January 2013 FAQs
January 2013 FAQs Heading link
Does parenteral iron administration increase the risk of infection?
Does parenteral iron administration increase the risk of infection?
Iron deficiency anemia (IDA) is a common complication in critically ill and renally impaired patients, particularly those with chronic kidney disease (CKD) receiving hemodialysis (HD).1 IDA can be treated with intravenous iron, which is often preferred over oral formulations due to its greater bioavailability and favorable tolerance, and when oral administration is unfeasible in critically ill patients. However, there is concern that when iron is administered via the parenteral route, the increased bioavailability may promote bacterial growth and increase the risk of infection.
Physiology of Iron in Bacterial Infection
Bacteria require iron for growth and use iron as an enzyme cofactor.2 Human defense barriers are well accommodated to this requirement; the iron concentration in human plasma is practically zero because of the high affinity of the iron-binding protein transferrin for free iron.3 Indeed, some theorize that the decreased iron concentrations seen in critically ill patients may be advantageous by further reducing the availability of iron for bacterial growth.1 Natural barriers such as tissue fluid and phagocytes require these low-iron environments in order to function effectively, andthe antibacterial effectiveness of human serum can be attenuated by increased free iron concentrations.3,4
To deal with the low-iron environment, many pathogenic bacteria have evolved mechanisms to compete with the host for iron.5 For example, Escherichia coli and Salmonella sp. produce siderophores that compete with unsaturated transferrin by chelating iron and promoting bacterial uptake. Additionally, Haemophilus influenzae and Neisseria meningitides produce receptors that can directly remove iron from transferrin.
Many laboratory studies have associated increased iron levels with infection risk, contributing to the concern over iron administration in patients at risk for or with established infection. Bacterial growth in human serum has been shown to increase when transferrin saturations exceed normal levels by 30 to 50%.5 Furthermore, 2 studies documented that transferrin saturations exceeding 60% or 80% caused a loss of bacterial inhibition and subsequent growth of K. pneumonia and S. epidermidis, respectively, in human serum.6,7
Indeed, administration of intravenous iron has been shown to oversaturate transferrin.8 Dose- and infusion time-dependent effects were noted with ferric gluconate. Infusion protocols that utilized higher doses and shorter infusion times produced significantly higher serum iron levels and transferrin saturations than protocols that used lower doses and longer infusion times.
Risk of Infection with Intravenous Iron
While laboratory studies have shown a deleterious effect of increased free iron concentration on host immune function, human clinical data are limited. To date, studies are small and confined to CKD patients because of their frequent receipt of intravenous iron therapy and baseline risk for infection. 5 Not surprisingly, results are conflicting and lack generalizability.
Brewster and colleagues prospectively compared the rate of new catheter colonization during and after iron treatment.9 Fifteen HD patients received 125 mg iron gluconate intravenously for 5 HD sessions and were compared with 6 control HD patients that received no iron.After treatment, there was no difference in the rate of new colonization between the iron-treated and control groups (50% versus 0%, respectively; p=0.13). Of the 15 iron-treated patients, 5 were colonized at baseline compared with 10 after iron treatment (33% versus 66%; p=0.07). Throughout a 30-day follow-up period, only 1 patient (an iron-treated patient who developed candidemia) experienced infection (7%; p>0.99). These results indicate no significantly increased risk for acute catheter colonization or rate of infection with intravenous iron gluconate.
Conflicting findings were reported by Canziani and colleagues, who found a dose-dependent risk of infection with iron treatment.10 One hundred eleven HD patients were prospectively assigned to 3 iron treatment groups. Group 1 received a total cumulative dose of 1 g of iron saccharate over 28 days, group 2 received 2 g cumulative dose over 70 days, and group 3 received 1 g cumulative dose over 70 days. After 150 days, the incidence of infectious episodes per patient per month was not significantly different between groups 1 and 3 (0.08 versus 0.06, respectively; p=0.24), suggesting different treatment durations for an equivalent dose did not affect infection rate. In contrast, incidence was significantly higher in group 2 versus group 3 (0.13 versus 0.06, respectively; p=0.04), suggesting that a higher dose in an equivalent time period may contribute to increased infection risk.
