Levofloxacin and Amiodarone Interaction: Case Study

Wonderful Guest Post via Amanuel T. B.Sc., Pharm.D. – Clinical Pharmacist: View his profile on Linked In – If you are interested in donating a brief case, or educational post, contact me.

The following case study is intended to illustrate the vital importance of reviewing patient’s medication history prior to recommending an antibiotic for a specified infection.

During one of his routine assignment in cardiac unit a pharmacist received a call from a Physician Assistant to assist in selecting an appropriate Levofloxacin regimen for a patient with a history of documented uncomplicated urinary tract infection (UTI).

Below is the patient’s demography, a brief medical history and pertinent labs.

MC is a 83 year old woman with a history of heart disease s/p bicuspid repair (10/8/14) and history of atrial fibrillation. She has no known drug allergy. Microanalysis of the urine run shortly after admission shows presence of gram negative rods. Strip of her Electrocardiogram (ECG) performed on day of admission reads Normal Sinus Rhythm (NSR) and a QTc interval of 507. Other labs include: srcr = 1.32 mg/dl with est crcl = 27ml/min wbc = 16.4

Current meds include:

  • Amiodarone 400mg po q12h
  • Atorvastatin 40mg po qhs
  • Aspirin 325mg po qday
  • Furosemide 40mg qday
  • Metoprolol 50mg po q12h

Based on the initial assessment an order was initiated for Levofloxacin 500mg load dose followed by 250mg po qday which has yet to be verified. Upon reviewing the chart further by the pharmacist it was determined that Levofloxacin, although very effective antibiotic for UTI, not to be an ideal choice for this particular case and was suggested that it be discontinued and substituted with another safer antibiotic with similar efficacy.

Other antimicrobial therapy options that were considered include: Nitrofurantoin, Penicillins, Cephalosporins and Sulfamethoxazole-Trimethprim (SMX/TMP). Nitrofurantoin can be used for uncomplicated UTIs. However, nitrofurantoin is contraindicated in patients with significant renal impairment with CrCl less than 60 mL/min or clinically significant elevated serum creatinine.

While Penicillins and cephalosporins have been used in treating UTI for decades, the high prevalence of side effects, decrease in efficacy in recent years and emergence of resistance have restricted their routine use as first line drugs.

According to IDSA* 2010 guidelines, Trimethoprim-sulfamethoxazole (160/800 mg [1 DS tablet] twice-daily for 3days) is an appropriate choice for therapy, given its efficacy as assessed in numerous clinical trials, if local resistance rates of uropathogens causing acute uncomplicated cystitis do not exceed 20% or if the infecting strain is known to be susceptible.1

After reviewing and carefully weighing in the pros and cons in the use of the antibiotics that can treat UTI, a recommendation was made to start the patient on SMX/TMP single strength po daily for 3 days. Note that the dose is reduced because of patient’s declined renal function.

The Levofloxacin and Amiodarone interaction – The decision against the use of Levofloxacin is because of its potential for major interaction with Amiodarone. Patient’s QTc from the most recent reading is 507. Concurrent use of these two agents is known to cause ventricular arrhythmia by prolonging QT interval.


Many commonly prescribed non-cardiac drugs have the potential for pro-arrhythmic effects associated with QT interval prolongation on the ECG. This is a safety concern in that prolongation of the QT interval is a simple (but not entirely precise) sign of repolarization changes that can lead to the polymorphic ventricular tachyarrhythmia known as torsades de pointes (TdP). 2

Although the precise relationship between the extent of QTc prolongation and the risk of sudden death is unknown, and it is recognized that an absolute threshold of risk for TdP cannot be proved, it is evident that almost all reported cases of TdP have occurred in individuals with a measured uncorrected QT exceeding 500 ms.5 Consequently, values of QT greater than 500 ms should cause concern.

In this particular case in which MC’s QTc interval has already exceeded 500 ms, adding another medication that is known to prolong Q-T interval would certainly put her on high risk for ventricular tachyarrhythmia related complication(s).

You need this. 6 page PDF on 30 medication mistakes you should know.  I created the content based on my real life experiences as a clinical pharmacist – please Click Here to check it out for free!


