What the FDA labels say about taking them together
Diltiazem and quinidine
Diltiazem's FDA label of August 7, 2026 names quinidine in its drug interactions section, and quinidine's label names diltiazem too. The diltiazem label: “Diltiazem significantly increases the AUC (0→∞) of quinidine by 51%, T ½ by 36%, and decreases its CL oral by 33%.”
Check it at the source: the diltiazem FDA label on DailyMed (effective August 7, 2026, Bausch Health US, LLC); the quinidine FDA label on DailyMed (effective February 1, 2018, Sun Pharmaceutical Industries, Inc.).
What does the diltiazem label say about quinidine?
Diltiazem label, drug interactionsDiltiazem significantly increases the AUC (0→∞) of quinidine by 51%, T ½ by 36%, and decreases its CL oral by 33%.
Source: FDA drug label (Cardizem Cd, NDA020062), Bausch Health US LLC, effective December 10, 2025 (SPL set 1042fa13-e6af-46b9-8008-6c941f0978b1), via openFDA
Source: FDA drug label (TIAZAC EXTENDED RELEASE), Bausch Health US, LLC, effective August 7, 2026 (SPL set c567fe7e-887e-4291-a0d1-2dd3f25cbf25), via openFDA; the full label on DailyMed
What does the quinidine label say about diltiazem?
Quinidine label, drug interactionsDrug and Diet Interactions Altered pharmacokinetics of quinidine: Diltiazem significantly decreases the clearance and increases the t 1/2 of quinidine, but quinidine does not alter the kinetics of diltiazem.
Quinidine label, warningsThis hazard may be decreased if partial atrioventricular block is achieved prior to initiation of quinidine therapy, using conduction-reducing drugs such as digitalis, verapamil, diltiazem, or a β-receptor blocking agent.
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
| Diltiazem | Quinidine | |
|---|---|---|
| Labeled for | High blood pressure, Angina, Atrial fibrillation | Atrial fibrillation |
| Boxed warning | No | Yes |
| Pharmacy cost (NADAC) | $0.144 per capsule 24h ER(cd) 120 mg capsule | $4.92 per tablet 324 mg tablet |
| Shortage now | A presentation being discontinued | 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