Additional dose-dependent risk was reported by Hoen and colleagues, who reviewed prospective data of 985 HD patients who received oral or intravenous iron. 11 Intravenous administration of iron was not a significant risk factor for development of bacteremia. However, among patients treated with IV iron, administration was more frequent and at higher doses in patients that developed bacteremia than in patients who did not.
Lastly, a phase IV safety study compared 665 HD patients receiving iron sucrose for both treatment and prevention of IDA to historical control patients from the United States Renal Data System.12 In secondary analyses, the authors found no significant difference between intervention and historical control patients in infection-related mortality rates (21 versus 34.2 deaths per 1000 patient-years, respectively; p=0.08). However, the infection-related hospitalization rate was significantly lower in intervention versus historical controls (226.5 versus 422 hospitalizations per 1000 patient-years, respectively, p<0.001).
Compared with data describing the effect of intravenous iron on risk of new infection, no human data are available in established infection. Nonetheless, many clinicians are averse to using intravenous iron in patients with concomitant infection based on animal data in experimental models of sepsis that suggest exacerbation of infection after intravenous iron administration.13,14
While data remain conflicting, the practical application of information on infection risk with intravenous iron is potentially great. The national prevalence of CKD is approximately 15%, with new cases of later disease stages increasing in frequency.15 Patients with CKD, particularly those receiving HD, frequently receive intravenous iron treatment and are at increased baseline risk for infection. This risk should be considered in conjunction with the necessity of iron therapy, as illustrated by findings at a university hospital. Of 100 patients receiving intravenous iron sucrose, 22% also had concomitant active infection and 20% were either not iron deficient or were actually iron overloaded.16 Furthermore, the Kidney Disease Outcomes Quality Initiative guidelines for treatment of anemia in CKD recommend targeting serum ferritin and transferrin saturation levels; however, the correlation between infection risk and levels of these indices of iron status has not been explored.17
No conclusive data are available to predict the risk of new infection or exacerbation of existing infection as a result of intravenous iron treatment. Cause for this concern is mostly due to animal and laboratory data, which indicate increased bacterial growth with higher free iron concentrations and an exacerbation of existing infection with iron administration. Human data are limited, confined to patients with CKD, and conflicting, but suggest any risk may be dose-dependent. Patients with clear indications should not be deprived of iron therapy based on the limited evidence that is currently available. Clinicians must assess the benefits and risks of intravenous iron therapy for individual patients when deciding if this treatment is appropriate. 13
1. Cook K, Ineck B, Lyons W. Anemias. In: Talbert RL, DiPiro JT, Matzke GR, Posey LM, Wells BG, Yee GC, eds. Pharmacotherapy: A Pathophysiologic Approach. 8th ed. New York: McGraw-Hill; 2011. http://www.accesspharmacy.com/content.aspx?aID=799956. Accessed December 17, 2012.
2. Donnenberg MS. Enterobacteriaceae. In: Mandell GL. Mandell, Douglas, And Bennett's Principles and Practice of Infectious Disease. 7th ed. Philadelphia, PA: Elsevier Inc; 2010:2815-2833.
3. Bullen J, Griffiths E, Rogers H, Ward G. Sepsis: the critical role of iron. Microbes Infect. 2000;2(4):409-415.
4. Bullen JJ, Spalding PB, Ward CG, Rogers HJ. The role of Eh, pH and iron in the bactericidal power of human plasma. FEMS Microbiol Lett. 1992;73(1-2):47-52.
5. Maynor L, Brophy DF. Risk of infection with intravenous iron therapy. Ann Pharmacother. 2007;41(9):1476-1480.
6. Cieri E. Does iron cause bacterial infections in patients with end stage renal disease? ANNA J. 1999;26(6):591-596.
7. Brewster UC, Perazella MA. Intravenous iron and the risk of infection in end-stage renal disease patients. Semin Dial. 17(1):57-60.
