Methadone-associated long QT syndrome: improving pharmacotherapy for dependence on illegal opioids and lessons learned for pharmacology

Methadone is used as the pharmacologic mainstay for substitution for illegal opiates and as analgesic for chronic or cancer-related pain. Given the benefits of methadone substitution for illicit opioids, the finding of an association between methadone and prolongation of cardiac depolarization (QT prolongation) and torsades de pointes is of great concern. QT prolongation can occur with many drugs and is a potentially lethal adverse drug reaction, necessitating risk monitoring and therapeutic alternatives in some patients. Recent studies suggest that QT prolongation with methadone is context dependent: occurrence is more frequent with high doses of methadone, concomitant administration of CYP3A4 inhibitors, hypokalemia, hepatic failure, administration of other QT prolonging drugs and pre-existing heart disease. The valued benefit of methadone substitution therapy on the one hand and the increased cardiovascular risk in particular situations on the other illustrate the difficulties in dealing with drug-induced QT prolongation in general.     

Torsades de pointes with methadone

(1) Methadone is an opiate used for replacement therapy of opiate addiction that causes dose-dependent QT prolongation. (2) Severe ventricular arrhythmias such as torsades de pointes have been reported, usually in patients on high doses (100 mg to 400 mg/day). (3) Methadone has a long plasma elimination half-life, and this poses a risk of accumulation. Accumulation is especially problematic when the dose is increased too rapidly. Combining methadone with a CYP 3A4 inhibitor increases the risk of torsades de pointes, as methadone is metabolised by this enzyme system. (4) Factors potentially predisposing patients to torsades de pointes must be analysed in each case; these include preexisting bradycardia, congenital QT prolongation, hypokalemia, and concomitant use of other drugs inducing QT prolongation. (5) This adverse effect has also been reported with levacetylmethadol (another opiate) and with heroin. It does not seem to occur with buprenorphine.     

QTc interval prolongation by d-propoxyphene: what about other analgesics?

INTRODUCTION: d-Propoxyphene, which was previously available in many single-agent and combination products, was recently voluntarily withdrawn from the US market following an FDA recommendation based partly on the concern that the risk associated with QT prolongation exceeded the clinical benefit of the drug. The drug had previously been withdrawn from European markets. These recent actions prompt the question: what is known about QT prolongation and analgesic drugs? AREAS COVERED: A systematic search was conducted of 50 opioid and non-opioid analgesic drugs using PubMed, the FDA website, and the Internet. Search terms for opioids, NSAIDs, acetaminophen and other analgesics were used (including both generic and brand names), along with QTc, QTc prolongation, QTc interval, hERG, torsades de pointes (TdP), ventricular arrhythmias, and other relevant terms. EXPERT OPINION: There is a paucity of available information on the QT interval for most analgesics. Of those for which there is a lot of data, only methadone, oxycodone, and LAAM (levo--acetylmethadol) appear to have a known and accepted level of effect on the QT interval.     

QT prolongation and torsades de pointes among methadone users: reports to the FDA spontaneous reporting system

BACKGROUND: Recent case series have associated the synthetic opioid, methadone, with QT prolongation and torsades de pointes (TdP) ventricular arrhythmia. STUDY OBJECTIVE: To review and analyze adverse events (QT prolongation and TdP) reported to the Food and Drug Administration (FDA) to determine the patient characteristics, dosages of methadone, and outcomes of methadone-treated patients. METHODS: The study design was a retrieval and retrospective analysis of reports of adverse events associated with methadone voluntarily reported to the FDA MedWatch program from 1969 to October 2002. Reports were accessed via QSCAN (DrugLogic, Reston, VA), a commercially available software interface. RESULTS: In a total of 5,503 reports of adverse events associated with methadone, 43 (0.78%) noted the occurrence of TdP and 16 (0.29%) QT prolongation. Doses were reported in 42/59 (71%) of cases; mean dose was 410 +/- 349 mg/day (median 345, range 29-1680). The dosages for 10 of the 42 cases (29%) were within the recommended range for methadone maintenance treatment, 60-100 mg/day. Female gender, interacting medications, hypokalemia, hypomagnesemia, and structural heart disease, risk factors previously identified with other drugs known to cause TdP, were found in 44 (75%) cases. Most adverse events required hospitalization or resulted in prolonged hospitalization (28/59, 47%) and 5/59 (8%) were fatal. CONCLUSIONS: Cases of TdP associated with methadone have been reported to the FDA MedWatch system. Analysis of the cases provides evidence that prolonged QT and TdP can occur over a wide range of dosages including those usually recommended for addiction treatment.     

