Prolongation of the QT interval can lead to a life threatening ventricular arrhythmia known as torsades de pointes which can result in sudden cardiac death.

The risk of torsades de pointes depends on patient factors and current medication. A safe drug in one patient may be potentially harmful in another. The risks and benefits must be determined on a case by case basis.

In general, manufacturers advise that the use of two or more drugs that are associated with QT prolongation should be avoided. Increasing age, female sex, cardiac disease and some metabolic disorders (notably hypokalaemia) predispose to QT prolongation. Prescribers should also use caution when prescribing concurrent drugs that reduce serum potassium.

Print versions of the BNF contain a table with a list of some drugs that prolong the QT interval within Appendix 1, Interactions. The BNF 84 (September 2022 – March 2023) lists the following examples of drugs which prolong the QT interval (note this list is not exhaustive, and not all drugs are included within the Devon Formulary):

The BNF 84 (September 2022 – March 2023) also lists the following drugs that are predicted by the manufacturer to increase the risk of QT prolongation, and therefore concurrent use alongside drugs that prolong the QT interval should be avoided:

Further guidance can also be found on the Specialist Pharmacy Service website; 'Identifying risk factors for developing a long QT interval' is available here, which contains safety concerns, risk factors, medicine risk factors, strategies for risk minimisation, and useful resources.

Individual drug interactions can also be checked using the online BNF, here.