8. Zanen AL, Adriaansen HJ, Van bommel EF, Posthuma R, Th de jong GM. 'Oversaturation' of transferrin after intravenous ferric gluconate (Ferrlecit®) in haemodialysis patients. Nephrol Dial Transplant. 1996;11(5):820-824.
9. Brewster UC, Coca SG, Reilly RF, Perazella MA. Effect of intravenous iron on haemodialysis catheter microbial colonization and blood-borne infection. Nephrology. 2005;10(2):124-128.
10. Canziani ME, Yumiya ST, Rangel EB, Manfredi SR, Neto MC, Draibe SA. Risk of bacterial infection in patients under intravenous iron therapy: dose versus length of treatment. Artif Organs. 2001;25(11):866-869.
11. Hoen B, Paul-Dauphin A, Kessler M. Intravenous iron administration does not significantly increase the risk of bacteremia in chronic hemodialysis patients. Clin Nephrol. 2002;57(6):457-461.
12. Aronoff GR, Bennett WM, Blumenthal S, et al. Iron sucrose in hemodialysis patients: safety of replacement and maintenance regimens. Kidney Int . 2004;66(3):1193-1198.
13. Daoud E, Nakhla E, Sharma R. Q: Is iron therapy for anemia harmful in the setting of infection? Cleve Clin J Med. 2011;78(3):168-170.
14. Zager RA, Johnson AC, Hanson SY. Parenteral iron therapy exacerbates experimental sepsis. Kidney Int. 2004;65(6):2108-2112.
15. Derebail VK, Kshirsagar AV, Joy MS. Chronic kidney disease: progression-modifying therapies. In: Talbert RL, DiPiro JT, Matzke GR, Posey LM, Wells BG, Yee GC, eds. Pharmacotherapy: A Pathophysiologic Approach. 8th ed. New York: McGraw-Hill; 2011. http://www.accesspharmacy.com/content.aspx?aID=7981349. Accessed December 17, 2012.
16. Hein B. Iron sucrose medication use evaluation. Poster presented at: 2011 American Society of Health-Systems Pharmacists Midyear Clinical Meeting; December 5, 2011; New Orleans, LA.
17. KDOQI Clinical Practice Guidelines and Clinical Practice Recommendations for Anemia in Chronic Kidney Disease. Am J Kidney Dis. 2006;47(5 Suppl 3):S11-S145.
Drug-induced QT prolongation (Part 1): presentation, risks, and management
Drug-induced QT prolongation (Part 1): presentation, risks, and management
Healthcare professionals have become increasingly frustrated with electronic drug alerts concerning QT prolongation. The alerts associated with commonly prescribed drugs such as fluoroquinolones, ondansetron, and azithromycin are particularly troublesome. Many drugs are known to cause or have the potential to cause QT prolongation and, more importantly, torsade de pointes (TdP). In addition, there have been several medications removed from the market due to adverse cardiac events such as TdP.1 The actual incidence of TdP is unknown. However, one small study estimated an annual incidence rate of approximately 12,000 cases of drug-induced TdP in the United States.2 Although TdP is a rare drug-induced disease, it is a serious, life-threatening, ventricular arrhythmia which can lead to sudden cardiac death. Thus, there is a need for a better understanding of QT prolongation and the risk of TdP induced by these drugs. This is part 1 of a 2-part paper on drugs associated with QT prolongation.
The QT interval is the time of cardiac depolarization and ventricular repolarization, which are represented by the QRS complex and ST segment with T wave, respectively.3 During cardiac depolarization, positive ions such as sodium and calcium flow into the cardiac cells. This is followed by an efflux of potassium which exceeds the influx of sodium and calcium resulting in ventricular repolarization. Disruption of this process may lead to an excess of positive ions intracellularly causing further ventricular repolarization and prolongation of the QT interval.4 Typically, the QT interval is measured at the onset of the QRS complex and terminates at the T wave.2-4 The QT interval varies with changes in heart rate; therefore, it is usually corrected for heart rate (QTc). A normal QTc interval ranges from 370 milliseconds (msec) to 440 msec for men, and up to 460 msec in women. A QTc greater than or equal to 500 msec or an increase in the QTc interval by 60 msec from baseline, increases the risk of drug-induced TdP. 2
Although the majority of QT prolongation is due to lengthening repolarization, it may also be caused by depolarization abnormalities.3 Furthermore, lengthening the duration of the ventricular repolarization may increase the susceptibility to early afterdepolarizations (EADs), which are oscillations in the membrane potential that may trigger another action potential. These EADs can propagate into a rapid polymorphic ventricular tachycardia known as TdP or “twisting of the points”.2,5-6 Thus, QT prolongation may subsequently lead to TdP; however, prolonged QT may occur without TdP. One may consider QT interval prolongation a surrogate marker for adverse events such as TdP.
