Primaquine Drug Interactions: What to Avoid and What to Tell Your Doctor

Primaquine is not a drug you start without a full review of your current medication list. It has one absolute contraindication (quinacrine), several interactions that can increase the risk of dangerous cardiac arrhythmias, and drug interactions that can raise or lower primaquine's blood levels in ways that affect both efficacy and safety. Here's a comprehensive guide to primaquine drug interactions for 2026.

The Absolute Contraindication: Quinacrine

Never take primaquine if you are taking quinacrine (Atabrine). Quinacrine is an older antimalarial and antiprotozoal drug that is occasionally used off-label for conditions like lupus and giardiasis. When combined with primaquine, quinacrine dramatically increases primaquine's blood levels — by potentially more than 3-fold — dramatically amplifying both its effects and its toxicity, including the risk of severe hemolytic anemia. This combination is absolutely contraindicated and should never be used.

Always tell your doctor if you have taken quinacrine in the past 30 days before starting primaquine.

Major Interactions: QTc-Prolonging Medications

Primaquine can prolong the QT interval — a measurement of the heart's electrical cycle. QT prolongation raises the risk of serious cardiac arrhythmias, including torsades de pointes, a potentially life-threatening irregular heartbeat. When primaquine is combined with other drugs that also prolong the QT interval, the risk increases.

Medications with significant QTc-prolonging potential that should be used with caution or avoided with primaquine include:

Antipsychotics: Haloperidol, ziprasidone, thioridazine, pimozide, amisulpride

Antibiotics: Fluoroquinolones (ciprofloxacin, levofloxacin, moxifloxacin), azithromycin, clarithromycin, erythromycin

Antifungals: Fluconazole, itraconazole, ketoconazole

Antiarrhythmics: Amiodarone, sotalol, quinidine, disopyramide

Oncology drugs: Glasdegib, certain tyrosine kinase inhibitors

This is not a complete list. Your doctor should review your full medication list for QTc-prolonging potential before prescribing primaquine. The reference database CredibleMeds (crediblemeds.org) maintains a regularly updated list of drugs with known QTc risk.

Moderate Interactions: CYP3A4 Inhibitors and Inducers

Primaquine is primarily metabolized by the CYP3A4 enzyme in the liver. Drugs that affect CYP3A4 activity can alter primaquine's blood levels:

Strong CYP3A4 inhibitors (increase primaquine levels): Clarithromycin, idelalisib, itraconazole, ketoconazole, ritonavir and other HIV protease inhibitors. These drugs slow the metabolism of primaquine, causing it to accumulate in the blood — raising the risk of side effects including hemolysis.

Strong CYP3A4 inducers (decrease primaquine levels): Apalutamide, carbamazepine, enzalutamide, phenytoin, rifampin, St. John's Wort. These drugs speed up primaquine metabolism, reducing blood levels and potentially reducing efficacy — a concern for anti-relapse therapy.

Food Interaction: Grapefruit Juice

Grapefruit and grapefruit juice are significant CYP3A4 inhibitors. Drinking grapefruit juice while taking primaquine can increase primaquine's blood levels by slowing its breakdown. Avoid grapefruit products for the duration of your primaquine treatment course.

Interactions That Increase Hemolysis Risk

Several drugs share hemolytic potential with primaquine and may increase the risk when combined:

Dapsone: Used for PCP prevention and dermatitis herpetiformis; has independent hemolytic potential in G6PD-deficient patients.

Rasburicase: Contraindicated in G6PD deficiency; concurrent use with primaquine in G6PD-deficient patients amplifies hemolysis risk.

Other oxidant drugs: Nitrofurantoin, certain sulfonamides, and some antimalarials also have oxidant properties. Concurrent use warrants clinical judgment, especially in G6PD-deficient patients.

What to Tell Your Doctor Before Starting Primaquine

When your provider reviews your medication list, make sure you mention:

All prescription medications, including antibiotics, antifungals, HIV medications, and any cardiac medications

All OTC medications, vitamins, and supplements — including St. John's Wort

Any history of quinacrine use in the past 30 days

Any history of heart rhythm problems, including QT prolongation or arrhythmias

For a full review of side effects and serious warnings while taking primaquine, see our primaquine side effects guide. And if you're still looking for a pharmacy that has primaquine in stock, medfinder can help find one near you.