Dextromethorphan and quinidine and Quinine interaction
Dextromethorphan and quinidine and Quinine: 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 Quinine (QUININE SULFATE) label · effective 2025-10-31
Known hypersensitivity to quinine, mefloquine, or quinidine ( 4 )
…Thrombocytopenia • Idiopathic thrombocytopenia purpura (ITP) and Thrombotic thrombocytopenic purpura (TTP) • Hemolytic uremic syndrome (HUS) • Blackwater fever (acute intravascular hemolysis, hemoglobinuria, and hemoglobinemia) • Known hypersensitivity to mefloquine or quinidine: cross-sensitivity to quinine has been documented [see WARNINGS AND PRECAUTIONS ( 5.6 )].
Quinine sulfate is not recommended for use with other drugs known to cause QT prolongation, including Class IA antiarrhythmic agents (e.g., quinidine, procainamide, disopyramide), and Class III antiarrhythmic agents (e.g., amiodarone, sotalol, dofetilide).
The concurrent use of quinine sulfate with astemizole and other CYP3A4 substrates with QT prolongation potential (e.g., cisapride, terfenadine, halofantrine, pimozide and quinidine ) should also be avoided [see WARNINGS AND PRECAUTIONS ( 5.3 )] .
…disease and preexisting conduction system abnormalities, elderly patients with sick sinus syndrome, patients with atrial fibrillation with slow ventricular response, patients with myocardial ischemia or patients receiving drugs known to prolong the PR interval (e.g. verapamil) or QRS interval (e.g. flecainide or quinidine) [see CLINICAL PHARMACOLOGY ( 12.2 )] .
From the Dextromethorphan and quinidine (Nuedexta) label · effective 2026-01-22
Concomitant use with quinidine, quinine, or mefloquine.
Patients with a history of quinidine, quinine or mefloquine-induced thrombocytopenia, hepatitis, or other hypersensitivity reactions.
Quinidine and Related D rugs NUEDEXTA contains quinidine and should not be used concomitantly with other drugs containing quinidine, quinine, or mefloquine.
Hypersensitivity NUEDEXTA is contraindicated in patients with a history of NUEDEXTA, quinine, mefloquine or quinidine-induced thrombocytopenia, hepatitis, bone marrow depression or lupus-like syndrome.
NUEDEXTA should not be used if immune-mediated thrombocytopenia from structurally related drugs, including quinine and mefloquine is suspected, as cross-sensitivity can occur.
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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.