Symptoms related to TdP are similar to other arrhythmias and include tachycardia, hypotension, dizziness, chest pain, shortness of breath, syncope, and seizure. Accordingly, the diagnosis of TdP is dependent on the electrocardiogram (ECG). The ECG in patients with TdP is characterized by twisting around the central axis with a long-short initiating sequence resulting from a premature beat followed by a pause. 2,7 Moreover, it is associated with a rapid heart rate ranging from 150 beats to 300 beats per minute. Torsade de pointes can be self-limiting but may also rapidly degenerate into ventricular fibrillation causing sudden cardiac death due to lack of circulation.5,7 QT prolongation and TdP can be congenital or acquired, with the latter being more common. In addition, the majority of acquired TdP with QT prolongation is drug-induced via inhibition of voltage-gated potassium channels, especially the rapid component of the delayed rectifier potassium current (IKr), expressed by human ether-a-go-go-related gene (HERG). 1,2,6 Although characteristic of TdP, inhibition of IKr and QT prolongation do not alone cause this arrhythmia. Many patients taking drugs that block IKr may have QT prolongation but do not have TdP. In addition, some drugs, such as verapamil, block IKr but do not cause QT prolongation or TdP. Therefore, drugs that block IKr are not the only medications screened for TdP with QT prolongation. Drugs such as tricyclic antidepressants, phenothiazines, and antihistamines may block sodium channels that slow ventricular conduction thus causing re-entry and risk of ventricular arrhythmia.
Specific risk factors for TdP have been identified (see Table 1). Most patients with drug-induced TdP have concomitant risk factors. One study found that 96% of patients who had TdP associated with a non-cardiac drug had at least 1 concomitant risk factor and 71% of patients had at least 2 risk factors. 8 Therefore, one method of TdP prevention is identification of patients with risk factors.
Table 1. Risk factors for drug-induced TdP. 2-4,9,10
Risk Factor Comments QTc interval > 500 msec or increase in QTc interval by > 60 msec compared to baseline A higher risk of TdP is correlated with a QTc interval > 500 msec, but there is no established threshold. The AHA/ACC/AACN/ISCE guidelines recommend considering QTc intervals > 480 msec abnormal for women and > 470 msec abnormal for men. Some clinicians use a QTc interval of 520 msec to 550 msec as the cut-off to discontinue the offending drug. Female sex The exact mechanism is unknown, but there may be hormonal influence on repolarization. This has been demonstrated through variations in the QT interval during menstrual cycles. In addition, androgens are reported to be protective against drug-induced repolarization while estrogens may be pro-arrhythmic. Women also have a higher baseline QTc interval. Left ventricular systolic dysfunction The mechanism is unclear; however, these patients may have down-regulation in potassium channels. Some experts recommend avoiding QT- prolonging drugs in patients with a left ventricular ejection fraction < 20% due to the risk of sudden cardiac death. Elderly Patients > 65 years of age are at increased risk of TdP. They may have other risk factors including heart disease. In addition, they often have reduced renal function which predisposes them to higher serum concentrations of QT-prolonging drugs. Hypokalemia or hypomagnesemia Potassium and magnesium should be monitored in patients who start QT-prolonging medications. Supplementation with IV potassium and magnesium should be provided as necessary. This is especially important in patients who are also taking medications that cause hypokalemia and hypomagnesemia (i.e., diuretics). Bradycardia Patients with slower heart rates are predisposed to TdP since ventricular repolarization is dependent on the heart rate. In addition, cardiac pauses can generate a long QT interval that is susceptible to EADs, which can propagate an arrhythmia. Drug interactions or organ dysfunction that cause elevated plasma concentrations of QT-prolonging drugs Interference with CYP450 enzyme metabolism may increase concentrations of QT-prolonging drugs. Lack of dose adjustment in a renally impaired or hepatically impaired patient may increase the risk of TdP. Concomitant administration of > 1 drug known to cause QT prolongation or TdP Manufacturers for the majority of the QT-prolonging drugs state concurrent use with other drugs that prolong the QT interval is not recommended due to the increased risk of TdP. Genetic predisposition Patients with congenital LQTS have mutations in ion channels that influence cardiac conduction. The most common mutation forms are KCNQ1 (LQT1) and KCNH2 (LQT2). All drugs with QT prolongation potential should be avoided in these high-risk patients. History of drug-induced TdP There are also reports of increased TdP risk in patients with a history of ventricular tachycardia or ventricular fibrillation.
