Azithromycin Can Prolong QT Interval and Suppress Ventricular Contraction, but Will Not Induce Torsade de Pointes

Short-term azithromycin use is associated with QTc interval prolongation in children with cystic fibrosis

BACKGROUND

Azithromycin is used for children with cystic fibrosis (CF) for its immunomodulatory and anti-inflammatory action. This study investigated the short-term alterations in QTc interval associated with azithromycin prophylaxis in pediatric patients with CF.

METHODS

This study included 121 patients with mild CF, of whom 76 received azithromycin (patient group) and 45 did not receive azithromycin (control group). The patient and control groups were categorized according to age as under 12 years of age and over 12 years of age. The first presentation measured all the patient and control groups at basic QTc time intervals. The QTc intervals of all patients were then remeasured systemically at 1, 3, and 6 months. Age categories and QTc intervals that were calculated at each month in the patient and control groups were compared statistically.

RESULTS

A statistically significant difference was detected in the patient group between the initial QTc interval time and the electrocardiogram (ECG) findings in the first and third months after prophylaxis treatment (p < 0.001; p = 0.01). However, no statistically significant difference was detected in the sixth month (p > 0.05) in all groups. Almost all of the children's QTc intervals were within normal range and within the safety zone (under 0.44 s). No statistically significant difference was detected in the control group between the initial ECG and the QTc intervals measured at 1, 3, and 6 months.

CONCLUSION

Short-term use of azithromycin prophylaxis in pediatric patients with mild CF slightly increased the QTc interval in the first and third months of follow-up. Nevertheless, all QTc interval changes fell within the safety zone. Notably, 1 month of follow-up treatment should be performed to check for any alteration in the QTc interval. If increased QTc interval duration is not detected in the first month, azithromycin prophylaxis can be safely prescribed.

Hydroxychloroquine and azithromycin alter the contractility of living porcine heart slices

The cardiotoxicity risk of hydroxychloroquine (HCQ) and azithromycin (AZM) has been the subject of intensive research triggered by safety concerns in COVID-19 patients. HCQ and AZM have been associated with QT interval prolongation and drug-induced arrhythmias, however other cardiotoxicity mechanisms remain largely unexplored. Our group has pioneered the living heart slice preparation, an ex-vivo platform that maintains native cardiac tissue architecture and physiological electrical and contractile properties. Here, we evaluated the cardiotoxic effect of HCQ and AZM applied alone or in combination on cardiac contractility by measuring contractile force and contraction kinetics in heart slices prepared from porcine hearts. Our results show that clinically relevant concentrations of HCQ monotherapy (1-10 µM) reduced contractile force and contraction kinetics in porcine slices in a dose-dependent manner. However, AZM monotherapy decreased contractile force and contraction kinetics only at higher concentrations (30 µM). Combination of HCQ and AZM induced a dose-dependent effect similar to HCQ alone. Furthermore, pre-treating porcine heart slices with the L-type calcium channel agonist Bay K8644 prevented the effect of both drugs, while administration of Bay K8644 after drugs interventions largely reversed the effects, suggesting a mechanism involving inhibition of L-type calcium channels. These findings indicate that HCQ and AZM alter cardiac function beyond QT prolongation with significant contractile dysfunction in intact cardiac tissue. Our porcine heart slices provide a powerful platform to investigate mechanisms of drug cardiotoxicity.

In silico investigation of pro-arrhythmic effects of azithromycin on the human ventricle

