Citalopram × Quetiapine

Quetiapine is an atypical antipsychotic, and antipsychotics appear among the QT examples in both SSRI labels. Post-marketing reports describe QT prolongation at therapeutic doses, and the quetiapine SmPC calls for caution with any QT-prolonging drug. The citalopram SmPC lists ongoing treatment with any drug capable of prolonging the QT interval among its contraindications, with no exceptions.

QTc prolongation on ECG, palpitations, dizziness, syncope. The end point is polymorphic ventricular tachycardia of the torsade type progressing to ventricular fibrillation. The risk is higher with hypokalaemia, hypomagnesaemia, bradycardia, decompensated heart failure and in women.

The pair sits in the citalopram SmPC contraindications, so the question is which drug stays, not how far to cut the dose. Quetiapine is often added to an antidepressant in resistant depression, which is exactly why this pair deserves attention up front: the SSRI label files antipsychotics under contraindicated combinations. If the regimen is assembled anyway, an ECG with QTc is taken before the start and two weeks in, with potassium and magnesium kept normal.