drug induced qt prolongation and torsades de...
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Drug induced QT prolongation and Torsades de Pointes
(TdP)
Mark Friesen, PharmD March 13, 2013
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Conflict of Interest
None
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TdP: Learning objectives To review the pathophysiology of
QT prolongation and TdP To become aware of the risk
factors (including medication-related) for QT prolongation and TdP
To understand and apply a systematic approach for dealing with drug interactions that may cause prolonged QT and TdP
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Clinical Scenario
You receive an order for a patient: Levofloxacin 500 mg PO daily Fluconazole 400 mg PO daily
Your drug interaction program flags this as a major interaction due to QT prolonging effect of both drugs increasing risk for TdP.
What do you do?
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TdP: History Quinidine associated syncope since 1920’s Congenital syndromes with prolonged QT and
syncope or sudden death described in 1950’s, and early 1960’s.
1966 Francois Dessertenne described a specific EKG form of polymorphic VT he termed “torsades de pointes”
Over past decade single most common cause of drug withdrawal/restriction from market
9 structurally unrelated non-cardiac drugs: terfenadine, astemizole, grepafloxicin, terodiline, droperidol, terodiline, droperidol, lidoflazaine, sertindole, levomethadyl, cisapride
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TdP: Definition
Polymorphic VT with a preexistant prolonged QT interval
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Ventricular Action Potential
Na+ IKr
Ca++
IKs
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IKr Channel: hERG controlled
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Delayed repolarization=prolonged QT interval
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Mechanism of Torsades de Pointes
Early afterdepolarizations (extra beat) Transmural reentry (Unusual pathway)
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Mechanisms Of Drug - Induced QT Prolongation and Tdp
Block of repolarizing K+ currents Stimulation of ICa-l Stimulation of INa
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Early afterdepolarizations
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Yan & Antzelevitch Circulation. 1998;98:1921-1927
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Yan & Antzelevitch Circulation. 1998;98:1928-1936
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Torsades de Pointes
EPI
M
ENDO
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Ann Phamacotherp 1999; 33:1046-50
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ECG - QT Interval
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Rate-Corrected QT Interval (QTc)
QT Interval corrected for heart rate = QTc (Bazett)
QTc =
General Population Average QTc = 380-400 msec Bazett correction has major limitations
Overcorrects for HR > 85 BPM
HR 66 bpm
QT 350 msec
QTc 370 msec
HR 83 bpm
QT 350 msec
QTc 410 msec
QT √ RR
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Normal QTc Interval - Criteria
QTc (msec) Male Female Normal <430 <450
Borderline 431-450 451-470
Prolonged (Top 1%) >450 >470
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QTc Interval and TdP risk
For every 10 msec increase in QTc above normal= 5-7% exponential increase in risk of TdP
QTc>500msec= 2-3X increased risk for TdP
Prevention of Torsade de Pointes in Hospital Settings; J. Am. Coll. Cardiol. 2010;55;934-947
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Assessing the risk of TdP with QT prolonging drug
Class 1a anti-arrhythmic agents Quinidine/ Disopyrimyde/procainamide : 2-
8% Class III anti-arrhythmic agents
Sotalol: 2-4% Ibutilide: 4-8% Dofetilide 1-10% Amiodarone <1%
Non-cardiac drugs: 1-10/100,000
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Assessing the risk of TdP with QT prolonging drug
www.qtdrugs.org Risk, Possible risk, Conditional risk
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The Cordarone Paradox
QT prolongation Low TdP risk Multichannel blockade:
Both Kr & Ks: minimize QT dispersion Na, Ca, Beta: minimize EAD
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Risk factors: Non-modifiable History of TdP Congenital Long QT syndrome Cardiac disease
Heart failure Hypertrophy Ischemia Myocardititis
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Risk factors: Non-modifiable
Epinepherine surge Cocaine Pheochromocytoma Stroke/subarachnoid hemorrhage Drug withdrawal
Starvation Female (minor) Age?