The macrolide antibiotic azithromycin (AZM) is widely used for respiratory infections and has been suggested to be a possible treatment for the Coronavirus Disease of 2019 (COVID-19). However, AZM-associated QT interval prolongation and arrhythmias have been reported. Integrated mechanistic information on AZM actions on human ventricular excitation and conduction is lacking. Therefore, this study was undertaken to investigate the actions of AZM on ventricular cell and tissue electrical activity. The O'Hara- Virag-Varro-Rudy dynamic (ORd) model of human ventricular cells was modified to incorporate experimental data on the concentration-dependent actions of AZM on multiple ion channels, including INa, ICaL, IKr, IKs, IK1 and INaL in both acute and chronic exposure conditions. In the single cell model, AZM prolonged the action potential duration (APD) in a concentration-dependent manner, which was predominantly attributable to IKr reduction in the acute condition and potentiated INaL in the chronic condition. High concentrations of AZM also increased action potential (AP) triangulation (determined as an increased difference between APD30 and APD90) which is a marker of arrhythmia risk. In the chronic condition, the potentiated INaL caused a modest intracellular Na + concentration accumulation at fast pacing rates. At the 1D tissue level, the AZM-prolonged APD at the cellular level was reflected by an increased QT interval in the simulated pseudo-ECG, consistent with clinical observations. Additionally, AZM reduced the conduction velocity (CV) of APs in the acute condition due to a reduced INa, and it augmented the transmural APD dispersion of the ventricular tissue, which is also pro-arrhythmic. Such actions were markedly augmented when the effects of chronic exposure of AZM were also considered, or with additional IKr block, as may occur with concurrent use of other medications. This study provides insights into the ionic mechanisms by which high concentrations of AZM may modulate ventricular electrophysiology and susceptibility to arrhythmia.

Cardiotoxic Potential of Hydroxychloroquine, Chloroquine and Azithromycin in Adult Human Primary Cardiomyocytes

Substantial efforts have been recently committed to develop coronavirus disease-2019 (COVID-19) medications, and Hydroxychloroquine alone or in combination with Azithromycin has been promoted as a repurposed treatment. Although these drugs may increase cardiac toxicity risk, cardiomyocyte mechanisms underlying this risk remain poorly understood in humans. Therefore, we evaluated the proarrhythmia risk and inotropic effects of these drugs in the cardiomyocyte contractility-based model of the human heart. We found Hydroxychloroquine to have a low proarrhythmia risk, whereas Chloroquine and Azithromycin were associated with high risk. Hydroxychloroquine proarrhythmia risk changed to high with low level of K+, whereas high level of Mg2+ protected against proarrhythmic effect of high Hydroxychloroquine concentrations. Moreover, therapeutic concentration of Hydroxychloroquine caused no enhancement of elevated temperature-induced proarrhythmia. Polytherapy of Hydroxychloroquine plus Azithromycin and sequential application of these drugs were also found to influence proarrhythmia risk categorization. Hydroxychloroquine proarrhythmia risk changed to high when combined with Azithromycin at therapeutic concentration. However, Hydroxychloroquine at therapeutic concentration impacted the cardiac safety profile of Azithromycin and its proarrhythmia risk only at concentrations above therapeutic level. We also report that Hydroxychloroquine and Chloroquine, but not Azithromycin, decreased contractility while exhibiting multi-ion channel block features, and Hydroxychloroquine's contractility effect was abolished by Azithromycin. Thus, this study has the potential to inform clinical studies evaluating repurposed therapies, including those in the COVID-19 context. Additionally, it demonstrates the translational value of the human cardiomyocyte contractility-based model as a key early discovery path to inform decisions on novel therapies for COVID-19, malaria, and inflammatory diseases.

The canine chronic atrioventricular block model in cardiovascular preclinical drug research

Ventricular cardiac arrhythmia is a life threating condition arising from abnormal functioning of many factors in concert. Animal models mirroring human electrophysiology are essential to predict and understand the rare pro- and anti-arrhythmic effects of drugs. This is very well accomplished by the canine chronic atrioventricular block (CAVB) model. Here we summarize canine models for cardiovascular research, and describe the development of the CAVB model from its beginning. Understanding of the structural, contractile and electrical remodelling processes following atrioventricular (AV) block provides insight in the many factors contributing to drug-induced arrhythmia. We also review all safety pharmacology studies, efficacy and mechanistic studies on anti-arrhythmic drugs in CAVB dogs. Finally, we compare pros and cons with other in vivo preclinical animal models. In view of the tremendous amount of data obtained over the last 100 years from the CAVB dog model, it can be considered as man's best friend in preclinical drug research.

