Do lorazepam and diazepam cause QT (QT interval) prolongation?

Do Lorazepam and Diazepam Cause QT Prolongation?

No, lorazepam and diazepam do not cause QT prolongation and are considered safe from a cardiac arrhythmia perspective. Both benzodiazepines are classified as "Class A" drugs without any risk of QT prolongation or Torsades de Pointes according to European Heart Journal guidelines 1.

Evidence for Benzodiazepine Safety

Lorazepam

• The European Society of Cardiology specifically recommends lorazepam as a safe option for patients at risk of QT prolongation 1
• Lorazepam is notably absent from comprehensive lists of QT-prolonging medications in major cardiology guidelines from both the European Heart Journal and Circulation 1
• ECG monitoring is not specifically required when administering lorazepam alone 1

Diazepam

• Benzodiazepines including diazepam are classified as "Class A" drugs, considered to be without any risk of QT prolongation or Torsades de Pointes 1
• While in vitro studies have shown both inhibition and activation of potassium currents during benzodiazepine exposure, no changes in QT duration have been reported in clinical use 1

Contradictory Evidence Requiring Clarification

One multicenter observational study from 2016 found diazepam associated with QTc prolongation at univariate analysis, but this association did not remain significant after multivariate analysis 2. This suggests the initial finding was likely due to confounding factors rather than a true causal relationship. The guideline-level evidence from the European Heart Journal clearly classifies benzodiazepines as Class A drugs without QT risk, which takes precedence over this single observational study 1.

A separate large study of 1017 schizophrenia patients explicitly found that benzodiazepines did not prolong the QTc interval 3.

Clinical Context: Medications That DO Cause QT Prolongation

For comparison, medications that genuinely cause QT prolongation include:

High-risk antipsychotics:

• Thioridazine: 25-30ms prolongation with FDA black box warning 1, 4
• Ziprasidone: 5-22ms prolongation 1, 4
• Haloperidol: 7ms prolongation (higher with IV administration) 1, 4

Moderate-risk antipsychotics:

• Quetiapine: 6ms prolongation 1, 4
• Clozapine: 8-10ms prolongation 4

Antidepressants:

• Tricyclic antidepressants increase cardiac arrest risk (OR=1.69) 1
• Citalopram has FDA warnings about QT prolongation 1

Practical Recommendations

• Lorazepam and diazepam can be safely used in patients with QT concerns or those taking other QT-prolonging medications 1
• When combining lorazepam with medications known to prolong QT (such as haloperidol), ECG monitoring may be warranted due to the other medication, not the benzodiazepine 1
• Consider lorazepam as a safer alternative to QT-prolonging medications like haloperidol in patients at risk 1

Common Pitfalls to Avoid

• Do not confuse benzodiazepines with other psychotropic medications that do carry QT risk, particularly antipsychotics and tricyclic antidepressants 1
• Do not assume all psychiatric medications carry the same cardiac risk profile 5
• Remember that multiple QT-prolonging medications can have additive effects, but benzodiazepines do not contribute to this risk 5