What Is Quinidine? Uses, Dosage, and What You Need to Know in 2026

Quinidine is one of the oldest medications used to treat abnormal heart rhythms. Derived from the bark of the South American cinchona tree, it has been used in medicine for over a century. While newer antiarrhythmics have largely taken its place as first-line treatment, quinidine still plays a critical role for certain patients — particularly those with rare cardiac conditions or malaria. Here's everything you need to know.

What Type of Drug Is Quinidine?

Quinidine is classified as a Class IA antiarrhythmic — one of the original antiarrhythmic drug classes under the Vaughan Williams classification. It is also an antimalarial agent. Quinidine is available only by prescription and is not a controlled substance.

Quinidine is structurally related to quinine — the old malaria medication you may have heard of — but the two are different drugs with different uses. Quinidine is a stereoisomer of quinine, meaning they share the same atoms but in a slightly different spatial arrangement.

What Is Quinidine Used For?

Quinidine has FDA-approved indications for:

Atrial fibrillation (AFib) and atrial flutter — quinidine can restore normal sinus rhythm and reduce the frequency of relapses

Life-threatening ventricular arrhythmias — quinidine can help prevent dangerous rhythms like ventricular tachycardia and ventricular fibrillation when other treatments have failed

Plasmodium falciparum malaria — oral quinidine treats severe malaria (note: IV quinidine was permanently discontinued in the US in 2019)

Pseudobulbar affect (PBA) — a low dose of quinidine is combined with dextromethorphan in the drug Nuedexta to treat PBA, a condition characterized by involuntary laughing or crying in patients with neurological conditions

Off-label, quinidine is also used for Brugada syndrome, idiopathic ventricular fibrillation, and short QT syndrome — rare but serious cardiac conditions.

What Forms Does Quinidine Come In?

Today, quinidine is only available as an oral generic medication — all brand names have been discontinued. Three tablet forms are available:

Quinidine sulfate 200 mg tablets (immediate-release) — taken every 6 hours

Quinidine sulfate 300 mg tablets (immediate-release) — taken every 6 hours

Quinidine gluconate 324 mg extended-release tablets — taken every 8–12 hours (this is the ER version, branded formerly as Quinaglute)

Note that quinidine sulfate and quinidine gluconate are not interchangeable — they have different potencies and dosing schedules. Always use the formulation your doctor prescribed.

How Should I Take Quinidine?

Take quinidine exactly as prescribed by your doctor. Key instructions:

Take with food to reduce stomach upset

Do not crush or chew extended-release tablets — swallow whole (or break in half if directed, but never crush)

Take at the same times each day for consistent blood levels

Do not skip doses or stop taking quinidine without your doctor's guidance

Avoid large amounts of grapefruit juice — it can raise quinidine blood levels and increase side effects

Is Quinidine Right for Me?

Your cardiologist or electrophysiologist is best placed to answer that question. Quinidine carries an FDA boxed warning about increased risk of death in patients with non-life-threatening arrhythmias — so its use is reserved for patients with serious cardiac conditions where the benefits outweigh the risks. If prescribed appropriately, quinidine can be a highly effective and life-saving medication.

Having Trouble Filling Your Quinidine Prescription?

Finding quinidine in stock can be challenging since it's only available as a generic with limited manufacturers. medfinder calls pharmacies in your area on your behalf to locate which ones can fill your prescription. Read our full guide on how to find quinidine in stock near you.