CriticalSSRI (selective serotonin reuptake inhibitor)×Synthetic opioid, full mu-receptor agonist
Updated · Methodology
Mechanism
Methadone prolongs QT, and its SmPC ties torsade mainly to doses above 100 mg a day. The same label warns about serotonin syndrome with SSRIs. The citalopram SmPC lists ongoing treatment with any drug capable of prolonging the QT interval among its contraindications, with no exceptions.
Symptoms
QTc prolongation on ECG, palpitations, dizziness, syncope, with torsade at the far end. Serotonin syndrome is tracked separately: agitation, confusion, tremor, myoclonus, sweating, hyperthermia. Arrhythmia risk is higher with hypokalaemia, hypomagnesaemia and bradycardia.
Management
The pair sits in the citalopram SmPC contraindications, so the question is which drug stays, not how far to cut the dose. Opioid substitution is not interrupted for an antidepressant, so the question is settled on the antidepressant side. If the pair is already running, an ECG with QTc is taken before the start and at every methadone dose increase, with potassium and magnesium kept normal.
Check the full regimen, not just this pair
Opens the checker with these two drugs prefilled. Add the rest of the regimen and recompute additive risks.
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Sources
- FDA: Methadone hydrochloride tablet (Vistapharm, LLC) – Prescribing Information – QT prolongation and CYP interactions (2014)– FDA Dolophine label, Boxed Warning – QT prolongation, serious cardiac arrhythmias; DailyMed setid c54baaee-8ea4-45f5-a5c8-bb84cf86832f
- AEMPS: Ficha técnica de Metasedin 5 mg (metadona) (2026)– AEMPS CIMA, nregistro 17129, revisión 05/2026, secciones 4.4 y 4.5
- AEMPS: Ficha técnica de Seropram 30 mg (citalopram) (2024)– AEMPS CIMA, nregistro 63564, revisión 01/2024, secciones 4.2, 4.3 y 4.4