Levofloxacin and Amiodarone Interaction: Case Study
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).
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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