The Problem With Quinolones


I have a confession to make. I like fluroquinolones. I know. They’re broad spectrum, especially levofloxacin and moxifloxacin. They have pretty good bioavailability (almost 100%), and they cover pseudomonas (ciprofloxacin and levofloxacin) making them good PO stepdown therapy for severe pseudomonas bacteremia. Having said that, if you have spent any time in the internet you would have noticed that FQs have been falling out of favor due to the significant side effects that have been reported.

The initial compound which quinolones are based off is the biproduct of chloroquine synthesis (yes, that chloroquine), nalidixic acid (1). It was found to be able to inhibit topoisomerase IV. Ciprofloxacin was subsequently synthetized in 1981 after initial resistance began to develop for the early quinolones. This new antibiotic was found to have good activity against gram negatives, including pseudomonas aeruginosa and Acinetobacter.  As the years went on, especially in the 1990s and in the early 2000s, other quinolones were developed that had greater activity against frequent causes of respiratory infections, including Streptococcal pneumonia and Haemophilus Influenza (2).

The more commonly used are levofloxacin and moxifloxacin. These tend to have fairly good susceptibility patterns against a variety of bacteria, including gram negatives, atypicals, and some gram positives:

You may have noticed there are several other quinolones that are not used in the US. This is because these have been removed from the market due to several adverse events (1, 2):

  • 1992 – temafloxacin taken off market due to several side effects (mostly hemolytic abnormalities) and 3 deaths
  • 1999 – grepafloxacin taken off market due to QTc prolongation and torsades
  • 1999 – trovafloxacin – removed due to hepatotoxicity, including 6 deaths reported
  • 2001 – sparfloxacin withdrawn – SJS/TEN, QTc prolongation
  • 2006 – gatifloxacin withdrawn due to hypoglycemia

The point here is that significant adverse events in the quinolone family is not new. While rare, the fact these antibiotics are prescribed at such a high rate means that more than likely we will see one of these adverse events. For instance, in a study evaluating quinolone prescription between 1995-2002 (3) found that broad spectrum quinolone prescription (levofloxacin, gatifloxacin, and moxifloxacin) increased significantly during this time:

Peripheral Neuropathy

The mechanism behind this adverse event is unclear, but data dates back to the mid-90s. In one report from Sweden (4), peripheral neuropathy was reported in 37 patients between 1985 and 1993. Most of these were due to norfloxacin. A more recent case-control study (5) evaluated patients between 2001 and 2011 and compared the risk of FQ-induced peripheral neuropathy with finasteride as a negative control. Current users of FQ had a higher risk of developing peripheral neuropathy (RR 1.83, 95% CI 1.49-2.27 with new current users having the highest risk (RR 2.07, 95% CI 1.56-2.74). Unfortunately, there was no distinction between the type of quinolone used:

How long these effects cause is unknown, however a case series (6) of 45 patients demonstrated that while onset tends to be quite rapid (usually within 20 days), some patients were disabled for up to 6 years.

Tendon Rupture

This is one of the ones that is more well known. The reason for this seems to be that quinolones tend to upregulate the matrix metalloproteinases leading to reduction in the quantity and quality of collagen fibrils (7). A population based longitudinal cohort study from Canada (7) found that those who were exposed to fluroquinolones within 30 days had a higher risk for tendon rupture after adjusting for several variables, including age, sex, and other co-morbidities:

While this was also seen for amoxicillin (the comparator), the risk was not as significant as that for quinolones. An analysis from the FAERS database (FDA Adverse Event Reporting System) reviewed the reports of tendon rupture using empirical Bayes geometric mean (8). During a period between 2004 and 2013, there were 2495 reports of tendon rupture associated with FQs. Most of them were attributed to levofloxacin, followed by ciprofloxacin and moxifloxacin.