Combination of Hydroxychloroquine Plus Azithromycin As Potential Treatment for COVID-19 Patients: Safety Profile, Drug Interactions, and Management of Toxicity

The coronavirus disease 2019 (COVID-19), caused by infection with severe acute respiratory syndrome coronavirus 2, has recently emerged worldwide. In this context, there is an urgent need to identify safe and effective therapeutic strategies for treatment of such highly contagious disease. We recently reported promising results of combining hydroxychloroquine and azithromycin as an early treatment option. Although ongoing clinical trials are challenging the efficacy of this combination, many clinicians claim the authorization to or have already begun to use it to treat COVID-19 patients worldwide. The aim of this article is to share pharmacology considerations contributing to the rationale of this combination, and to provide safety information to prevent toxicity and drug-drug interactions, based on available evidence.

Hydroxychloroquine/azithromycin treatment, QT interval and ventricular arrhythmias in hospitalised patients with COVID-19

BACKGROUND

Hydroxychloroquine (HCQ) and azithromycin (AZM) are widely used in off-label treatment of novel coronavirus disease (COVID-19). However, cardiac safety of these drugs is still controversial in COVID-19. Therefore, we aimed to evaluate association of HCQ or HCQ + AZM treatment regimens, corrected QT (QTc) interval and malignant ventricular arrhythmias in hospitalized patients.

METHODS

This is a single-center, retrospective and observational study. All data were extracted from the electronic medical records. The initial and post-treatment mean QTc intervals were calculated and compared in patients with HCQ alone or HCQ + AZM therapy. Associated factors with QTc prolongation, the incidence of ventricular arrhythmia during treatment and in-hospital mortality because of ventricular arrhythmias were evaluated.

RESULTS

Our cohort comprised 101 hospitalized COVID-19 patients (mean age of 49.60 ± 18 years, 54.4% men). HCQ + AZM combination therapy group (n = 56) was more likely to have comorbidities. After 5-days treatment, 19 (18.8%) patients had QTc prolongation, and significant increase in the QTc interval was observed in both two groups (P < .001). However, HCQ + AZM combination group had significantly higher ΔQTc compared to HCQ group (22.5 ± 18.4 vs 7.5 ± 15.3 ms, P < .001). All of 101 patients completed the 5-days treatment without interruption. Also, no malignant ventricular arrhythmia or death secondary to ventricular arrhythmia occurred during the treatment in both groups.

CONCLUSIONS

The present study revealed that although HCQ + AZM treatment was independently associated with QTc prolongation, none of patients experienced malignant ventricular arrhythmia or death during treatment. Further prospective studies are needed to determine the exact implications of these drugs on arrhythmias in patients with COVID-19.

Liposomal delivery of azithromycin enhances its immunotherapeutic efficacy and reduces toxicity in myocardial infarction

A growing body of evidence shows that altering the inflammatory response by alternative macrophage polarization is protective against complications related to acute myocardial infarction (MI). We have previously shown that oral azithromycin (AZM), initiated prior to MI, reduces inflammation and its negative sequelae on the myocardium. Here, we investigated the immunomodulatory role of a liposomal AZM formulation (L-AZM) in a clinically relevant model to enhance its therapeutic potency and avoid off-target effects. L-AZM (40 or 10 mg/kg, IV) was administered immediately post-MI and compared to free AZM (F-AZM). L-AZM reduced cardiac toxicity and associated mortality by 50% in mice. We observed a significant shift favoring reparatory/anti-inflammatory macrophages with L-AZM formulation. L-AZM use resulted in a remarkable decrease in cardiac inflammatory neutrophils and the infiltration of inflammatory monocytes. Immune cell modulation was associated with the downregulation of pro-inflammatory genes and the upregulation of anti-inflammatory genes. The immunomodulatory effects of L-AZM were associated with a reduction in cardiac cell death and scar size as well as enhanced angiogenesis. Overall, L-AZM use enhanced cardiac recovery and survival after MI. Importantly, L-AZM was protective from F-AZM cardiac off-target effects. We demonstrate that the liposomal formulation of AZM enhances the drug’s efficacy and safety in an animal model of acute myocardial injury. This is the first study to establish the immunomodulatory properties of liposomal AZM formulations. Our findings strongly support clinical trials using L-AZM as a novel and clinically relevant therapeutic target to improve cardiac recovery and reduce heart failure post-MI in humans.

