What are the common medications that prolong the QT interval?

Common Medications That Prolong the QT Interval

The most common QT-prolonging drugs in clinical practice are antiarrhythmics (sotalol, dofetilide, amiodarone, procainamide), macrolide and fluoroquinolone antibiotics (erythromycin, ciprofloxacin), antipsychotics (haloperidol, ziprasidone), antidepressants (citalopram, escitalopram), antiemetics (ondansetron, droperidol, domperidone), and methadone. 1

Antiarrhythmic Agents

• Class IA antiarrhythmics (quinidine, disopyramide, procainamide) and Class III agents (sotalol, dofetilide, ibutilide, amiodarone) carry the highest risk, precipitating torsades de pointes in approximately 1–10% of treated patients—making this the medication class with the greatest TdP incidence. 1
• Amiodarone and procainamide must be avoided in patients with already prolonged QT intervals, as they exacerbate torsades de pointes risk. 1

Antibiotics

• Macrolides: Erythromycin carries the highest QT risk among macrolides, while azithromycin has the lowest risk within this class. 1
• Fluoroquinolones: All fluoroquinolones retain QT-prolonging potential; ciprofloxacin is specifically identified as high-risk, though it appears to have the lowest TdP rate among fluoroquinolones. 1, 2
• Moxifloxacin carries the greatest risk of QT prolongation among all available quinolones in clinical practice and should be used with extreme caution in patients with predisposing factors. 2
• Safer alternatives: Penicillins and cephalosporins are essentially benign and should replace macrolides/fluoroquinolones when QT prolongation is a concern. 1

Antipsychotics

• Highest-risk agents: Haloperidol (with multiple documented cases of TdP), ziprasidone, iloperidone, amisulpride, thioridazine (withdrawn from market due to severe TdP risk), and chlorpromazine. 1, 3
• Negligible-risk alternatives: Aripiprazole, clozapine, lurasidone, and olanzapine have minimal QT-prolonging potential. 1, 4

Antidepressants

• Highest-risk SSRIs: Citalopram produces the greatest QTc prolongation of any SSRI (FDA/EMA limit maximum dose to 40 mg daily, 20 mg in patients >60 years); escitalopram also causes significant prolongation (maximum 20 mg daily, 10 mg in elderly). 1, 5
• Negligible-risk SSRIs: Sertraline and paroxetine have essentially no QT-prolonging effect and should be used as substitutes when QT is a concern. 1
• Tricyclic antidepressants as a class prolong QTc; amitriptyline and maprotiline are specifically linked to torsades de pointes cases. 5

Antiemetics

• High-risk agents: Ondansetron (prolongs QTc by 7–20 ms even at standard 4 mg doses), droperidol (produces ~17 ms increase at 0.75 mg with FDA black-box warning), and domperidone. 1, 6, 4
• Safe alternatives when QTc ≥500 ms: Aprepitant (NK₁-receptor antagonist), dexamethasone, and low-dose olanzapine (5–10 mg) have no QT-prolonging potential. 4

Opioid Analgesics

• Methadone has well-documented association with TdP and requires baseline ECG plus repeat ECG after each dose adjustment. 1, 7
• Buprenorphine and oxycodone can block HERG channels with much lesser potency than methadone. 7

Other Common Agents

• Antihistamines: Diphenhydramine is not classified as high-risk in major guidelines, though caution is advised in overdose settings. 1
• Antifungals: Fluconazole and ketoconazole prolong QT and can also act as CYP3A4 inhibitors, dramatically elevating plasma levels of other QT-prolonging drugs. 1
• Antimalarials: Chloroquine and hydroxychloroquine are known QT-prolonging agents. 1
• Muscle relaxants: Alcuronium, pancuronium, and atracurium (especially when combined with atropine) significantly prolong QT. 7
• Chemotherapy agents: Anthracyclines, alkylating drugs, and cisplatin are associated with QT prolongation. 7

Risk Amplification Through Drug Interactions

• CYP3A4 inhibitors (ketoconazole, ritonavir, erythromycin) can dramatically increase QT risk by raising plasma concentrations of substrate drugs that prolong QT. 1
• Never combine multiple QT-prolonging agents without checking interactions on crediblemeds.org. 1

Critical Monitoring Thresholds

• QTc ≥500 ms mandates immediate discontinuation of all QT-prolonging drugs and continuous telemetry monitoring. 1
• Baseline ECG is required before starting any QT-prolonging drug when the patient is already receiving another QT-prolonging agent, or when multiple risk factors are present (female sex, age >60 years, structural heart disease, electrolyte disturbances, diuretic use, renal impairment). 1

Electrolyte Cofactors

• Hypokalemia and hypomagnesemia are the most common reversible contributors to drug-induced QT prolongation, especially in patients on diuretics; target potassium >4.5 mmol/L and magnesium >2.0 mg/dL. 1, 8

Practical Resource

• Use crediblemeds.org (website and smartphone app) to identify all QT-prolonging medications before prescribing and to check for drug-drug interactions. 1