Retinal Detachment

This is another “collagen related” adverse event (see above). In the previously cited cohort study (7), the HR for retinal detachment was 2.40 (95% CI 2.24 to 2.57). A case-cross cover study (9) evaluated the association between retinal detachment and FQ use during a 180 day period leading up to retinal detachment surgery and compared exposure to FQ during different time periods leading up to that event. Current use of FQ was associated wit ha higher likelihood of retinal detachment when compared to recent or past use:

Levofloxacin was associated with a higher likelihood of retinal detachment:

Another population-based cohort study (10) did not find increase risk of retinal detachment when compared to beta-lactams and macrolide antibiotics and after controlling for co-morbidities and age:

In another case control study (11) of over 4000 patients with retinal detachment found that current use of any fluroquinolone has associated with a higher risk of retinal detachment when compared to beta-lactam antibiotics or short acting beta-agonist:

Finally, a meta-analysis of 3 studies did not find increased risk of RD with quinolone use when analyzing case-control studies or self-controlled case series studies (12):

It may be that the risk of retinal detachment is small or that it is being under reported. That being said, there is some signal to suggest there may be a risk for retinal detachment and quinolone use, albeit a small one.

Aortic Dissection/Aneurysm

This is an interesting one. As mentioned previously, quinolone plays a role in collagen-associated adverse events and aorta is rich in collagen. FQ use has been associated with a 2-fold increase risk of aortic aneurysm (HR 2.24, 95% CI 2.02 to 2.49, 7). A nested case-control study from Taiwan (13) evaluated a cohort from 1998 to 2011 found that any quinolone use was associated with aortic aneurysm or dissection after propensity score matching:

The risk was higher in those undergoing aortic dissection surgery:

And the risk was higher when quinolones were given for anywhere between 3-14 days, however beyond 14 days was not found to be statistical significant:

A meta-analysis of 2 studies (14) which included the above study, found that quinolones increased the risk of dissection almost three-fold, while it doubled the risk of aortic aneurysm:

The reported NNH was 618 (95% CI 518-749), suggesting a small risk, however given the high prescription rate, it may be that we are missing some of these.


Quinolones have been found to block HERG gene that encodes the rapid component of the cardiac potassium channel, leading to QTc prolongation and higher risk for arrhythmias. This has been found in some cohort studies. In a cohort study from Canada (15), current and new quinolone use was associated with an aRR of 2.23 (95% CI 1.31-3.80) with moxifloxacin and gatifloxacin being the worst offenders:

A Taiwanese cohort study (16) compared the use of FQs, macrolides, and amoxicillin-clavulanate and their impact on the risk of arrythmias. After adjusting for confounders, both macrolides (specifically azithromycin) and quinolones (mostly moxifloxacin) were associated with higher incidence of ventricular arrhythmia and cardiovascular death:

This risk held up in the follow up period for up to 30 days for ventricular arrhythmias (2.88 OR for azithromycin at day 30 and 2.65 OR for moxifloxacin) and for cardiovascular death (OR 1.89 for azithromycin and OR 2.23 for moxifloxacin). This pattern does not hold for all cohort studies. For instance, in a bi-national cohort study (17) conducted between 1997 and 2011 there was no difference in risk of arrhythmia when comparing FQs and penicillin V:

One thing to note is they did not include information on the duration of treatment and they did not have information for other risk of arrhythmia. Despite this, it was a large cohort trial, suggesting that may be the effect may be quite small. A meta-analysis of 16 studies (18) totaling to over 6 million patients found a significant increase risk for arrhythmias:

Notably, there was no impact on all-cause death (RR 1.05, 95% CI 0.78 to 1.43). The biggest offenders in this meta-analysis were gatifloxacin (RR 6.27, 95% CI 3.11-12.66), moxifloxacin (RR 4.20, 95% CI 1.91-9.27) and levofloxacin (RR 1.41, 95% CI 1.16-1.7).