Predictive factors for cardiac conduction abnormalities with hydroxychloroquine-containing combinations for COVID-19

This longitudinal, prospective cohort study aimed to assess risk of QTc interval prolongation and its predicting factors in subjects treated with combinations containing hydroxychloroquine (HCQ) for COVID-19. Moderate-to-severe QTc prolongation during therapy was defined as a QTc interval >470 ms in men or >480 ms in women. Patients were treated under strict cardiac supervision. A total of 105 adults were included [56% male; median (IQR) age 69 (57-79) years]. All patients received therapy with HCQ in combination with azithromycin (AZM), and 95 (90%) also with lopinavir/ritonavir (LPV/r). Concomitant medications classified as having risk of developing torsades de pointes (TdP) were simultaneously used in 81 patients (77%). Moderate-to-severe QTc prolongation was observed in 14 patients (13%), mostly at Days 3-5 from baseline, with 6 (6%) developing severe prolongation (>500 ms). There was no evidence of TdP arrhythmia or TdP-associated death. Adding LPV/r to HCQ+AZM did not significantly prolong the QTc interval. Multivariable Cox regression revealed that comedications with known risk of TdP (HR = 11.28, 95% CI 1.08-117.41), higher neutrophil-to-lymphocyte (NLR) ratio (HR = 1.10, 95% CI 1.03-1.18 per unit increase) and higher serum hs-cardiac troponin I (HR = 4.09, 95% CI 1.36-12.2 per unit increase) were major contributors to moderate-to-severe QTc prolongation. In this closely screened and monitored cohort, no complications derived from QTc prolongation were observed during pharmacological therapy containing HCQ for COVID-19. Evidence of myocardial injury with elevated troponin and strong inflammatory response, specifically higher NLR, are conditions requiring careful QTc interval monitoring.

Hydroxychloroquine is protective to the heart, not harmful: a systematic review

Hydroxychloroquine (HCQ) has been shown to be at least somewhat effective in treating patients with coronavirus disease 2019 (COVID-19). Recently the US Food and Drug Administration and Centers for Disease Control and Prevention warnings of fatal cardiac toxicity from torsades de pointes (TDP) arrhythmia from HCQ receipt have been made, notwithstanding the long safe provision of HCQ to treat lupus and rheumatoid arthritis. This has resulted in restricted access of HCQ for COVID-19 treatment. We hypothesized that HCQ and azithromycin have not been reported to cause significant acute cardiac arrhythmic mortality. We performed a literature search for the effects of HCQ and azithromycin on the heart. No TDP or related deaths were found to have been reported as a result of HCQ and azithromycin receipt in the peer-reviewed literature. On the contrary, HCQ and azithromycin were both found to substantially reduce cardiac mortality and also decrease thrombosis, arrhythmia and cholesterol in treated patients in recent peer-reviewed studies and meeting presentations. HCQ and azithromycin do not cause TDP cardiac mortality; rather, HCQ decreases cardiac events. HCQ should not be restricted in COVID-19 patients out of fear of cardiac mortality.

Cardiovascular disease management during the coronavirus disease 2019 pandemic

Based on clinical presentation, pathophysiology, high infectivity, high cardiovascular involvement, and therapeutic agents with cardiovascular toxicity of coronavirus disease 2019 (COVID-19), regular cardiovascular treatment is being changing greatly. Despite angiotensin-converting enzyme 2 serving as the portal for infection, the continuation of clinically indicated renin-angiotensin-aldosterone blockers is recommended according to the present evidence. Fibrinolytic therapy can be considered a reasonable option for the relatively stable ST segment elevation myocardial infarction (STEMI) patient with suspected or known COVID-19. However, primary percutaneous coronary intervention is still the standard of care in patients with definite STEMI if personal protective equipment is available and cardiac catheterization laboratory has a good infection control. In patients with elevated cardiac enzymes, it is very important to differentiate patients with Type 2 myocardial infarction or myocarditis from those with true acute coronary syndromes because invasive percutaneous intervention management in the former may be unnecessary, especially if they are hemodynamically stable. Finally, patients with baseline QT prolongation or those taking QT prolonging drugs must be cautious when treating with lopinavir/ritonavir and hydroxychloroquine for COVID-19.

