This memo for prescribers and pharmacy staff has been produced in response to questions from primary care prescribers and pharmacists concerned about seemingly innocuous drug combinations flagged up on prescribing systems. Particular examples are:
- Salbutamol inhaler + clarithromycin
- Senna tablets + citalopram
These combinations have been prescribed uneventfully for many years but computer systems are now flagging them as “high risk alert – risk of torsade de pointes”.
The nature of the interaction is hypokalaemia is a risk factor for torsade de pointes.
Salbutamol is listed in the BNF as causing hypokalaemia (senna was listed in BNF 74 but removed in BNF 75); clarithromycin and citalopram are listed in the BNF as causing QT prolongation.
This memo (published January 2018, updated July 2018) provides further information.
Senior Medicines Information Pharmacist, North West Medicines Information Centre