Hydroxychloroquine & Azithromycin Interaction

Hydroxychloroquine (Plaquenil) and azithromycin (Zithromax) both independently prolong the QT interval, and their combination significantly increases the risk of potentially fatal cardiac arrhythmias, including torsades de pointes. This interaction gained widespread attention during the COVID-19 pandemic when both drugs were briefly used together as an experimental treatment.

Hydroxychloroquine is primarily used for autoimmune conditions such as lupus and rheumatoid arthritis, while azithromycin is a common broad-spectrum antibiotic. Patients with autoimmune diseases who develop infections may encounter this combination in clinical practice.

The FDA issued multiple safety communications during 2020 warning against the use of hydroxychloroquine and azithromycin together outside of clinical trials or hospital settings due to the cardiac risk.

Hydroxychloroquine blocks the hERG potassium channel and also inhibits the rapid (IKr) and slow (IKs) components of the delayed rectifier potassium current, causing dose-dependent QT prolongation. The drug has a very long half-life (40-50 days), meaning QT effects can persist for weeks after discontinuation.

Azithromycin also blocks hERG potassium channels, though with less potency than some other macrolide antibiotics. When both drugs inhibit cardiac repolarization channels simultaneously, the additive effect can push the QT interval into a dangerous range, particularly in patients with additional risk factors.

Large observational studies during the COVID-19 pandemic provided extensive data on this interaction. A study of over 900,000 hydroxychloroquine users found that adding azithromycin was associated with a significantly increased risk of cardiac arrest and cardiovascular mortality within the first 30 days of combined use.

The risk is highest in patients with pre-existing cardiac conditions (heart failure, coronary artery disease), electrolyte imbalances, advanced age, and those taking other QT-prolonging medications. Patients with autoimmune diseases on long-term hydroxychloroquine may have subclinical cardiac effects that increase their vulnerability.

Whenever possible, use an alternative antibiotic that does not prolong the QT interval. If azithromycin is necessary for a patient on hydroxychloroquine, ensure a baseline ECG is obtained and that the QTc is below 450 ms before starting. Correct any electrolyte abnormalities first.

Use the shortest effective course of azithromycin. Avoid concurrent use of other QT-prolonging medications, and advise patients to avoid dehydration and electrolyte-depleting conditions (vomiting, diarrhea). If QTc exceeds 500 ms at any point, discontinue azithromycin immediately.

Obtain a baseline ECG before starting azithromycin and repeat at 2-4 hours after the first dose, then daily for the duration of antibiotic therapy. Monitor QTc interval closely. Check serum potassium, magnesium, and calcium before starting and during therapy.

Instruct patients to report symptoms of arrhythmia immediately: palpitations, lightheadedness, dizziness, syncope, or seizures. Continuous cardiac monitoring (telemetry) is recommended for hospitalized patients receiving both drugs.

For bacterial infections in hydroxychloroquine patients, non-QT-prolonging antibiotics include amoxicillin, amoxicillin-clavulanate, doxycycline, cephalexin, and trimethoprim-sulfamethoxazole. These cover most common outpatient infections without QT risk.

If a macrolide is specifically needed, no macrolide is completely free of QT risk, but azithromycin is generally considered safer than erythromycin or clarithromycin. However, the safest approach is to choose a non-macrolide antibiotic when hydroxychloroquine cannot be paused.