Abbreviations: ACC/AHA/AACN/ISCE = American College of Cardiology/American Heart Association/American Association of Critical Care Nurses/International Society for Computerized Electrocardiology, EADs = early afterdepolarizations, LQTS = long QT syndrome, TdP = torsade de pointes.
Drugs commonly associated with TdP
The following tables (Table 2 through 4) are lists of drugs commonly associated with TdP. An updated list of drugs is maintained by CredibleMeds and can be found at www.azcert.org. This non-profit research education center reviews scientific literature and provides recommendations regarding the QT-prolonging potential of drugs.11 For drugs in the “risk” category, there is significant evidence that these drugs cause QT prolongation and have an increased risk of TdP. For the drugs in the “possible risk” category, there is significant evidence that these drugs prolong the QT interval; however, there is insufficient evidence as to whether these drugs have an increased risk of causing TdP. Finally, the drugs with “conditional risk” have significant evidence of prolonging QT and causing TdP but only under certain conditions, such as excessive dose or drug interaction. Of note, all 3 lists below include drugs which should be avoided in patients with congenital long QT syndrome. The most common drug classes associated with QT prolongation and/or TdP are antiarrhythmics, antibiotics, antipsychotics, and antidepressants.
Table 2. Drugs with risk of TdP. 1,2,4,11-20
Class/Clinical Use Drug Renally adjust Major CYP substrate Comments Anesthetic Sevoflurane 2E1 Antiarrhythmic* Amiodarone Disopyramide Dofetilide Flecainide Ibutilide Procainamide Quinidine
- The risk of TdP was found to be highest within the first few days of initiation of an anti-arrhythmic.4 Thus, hospitalization is necessary to monitor the patient, especially if they have other risk factors. One study found hospitalization for 3 days following initiation of an antiarrhythmic was cost-effective.
- Class Ia, Ic, and III have been associated with QT prolongation and TdP due to their mechanism of action of delaying repolarization and slowing cardiac conduction.12
- Among the antiarrhythmics, amiodarone is known to have a low risk of TdP because it blocks the potassium channels in concentrations that exceed therapeutic levels and has multiple mechanisms including blockage of calcium channels.1,12
Anticancer Arsenic trioxide Vandetanib X
3A4 Antidepressant Citalopram 2C19, 3A4
- Citalopram causes a dose-dependent increase in QT prolongation; doses > 40 mg per day are no longer recommended.13 In addition, doses > 20 mg are not recommended in patients with hepatic impairment, age > 60 years, or patients who are CYP2C19 poor metabolizers or taking medications that may increase concentrations of citalopram due to the risk of QT prolongation and TdP.
Antiinfective† Azithromycin Chloroquine Clarithromycin Erythromycin Moxifloxacin Pentamidine
2D6, 3A4 3A4
- Macrolides may cause QT prolongation and TdP if used in patients with additional risk factors (the majority of patients have > 2 risk factors).12 Erythromycin has been most frequently implicated, followed by clarithromycin. Azithromycin has less association with QT prolongation, which may be due to its minimal CYP3A4 metabolism. In addition, oral macrolide administration is associated with less risk of QT prolongation because bioavailability is 50%; thus, decreasing the amount of drug exposure.