Guidelines for the treatment of dysentery (shigellosis): a systematic review of the evidence

BACKGROUND

Shigella remains the primary cause of diarrhoea in paediatric patients worldwide and accounts for up to 40,000 deaths per year. Current guidelines for the treatment of shigellosis are based on data which are over a decade old. In an era of increasing antimicrobial resistance, an updated review of the appropriate empirical therapy for shigellosis in children is necessary, taking into account susceptibility patterns, cost and the risk of adverse events.

METHODS

A systematic review of the current published literature on the treatment of shigella dysentery was undertaken in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA).

RESULTS

The initial search produced 131 results, of which nine studies met the inclusion criteria. The quality of the studies was assessed as per the Grading of Recommendations Assessment, Development and Evaluation (GRADE) guidelines. International guidelines were also reviewed. There is a lack of current research regarding the clinical treatment of shigellosis in paediatric and adult patients, despite rising antimicrobial resistance worldwide. In particular, there is a lack of studies assessing the non-susceptibility of community-acquired strains, with almost all published research pertaining to microbiological data from hospital-based settings.

DISCUSSION

Current WHO guidelines support the use of fluoroquinolones (first-line), β-lactams (second-line) and cephalosporins (second-line) which accords with currently available evidence and other international guidelines, and there is no strong evidence for changing this guidance. Azithromycin is appropriate as a second-line therapy in regions where the rate of non-susceptibility of ciprofloxacin is known to be high, and research suggests that, from a cardiac point of view, azithromycin is safer than other macrolide antibiotics. Cefixime is also a reasonable alternative, although its use must be weighed against the risk of dissemination of extended-spectrum β-lactamase-producing organisms.

Use of microminipigs for unveiling unknown mechanisms of azithromycin-induced cardiovascular death

Although azithromycin can suppress cardiac I_Na, I_Kr, I_Ks, I_Ca,L and I_K1, its onset mechanisms for cardiovascular death have not been fully investigated. We examined electropharmacological effects of azithromycin in intravenous doses of 0.3, 3 and 30 mg/kg using microminipigs under the halothane anesthesia (n = 4), which provided plasma concentrations of 3.1, 11.2 and 120.4 μg/mL, respectively. The low dose did not alter any of the cardiohemodynamic or electrocardiographic variables. The middle dose significantly shortened QT interval for 10-20 min and QTc for 10-30 min. The high dose significantly decreased mean blood pressure for 5-60 min, prolonged QRS width at 20 min, but shortened QT interval for 15-20 min and QTc for 15-30 min (n = 3). Cardiohemodynamic collapse occurred in 1 animal after the start of the high dose infusion, which might be associated with the cardiovascular death in patients with vasomotor dysfunction. Prolongation of QRS width indicates that azithromycin may suppress ventricular I_Na in vivo, which may unmask latent type of Brugada electrocardiographic genotype. Meanwhile, abbreviation of the QTc might cause potentially lethal, short QT-related, cardiac arrhythmia syndrome. These findings with microminipigs suggest the possible entry point for analyzing the mechanisms of cardiovascular death clinically seen with this antibiotic.

Risk Evaluation of Azithromycin-Induced QT Prolongation in Real-World Practice

Background

Azithromycin exposure has been reported to increase the risk of QT prolongation and cardiovascular death. However, findings on the association between azithromycin and cardiovascular death are controversial, and azithromycin is still used in actual practice. Additionally, quantitative assessments of risk have not been performed, including the risk of QT prolongation when patients are exposed to azithromycin in a real-world clinical setting. Therefore, in this study, we aimed to evaluate the risk of exposure to azithromycin on QT prolongation in a real-world clinical setting using a 21-year medical history database of a tertiary medical institution.

