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

Hydroxychloroquine has relatively few drug interactions compared to many other DMARDs — but the interactions it does have range from clinically significant to potentially dangerous. Knowing what to avoid and what information to share with all your healthcare providers can help you stay safe. This guide covers every major interaction category.

The Most Serious Interaction: QT-Prolonging Drugs

Hydroxychloroquine can prolong the QT interval — a measurement of your heart's electrical cycle. When combined with other QT-prolonging medications, the risk of a dangerous heart rhythm called Torsades de Pointes increases. This is the most important drug interaction to know about.

Drugs that significantly prolong the QT interval and should be avoided or used with extreme caution alongside hydroxychloroquine include:

• Azithromycin (Z-Pak): The combination of hydroxychloroquine and azithromycin significantly increases QT prolongation and has been associated with cardiovascular events including chest pain, heart failure, and increased mortality risk. Avoid concurrent use when possible.
• Clarithromycin and erythromycin: Other macrolide antibiotics with QT-prolonging effects. These are often prescribed for respiratory infections — if you need an antibiotic, tell your prescriber you take hydroxychloroquine so they can choose an alternative like amoxicillin or doxycycline.
• Antiarrhythmic drugs: Amiodarone, sotalol, quinidine, and other Class Ia/III antiarrhythmics significantly prolong QT. Concurrent use with hydroxychloroquine requires close cardiac monitoring.
• Dasatinib and other targeted cancer therapies: Several cancer drugs prolong QT. Tell your oncologist you take hydroxychloroquine before starting any new cancer treatment.
• Haloperidol and other antipsychotics: Some antipsychotic medications also prolong QT; combination warrants monitoring.

Digoxin: Increased Blood Levels

Hydroxychloroquine increases blood levels of digoxin (Lanoxin), a heart medication used for heart failure and atrial fibrillation. Higher digoxin levels can cause toxicity — symptoms include nausea, vomiting, irregular heartbeat, and visual disturbances. If you take digoxin and are starting hydroxychloroquine (or vice versa), your doctor should monitor digoxin blood levels closely and potentially adjust the dose.

Diabetes Medications: Risk of Low Blood Sugar

Hydroxychloroquine has a well-documented blood sugar-lowering effect. It enhances the hypoglycemic effects of both insulin and oral diabetes medications. This is actually a benefit for some patients — but it can become dangerous if your diabetes medications aren't adjusted.

If you take insulin, metformin, sulfonylureas, or other diabetes drugs and are starting hydroxychloroquine, tell your prescriber. Blood glucose monitoring should be intensified and your diabetes medication doses may need to be lowered to prevent hypoglycemia.

Antacids: Reduced Absorption

Antacids (like Maalox, Mylanta, Tums, and others containing aluminum or magnesium) can bind to hydroxychloroquine and prevent it from being absorbed properly. This can reduce the amount of hydroxychloroquine that reaches your bloodstream, making it less effective.

Rule: Take antacids at least 4 hours before or after hydroxychloroquine. Kaolin-containing preparations also reduce absorption — same 4-hour spacing rule applies.

Cimetidine (Tagamet): Increased Hydroxychloroquine Levels

Cimetidine, an older H2 blocker used for heartburn (sold over the counter as Tagamet), can increase blood levels of hydroxychloroquine by reducing its metabolism. Higher-than-expected hydroxychloroquine levels could increase the risk of side effects, including retinopathy. Avoid cimetidine if you take hydroxychloroquine; omeprazole (Prilosec) and other PPIs are generally safer alternatives for heartburn.

Penicillamine: Increased Toxicity Risk

Hydroxychloroquine can increase plasma concentrations of penicillamine (Cuprimine, Depen), which is used for Wilson's disease, cystinuria, and some cases of RA. Higher penicillamine levels can cause serious side effects including kidney damage. This combination should be avoided or used only with very close monitoring.

Vaccines: Potential Reduced Effectiveness

Hydroxychloroquine may modestly reduce the effectiveness of some vaccines, particularly those relying on immune memory formation. However, unlike potent immunosuppressants, it does not significantly blunt vaccine responses. Live vaccines should still be discussed with your rheumatologist before receiving — avoid live attenuated vaccines during active disease.

Approved vaccines (flu, COVID-19, shingles [Shingrix], pneumococcal) are generally recommended and safe for patients on hydroxychloroquine.

Methotrexate: Additive Effects

Hydroxychloroquine and methotrexate are commonly prescribed together (especially in triple therapy for RA). This combination is generally well-tolerated and intentionally synergistic. However, methotrexate does increase the risk of adverse effects generally — not a contraindication, but warrants standard methotrexate monitoring (LFTs, CBC).

Rifampin: Reduced Hydroxychloroquine Effectiveness

Rifampin (used for tuberculosis and some other infections) is a potent inducer of drug-metabolizing enzymes and can significantly reduce hydroxychloroquine blood levels — potentially making it ineffective. This combination should be avoided. Inform your infectious disease provider if you are on hydroxychloroquine before starting rifampin-based TB therapy.

Key Message for Every Doctor's Visit

Because you may see multiple providers — your rheumatologist, PCP, urgent care, or specialists — always mention that you take hydroxychloroquine:

• Before any antibiotic prescription — to avoid macrolides that prolong QT
• Before any new cardiac medication — digoxin, antiarrhythmics, or QT-prolonging drugs
• Before starting diabetes medications or adjusting insulin — blood sugar may change
• To your eye doctor — so they perform the correct retinal screening tests

For more on side effects of hydroxychloroquine, read our guide: Hydroxychloroquine Side Effects: What to Expect and When to Call Your Doctor. Need help finding hydroxychloroquine in stock? medfinder can help.