- Moxifloxacin is the most potent fluoroquinolone and is associated with a greater risk of QT prolongation; however, the risk of TdP is low.14
- Intravenous pentamidine is associated with delayed QT prolongation and TdP; however, inhaled pentamidine is not associated with an increased risk.12
Antipsychotic‡ Chlorpromazine§ Haloperidol Pimozide Thioridazine 2D6
2D6, 3A4 1A2, 3A4 2D6
- Among the older antipsychotics, thioridazine has the greatest QT prolongation, followed by pimozide and haloperidol.15,16 Thioridiazine is also associated with TdP more than other antipsychotics and should be avoided in patients with cardiovascular disease. 16 When thioridazine must be used, routine ECG monitoring is warranted.
- High risk of TdP is also associated with high IV doses of haloperidol.15 If IV administration is warranted, continuous ECG monitoring is recommended.15,17
- Chlorpromazine, a low potency antipsychotic, is only reported to cause QT prolongation at high doses.
- Ideally, antipsychotics should be prescribed as monotherapy and not in combination with other QT prolonging medications.15,16 Of note, the effect on QTc prolongation seems to be dose-dependent.
- Droperidol has been reserved for refractory cases of nausea and vomiting due to its reported dose-dependent QT prolongation (dose >
0.1 mg/kg) and risk of TdP.18,19 If droperidol is necessary, it is recommended to monitor with an ECG prior to initiation and 2 to 3 hours after completion of therapy. There is no strong evidence of lower doses causing TdP and monitoring may not be necessary.
Opioid Methadone X 2B6, 3A4
- It is recommended to obtain a baseline ECG, then 30 days after initiation and then annually.20 If the dose is > 100 mg/day or the patient has symptoms of unexplained syncope or seizures, more frequent monitoring is necessary. If the QTc interval is between 450 msec and 499 msec, monitor patient more frequently. If QTc is > 500 msec, consider decreasing the dose or discontinuing methadone. Reduce and/or eliminate contributing factors such as electrolyte disturbances, drug-drug interactions, and drugs that may reduce the clearance of methadone.
Abbreviations: ECG = electrocardiogram, IV = intravenous, TdP = torsade de pointes.
* Incidence rates of anti-arrhythmics2: amiodarone (0.7%), dofetilide (0-10%), ibutilide (1.4%-11.5%), procainamide (0-3.6%), quinidine (2%-12%), sotalol (0.4%-5%); the incidence with dofetilide, procainamide, and sotalol depends on the presence of left ventricular dysfunction and whether the drug was dose adjusted appropriately for renal function
† Incidence rates of anti-infectives2: erythromycin (0.4%), pentamidine (< 21%)
‡ Incidence rates of anti-psychotics2: haloperidol (3.6%; reported with intravenous use in critically ill patients)
§ Chlorpromazine is also an antinausea medication
Table 3. Drugs with possible risk of TdP. 2,11,14-17,21,22
Class/Clinical Use Drug Renally adjust Major CYP substrate Comments Antianginal Ranolazine 3A4 Antiarrhythmic Dronedarone 3A4 Anticancer Eribulin Lapatinib Nilotinib Sunitinib Tamoxifen X 3A4
Anticonvulsant Felbamate Fosphenytoin X 3A4
Antidepressant Escitalopram Mirtazapine Venlafaxine
2C19, 3A4 1A2, 2D6, 3A4
- QTc prolongation may occur with excessive doses above the therapeutic range or with additional risk factors; placing the patient at risk of developing TdP.15,17
Antihypertensive Isradipine Moexipril/ HCTZ Nicardipine 3A4
Antiinfective Amantadine Foscarnet Gatifloxacin Gemifloxacin Levofloxacin Ofloxacin Telithromycin Voriconazole X
- Fluroquinolones inhibit the potassium channel and increase the QT interval in a dose-depended manner.14 However, inhibition also varies in potency among the agents (moxifloxacin > gatifloxacin > levofloxacin > ciprofloxacin > ofloxacin). Overall, the risk of TdP is small, with ciprofloxacin reported as the safest.
