Dextromethorphan and quinidine and Isoniazid interaction
Dextromethorphan and quinidine and Isoniazid: the Dextromethorphan and quinidine prescribing label flags 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
Use with an MAOI or within 14 days of stopping an MAOI.
Allow 14 days after stopping NUEDEXTA before starting an MAOI.
MAOIs NUEDEXTA is contraindicated in patients taking monoamine oxidase inhibitors (MAOIs) or in patients who have taken MAOIs within the preceding 14 days, due to the risk of serious and possibly fatal drug interactions, including serotonin syndrome.
Allow at least 14 days after stopping NUEDEXTA before starting an MAOI [ see Drug Interactions ( 7.1 ) ] .
QT Prolongation: Monitor ECG if concomitant use of drugs that prolong QT interval cannot be avoided or if concomitant CYP3A4 inhibitors used.
Taking more than these two? Interactions stack. Check your whole list at once; it stays in your browser.
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.