Dextromethorphan and quinidine and Posaconazole interaction
Dextromethorphan and quinidine and Posaconazole: 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 Posaconazole (NOXAFIL) label · effective 2026-02-13
CYP3A4 substrates (pimozide, quinidine): can result in QTc interval prolongation and cases of torsades de pointes (TdP) ( 4.3 , 5.2 , 7.2 )
Concomitant administration of Noxafil with the CYP3A4 substrates, pimozide and quinidine may result in increased plasma concentrations of these drugs, leading to QTc prolongation and cases of torsades de pointes [see Warnings and Precautions (5.2) and Drug Interactions (7.2) ] .
CYP3A4 Substrates that Prolong QTc Interval Mechanism and Clinical Effect(s) Concomitant use of posaconazole with CYP3A4 substrates such as pimozide and quinidine may result in increased plasma concentrations of the CYP3A4 substrates leading to QTc interval prolongation and torsades de pointes [see Warnings and Precautions (5.2) ].
Quinidine HMG-CoA Reductase Inhibitors (Statins) that are CYP3A4 Substrates Mechanism and Clinical Effect(s) Concomitant use of posaconazole with simvastatin increased simvastatin plasma concentrations which can lead to rhabdomyolysis [see Clinical Pharmacology (12.3) ].
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.
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).
Drugs that Prolong QT and Concomitant CYP3A4 Inhibitors Recommend ECG in patients taking drugs with NUEDEXTA that prolong the QT interval and in patients taking concomitant moderate or strong CYP3A4 inhibitors [ see Warnings and Precautions ( 5.3 ) ] .
Strong and moderate CYP3A inhibitors include, but are not limited to, atazanavir, clarithromycin, indinavir, itraconazole, ketoconazole, nefazodone, nelfinavir, ritonavir, saquinavir, telithromycin, amprenavir, aprepitant, diltiazem, erythromycin, fluconazole, fosamprenavir, grapefruit juice, and verapamil.
Digoxin Quinidine is an inhibitor of P-glycoprotein.
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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.