- Patients with prolonged QT interval at baseline are at greater risk of TdP. Due to equivalent bioavailability between oral and IV, the route of fluoroquinolone administration does not contribute to the risk of TdP unless the IV is administered too rapidly. Monitoring with an ECG is not necessary during the initiation of therapy unless the patient has risk factors that predisposes them to TdP, including concomitant medications that prolong the QT interval.
Antipsychotic Clozapine Iloperidone Paliperidone Quetiapine Risperidone Ziprasidone
- Among the newer antipsychotics, ziprasidone has the greatest potential for prolonging the QT interval.15-17 Risperidone and paliperidone are associated with moderate QT prolongation, while quetiapine and clozapine are associated with mild QT prolongation.
- Clozapine has other cardiac complications, such as myocarditis and T-wave changes that may complicate measurement of the QT interval. 16
- Prolongation of the QT interval was reported with excessive doses of olanzapine.15,17
- Ziprasidone is associated with a higher risk of TdP and should be avoided in patients with cardiovascular disease.15,16 If ziprasidone is necessary, routine ECG is warranted.
Antimania Lithium X
- Lithium concentrations above 1.2 mmol/L may prolong the QT interval.17 However, this is not considered high risk for TdP.
Antinausea Dolasetron Granisetron Ondansetron
- QT prolongation has been associated with ondansetron ranging from 4 mg to 32 mg with a few cases of arrhythmias.21 When administering ondansetron long-term for inpatients, patients with cardiovascular disease at high risk of TdP should be monitored via telemetry.
- QT prolongation is dose-dependent and has been specifically observed with a single IV dose of 32 mg.22 Thus, the 32 mg IV dose of ondansetron has been removed from the market. The product labeling now states that single IV doses should not exceed 16 mg.
Diuretic Indapamide Endocrine Octreotide H2-receptor antagonist Famotidine X Imaging contrast agent Perflutren lipid microspheres Immuno-suppressant Fingolimod Tacrolimus 3A4 Labor stimulant Oxytocin Muscle relaxant Tizanidine 1A2 Phosphodiesterase inhibitor Vardenafil 3A4 Protease inhibitor Atazanavir 3A4 Sedative Chloral hydrate
Abbreviations: ECG = electrocardiogram, IV = intravenous, TdP = torsade de pointes.
Table 4. Drugs with conditional risk of TdP. 2,11,12,14,15,17
Class/Clinical Use Drug Renally adjust Major CYP substrate Comments Antidepressant Amitriptyline Clomipramine Desipramine Doxepin
Fluoxetine Imipramine Nortriptyline Paroxetine Protriptyline Sertraline Trazodone Trimipramine
1A2, 2C19 2D6
- QTc prolongation may occur with excessive doses or in patients with additional risk factors.15,17
Antihistamine Diphenhydramine Antiinfective Ciprofloxacin Fluconazole Itraconazole Ketoconazole Trimethoprim-sulfamethoxazole X
- Ciprofloxacin is the safest fluoroquinolone in terms of risk of TdP.14
- It has been suggested that the azole antifungals’ association with QT prolongation is due to drug-drug interactions with other QT-prolonging drugs via strong inhibition of CYP3A4 metabolism.12 Itraconazole and ketoconazole have the highest risk of causing a drug-drug interaction via CYP3A4 inhibition. Fluconazole has been implicated in cases of TdP with or without risk factors. Risk factors must be minimized prior to starting azole antifungals.
Cholinesterase inhibitor Galantamine X Muscarinic antagonist Solifenacin X 3A4 Protease inhibitor Ritonavir 3A4
Abbreviations: TdP = torsade de pointes
Prevention and management
There are many factors to consider when initiating a drug with QT prolonging potential. The benefit must outweigh the risk of TdP. There are several questions to address including:
- Are the benefits clinically important, and are the risks minimized?