Methods

We analyzed the electrocardiogram results and relevant electronic health records of 402,607 subjects in a tertiary teaching hospital in Korea from 1996 to 2015. To evaluate the risk of QT prolongation of azithromycin, we conducted a case-control analysis using amoxicillin for comparison. Multiple logistic regression analysis was performed to correct for age, sex, accompanying drugs, and disease.

Results

The odds ratio (OR) for QT prolongation (QTc>450 ms in male and >460 ms in female) on azithromycin exposure was 1.40 (95% confidence interval [CI], 1.23-1.59), and the OR for severe QT prolongation (QTc>500 ms) was 1.43 (95% CI, 1.13-1.82). On the other hand, the ORs on exposure to amoxicillin were 1.06 (95% CI, 0.97-1.15) and 0.88 (95% CI, 0.70-1.09). In a subgroup analysis, the risk of QT prolongation in patients aged between 60 and 80 years was significantly higher when they are exposed to azithromycin.

Conclusions

The risk of QT prolongation was increased when patients, particularly the elderly aged 60-79 years, were exposed to azithromycin. Therefore, clinicians should pay exercise caution using azithromycin or consider using other antibiotics, such as amoxicillin, instead of azithromycin.

Electrophysiologic Studies on the Risks and Potential Mechanism Underlying the Proarrhythmic Nature of Azithromycin

The mechanisms underlying arrhythmia induced by the clinical use of azithromycin are poorly understood. We aimed to investigate the proarrhythmic effects of azithromycin using electrocardiogram (ECG) and ion channel models. In vivo and in vitro guinea pig ECG and current and voltage clamp recordings were carried out. Azithromycin at 114.6 mg/kg (three times the clinically relevant dose) reduced heart rate (HR) and prolonged the PR, QRS and rate-corrected QT (QTc) intervals of guinea pig ECG in vivo. In vitro technique revealed that azithromycin at 207.5 and 415 mg/L [five and ten times clinically relevant concentration (CRC)] reduced HR and prolonged the PR, QRS and QTc intervals in the isolated guinea pig heart ECG. Both arrhythmias presented bradyarrhythmic features, mainly with reduced HR and prolonged PR interval. Action potential analysis from the guinea pig cardiomyocytes indicated that azithromycin at 830 mg/L (20 times CRC) significantly prolonged the action potential durations at 50% (APD₅₀) and 90% (APD₉₀) of full repolarization levels with a rectangular pattern. Azithromycin significantly suppressed the L-type Ca²⁺ and Na⁺ currents from the left ventricular myocytes of guinea pig at 50% inhibiting concentrations (IC₅₀) of 942.5 ± 68.4 mg/L (22.7 times CRC) and 1123.0 ± 87.7 mg/L (27.1 times CRC), respectively. However, azithromycin at 50 times CRC (2075 mg/L) inhibited I_Kr current at an inhibition rate of 30.99 ± 5.23% with an undetectable IC₅₀. Azithromycin caused bradyarrhythmia primarily by inhibiting L-type Ca²⁺ and Na⁺ currents.

Use of azithromycin and risk of ventricular arrhythmia

BACKGROUND

There are conflicting findings from observational studies of the arrhythrogenic potential of azithromycin. Our aim was to quantify the association between azithromycin use and the risk of ventricular arrhythmia.

METHODS

We conducted a nested case-control study within a cohort of new antibiotic users identified from a network of 7 population-based health care databases in Denmark, Germany, Italy, the Netherlands and the United Kingdom for the period 1997-2010. Up to 100 controls per case were selected and matched by age, sex and database. Recency of antibiotic use and type of drug (azithromycin was the exposure of interest) at the index date (occurrence of ventricular arrhythmia) were identified. We estimated the odds of ventricular arrhythmia associated with current azithromycin use relative to current amoxicillin use or nonuse of antibiotics (≥ 365 d without antibiotic exposure) using conditional logistic regression, adjusting for confounders.

