The US Food and Drug Administration Cardiorenal Advisory Panel and the Drug Approval Process

Evaluation of the Tp-Te interval, Tp-Te/QTc ratio, and QT dispersion in patients with Turner syndrome

Objective:

To evaluate ventricular repolarization parameters using the interval from the peak to the end of the T wave (Tp–Te), together with QT and corrected QT (QTc) intervals, QT dispersion (QTd), and Tp-Te/QTc ratio in patients with Turner syndrome (pwTS) and to compare the results with those from healthy controls.

Methods:

In total, 38 patients previously diagnosed with Turner syndrome (TS) and 35 healthy girls (controls) were included in our cross-sectional study. Twelve-lead electrocardiography (ECG) and echocardiography after a 30-min rest were performed. The QT, QTc, QTd, Tp-Te interval, and Tp-Te/QTc ratio were determined.

Results:

No differences in age or sex were observed between the groups. QT intervals were similar in both groups [pwTS: 354.76±25.33 ms, controls (C): 353.29±17.51 ms, p=0.775]. pwTS had significantly longer QTc and QTd than controls (411.87±22.66 ms vs. 392.06±13.21 ms, p<0.001 and 40.31±2.02 ms vs. 37.54±1.83 ms, p<0.001, respectively). Similarly, the Tp-Te interval and Tp-Te/QTc ratio were significantly longer in pwTS than in controls (71.89±3.39 ms vs. 65.34±2.88 ms, p<0.001 and 0.17±0.01 vs. 0.16±0.01, p=0.01).

Conclusion:

As pwTS have longer QTc, QTd, Tp–Te interval, and Tp-Te/QTc ratio, an annual follow-up with ECG can provide awareness and even prevent sudden death in them. Also avoiding the use of drugs that makes repolarization anomaly and having knowledge about the side effects of these drugs are essential in pwTS.

A fresh perspective on comparing the FDA and the CHMP/EMA: approval of antineoplastic tyrosine kinase inhibitors

We compared and determined the reasons for any differences in the review and approval times of tyrosine kinase inhibitors (TKIs) by the US Food and Drug Administration (FDA) and the European EMA/CHMP. Applications for these novel cancer drugs were submitted to them within a mean of 31.2 days of each other, providing a fair basis for comparison. The FDA had granted priority review to 12 TKIs but the EMA/CHMP did not grant the equivalent accelerated assessment to any. The FDA granted accelerated approvals to six (38%) and CHMP granted (the equivalent) conditional approvals to four (29%) of these agents. On average, the review and approval times were 205.3 days in the US compared with 409.6 days in the European Union (EU). The active review times, however, were comparable (225.4 days in the EU and 205.3 days in the US). Since oncology drug development lasts about 7 years, the 20 days difference in review times between the two agencies is inconsequential. Clock stops during review and the time required to issue an approval had added the extra 184.2 days to review time in the EU. We suggest possible solutions to expedite the EU review and approval processes. However, post-marketing emergence of adverse efficacy and safety data on gefitinib and lapatinib, respectively, indicate potential risks of expedited approvals. We challenge the widely prevalent myth that early approval translates into early access or beneficial impact on public health. Both the agencies collaborate closely but conduct independent assessments and make decisions based on distinct legislation, procedures, precedents and societal expectations.

Zebrafish-based small molecule screens for novel cardiovascular drugs

The zebrafish is increasingly being adopted as an in vivo model of high throughput drug screening. In this brief review we outline the advantages and disadvantages of this approach and summarize recent screens that have attempted to identify novel small molecules with activity on the cardiovascular system.

High-precision recording of the action potential in isolated cardiomyocytes using the near-infrared fluorescent dye di-4-ANBDQBS

The use of voltage-sensitive fluorescent dyes (VSD) for noninvasive measurement of the action potential (AP) in isolated cells has been hindered by low-photon yield of the preparation, dye toxicity, and photodynamic damage. Here we used a new red-shifted VSD, di-4-ANBDQBS, and a fast electron-multiplied charge-coupled device camera for optical AP (OAP) recording in guinea pig cardiac myocytes. Loading di-4-ANBDQBS did not alter APs recorded with micropipette. With short laser exposures (just enough to record one OAP every 1-5 min), di-4-ANBDQBS yielded fluorescent signals with very high signal-to-background ratios (change in fluorescence on depolarization/fluorescence at resting potential: 19.2 ± 4.1%) and signal-to-noise ratios (40 ± 13.2). Quantum chemical calculations comparing the ANBDQ chromophore to the conventional ANEP chromophore showed that the higher wavelength and the greater voltage sensitivity of the former have the same electro-optical origin: a longer path for electron redistribution in the excited state. OAP closely tracked simultaneously recorded electrical APs, permitting measurement of AP duration within 1% error. Prolonged laser exposure caused progressive AP duration prolongation and instability. However, these effects were alleviated or abolished by reducing the dye concentration and by perfusion with antioxidants. Thus the presented technique provides a unique opportunity for noninvasive AP recording in single cardiomyocytes.

QTc interval prolongation in children with Turner syndrome: the results of exercise testing and 24-h ECG

BACKGROUND

Turner syndrome (TS) is the most common sex chromosome abnormality in females. Recently, a prolongation of the rate-corrected QT (QTc) interval in the electrocardiogram (ECG) of TS patients has been reported. A prolonged QTc interval has been correlated to an increased risk for sudden cardiac death, and medical treatment is warranted in patients with congenital long QT syndrome (LQTS). Additionally, several drugs of common use are contraindicated in LQTS because of their effects on myocardial repolarization. The importance of the QTc prolongation in TS patients is not known at present.

