From the Research
QT Interval Prolongation and Phenergan (Promethazine)
- Phenergan, also known as promethazine, has been studied for its effects on the QT interval corrected for heart rate (QTc) [ 1 ].
- A double-blind, midazolam-controlled study found that promethazine induces significant QTc prolongation [ 1 ].
- The study used Bazett's formula and Fridericia's correction to calculate the QTc interval and found significant prolongation in patients receiving promethazine [ 1 ].
- However, the study also found that promethazine had no significant effect on transmural dispersion of repolarisation, which suggests a low risk of torsadogenic action [ 1 ].
Risk Factors and Management
- QTc prolongation is associated with an increased risk of ventricular tachydysrhythmias, particularly Torsades de Pointes (TdP) [ 2, 3, 4 ].
- Several factors can influence QTc prolongation, including congenital causes, heart rate, metabolic imbalances, and pharmacotherapy [ 2, 3, 4 ].
- Clinicians should be aware of medications that can prolong the QT interval, including antipsychotics and antiemetics, and thoroughly investigate patient history that may contribute to QTc prolongation [ 2, 3 ].
- Close monitoring for QTc prolongation is necessary to prevent TdP, and patients at risk should be educated to seek emergency care if they experience symptoms such as palpitations, lightheadedness, dizziness, or syncope [ 4 ].