胺碘酮对房颤患者QTc间期的影响及安全性评价

目的:评价胺碘酮对我院房颤患者QTc间期的影响及其药品不良反应。方法:研究纳入2013年1月—2014年5月间上海交通大学医学院附属仁济医院房颤住院患者共l56例,记录患者一般资料及合用药物等信息,观察应用胺碘酮注射液或胺碘酮片剂后心率、QT间期、QTc间期的变化,以及在胺碘酮用药期间是否发生与用药相关的不良反应。结果:用药后房颤患者的平均心率显著减慢(79.2±21.6)bpm比(72.9±13.1)bpm(P<0.01),QT间期(386.5±45.7)ms比(415.8±53.1)ms(P<0.01)、QTc间期均显著延长(413.9±32.1)ms比(438.0±44.4)ms(P<0.01)。有16例患者用药后QTc>500ms,17例患者用药后QTc<500ms,但△QTc>50ms。共有22例患者合并使用一种或多种可延长QT间期的药物,包括氟哌噻吨美利曲辛片(10例),多塞平(7例),左氧氟沙星(6例)等。心动过缓、2型糖尿病、合用其他影响QT间期药物为延长QTc间期的因素(P<0.05)。44例患者使用胺碘酮注射液中有5例发生注射部位反应,未出现与胺碘酮相关的心律失常(包括尖端扭转性室速)。结论:胺碘酮应用后QT间期、QTc间期均不同程度延长,对于用药后QTc>500ms、△QTc>50ms或合并使用其他可延长QT间期药物的患者,需调整胺碘酮剂量并严密监测心电图,警惕恶性心律失常的发生。     

QTc interval prolongation by d-propoxyphene: what about other analgesics?

Introduction: d-Propoxyphene, which was previously available in many single-agent and combination products, was recently voluntarily withdrawn from the US market following an FDA recommendation based partly on the concern that the risk associated with QT prolongation exceeded the clinical benefit of the drug. The drug had previously been withdrawn from European markets. These recent actions prompt the question: what is known about QT prolongation and analgesic drugs?

Areas covered: A systematic search was conducted of 50 opioid and non-opioid analgesic drugs using PubMed, the FDA website, and the Internet. Search terms for opioids, NSAIDs, acetaminophen and other analgesics were used (including both generic and brand names), along with QTc, QTc prolongation, QTc interval, hERG, torsades de pointes (TdP), ventricular arrhythmias, and other relevant terms.

Expert opinion: There is a paucity of available information on the QT interval for most analgesics. Of those for which there is a lot of data, only methadone, oxycodone, and LAAM (levo--acetylmethadol) appear to have a known and accepted level of effect on the QT interval.     

