Common Drugs Trigger Heart Rhythm Irregularities

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According to the Mayo Clinic web site, “More than 50 medications, many of them common, can lengthen the QT interval in otherwise healthy people and cause a form of acquired long QT syndrome known as drug-induced long QT syndrome. Medications that can lengthen the QT interval and upset heart rhythm include certain antibiotics, antidepressants, antihistamines, diuretics, heart medications, cholesterol-lowering drugs, diabetes medications, as well as some antifungal and antipsychotic drugs.”

A layman’s description of the QT interval is also found on the Mayo Clinic web site, “After each heartbeat, your heart’s electrical system recharges itself in preparation for the next heartbeat. This process is known as repolarization. In long QT syndrome, your heart muscle takes longer than normal to recharge between beats. This electrical disturbance, which often can be seen on an electrocardiogram (ECG), is called a prolonged Q-T interval.”

A prolonged QT interval is significant because, “The prolongation of QT interval is a risk factor for sudden cardiac death independent of the patient’s age, history of myocardial infarction, heart rate, and history of drug use; the patients with a QTc interval of >440 milliseconds are at 2 to 3 times higher risk for sudden cardiac death than those with a QTc interval of <440 milliseconds. The mortality rate in untreated patients with LQT is in the range of 1% to 2% per year” (emphasis added).

Many common medications, including heart medications and cholesterol-lowering drugs (oh, the irony), can cause serious heart rhythm irregularities that can lead to death.

Drugs that lengthen the QT interval include tricyclic antidepressants, fluoxetine/Prozac, Haldol, macrolide antibiotics (azithromycin being the most popular), fluoroquinolone antibiotics (Cipro/ciprofloxacin, Levaquin/levofloxacin, Avelox/moxifloxacin and a few others), and others. A complete list of drugs that cause elongated QT can be found at

These drugs worsen the elongation of the QT interval in a dose-dependent manner, so drugs that are known to lengthen the QT interval should not be taken concurrently.  Additionally, drugs and foods that interfere with the CYP450 enzymatic pathways, which are necessary for drug metabolism, may cause a build-up of QT elongating drugs in the body. Drugs and foods that inhibit CYP450 enzymes should not be taken with QT interval elongating drugs.

To put this into real-world terms, if you’re on Prozac, you should avoid (or at least exercise caution with) azithromycin. If you’re on Amiodarone (a heart medication), you should avoid (or at least exercise caution with) fluoroquinolone antibiotics. When you’re on any drug that elongates the QT interval you shouldn’t drink grapefruit juice because it interferes with CYP450 enzymes.

Antibiotics that Elongate the QT Interval

In March, 2013, the FDA announced that they were, “warning the public that azithromycin (Zithromax or Zmax) can cause abnormal changes in the electrical activity of the heart that may lead to a potentially fatal irregular heart rhythm. Patients at particular risk for developing this condition include those with known risk factors such as existing QT interval prolongation, low blood levels of potassium or magnesium, a slower than normal heart rate, or use of certain drugs used to treat abnormal heart rhythms, or arrhythmias.”  The warning label for azithromycin was adjusted accordingly. Whether or not enough attention was paid to the updated warning label to change prescribing habits, or whether or not the updated warning label resulted in prevention of any irregular heart rhythm related deaths, are unknown.

The FDA announcement of the warning label changes for azithromycin noted that, “The risks of cardiovascular death associated with levofloxacin treatment were similar to those associated with azithromycin treatment.”

The warning label for Levaquin/levofloxacin (and the other fluoroquinolone antibiotics) notes that:

“Prolongation of the QT interval and isolated cases of torsade de pointes have been reported. Avoid use in patients with known prolongation, those with hypokalemia, and with other drugs that prolong the QT interval.”

In 2014, a study entitled “Azithromycin and Levofloxacin Use and Increased Risk of Cardiac Arrhythmia and Death” compared the risk of cardiac arrhythmia for U.S. Veterans taking amoxicillin, azithromycin and levofloxacin. The study concluded that:

“Compared with amoxicillin, azithromycin resulted in a statistically significant increase in mortality and arrhythmia risks on days 1 to 5, but not 6 to 10. Levofloxacin, which was predominantly dispensed for a minimum of 10 days, resulted in an increased risk throughout the 10-day period.”

Yes, azithromycin can increase the risk of serious cardiac events in those who take it, but levofloxacin is more dangerous, with an increase in serious cardiac events occurring for ten days, as opposed to five with azithromycin. Longer term tests – comparing health outcomes for those who took various kinds of antibiotics months or years after administration of the drugs – were not conducted. There seems to be an assumption that drugs are only dangerous while they are being administered. As a consequence, long-term adverse effects are systematically under-studied.

