Which agents are potent QT prolongers and require monitoring for drug interactions and electrolyte disturbances?

• A. Macrolides, fluoroquinolones, and some antipsychotics; monitor QT interval and electrolytes.
• B. Beta blockers and ACE inhibitors; monitor blood pressure.
• C. Tetracyclines and penicillins; monitor liver enzymes.
• D. Metformin and acetaminophen; monitor renal function.

Answer: (A)

Prolongation of the QT interval increases the risk of a dangerous rhythm called torsades de pointes, so certain drugs demand closer watching for interactions and electrolyte changes. Macrolide antibiotics, fluoroquinolone antibiotics, and some antipsychotics have well-established potential to lengthen the QT, especially when other risk factors are present. Because this risk rises when electrolyte levels are off (low potassium or magnesium) or when other QT-prolonging drugs or interactions boost drug exposure, the safest practice is to monitor the QT interval with ECGs and regularly check electrolytes while these meds are active.

Other drug groups listed don’t typically carry the same QT risk profile, and their common monitoring targets differ. Beta blockers and ACE inhibitors are watched for blood pressure and heart rate effects, not QT changes. Tetracyclines and penicillins focus monitoring on organ systems like liver or kidneys but not QT safety. Metformin and acetaminophen are evaluated for renal and hepatic function, respectively, rather than QT.