What the FDA labels say about taking them together
Clozapine and quinidine
Clozapine's FDA label of June 6, 2025 names quinidine in its drug interactions section; the quinidine label PlainMeds reads does not name clozapine. The clozapine label: “CYP2D6 and CYP3A4 Inhibitors Concomitant treatment with CLOZARIL and CYP2D6 or CYP3A4 inhibitors can increase clozapine levels and lead to adverse reactions.”
Check it at the source: the clozapine FDA label on DailyMed (effective June 6, 2025, HLS Therapeutics (USA), Inc.); the quinidine FDA label on DailyMed (effective February 1, 2018, Sun Pharmaceutical Industries, Inc.).
What does the clozapine label say about quinidine?
Clozapine label, drug interactionsCYP2D6 and CYP3A4 Inhibitors Concomitant treatment with CLOZARIL and CYP2D6 or CYP3A4 inhibitors (e.g., cimetidine, escitalopram, erythromycin, paroxetine, bupropion, fluoxetine, quinidine, duloxetine, terbinafine, or sertraline) can increase clozapine levels and lead to adverse reactions [see Clinical Pharmacology ( 12.3 )].
Clozapine label, warnings and precautionsDrugs that cause QT prolongation include: specific antipsychotics (e.g., ziprasidone, iloperidone, chlorpromazine, thioridazine, mesoridazine, droperidol, pimozide), specific antibiotics (e.g., erythromycin, gatifloxacin, moxifloxacin, sparfloxacin), Class 1A antiarrhythmic medications (e.g., quinidine, procainamide) or Class III antiarrhythmics (e.g., amiodarone, sotalol), and others (e.g., pentamidine, levomethadyl acetate, methadone, halofantrine, mefloquine, dolasetron mesylate, probucol or tacrolimus).
Source: FDA drug label (Versacloz, NDA203479), TruPharma LLC, effective September 6, 2026 (SPL set 2592c9a8-fd74-4e0d-a895-b07b014cf355), via openFDA
Source: FDA drug label (Clozaril), NDA019758 (Heritage Life), as published by HLS Therapeutics (USA), Inc., effective June 6, 2025 (SPL set 90876802-0e3a-44c9-9ff7-1754dfbe736a), via openFDA; the full label on DailyMed
What does the quinidine label say about clozapine?
Quinidine's label (effective February 1, 2018) does not name clozapine in these sections. A label lists what its studies and reports found; it is not a complete list.
Source: FDA drug label (Quinidine Gluconate), Sun Pharmaceutical Industries, Inc., effective February 1, 2018 (SPL set 5023f053-fcc4-4c2c-aa59-9ec198ad185e), via openFDA; the full label on DailyMed
These are the labels' own sentences. PlainMeds does not grade interactions; a pharmacist or prescriber can say what they mean for one person's medicines.
Both medicines on the record
| Clozapine | Quinidine | |
|---|---|---|
| Labeled for | Schizophrenia | Atrial fibrillation |
| Boxed warning | Yes | Yes |
| Pharmacy cost (NADAC) | $0.610 per tablet 100 mg tablet | $4.92 per tablet 324 mg tablet |
| Shortage now | No current entry | No current entry |
Source: FDA NDC Directory, CMS NADAC of October 7, 2026 and the FDA Drug Shortage Database (FDA files October 8, 2026)
What next?
- Check more medicines together
- up to five at once