Escitalopram × Pimozide

Both drugs prolong the QT interval: escitalopram in a dose-dependent way (escitalopram label), pimozide up to ventricular arrhythmias at therapeutic doses (pimozide label). No study of this exact pair exists. The labels rely on data with racemic citalopram: a single 2 mg dose of pimozide given with citalopram 40 mg once daily increased QTc by a mean of about 10 ms (pimozide label, FDA). The US escitalopram label adds that racemic citalopram increases plasma concentrations of pimozide, a drug with a narrow therapeutic index. There is also a kinetic side: escitalopram inhibits CYP2D6 (escitalopram label), this enzyme partly metabolises pimozide, and the Spanish pimozide label contraindicates CYP2D6 inhibitors (pimozide label).

QT prolongation causes no symptoms and shows only on the ECG. The danger is ventricular arrhythmia, above all torsade de pointes. The escitalopram label reports such cases mainly in women and in patients with hypokalaemia, a pre-existing long QT interval or other heart disease. The pimozide label also reports ventricular tachycardia, ventricular fibrillation and sudden death. Arrhythmia presents as dizziness, palpitations or syncope.

The combination is contraindicated. The Spanish pimozide label names escitalopram in its contraindications (pimozide label, AEMPS). The Spanish escitalopram label bans concomitant use with drugs that prolong the QT interval and names pimozide among the examples (escitalopram label). The US labels of both drugs repeat the ban (escitalopram and pimozide labels, FDA). Do not give escitalopram to a patient on pimozide; if a patient already takes both, stop one of the drugs. The pimozide ban extends to sertraline, paroxetine and citalopram (pimozide label) and to any drug that prolongs the QT interval (pimozide and escitalopram labels). Choose the replacement outside those lists. For any pimozide treatment, take an ECG before the start and repeat it during treatment, correct potassium and magnesium before the start, and stop pimozide if QT or QTc exceeds 500 ms (pimozide label). If signs of arrhythmia appear on escitalopram, stop it and take an ECG (escitalopram label).