare System Columbus (n.d.). Drug-Induced QT Prolongation. [online] www.uspharmacist.com. Available at: https://www.uspharmacist.com/article/drug-induced-qt-prolongation