Which medications most commonly prolong the QT interval and increase risk of torsades and sudden death?

1. The usual suspects: antiarrhythmics that reliably lengthen QT and carry high TdP risk

Class III antiarrhythmics — particularly sotalol, dofetilide and ibutilide — stand out because their QT‑prolonging effect is predictable and sufficiently frequent that guidelines recommend in‑hospital initiation and monitoring when these agents are started, reflecting a well‑documented risk of TdP at typical doses ^{[2] [7]}.

2. Psychiatric medicines: broad class effects but variable absolute danger

Many antipsychotics and some antidepressants have been associated with QT prolongation; examples with the strongest evidence or regulatory attention include ziprasidone, haloperidol and citalopram/escitalopram, but the degree of risk is heterogeneous and for some drugs (quetiapine, venlafaxine, risperidone) large datasets suggest low TdP incidence despite QT changes ^{[8] [7] [9]}.

3. Anti‑infectives and other noncardiac agents: antibiotics, antifungals, antimalarials and beyond

Macrolide antibiotics such as erythromycin and certain fluoroquinolones have repeatedly been linked to QTc prolongation and case reports of TdP, with erythromycin singled out in several systematic discussions; quinine‑class antimalarials and some antifungals similarly carry risk, while drug‑specific issues (e.g., levofloxacin producing >30 ms QTc shifts in subsets of patients) show that even widely used antimicrobials can be culprits under the right conditions ^{[3] [10] [1]}.

4. High‑risk single agents outside those classes: methadone, arsenic trioxide and others

Methadone has documented associations with QT dispersion and reported cases of TdP, prompting monitoring advice for high doses, and cancer therapy with arsenic trioxide produces marked QT prolongation that has altered clinical practice and surveillance in oncology ^[4].

5. Mechanisms, interactions and patient context that convert prolongation into danger

Most implicated drugs block the hERG (IKr) potassium channel, delaying ventricular repolarization and lengthening QTc, yet not every QT‑prolonging drug produces TdP with the same frequency — amiodarone, for example, often prolongs QT but less commonly triggers TdP, illustrating that mechanism, reverse‑use dependence, pharmacokinetics, and genetic susceptibility all modulate risk ^{[9] [6] [7]}. Co‑prescription of multiple QT‑prolonging drugs, CYP3A4 inhibition that raises serum levels, electrolyte abnormalities (hypokalemia, hypomagnesemia), renal/hepatic impairment, bradycardia, female sex and structural heart disease amplify the chance that QT prolongation will progress to TdP ^{[1] [5] [11]}.

6. Evidence quality, regulatory action and the politics of drug withdrawal

Regulatory responses and the literature reflect both strong signals (market withdrawals of cisapride and some antihistamines) and uncertain areas where evidence is mostly case reports or small series; systematic reviews and pharmacovigilance data drive removals or label changes, but the clinical literature also notes gaps — some drugs have robust trial and post‑market data (sotalol, dofetilide, citalopram), whereas for many others quantification of absolute TdP risk remains imprecise ^{[7] [3] [1]}.

7. Practical implications: how clinicians and pharmacists reduce harm

Best practice focuses on avoiding combinations of QT‑prolonging agents when possible, correcting electrolytes, reviewing interacting drugs that raise concentrations, considering baseline and follow‑up ECGs for high‑risk drugs, and involving pharmacists in risk assessment — interventions endorsed in multiple reviews as the realistic path to preventing drug‑induced TdP ^{[5] [11]}.