Drug- and non-drug-associated QT interval prolongation

Sudden cardiac death is among the most common causes of cardiovascular death in developed countries. The majority of sudden cardiac deaths are caused by acute ventricular arrhythmia following repolarization disturbances. An important risk factor for repolarization disturbances is use of QT prolonging drugs, probably partly explained by gene–drug interactions. In this review, we will summarize QT interval physiology, known risk factors for QT prolongation, including drugs and the contribution of pharmacogenetics. The long QT syndrome can be congenital or acquired. The congenital long QT syndrome is caused by mutations in ion channel subunits or regulatory protein coding genes and is a rare monogenic disorder with a mendelian pattern of inheritance. Apart from that, several common genetic variants that are associated with QT interval duration have been identified. Acquired QT prolongation is more prevalent than the congenital form. Several risk factors have been identified with use of QT prolonging drugs as the most frequent cause. Most drugs that prolong the QT interval act by blocking hERG-encoded potassium channels, although some drugs mainly modify sodium channels. Both pharmacodynamic as well as pharmacokinetic mechanisms may be responsible for QT prolongation. Pharmacokinetic interactions often involve drugs that are metabolized by cytochrome P450 enzymes. Pharmacodynamic gene–drug interactions are due to genetic variants that potentiate the QT prolonging effect of drugs. QT prolongation, often due to use of QT prolonging drugs, is a major public health issue. Recently, common genetic variants associated with QT prolongation have been identified. Few pharmacogenetic studies have been performed to establish the genetic background of acquired QT prolongation but additional studies in this newly developing field are warranted.     

Quetiapine and other antipsychotics combined with opioids in legal autopsy cases: A random finding or cause of fatal outcome?

Opioid poisoning is a frequent cause of death in drug addicts and occurs with opioid treatment. Quetiapine is often found in forensic autopsies and may increase the risk of fatal opioid poisoning by enhancing sedation, respiratory depression, hypotension and QT prolongation. We systematically searched for studies of acute toxicity of quetiapine or other antipsychotics combined with morphine or methadone. Case reports describing toxicity of quetiapine combined with morphine or methadone were also included. We retrieved one human study that observed pharmacokinetic interaction between quetiapine and methadone, and 16 other human studies. Fourteen investigated the combination of droperidol and morphine in treatment doses, and some indicated an additive sedative effect. Five animal studies with acepromazine in combination with morphine or methadone were located and indicated an additive effect on sedation and hypotension. Six forensic case reports in which death could have been caused solely by quetiapine, the opioid, or other drugs were found. Thus, acute toxicity of quetiapine combined with morphine or methadone has not been studied. Because of quetiapine's effects on alpha‐adrenoceptors, muscarinic and histamine receptors, human ether‐a‐go‐go‐channels and methadone kinetics, we suggest further research to clarify if the indicated additive effects of opioids and droperidol or acepromazine are also true for quetiapine.     

Clinical relevance and management of drug-related QT interval prolongation

Much attention recently has focused on drugs that prolong the QT interval, potentially leading to fatal cardiac dysrhythmias (e.g., torsade de pointes). We provide a detailed review of the published evidence that supports or does not support an association between drugs and their risk of QT prolongation. The mechanism of drug-induced QT prolongation is reviewed briefly, followed by an extensive evaluation of drugs associated with QT prolongation, torsade de pointes, or both. Drugs associated with QT prolongation are identified as having definite, probable, or proposed associations. The role of the clinician in the prevention and management of QT prolongation, drug-drug interactions that may occur with agents known to affect the QT interval, and the impact of this adverse effect on the regulatory process are addressed.     

Itraconazole‐induced Torsade de Pointes in a patient receiving methadone substitution therapy

Issues. Methadone, a pharmacological agent used to treat heroin dependence is relatively safe, but may cause cardiac arrhythmias in the concurrent presence of other risk factors. Approach and Key Findings. This case report highlights the risk of Torsade de Pointes, a life‐threatening cardiac arrhythmia, in a heroin‐dependent patient receiving methadone substitution therapy who was prescribed itraconazole for vaginal thrush. The patient presented to the accident and emergency department for chest discomfort and an episode of syncope following two doses of itraconazole (200 mg). Electrocardiogram monitoring at the accident and emergency department showed prolonged rate‐corrected QT interval leading to Torsade de Pointes. The patient was admitted for cardiac monitoring, and electrocardiogram returned to normal upon discontinuation of methadone. Implication. This cardiac arrhythmia was most likely as a result of a drug interaction between methadone and itraconazole because the patient presented with no other risk factors. Conclusion. Given the benefits of methadone as a substitution treatment for heroin‐dependent individuals, the association between methadone and cardiac arrhythmias is of great concern. Physicians treating heroin‐dependent patients on methadone substitution therapy should therefore be cautious of the potential risk of drug interactions that may lead to fatal cardiac arrhythmias.[NoorZurani MHR, Vicknasingam B, Narayanan S. Itraconazole‐induced Torsade de Pointes in a patient receiving methadone substitution therapy. Drug Alcohol Rev 2009;28:688–690]     