RESULTS

We identified 14 040 688 new antibiotic users who met the inclusion criteria. Ventricular arrhythmia developed in 12 874, of whom 30 were current azithromycin users. The mean age of the cases and controls was 63 years, and two-thirds were male. In the pooled data analyses across databases, azithromycin use was associated with an increased risk of ventricular arrhythmia relative to nonuse of antibiotics (adjusted odds ratio [OR] 1.97, 95% confidence interval [CI] 1.35-2.86). This increased risk disappeared when current amoxicillin use was the comparator (adjusted OR 0.90, 95% CI 0.48-1.71). Database-specific estimates and meta-analysis confirmed results from the pooled data analysis.

INTERPRETATION

Current azithromycin use was associated with an increased risk of ventricular arrhythmia when compared with nonuse of antibiotics, but not when compared with current amoxicillin use. The decreased risk with an active comparator suggests significant confounding by indication.

Protective Effects of Carvedilol and Vitamin C against Azithromycin-Induced Cardiotoxicity in Rats via Decreasing ROS, IL1-β, and TNF-α Production and Inhibiting NF-κB and Caspase-3 Expression

The Food and Drug Administration recently warned of the fatal cardiovascular risks of azithromycin in humans. In addition, a recently published study documented azithromycin-induced cardiotoxicity in rats. This study aimed to justify the exact cardiovascular events accompanying azithromycin administration in rats, focusing on electrocardiographic, biochemical, and histopathological changes. In addition, the underlying mechanisms were studied regarding reactive oxygen species production, cytokine release, and apoptotic cell-death. Finally, the supposed protective effects of both carvedilol and vitamin C were assessed. Four groups of rats were used: (1) control, (2) azithromycin, (3) azithromycin + carvedilol, and (4) azithromycin + vitamin C. Azithromycin resulted in marked atrophy of cardiac muscle fibers and electrocardiographic segment alteration. It increased the heart rate, lactate dehydrogenase, creatine phosphokinase, malondialdehyde, nitric oxide, interleukin-1 beta (IL1-β), tumor necrosis factor alpha (TNF-α), nuclear factor kappa beta (NF-κB), and caspase-3. It decreased reduced glutathione, glutathione peroxidase, and superoxide dismutase. Carvedilol and vitamin C prevented most of the azithromycin-induced electrocardiographic and histopathological changes. Carvedilol and vitamin C decreased lactate dehydrogenase, malondialdehyde, IL1-β, TNF-α, NF-κB, and caspase-3. Both agents increased glutathione peroxidase. This study shows that both carvedilol and vitamin C protect against azithromycin-induced cardiotoxicity through antioxidant, immunomodulatory, and antiapoptotic mechanisms.

Drug-induced proarrhythmia: risk factors and electrophysiological mechanisms

Drug-induced ventricular tachyarrhythmias can be caused by cardiovascular drugs, noncardiovascular drugs, and even nonprescription agents. They can result in arrhythmic emergencies and sudden cardiac death. If a new arrhythmia or aggravation of an existing arrhythmia develops during therapy with a drug at a concentration usually considered not to be toxic, the situation can be defined as proarrhythmia. Various cardiovascular and noncardiovascular drugs can increase the occurrence of polymorphic ventricular tachycardia of the 'torsade de pointes' type. Antiarrhythmic drugs, antimicrobial agents, and antipsychotic and antidepressant drugs are the most important groups. Age, female sex, and structural heart disease are important risk factors for the occurrence of torsade de pointes. Genetic predisposition and individual pharmacodynamic and pharmacokinetic sensitivity also have important roles in the generation of arrhythmias. An increase in spatial or temporal dispersion of repolarization and a triangular action-potential configuration have been identified as crucial predictors of proarrhythmia in experimental models. These studies emphasized that sole consideration of the QT interval is not sufficient to assess the proarrhythmic risk. In this Review, we focus on important triggers of proarrhythmia and the underlying electrophysiological mechanisms that can enhance or prevent the development of torsade de pointes.