- Will this medication affect mortality or morbidity compared to other medications?
- Is this medication superior to other medications or do other medications carry the same risk?
To reduce or prevent TdP, consider the medication’s route of elimination, drug interactions, and other risk factors mentioned above.4 Ideally when starting a new medication with a risk for TdP, obtain a baseline ECG prior to initiation and at steady state, and monitor/correct electrolyte abnormalities throughout the course of therapy.4,16 Some clinicians believe the measurement of the QT interval at baseline may not be cost-effective for medications that have low potential for TdP.4 However, it is practical to consider the cost versus benefit with each individual drug and patient. Well-known risk factors should be considered and minimized if possible. Furthermore, IV administration may have greater association with TdP than oral administration due to exposure to higher serum drug concentrations. Therefore, it is appropriate to measure the QT interval at the time of higher plasma concentrations to assess the risk for TdP. Minimally, an ECG should be obtained when a patient has symptoms (e.g., tachycardia, hypotension, chest pain, syncope), when 2 or more QT-prolonging medications are prescribed concomitantly, or when electrolyte abnormalities or cardiovascular disease is evident.16
Treatment of drug-induced TdP
When TdP occurs offending agents must be discontinued. Hemodynamically stable patients should be treated with 2 g of IV magnesium over 5 minutes followed by 1 to 2 g over 60 minutes .10,23 In patients who are hemodynamically unstable, defibrillation with asynchronous shocks may be necessary. 2 It may be difficult to cardiovert a patient with TdP. It is almost impossible to synchronize multiple QRS complexes with varying heart rates. Moreover, cardiac overdrive pacing may be used to shorten the QT interval and thus terminate TdP.2,9 Similarly, intravenous isoproterenol, dopamine, and atropine may be used to increase the heart rate and shorten the QT interval.2,3 However, this must be done cautiously in patients with heart block as this may worsen TdP. Other therapeutic options include agents that block sodium channels, such as phenytoin and lidocaine, and calcium channel blockers, such as verapamil. Patients with congenital long QT syndrome are at increased risk and may require long-term prophylactic therapy with beta-blockers or permanent cardiac pacing to prevent TdP.
Prolongation of the QT-interval may occur with a variety of medications. The most common classes of medications implicated in QT prolongation are antiarrhythmics, antibiotics, antipsychotics, and antidepressants. As a result, these medications are associated with an increased risk of TdP, which is a serious life-threatening arrhythmia. However, TdP is a rare complication, especially in patients without contributing risk factors. The majority of patients with drug-induced TdP present with 2 or more risk factors. Risk factors for TdP include: female gender, age greater than or equal to 65 years, cardiovascular disease, electrolyte abnormalities, 2 or more QT prolonging medications, and drug-drug interactions. An ECG may not always be warranted prior to initiation of a medication associated with QT prolongation. However, if a patient presents with symptoms of TdP, has evidence of cardiovascular disease (i.e., left ventricular systolic dysfunction or a history of myocardial infarction), or is prescribed 2 or more drugs with potential for QT prolongation, then ECG monitoring should be performed. Risk factors should be identified and minimized, including electrolyte supplementation for hypokalemia and hypomagnesemia. As a rule of thumb, a QTc interval greater than 500 msec deserves discontinuation of the offending agent and reevaluation of therapy. Understanding QT prolongation and the risks associated with TdP may help healthcare professionals better manage therapy with QT prolonging medications.
1. Van Noord C, Eijgelsheim M, Stricker BH. Drug- and non-drug-associated QT interval prolongation. Br J Clin Pharmacol. 2010;70(1):16-23.
2. Tisdale JE. Ventricular arrhythmias. In: Tisdale JE, Miller DA, eds. Drug Induced Diseases: Prevention, Detection, and Management. 2nd Ed. Bethesda, MD: American Society of Health-System Pharmacists; 2010:405-515.
3. Kramer DB, Zimetbaum PJ. Long-QT syndrome. Cardiol Rev. 2011;19(5):217-225.
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Roseanne Patel, PharmD, PGY1