Macrolide Risk Assessment Tool
Assess Your Risk Before Starting Macrolides
This tool helps determine if you should get an ECG before starting azithromycin, clarithromycin, or erythromycin based on clinical guidelines.
When you’re prescribed an antibiotic like azithromycin or clarithromycin for a stubborn chest infection, you probably don’t think about your heart. But here’s the thing: these common drugs can quietly mess with your heart’s electrical rhythm. That’s where ECG monitoring comes in-not for everyone, but for a clear group of people who are at real risk.
Why Macrolides Can Be Risky for Your Heart
Macrolide antibiotics-azithromycin, clarithromycin, erythromycin-are workhorses for treating pneumonia, bronchitis, and sinus infections. But they also block a specific potassium channel in heart cells called hERG. When that happens, the heart takes longer to reset between beats. On an ECG, that shows up as a longer QT interval. If it stretches too far, it can trigger a dangerous rhythm called Torsades de Pointes. It’s rare, but it can be fatal.
A 2012 study in the New England Journal of Medicine found that people taking azithromycin had a 2.7 times higher risk of dying from heart problems than those taking amoxicillin. Erythromycin carries even higher risk-nearly five times more likely to cause QT prolongation than azithromycin, based on pooled data from 13 studies. The risk isn’t huge for most healthy people, but it spikes when other factors line up.
Who Should Get an ECG Before Starting Macrolides?
Not everyone needs an ECG. But if you have any of these, you absolutely should:
- Age 65 or older-Your heart’s electrical system slows down naturally with age.
- Female-Women have longer baseline QT intervals and are nearly three times more likely to develop drug-induced arrhythmias.
- Already on other QT-prolonging drugs-Antidepressants, antifungals, anti-nausea meds, or even some allergy pills can stack the risk.
- History of heart disease, heart failure, or prior arrhythmia-Your heart is already vulnerable.
- Low potassium or magnesium levels-Common in people with kidney disease, eating disorders, or on diuretics.
- Known Long QT Syndrome-Either inherited or previously diagnosed.
- Chronic kidney disease-Macrolides are cleared by the liver and kidneys. Poor kidney function means higher drug levels in your blood.
The British Thoracic Society says if you’re starting long-term macrolide therapy-for example, for bronchiectasis or cystic fibrosis-you need a baseline ECG before the first dose. The cutoff? QTc over 450 ms for men, 470 ms for women. If it’s above 500 ms, don’t start the drug at all. That’s not a gray zone-it’s a red line.
What About Short-Term Use?
If you’re taking azithromycin for five days for a sinus infection and you’re a healthy 30-year-old with no other meds or heart issues? The risk is extremely low. The American Heart Association doesn’t recommend routine ECGs in these cases. But here’s the catch: many people who seem “healthy” aren’t.
One 2024 survey of primary care doctors found that 78% knew macrolides could prolong QT-but only 22% ever ordered a baseline ECG. Why? They thought the patient was fine. But in one case reported on Reddit, a 68-year-old woman with a QTc of 480 ms (borderline) got clarithromycin for pneumonia. Five days later, she went into Torsades. She survived, but barely.
That’s the problem with assuming risk. You can’t see it until it’s too late.
When Should You Repeat the ECG?
For people on long-term macrolides-like those taking azithromycin three times a week for bronchiectasis-the British Thoracic Society recommends a second ECG after one month. Why? Because QT prolongation doesn’t always show up right away. It can creep in slowly, especially if kidney function dips or if another drug gets added.
In hospital settings, if you’re on continuous cardiac monitoring, you’re watched. But if you’re discharged to home? You need a follow-up ECG. The REMAP-CAP ICU guidelines say: if your QT interval gets longer after starting the drug, stop it. No exceptions.
What Happens If Your QTc Is Too Long?
If your baseline ECG shows QTc over 450 ms (men) or 470 ms (women), your doctor should consider alternatives. Amoxicillin, doxycycline, or cefdinir are often safe substitutes. If you absolutely need a macrolide, they might:
- Reduce the dose
- Check electrolytes and correct low potassium or magnesium
- Delay treatment until you’re stable
- Use a different antibiotic entirely
And if your QTc hits 500 ms or higher? The NIH says your risk of Torsades jumps by 5-7% for every 10 ms beyond that. At 520 ms, your risk is 15-20%. That’s not a gamble worth taking.
Why Don’t All Doctors Order ECGs?
Cost. Time. Confusion.
An ECG in the UK costs about £28.50. Multiply that by the 12 million macrolide prescriptions written each year in the UK alone, and you’re looking at £342 million. That’s not practical. And most primary care clinics don’t have ECG machines on-site. You’d have to book an appointment, wait days, and delay treatment.
But here’s what’s worse: many doctors don’t know the guidelines. A 2023 study found that in specialized respiratory clinics following British Thoracic Society rules, 87% of patients got ECGs. In regular GP offices? Only 12% did.