1. International Clinical Practice Guidelines for the Treatment of Acute Uncomplicated Cystitis and Pyelonephritis in Women: A 2010 Update by theInfectious Diseases Society of America and the European Society for Microbiology and Infectious Diseases

2. Peter R. Kowey, Marek Malik DOI:http://dx.doi.org/10.1093/eurheartj/sum047G3-G8First published online: 20 September 2007


  1. mary

    Great article! So practical and fun to read. You included that document you created yourself. I just love that. Good work! We should do a webinar together.

    • Amanuel Tseggai

      Dear Mary,
      Thanks for approving. It means a lot.
      So as to make it clear the piece is based on actual case in which I, as a pharmacist, was directly involved. It was not something I created.
      If I misunderstood or in any way misinterpret your message, please accept my apology in advance.

      • mary

        Yes, I understand it to be an actual case, I was referring to how you presented it. It was nicely done. So there was the science (the case) and the art (the way you presented it).

  2. chri1599

    It is a really awesome case, can’t wait to post more! Thanks again Amanuel – Eric

    • Amanuel Tseggai

      Thanks Eric for complementing my piece and for providing us with the platoforum to discuss issues very relevant to patient care.

  3. lawrence

    It seems the choice of antibiotics was for empirical treatment pending lab result of culture test comes through. SMX/TMP is not a broad spectrum antibiotic and higher adverse effect outcome. Aminoglycosides would have being my first choice until lab results comes through since it has no effect on the QT interval.

    I further query the use of Aspirin 325mg for an in-patient due to re disposition to git ulceration.

    • Amanuel

      True, Aminoglycosides are effective in treating UTI and less likely to cause ECG changes when given with Amiodarone.
      However, the nephrotoxic nature of these agents ; coupled with the fact that we’re dealing with an uncomplicated UTI make their use in elderly patients with a compromised renal function less favourable when compared to SMX/TMP.
      As with regard to use of Aspirin, damage to the g.i tract is real and certainly something that must be addressed , especially given that patient will most likely be on it chronically . While Aspirin is currently one of the regimen used in managing heart disease as per AHA guidelines and it can’t completely be avoided, one way to get around it or minimize its gi side effects would be by using enteric coated or buffered tablet formulations.

    • irfan Ali

      Would ciprofloxacin prolong QT interval?
      If no, so cant it be best used in UTI RX?

  4. mayada

    also SMX/TMP is known to cause QT prolongation also how come it will be the alternative antibiotic??

  5. Raul

    Estoy de acuerdo que si tiene un qt corregido prolongado basal se debe evitar el uso de amiodarona y levofloxacino Pero además está paciente tiene una dosis de amiodarona muy alta para mantenimiento a no ser que la estén impregnando. Igual si tiene una fibrilación auricular permanente se debe controlar frecuencia ventricular con betabloqueador o anticalcicos. La amiodarona en caso de Fibrilacion articular permanente serial ultima opcion por su efecto tóxico en tiroides, fibrosis pulmonar, neumonitis intersticial, etc. Recordar que tiene tiempo de vida medio 105 Dias. 75 miligramos de aspirina por día es suficiente pero no la protege bien de eventos tromoemboloicos. Usar apixaban. lo otro es que esta mujer tiene uso de furosemida lo cual hay que tener cuidado con el magnesio porque la hipomagnesemia también es un factor de riesgo para que haga torsión de puntas. Gracias.

  6. Anh

    What if the baseline of the qt interval is normal , would levaquin still be acceptable for this case? Or second scenario what if the pt had true allergy to penicillin and sulfa, failed macrobid , with the above prolongation qt interval at baseline, what will u recommend?

  7. Rachel

    Bactrim also prolongs QT interval with amiodarone. I would have felt more comfortable with a cephalosporin.



  1. How to Address QTc Prolongation Drug Interactions - Med Ed 101 - […] a case scenario with levofloxacin and amiodarone.  What other pearls do you think about when assessing for QTc prolongation…
  2. Amiodarone Adverse Effects And Prescribing Cascade - Med Ed 101 - […] for more on amiodarone adverse effects? Check out this previous post with a case scenario on QTc […]

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Written By Eric Christianson

October 26, 2014

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