Many patients who have experienced fluoroquinolone toxicity syndrome have reported heart rhythm abnormalities long after they have stopped taking fluoroquinolone antibiotics.  Whether or not past use of fluoroquinolones makes people more subject to long QT syndrome, torsades de pointes or other potentially fatal heart rhythm irregularities over their lifetime, has not, to my knowledge, been examined.  What has been examined is that both azithromycin and levofloxacin increase the risk of heart rhythm abnormalities significantly while taking them. Even that information is enough to warrant caution with both drugs.

Treatment for Medication-Induced Heart Rhythm Irregularities

For the treatment of long QT syndrome, it is recommended that the offending medication be ceased. Please note, one should not stop a medication without physician assistance. For acute QT attacks, IV magnesium and potassium may be necessary. “Magnesium is very effective for suppression of the short-term recurrences of torsades and is the agent of choice for the immediate treatment of the torsades associated with both congenital and acquired forms of LQT, irrespective of serum magnesium levels.” Additionally, “Administration of potassium is considered an important adjunct to the intravenous magnesium therapy for the short-term prevention of the torsades, especially in the cases where the serum potassium level is in the lower limits.”  A pacemaker is a longer-term treatment option for those whose condition demands one.

The cases of long QT syndrome that are caused by drugs can be avoided entirely by avoiding the drugs that elongate the QT interval. Of course, don’t go off any medication without first consulting your doctor. I am not a doctor, so this post should not be interpreted as medical advice. I know that given my past adverse reaction to a fluoroquinolone antibiotic (ciprofloxacin), I will do my best to avoid the drugs listed on Your heart may thank you if you do the same.

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Image by Jan Alexander from Pixabay

This post was published originally on Hormones Matter on July 20, 2015. 

Lisa Bloomquist was "Floxed" on her 32nd birthday by Cipro, a fluoroquinolone antibiotic. After 2 years of battling the mysterious health ailments that come with an adverse reaction to a fluoroquinolone, she has fought her way back to health. Lisa is now fighting for recognition of the harm that these drugs can cause and hoping to help those who are suffering from them through their fluoroquinolone induced illness to find recovery. Her web site, highlighting stories of hope and recovery, is After a while of studying how fluoroquinolones damage mitochondria, she noted that mitochondria were being systematically ignored when forming disease models. She started to bring attention to the role that mitochondria play in health and disease.


  1. I have had irregular heartbeats for over 20 years marked off to panic and anxiety I still suffer from. I was given Prozac 20 years ago and it was a blessing for normal functioning!
    My husband travels the U.S. In his job. Two years ago, I developed C-Diff not properly diagnosed and given antibiotics and repeated Z packs. About a month later, I contracted MRSA, also not correctly diagnosed.More antibiotics!! I ended up with a MRSA tumor the size of an apple, surgically removed at university hospital with plenty IV’s. Not long after that in span of 2-3 hours, my body painfully swelled. With spiking heart rates, I went by ambulance to ER where I had LQT with 2 episodes of cardiac arrest! I was successfully resuscitated with paddles and CPR not once but twice! Had I not went by ambulance to ER, I would have not survived!!
    I stayed 5 days in hospital. The long term antibiotics made my heart develop very low magnesium and potassium contributing to 2
    Cardiac arrests! I have seen numerous cardiologists, Zoll packs, and monitors. I still do not have the full understanding I want.
    I Do Know God Blessed Me!!!
    Any info appreciated!!!

  2. I am so fortunate to have found this information.
    In February 2016 I went for my annual ‘wellness’ exam’ only to find out I had hypertension. Wasn’t sked 1 question about what was going on in my life, what I ate…nada. Lost my best friend, divorced after 36 yrs, sold my house, moved…
    I am not overweight, diabetic or have high cholesterol.EXCELLENT health
    Had an echocardiogram that came back fine. Heart in good shape.
    Given 50mg Metoprolol and 2 weeks later 100mg. Had severe diarrhea, couldn’t get out of bed, headache, pounding heart, vision blurred
    March, abruptly taken off Metoprolol and put on 100 mg Losartan and a Z PACK and a ProAir inhaler due to my ‘severe flu-like and possible pleurisy.’2 days later in ER with AFIB!Put back on 25mg Metoprolol with the Losartan
    BLOOD THINNERS (Eliquis) recommended I declined
    Short version is I weaned myself off these meds, since Dr refused to. Changed Drs. BENICAR 20mg recommended by another cardiologist. Took it for 1 month and refused any more. A calcium blocker and diuretic was recommended.Said no.I thought my THYROID may be the problem since it regulates the heart and went on NatureThroid instead of Armour. PROBLEM is I have AFIB, racing , pounding heart all the time now. I’m off the meds, except for thyroid meds, for about a month now.
    Is it possible I STILL am reacting to Metoprolol/Losartan, that have arrhythmia as a side effect? SOMETHING happened in March! I was in great health before all the meds. Is Suxiaojiuxinwan recommended? Not 1 doctor can focus on CAUSE…just dangerous meds to treat symptoms and side effects! I trust acupuncture and Chinese herbal remedies before a DR, brainwashed to promote the Pharma profit train! Is there ANYONE who had an onset of AFIB/arrhythmia (drug induced)and returned to normal heart rhythm after being off meds? Does CALM, magnesium drink, magnesium oil, Hawthorn, L-carnitine, COQ10 and acupuncture benefit stopping AFIB ?