Some doctors think, “She’s young, she’s healthy, it’s fine.” But 1.2% of patients screened in BTS clinics turned out to have undiagnosed inherited Long QT Syndrome. That’s one in 80 people who didn’t know they were at risk-until an ECG caught it.
What’s Changing in 2025?
Things are getting smarter. The American Heart Association now uses a 9-point scoring system to assess risk: age, sex, kidney function, meds, history. You don’t need an ECG for everyone-but you do for those scoring 5 or higher.
In the UK, 15 clinics are testing handheld ECG devices that give results in 90 seconds. No waiting. No referral. Just plug it in, do the reading, and decide on the spot. Early data shows treatment delays dropped from 5.2 days to under a day.
Electronic health records are catching up too. Epic Systems now auto-alerts doctors if a patient with a history of QT prolongation gets prescribed azithromycin. That’s a game-changer.
Bottom Line: Don’t Guess. Check.
Macrolides are safe for most people. But they’re not safe for everyone. If you’re over 65, female, on other meds, have kidney trouble, or have any heart history-ask for an ECG before starting the antibiotic. It takes five minutes. It might save your life.
And if you’re a doctor? Don’t rely on gut feeling. Use the guidelines. Screen the high-risk. Skip the low-risk. That’s not overtesting-that’s smart medicine.
Do all macrolide antibiotics carry the same heart risk?
No. Erythromycin has the highest risk of QT prolongation, followed by clarithromycin. Azithromycin carries the lowest risk among the three, but it’s still significant-especially in high-risk patients. A meta-analysis found erythromycin was nearly five times more likely than azithromycin to cause QT prolongation.
Can I get an ECG at my GP’s office?
Many GP practices don’t have ECG machines, but some do. If you’re at risk, your doctor can refer you to a local clinic, hospital, or pharmacy that offers ECG services. In the UK, some pharmacies now provide ECGs for under £15. Portable devices are also becoming more common in clinics.
What if my QTc is borderline-470-499 ms?
A QTc in that range is a warning sign. Don’t ignore it. Your doctor should check your electrolytes, review all your medications, and consider alternatives. If you’re on long-term macrolides, repeat the ECG in one month. If it climbs further, stop the drug. Many doctors misinterpret borderline values-get a second opinion if needed.
Are there safer antibiotics than macrolides?
Yes. For most respiratory infections, amoxicillin, doxycycline, or cefdinir are just as effective and carry no QT risk. Macrolides are often overused. If you’re high-risk, ask your doctor: “Is there a safer option?”
How long does QT prolongation last after stopping the drug?
Usually, the QT interval returns to normal within a few days to a week after stopping the macrolide. But if you have underlying heart disease or electrolyte imbalances, it can take longer. Always follow up with your doctor if you had QT prolongation-even after stopping the drug.
Can I take macrolides if I have a pacemaker?
Having a pacemaker doesn’t protect you from QT prolongation or Torsades. Pacemakers manage slow heart rates, not dangerous fast rhythms like Torsades. You still need ECG monitoring before starting macrolides, especially if you’re on other QT-prolonging drugs or have heart disease.
Is ECG monitoring covered by the NHS?
Yes. If your doctor determines ECG monitoring is clinically necessary-for example, because you’re starting long-term macrolide therapy or have risk factors-it’s covered under NHS services. You won’t be charged. But you still need to ask for it. Don’t assume it’s automatic.
6 Comments
Been on azithromycin twice for pneumonia and never thought twice about my heart. Guess I got lucky. Still, this post made me check my med list-turns out I’m on an antifungal that also messes with QT. Time to call my doc.
As someone who’s worked in primary care for 15 years, I’ve seen too many patients assume ‘young and healthy’ means ‘immune to side effects.’ This is exactly why we need better screening-not because we don’t trust patients, but because we don’t trust assumptions. An ECG takes five minutes. A funeral doesn’t take long at all.
OMG YES. I’m a nurse and last month a 72-year-old man coded in the ER after a 5-day azithromycin course. No history. No symptoms. Just a QTc of 512. He’s fine now but I swear-every time I see a macrolide script now, I ask: ‘Did you check the ECG?’
They say it’s rare but let’s be real-the system is designed to ignore this until someone dies. The FDA knew about hERG blockade in the 90s. They just didn’t want to scare people off antibiotics. Now they slap on a tiny warning and call it a day. Meanwhile, grandma’s on 7 meds and gets clarithromycin like it’s Advil
Let me just say: the British Thoracic Society guidelines are a masterpiece of clinical pragmatism. Contrast that with American primary care, where ‘I think she’s fine’ is still a valid diagnostic criterion. The 87% vs 12% ECG compliance gap isn’t negligence-it’s systemic failure. And yes, I’ve seen the £342 million cost argument. That’s not a budget issue. That’s a moral one.
QTc thresholds are misleading. The 450/470 cutoffs are arbitrary. Studies show arrhythmia risk increases linearly from 420 ms upward. The real red flag isn’t crossing 500-it’s a >30ms increase from baseline. If you’re not tracking delta QTc, you’re not monitoring-you’re guessing.