Can promethazine (Phenergan) cause supraventricular tachycardia (SVT)?

Can Promethazine Cause Supraventricular Tachycardia (SVT)?

Yes, promethazine can potentially cause supraventricular tachycardia (SVT) due to its anticholinergic properties and direct effects on cardiac ion channels, particularly the hERG potassium channels. 1

Mechanism of Promethazine's Cardiac Effects

• Promethazine is a phenothiazine derivative with antihistaminic (H1), sedative, antiemetic, and anticholinergic properties 2
• It directly blocks hERG K+ channels, which can lead to QT prolongation and potentially trigger arrhythmias 1
• The anticholinergic effects of promethazine can cause tachycardia by reducing vagal tone on the heart 2
• Research has demonstrated that promethazine can increase action potential duration in cardiac cells in a concentration-dependent manner 1

Cardiac Risks Associated with Promethazine

• Promethazine has been documented to cause hypotension, which can trigger reflex tachycardia 2
• Case reports have linked promethazine to life-threatening ventricular arrhythmias, including polymorphous ventricular tachycardia and Torsades de Pointes 3
• Phenothiazine derivatives as a class have been associated with various cardiac arrhythmias 4
• The drug can exert its effects on cardiac tissue within 5 minutes of intravenous administration, with effects lasting 4-6 hours 2

Risk Factors for Promethazine-Induced SVT

• Pre-existing cardiac conditions increase the risk of promethazine-induced arrhythmias 3
• Concomitant use with other QT-prolonging medications can enhance arrhythmogenic potential 4
• Electrolyte abnormalities (particularly hypokalemia) may increase the risk of arrhythmias when taking promethazine 3
• Higher doses of promethazine (particularly IV administration) carry greater risk of cardiac effects 2

Management of Promethazine-Induced SVT

If SVT occurs in a patient taking promethazine:

• Discontinue promethazine immediately 3
• For hemodynamically unstable patients: synchronized cardioversion is recommended 2
• For stable patients: vagal maneuvers followed by adenosine are first-line treatments 2
• If adenosine fails, IV beta blockers, diltiazem, or verapamil can be considered in hemodynamically stable patients 2
• Monitor ECG for QT prolongation and other arrhythmias 3

Prevention and Monitoring

• Use caution when prescribing promethazine to patients with known cardiac disease 3
• Consider ECG monitoring when administering promethazine intravenously, particularly at higher doses 3
• Avoid combining promethazine with other medications known to prolong QT interval 4
• Use the lowest effective dose of promethazine, especially in patients with risk factors for arrhythmias 2

Clinical Perspective

While SVT is not the most commonly reported arrhythmia associated with promethazine (ventricular arrhythmias are more frequently documented), the drug's anticholinergic properties and direct cardiac effects provide a plausible mechanism for SVT induction. Clinicians should be aware of this potential adverse effect, especially when administering promethazine to patients with pre-existing cardiac conditions or those taking other medications that affect cardiac conduction.