    • Thank you very much for reading the article, and I’m glad that it was validating! I’m so sorry for all that you’re going through though, and I wish I had answers for you. Unfortunately, answers are very hard to come by. I can tell you that the Suxiaojuixinwan works well for me. A Chinese herbalist should be consulted prior to taking it, and a doctor too. I also find magnesium, antioxidant supplements (like CoQ10) and acupuncture to be helpful. Here are some web sites that have a lot of good info on them as well:


      • Appreciate your response and links.
        Found an acupuncturist and Chinese herbalist. Of course, insurance will not cover the costs. In my opinion, Doctors are not qualified or trained in nutrition, acupuncture and or Chinese herbal treatments. In Europe, the pharmacies sell BOTH herbal remedies and prescription drugs. Even THERMOGRAPHY was recommended over mammograms(radiation) My recent experience with conventional doctors has been rather frightening. I have read abstracts, medical journals and done my best to educate myself and the doctors treat me like I’m an idiot! I have 24/7 to be proactive for MY health as I take the RISK.
        Magnesium deficiency seems to be the center of many problems.
        Would encourage people to have their THYROID (TSH, freeT3 and freeT4) checked, as many people are treated for heart problems, instead of thyroid.
        Have a Chinese friend who recommended the Su Xiao Jiu Wan AND for hypertension Dogbane Combo (luobuma jiangya pian) Amazon sells both. Will consult with the acupuncturist before I take anything
        Dr Sinatra’s website is helpful too.
        Thanks again for your response. I will continue in my quest for determining the cause of my afib!

  3. After reading this, I’m beginning to believe that my Atrial Fibrillation caused the condition. I’ve always wondered if time affected the onset of these conditions. Like tendon tears, it appears it can appear months after stopping the medication. I’ve taken FQ’s and Zpak as well and in the year I developed Afib. This article really helps me understand how the drugs are causing these problems.
    One question I had, if heart rate is electrical, isn’t it associated with the neurological effects of FQ’s? In other words, we know FQ’s cause neurological problems, is this the same?

  4. Hi, i would like to know if the heart irregularities will stop after i cease medicine? And how long does it take?thanks

    • Hi John,

      Many people have heart rhythm irregularities long after they finish taking fluoroquinolones. Unfortunately, I’m not able to say how long it will last for anyone else. I can tell you that I still felt as if I had a racing heart occasionally when I was three years out from getting “floxed.” A few things that helped me are: 1) cutting out caffeine, 2) a Chinese herb called Suxiao jiuxin wan, 3) Kava (I only use it occasionally to avoid dependence), 4) meditation, 5) magnesium supplementation.

      I hope that those things help you!


  5. My mother passed away in June after being admitted to the hospital. She was first diagnosed with pneumonia but later it was found to be congestive heart failure, of which we already knew she routinely suffered. She walked into the hospital and in less than 24 hours she died. The ER doc prescribed IV antibiotics which were immediately pulled by her cardiologist when he came a short time after they were started. However, in less than an hour hear pulse went from 55 to 150+. He gave her something to slow the pulse which in a couple of hours had it dropping so fast they couldn’t stop it and eventually she died. I thought you might want to know that our belief is that the antibiotic promoted arrhythmia and eventually killed her. Please understand this is not a legal case in the making but just a daughter looking for answers. Thanks.

    • I am so, so sorry for your loss, Deborah!

      Given that a couple classes of popular antibiotics have been shown to cause arrhythmia, I suspect that you are correct about the antibiotics leading to her arrhythmia and death. I really, really, really wish that more doctors recognized that this was an effect of fluoroquinolones, macrolides, and maybe other antibiotics too. Proper precaution should be taken with these drugs – they are not benign. It would be even nicer if they knew how to reverse the effects of the drugs. In your Mom’s case, maybe it could have saved her life. Unfortunately, undoing damage is more difficult than inflicting it, and how to undo the adverse effects of antibiotics is unknown.

      If your Mom was given a fluoroquinolone antibiotic – cipro, levaquin, avelox, floxin or their generic equivalents – you may find answers to your questions in the articles on this page – Fluoroquinolones deplete vital minerals from cells, and also adversely affect GABA neurotransmitters, both of which could lead to arrhythmia.

      Again, my condolences.

      Lisa Bloomquist

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