Other Adverse Events:

  • Cognitive dysfunction: this has been reported in some case reports, for instance one (19) described 4 cases associated with quinolones causing autonomic dysfunction, sleep disturbance, cognitive dysfunction that left these patients disabled. Another review (20) cites CNS side effects in 1-7% of patients ranging from confusion to hallucinations, however this was limited to lomefloxacin and pefloxacin.
  • Myasthenia gravis exacerbation – using the FDA Adverse Event Reporting System (AERS), one cohort study (21) found 27 patients and 9 published case reports with 10 patients, totaling to 37 patients. Myasthenia gravis exacerbation occurred withing one day, ranging from ½ hour to 10 days, and over 90% of patients improved rapidly following quinolone cessation.
  • Renal injury – one cohort study (22) of older male patients found that current fluroquinolone use was associated with RR of 2.16 (95% CI 1.52-3.18) when compared to amoxicillin and azithromycin.
  • Gastric perforation – a nested case control study from Taiwan (23) found increased risk of gastric perforation with quinolone use, which held when using macrolide as a comparator:

It goes without saying there are issues with cohort studies, and it may be the overall adverse event rate is actually lower. Nevertheless, given how often this class of antibiotics are given and how many patients are exposed, I think it is reasonable to take a step back and re-evaluate why we are given those drugs. I contend that for those who have pseudomonal infections or serious infections where high bioavailability is needed (i.e. osteomyelitis, infective endocarditis, etc) it is reasonable to proceed with quinolones, as the benefits would outweigh any potential adverse event. What about for other infections such as uncomplicated cystitis or bronchitis? One letter (24) suggests the use of amox/clav and doxycycline for bronchitis and TMP-SMX, Fosfomycin, and Nitrofurantoin for UTIs. They also suggest the use of amox-clav (good gram negative coverage), or a cephalosporin (3rd gen cephalosporin such as cefpodioxime if able) in pregnancy:


  1. Emmerson AM, Jones AM. The quinolones: decades of development and use. J Antimicrob Chemother. 2003 May;51 Suppl 1:13-20. doi: 10.1093/jac/dkg208. PMID: 12702699.
  2. Andersson MI, MacGowan AP. Development of the quinolones. J Antimicrob Chemother. 2003 May;51 Suppl 1:1-11. doi: 10.1093/jac/dkg212. PMID: 12702698.
  3. Linder JA, Huang ES, Steinman MA, Gonzales R, Stafford RS. Fluoroquinolone prescribing in the United States: 1995 to 2002. Am J Med. 2005 Mar;118(3):259-68. doi: 10.1016/j.amjmed.2004.09.015. PMID: 15745724.
  4. Hedenmalm K, Spigset O. Peripheral sensory disturbances related to treatment with fluoroquinolones. J Antimicrob Chemother. 1996 Apr;37(4):831-7. doi: 10.1093/jac/37.4.831. PMID: 8722551.
  5. Etminan M, Brophy JM, Samii A. Oral fluoroquinolone use and risk of peripheral neuropathy: a pharmacoepidemiologic study. Neurology. 2014 Sep 30;83(14):1261-3. doi: 10.1212/WNL.0000000000000846. Epub 2014 Aug 22. PMID: 25150290.
  6. Cohen JS. Peripheral neuropathy associated with fluoroquinolones. Ann Pharmacother. 2001 Dec;35(12):1540-7. doi: 10.1345/aph.1Z429. PMID: 11793615.
  7. Daneman N, Lu H, Redelmeier DA. Fluoroquinolones and collagen associated severe adverse events: a longitudinal cohort study. BMJ Open. 2015 Nov 18;5(11):e010077. doi: 10.1136/bmjopen-2015-010077. PMID: 26582407; PMCID: PMC4654346.
  8. Arabyat RM, Raisch DW, McKoy JM, Bennett CL. Fluoroquinolone-associated tendon-rupture: a summary of reports in the Food and Drug Administration’s adverse event reporting system. Expert Opin Drug Saf. 2015;14(11):1653-60. doi: 10.1517/14740338.2015.1085968. Epub 2015 Sep 22. PMID: 26393387.
  9. Raguideau F, Lemaitre M, Dray-Spira R, Zureik M. Association Between Oral Fluoroquinolone Use and Retinal Detachment. JAMA Ophthalmol. 2016 Apr;134(4):415-21. doi: 10.1001/jamaophthalmol.2015.6205. PMID: 26967005.
  10. Kapoor KG, Hodge DO, St Sauver JL, Barkmeier AJ. Oral fluoroquinolones and the incidence of rhegmatogenous retinal detachment and symptomatic retinal breaks: a population-based study. Ophthalmology. 2014 Jun;121(6):1269-73. doi: 10.1016/j.ophtha.2013.12.006. Epub 2014 Jan 28. PMID: 24480710; PMCID: PMC4969082.
  11. Etminan M, Forooghian F, Brophy JM, Bird ST, Maberley D. Oral fluoroquinolones and the risk of retinal detachment. JAMA. 2012 Apr 4;307(13):1414-9. doi: 10.1001/jama.2012.383. PMID: 22474205.
  12. Chui CS, Wong IC, Wong LY, Chan EW. Association between oral fluoroquinolone use and the development of retinal detachment: a systematic review and meta-analysis of observational studies. J Antimicrob Chemother. 2015 Apr;70(4):971-8. doi: 10.1093/jac/dku507. Epub 2014 Dec 18. PMID: 25525200.
  13. Lee CC, Lee MT, Chen YS, Lee SH, Chen YS, Chen SC, Chang SC. Risk of Aortic Dissection and Aortic Aneurysm in Patients Taking Oral Fluoroquinolone. JAMA Intern Med. 2015 Nov;175(11):1839-47. doi: 10.1001/jamainternmed.2015.5389. PMID: 26436523.
  14. Singh S, Nautiyal A. Aortic Dissection and Aortic Aneurysms Associated with Fluoroquinolones: A Systematic Review and Meta-Analysis. Am J Med. 2017 Dec;130(12):1449-1457.e9. doi: 10.1016/j.amjmed.2017.06.029. Epub 2017 Jul 21. PMID: 28739200.
  15. Lapi F, Wilchesky M, Kezouh A, Benisty JI, Ernst P, Suissa S. Fluoroquinolones and the risk of serious arrhythmia: a population-based study. Clin Infect Dis. 2012 Dec;55(11):1457-65. doi: 10.1093/cid/cis664. Epub 2012 Aug 3. PMID: 22865870.
  16. Chou HW, Wang JL, Chang CH, Lai CL, Lai MS, Chan KA. Risks of cardiac arrhythmia and mortality among patients using new-generation macrolides, fluoroquinolones, and β-lactam/β-lactamase inhibitors: a Taiwanese nationwide study. Clin Infect Dis. 2015 Feb 15;60(4):566-77. doi: 10.1093/cid/ciu914. Epub 2014 Nov 18. PMID: 25409476.
  17. Inghammar M, Svanström H, Melbye M, Pasternak B, Hviid A. Oral fluoroquinolone use and serious arrhythmia: bi-national cohort study. BMJ. 2016 Feb 26;352:i843. doi: 10.1136/bmj.i843. PMID: 26920666; PMCID: PMC4770814.
  18. Liu X, Ma J, Huang L, Zhu W, Yuan P, Wan R, Hong K. Fluoroquinolones increase the risk of serious arrhythmias: A systematic review and meta-analysis. Medicine (Baltimore). 2017 Nov;96(44):e8273. doi: 10.1097/MD.0000000000008273. PMID: 29095256; PMCID: PMC5682775.
  19. Golomb BA, Koslik HJ, Redd AJ. Fluoroquinolone-induced serious, persistent, multisymptom adverse effects. BMJ Case Rep. 2015 Oct 5;2015:bcr2015209821. doi: 10.1136/bcr-2015-209821. PMID: 26438672; PMCID: PMC4600819.
  20. Khalifa AE. Antiinfective agents affecting cognition: a review. J Chemother. 2007 Dec;19(6):620-31. doi: 10.1179/joc.2007.19.6.620. PMID: 18230542.
  21. Jones SC, Sorbello A, Boucher RM. Fluoroquinolone-associated myasthenia gravis exacerbation: evaluation of postmarketing reports from the US FDA adverse event reporting system and a literature review. Drug Saf. 2011 Oct 1;34(10):839-47. doi: 10.2165/11593110-000000000-00000. PMID: 21879778.
  22. Bird ST, Etminan M, Brophy JM, Hartzema AG, Delaney JA. Risk of acute kidney injury associated with the use of fluoroquinolones. CMAJ. 2013 Jul 9;185(10):E475-82. doi: 10.1503/cmaj.121730. Epub 2013 Jun 3. PMID: 23734036; PMCID: PMC3708027.
  23. Hsu SC, Chang SS, Lee MG, Lee SH, Tsai YW, Lin SC, Chen ST, Weng YC, Porta L, Wu JY, Lee CC. Risk of gastrointestinal perforation in patients taking oral fluoroquinolone therapy: An analysis of nationally representative cohort. PLoS One. 2017 Sep 5;12(9):e0183813. doi: 10.1371/journal.pone.0183813. PMID: 28873440; PMCID: PMC5584983.
  24. Alternatives to Fluoroquinolones. JAMA. 2016 Oct 4;316(13):1404-1405. doi: 10.1001/jama.2016.8383. PMID: 27701658.