MATERIALS AND METHODS

Eighteen TS patients with a prolonged QTc interval (group 1) and 11 TS patients with a normal QTc interval (group 2) (mean age 12.6+/-3.1 vs. 11.8+/-2.1 years, respectively) were tested. The QTc interval was calculated during exercise testing and during 24-h ECG recordings.

RESULTS

None of the patients experienced adverse cardiac events during the tests. The mean QTc interval decreased from 0.467 to 0.432 s in group 1 and from 0.432 to 0.412 s in group 2. During the 24-h ECG, the maximum QTc interval was significantly prolonged in group 1 (0.51 vs. 0.465 s, p<0.05, respectively). We conclude that exercise testing and 24-h ECG recording provide valuable information about the cardiac risk in the single TS patient with a prolonged QTc interval. This helps in counseling these girls, as clear therapeutic guidelines are currently lacking.

QTc interval prolongation in children with Ulrich-Turner syndrome

INTRODUCTION

The Ullrich-Turner-Syndrome (UTS) is the most commonly occurring sex chromosome abnormality in females. Cardiac malformations are well known, but no data exist on specific electrocardiogram (ECG) patterns in children and adolescents. A prolongation of the QT interval on the ECG has been correlated to an increased risk for sudden cardiac death, and medical treatment is warranted in patients with long QT syndrome (LQTS). Moreover, several drugs of common use are contraindicated in LQTS because of their effects on myocardial repolarization.

METHODS

The ECG tracings of 86 UTS patients [mean age (+/-SD): 11.0+/-3.6 years; mean height-SD: -2.6+/-1.0] were analyzed and compared to age-matched control groups of 75 boys (mean age: 11.3+/-3.5 years; mean height-SD: -1.9+/-1.0) and 62 girls (mean age: 10.1+/-3.2 years; mean height-SD: -2.5+/-0.9) with short stature.

RESULTS

Eighteen UTS patients (20.9%) had an abnormally prolonged QTc >0.45 s in contrast to only one control subject (0.9%). The QTc interval of UTS patients was significantly prolonged compared to that of the controls (p<0.01) and normal values.

CONCLUSIONS

There is an increased prevalence of a long QT interval among UTS patients. This should be taken into account for the cardiovascular screening of such patients. Patients with UTS have an intrinsically prolonged QT interval and as such may be at higher risk for arrhythmias in the context of a QT-prolonging medication.

The challenges of new drugs benefits and risks analysis: Lessons from the ximelagatran FDA Cardiovascular Advisory Committee

Ximelagatran is a new oral anticoagulant that acts by direct and reversible inhibition of thrombin and has the potential to replace warfarin. In 2004, the FDA Cardiovascular and Renal drug Advisory Committee (CRAC) reviewed the ximelagatran clinical program. Three indications were proposed: the prevention of venous thromboembolism (VTE) in patients undergoing total knee replacement surgery (TKR), the prevention of stroke and other thromboembolic complications associated with atrial fibrillation (AF), and the long-term secondary prevention of VTE after standard treatment of an episode of acute VTE. The database consisted of a total of 30,698 subjects and included five phase III pivotal studies. During the advisory panel debate, widely divergent analyses of the benefits and risks of ximelagatran were presented. Ximelagatran hepatic toxicity was a key feature leading the CRAC to conclude that the benefit risk ratio of ximelagtran was unfavorable for the three proposed indications. Some design issues also undermined the strength of efficacy data. This paper reviews the benefits and risks of ximelagatran and analyzes the reasons leading to conflicting conclusions among various experts. The aim of this review is to facilitate the interpretation of benefits and risks associated with a new drug product and to improve future clinical drug developments.

An increase in late sodium current potentiates the proarrhythmic activities of low-risk QT-prolonging drugs in female rabbit hearts

Assessment of the proarrhythmic risk associated with drugs that prolong the QT interval is difficult. We hypothesized that the proarrhythmic activities of drugs with very low to moderate risk of causing torsades de pointes would be well differentiated when the late sodium current (I(NaL)) was greater than normal. The effects of selected QT-prolonging drugs on electrical activity of female rabbit isolated hearts were determined in the absence and presence of sea anemone toxin (ATX-II; an enhancer of I(NaL)). I(NaL) recorded from ventricular myocytes isolated from female rabbit hearts was slightly increased by 1 and 3 nM ATX-II (n = 13, P < 0.01). ATX-II (1 nM) prolonged the duration of the monophasic action potential (MAPD(90)) the isolated heart by of 19 +/- 3% (P < 0.001, n = 31) and shifted the concentration-response relationships for cisapride (1-30 nM), ziprasidone (0.01-3 microM), quinidine (0.1-1 microM), and moxifloxacin (0.01-1 microM) to prolong MAPD to the left by 2- to 12-fold. In contrast, the increases in MAPD(90) caused by 1 nM ATX-II and pentobarbital were only additive, and the increases in MAPD(90) caused by ATX-II and ranolazine [(+/-)-N-(2,6-dimethylphenyl)-(4[2-hydroxy-3-(2-methoxyphenoxy)propyl]-1-piperazine] were less than additive. Episodes of arrhythmic activity were commonly observed, and beat-to-beat variability of action potential duration was increased, during exposure of hearts to cisapride, ziprasidone, quinidine, and moxifloxacin but not during exposure of hearts to ranolazine or pentobarbital, in the presence of ATX-II. Thus, in the female rabbit heart, ATX-II potentiated the effects of QT-prolonging drugs to increase MAPD(90) and unmasked the proarrhythmic activities of these drugs at clinically relevant drug concentrations.