Draft ICH guideline S7B: guideline on safety pharmacology studies for assessing the potential for delayed ventricular repolarization (QT interval prolongation) by human pharmaceuticals

Nonclinical assessment of potential of QT interval prolongation caused by non-antiarrhythmic drugs has been an issue for drug development because QT interval prolongation increases the risk of ventricular tachyarrhythmia, including torsade de pointes when combined with other risk factors. However, there is no scientific consensus on approaches and no international consensus on regulatory recommendations. This guideline is being developed to provide the general nonclinical testing strategy for evaluating the potential risk of QT prolongation and presents some major principles for in vitro and in vivo electrophysiology studies. The basis of this guideline is the integrated risk assessment that provides overall evaluations based on nonclinical study results and chemical/pharmacological class information to predict the potential of a test substance to prolong QT interval in humans (i.e., evidence of risk) and that contributes clinical study design and interpretation of clinical results. Safety margins are also components of integrated risk assessment. Since this guideline addresses a field of research that is in a state of rapid evolution, the proposed concept for evidence of risk and safety margins needs to be further refined based on the data being collected by international initiatives. In this article, the draft S7B guideline is outlined.     

药物致Q-T间期延长的文献分析

近年来,临床实践有许多药物都会导致Q-T间期延长甚至尖端扭转型室性心律失常（TdP）。本文通过对1979年-2013年国内医药期刊公开报道的药物致Q-T间期延长的个案进行统计和分析,总结了56个病例的一般情况、引起Q-T间期延长的药物、发生时间及转归等,致Q-T间期延长药物中排在前三位的分别为抗心律失常药、抗微生物药、抗组胺药。大部分患者在用药后一个月内出现,停药及对症治疗后好转。临床医师应正确地认识药物致Q-T间期延长发生机制和易感因素,才能保证临床安全有效地使用药物。     

Haloperidol affects coupling between QT and RR intervals in guinea pig isolated heart

Prolonged QT interval is an independent risk factor for development of ventricular arrhythmias. Haloperidol is one of the drugs inducing QT prolongation. Previous studies showed that haloperidol affects not only QT duration but also heart rate (RR interval). The present work focused on relationship between QT and RR and its changes under acute and chronic haloperidol administration. The study included 14 male guinea pigs divided into control and haloperidol-treated group. After 21-days administration of haloperidol or vehiculum, electrograms in isolated hearts were recorded. QT/RR and dQT/dRR coupling were calculated. Chronic haloperidol administration significantly decreases the coupling between QT and RR. Acute haloperidol exposure significantly decreases the dQT/dRR coupling in both treated and untreated guinea pig hearts. Flatter QT/RR relationship reveals a lack of QT adaptation to increased heart rate. It should be emphasized that in such situation ECG recording will not show significant QT prolongation evaluated according to clinical rules. However, if QT interval does not adapt to increased heart rate sufficiently, the risk of ventricular arrhythmias may be increased despite practically normal QT interval length. The results are supported by findings in biochemical analyses, which proved eligibility of the used model.     