2 comments on “The Problem With Quinolones”

  1. “I like fluroquinolones.” As someone who has been bedridden and in AGONIZING full-body pain for over a decade now due to only twelve Cipro pills: Shame on you. Real human beings are having their lives destroyed by this shit. We’re not guinea pigs. We’re not rats. We’re not studies! We NEVER signed up for this.


    1. i am sorry you are going through this, but the point of this post is to be aware about the other side effects about quinolones physicians may not know about. you have to keep in mind that quinolones are prescribed at such a high rate these adverse events tend to be fairly rare, but still a possibility. the conclusion reached at the end of the post is these antibiotics are a reasonable option for certain infections such as:

      1. bone infections, which can take weeks to treat and may be preferable for some to take a pill rather than require an intravenous line for antibiotics (putting an intravenous line and getting certain antibiotics carries its own risk. Plus, not all antibiotics are benign. See: C. diff infection risk, renal injury with vancomycin, cephalosporins and risk of encephalopathy/seizures, daptomycin and muscle damage/pneumonia, linezolid and bone marrow suppression/peripheral neuropathy, not to mention bactrim and all of its drug-drug interactions, z-pack and its risk of arrhythmias, the list goes on). based on the risk-benefit of the infections these are typically given for and the rarity of these adverse events based on the number of people who get these antibiotics every day, id say in general the risk-benefit ratio favors giving them provider both parties are in agreement (i.e. patient and doctor).
      2. super bugs like Pseudomonas, of which quinolones are the only oral antibiotics available as of now
      3. heart valve infections
      4. bloodstream infections with high risk organisms.

      As I mentioned in the post, I like fluroquinolones because they are a good step down therapy for people who have severe infections, but this post is to highlight the less well-known reported side effects people may not know about. I do wonder if you read beyond the first few words, since I list the reported side effects, which include things beyond tendon rupture (including: retinal detachment, aortic dissection, brain fog, myasthenia gravis exacerbation, etc). I get the feeling you only read the first line and posted this comment without reading the rest of the post and looked at the sources. There are side effects folks are not familiar with; i did go through the rabbit hole of people who were “floxed” and hence, the post.


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