Dextromethorphan and quinidine and Nefazodone interaction
Dextromethorphan and quinidine and Nefazodone: both prescribing labels flag this combination with the strongest language, such as a contraindication, a boxed warning, or an instruction to avoid it.
Do not combine without a prescriber's guidance. The label language below is the strongest FDA uses.
What the FDA labels say
From the Dextromethorphan and quinidine (Nuedexta) label · effective 2026-01-22
QT Prolongation: Monitor ECG if concomitant use of drugs that prolong QT interval cannot be avoided or if concomitant CYP3A4 inhibitors used.
Serotonin syndrome: Use of NUEDEXTA with selective serotonin reuptake inhibitor (SSRIs) or tricyclic antidepressants increases the risk.
Serotonin Syndrome When used with SSRIs (such as fluoxetine) or tricyclic antidepressants (such as clomipramine and imipramine), NUEDEXTA may cause "serotonin syndrome", with changes including altered mental status, hypertension, restlessness, myoclonus, hyperthermia, hyperreflexia, diaphoresis, shivering, and tremor [ see Drug Interactions ( 7.4 ), Overdosage…
SSRIs and Tricyclic Antidepressants Use of NUEDEXTA with SSRIs or tricyclic antidepressants increases the risk of 'serotonin syndrome' [ see Warnings and Precautions ( 5.6 ) ] .
This includes patients concomitantly taking/initiating drugs that prolong the QT interval or that are strong or moderate CYP3A4 inhibitors, and patients with left ventricular hypertrophy (LVH) or left ventricular dysfunction (LVD).
From the Nefazodone (Nefazodone Hydrochloride) label · effective 2025-07-31
…nefazodone and its major metabolites are not altered in these “poor metabolizers.” Plasma concentrations of one minor metabolite (mCPP) are increased in this population; the adjustment of nefazodone dosage is not required when administered to “poor metabolizers.” Nefazodone and its metabolites have been shown in vitro to be extremely weak inhibitors of CYP2D6.
Such individuals are referred to commonly as “poor metabolizers” of drugs such as debrisoquin, dextromethorphan, and the tricyclic antidepressants.
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Open in the checkerNot medical advice. Interaction Checker quotes FDA label text and NIH fact sheets. Whether an interaction matters for you depends on doses, timing, kidney and liver function, and other conditions. Confirm with a pharmacist or prescriber.