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Risk factors: Modifiable (potential ADR’s)
Hypokalemia Hypomagnesemia Hypocalcemia (minor) Hypothyroid Bradyarrhythmias
Sinus bradycardia Complete AV block Recently terminated A fib
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Risk factors: Modifiable (potential ADR’s)
High QT drug concentrations (with exception of class1a anti-arrhythmic agents): High dose Renal/hepatic dysfunction Pharmacokinetic drug interactions Fast IV infusions Small body habitus
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35% PK interaction causing high levels of QT drug Cisapride/2nd gen H2 blockers plus
3A4 inhibitors (especially erythromycin)
19 % Excessive doses 18% Long QT (familial history, TdP
history, long baseline QT) Especially for antihistamines
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95% had at least 1 risk factor 71% had 2 or more risk factors 35% had 3 or more risk factors 80% of females had additional risk
factors
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Patient TdP risk
High Risk= History of TdP or LQTS Medium Risk= Multiple/severe risk
factors Low Risk= Minimal/mild risk factors
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Approach to patient prescribed QT prolonging drugs:
Disclaimer: This approach is only a rough guide and should not take the place of clinical judgment!
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Approach to patient prescribed QT prolonging drugs:
Determine risk level (known, possible, conditional) for QT drugs from www.qtdrugs.org
Determine risk level for patient from Table 2 High risk=History of Torsades de
Pointes/Congenital Long QT Syndrome
Medium risk Multiple/severe risk factors
Low risk=Minimal/mild risk factors
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Risk factors
Non-modifiable risk factor
Potentially modifiable risk factor (watch for drug related causes)
•History of TdP •Congenital Long QT syndrome •Female •Cardiac disease
•Heart failure •Hypertrophy •Ischemia •Myocardititis •A fib (esp. recently terminated)
•Epinepherine surge •Cocaine •Pheochromocytoma •Stroke/subarachnoid hemorrhage •Drug withdrawal
•Hypokalemia •Hypomagnesemia •Hypocalcemia •Hypothyroid •Bradycardia •High QT drug concentrations (with exception of quinidine):
•High dose •Renal/hepatic dysfunction •Drug interactions •IV route •Small body habitus
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Approach to patient prescribed QT (prolonging) drugs:
QT Drug Combination
risk
High risk
patient
Med risk patient
Low risk patient
Known risk +known risk
Avoid Avoid Avoid
Known risk + possible/ conditional risk
Avoid EKG monitoring
+/- EKG monitoring
Possible/ conditional risk + possible/ conditional risk
Avoid +/- EKG monitoring
No special monitoring
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Approach to patient prescribed QT (prolonging) drugs:
Determine general approach to patient from Table 1
Avoid: High risk, generally avoid QT drug combination
EKG monitoring: Baseline QTc >440 msec: avoid high risk drugs Baseline QTc >460 msec: avoid med risk drugs Baseline/On therapy* QTc >500 msec: avoid/stop
all QT drugs Change from baseline to on therapy* QTc > 60
msec: stop all TdP risk drugs *On therapy for >= 5 x half-lives of drug
No special monitoring: Low risk; QT drugs generally okay
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Drug Interaction Resources
Lexi-Drugs MicroMedex Facts and Comparisons Stockley’s www.torsades.org
Drug lists Pubmed search
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Bibliography Viskin S: Long QT and TdP. Lancet 1999;354:1625-33 Yap YG, Camm AJ: Drug induced QT prolongation
and TdP. Heart 2003;89:1363-72 Al-Khatib SM et al: What clinicians should know about
QT interval. JAMA 2003;289:2120-17. Roden DM: Drug induced prolongation of the QT
interval. NEJM 2004;350:1013-22. White CM, Coleman CI: Drug-Induced Cardiac
Diseases. PSAP 2007 6th edition. 41-5. ACC/AHA Guidelines: Prevention of Torsade de
Pointes in Hospital Settings. J. Am. Coll. Cardiol. 2010;55;934-947
www.fda.gov/ohrms/DOCKETS/ac/01/slides/3746s_01_ruskin.ppt
www.pha.nu.ac.th/apirukw/ambu/uploads/83F39_Drug_induced_cardiac_arrhythmia.pdf