No Untoward Effect of Long‐Term Ketoconazole Administration on Electrocardiographic QT Interval in Patients with Cushing's Disease

Ketoconazole is listed among drugs that prolong QT interval and may increase the risk of torsade de pointes, a severe ventricular arrhythmia. This compound has recently been approved for treatment of Cushing's syndrome, a severe endocrine disorder. These patients harbour several risk factors for prolonged QT interval, for example hypokalaemia and left ventricular hypertrophy, but no study has evaluated whether administration of ketoconazole affects their QT interval. The aim of this study was to assess the QT interval in patients with Cushing's disease during long‐term administration of ketoconazole. Electrocardiograms from 15 patients with Cushing's disease (12 women, 3 men, age: 37.8 ± 2.66 years) on ketoconazole treatment (100 mg–800 mg qd) for 1 month to 12 years were reviewed retrospectively. QT interval was measured and corrected for heart rate (QTc). Measurements before and during ketoconazole treatment were compared and any abnormal QTc value recorded. Concurrent medical therapies were also documented. On average, QTc was superimposable before and during ketoconazole treatment (393.2 ± 7.17 versus 403.3 ± 6.05 msec. in women; 424.3 ± 23.54 versus 398.0 ± 14.93 msec. in men, N.S.). QTc normalized on ketoconazole in one man with prolonged QTc prior to treatment; no abnormal QTc was observed in any other patient during the entire observation period, even during concurrent treatment with other QT‐prolonging drugs. In conclusion, long‐term ketoconazole administration does not appear to be associated with significant prolongation of QT interval in patients with Cushing's disease. ECG monitoring can follow recommendations drawn for other low‐risk QT‐prolonging drugs with attention to specific risk factors, for example hypokalaemia and drug interactions.     

Prediction of the risk of Torsade de Pointes using the model of isolated canine Purkinje fibres

Torsade de Pointes (TdP) is a well-described major risk associated with various kinds of drugs. However, prediction of this risk is still uncertain both in preclinical and clinical trials. We tested 45 reference compounds on the model of isolated canine Purkinje fibres. Of them, 22 are clearly associated and/or labelled with a risk of TdP, and 13 others are drugs with published clinical evidence of QT prolongation, with only one or two exceptional cases of TdP. The 10 remaining drugs are without reports of TdP and QT prolongation. The relevance of different indicators such as APD(90) increase, reverse use dependency, action potential triangulation or effect on V(max) was evaluated by comparison with available clinical data. Finally, a complex algorithm called TDPscreen and based on two subalgorithms corresponding to particular electrophysiological patterns was defined. This latter algorithm enabled a clear separation of drugs into three groups: (A) drugs with numerous or several reports (>2 cases) of TdP, (B) drugs causing QT prolongation and/or TdP only, the latter at a very low frequency (< or =2 cases), (C) drugs without reports of TdP or QT prolongation.The use of such an algorithm combined with a database accrued from reference compounds with available clinical data is suggested as a basis for testing new candidate drugs in the early stages of development for proarrhythmic risk prediction.     

Risk assessment for antimicrobial agent-induced QTc interval prolongation and torsades de pointes

Over the past several years a multitude of new pharmaceutical agents have been released to the market. Several of them were withdrawn altogether or their use severely restricted to certain indications due to unexpected adverse events, including fatalities. Progress in developing new compounds clearly has surpassed our technology, in some cases, to measure and predict certain toxicities. Prolongation of the QT interval, which may lead to potentially life-threatening ventricular arrhythmias such as torsades de pointes, is one example. Regulatory agencies such as the Food and Drug Administration are increasing standards by which drugs are evaluated for cardiac toxicity related to QT interval prolongation. It is imperative that clinicians be knowledgeable of the risk factors for QT prolongation and avoid the use of culpable agents in patients at risk for QT prolongation.     

Zoniporide: a potent and highly selective inhibitor of human Na(+)/H(+) exchanger-1

Many antipsychotic drugs produce QT interval prolongation on the electrocardiogram (ECG). Blockade of the human cardiac K(+) channel known as human ether-a-go-go-related gene (HERG) often underlies such clinical findings. In fact, HERG channel inhibition is now commonly used as a screen to predict the ability of a drug to prolong QT interval. However, the exact relationship between HERG channel blockade, target receptor binding affinity and clinical QT prolongation is not known. Using patch-clamp electrophysiology, we examined a series of seven antipsychotic drugs for their ability to block HERG, and determined their IC(50) values. We then compared these results to their binding affinities (K(i) values) for the dopamine D(2) receptor, the 5-HT(2A) receptor and, where available, to clinical QT prolongation data. We found that sertindole, pimozide and thioridazine displayed little (<10-fold) or no selectivity for dopamine D(2) or 5-HT(2A) receptors relative to their HERG channel affinities. This lack of selectivity likely underlies the significant QT interval prolongation observed with administration of these drugs. Of the other drugs tested (ziprasidone, quetiapine, risperidone and olanzapine), olanzapine displayed the greatest selectivity for dopamine D(2) and 5-HT(2A) receptor binding (100-1000-fold) compared to its HERG channel IC(50). We also compared these HERG channel IC(50) values to QT interval prolongation and plasma drug levels obtained in a recent clinical study. We found that the ratio of total plasma drug concentration to HERG IC(50) value was indicative of the degree of QT prolongation observed. Target receptor affinity and expected clinical plasma levels are important parameters to consider for the interpretation of HERG channel data.     

Understanding drug-induced torsades de pointes: a genetic stance

Drugs may produce a variety of arrhythmias, but drug-induced QT prolongation and the risk of the polymorphic ventricular tachycardia torsades de pointes (drug-induced long QT syndrome) has garnered the most attention. The wide array of drugs with potential for QT prolongation, the correspondingly large number of patients exposed to such drugs, the difficulty in predicting an individual's risk, and the potentially fatal outcome, make drug-induced long QT syndrome an important public health problem for clinicians, researchers, drug development programs, and regulatory agencies. This review focuses on the genetic risk factors and mechanisms underlying QT prolongation and proarrhythmia. The post-genomic era hints at an improved understanding (and prediction) of how the gene-environment interaction produces this particular adverse drug response.     

Methadone maintenance,QTc and torsade de pointes: Who needs an electrocardiogram and what is the prevalence of QTc prolongation?

Introduction and Aims. High‐dose methadone has been associated with rate‐corrected QT (QTc) prolongation and ‘torsade de pointes’. The Medicines and Healthcare products Regulatory Agency (MHRA) advise electrocardiograms (ECGs) for patients on methadone with heart/liver disease, electrolyte abnormalities, concomitant QT prolonging medications/CYP3A4 inhibitors or prescribed methadone >100 mg daily. The percentage of patients fulfilling MHRA criteria for ECG monitoring and prevalence of QT prolongation in patients who had an ECG was assessed. Design and Methods. A cross‐sectional study of opioid‐dependent patients prescribed opioid maintenance that completed a screening questionnaire prior to referral for an ECG. MHRA criteria were assessed in the referred group. The automated QTc score was analysed with methadone dose, substance use and QT risk factors. Results. Of 155 patients screened; 57.4% (n = 89) fulfilled MHRA criteria for ECG monitoring (75.5% (n = 117) if cocaine included as QT prolonging drug). Eighty‐three (53.5%) had ECGs; 19.3% (n = 16) prescribed QT prolonging medication, 22.9% (n = 19) prescribed >100 mg methadone and 47% (n = 39) used cocaine. Mean QTc interval was 429.0 ms (SD 26.4, 351–489). Eighteen per cent exceeded QTc gender‐specific thresholds (≥450 ms men and≥470 ms women). Linear regression found total daily methadone dose (β = 0.318, P = 0.003) and stimulant use (β = ?0.213, P = 0.043) predictive of QTc length. Discussion. Over half to three‐quarters of methadone maintenance patients fulfilled MHRA criteria for ECG monitoring, which has costly implications. QTc prolongation prevalence was 18.1% with no ‘clinically significant’ QTc prolongation >500 ms or torsade de pointes known to be present. Methadone dose and stimulant use were associated with longer QTc intervals. Further research on the clinical management of QTc prolongation with methadone is required.[Mayet S, Gossop M, Lintzeris N, Markides V, Strang J. Methadone maintenance, QTc and torsade de pointes: Who needs an electrocardiogram and what is the prevalence of QTc prolongation? Drug Alcohol Rev 2011;30:388–396]