Dilip R. Karnad

Update on the evaluation of a new drug for effects on cardiac repolarization in humans: issues in early drug development

Following reports of death from cardiac arrhythmias with drugs like terfenadine and cisapride, the International Conference for Harmonization formulated a guidance (E14) document. This specifies that all new drugs must undergo a ‘thorough QT/QTc’ (TQT) study to detect drug‐induced QT prolongation, a surrogate marker of ventricular tachycardia, especially torsades de pointes (TdPs). With better understanding of data from several completed TQT studies, regulatory requirements have undergone some changes since the E14 guidance was implemented in October 2005. This article reviews the implications of the E14 guidance and the changes in its interpretation including choice of baseline QT, demonstration of assay sensitivity, statistical analysis of the effect of new drug and positive control, and PK‐PD modelling. Some issues like use of automated QT measurements remain unresolved. Pharmaceutical companies too are modifying Phase 1 studies to detect QTc liability early in order to save time and resources. After the E14 guidance, development of several drugs that prolong QTc by >5u2003ms is being abandoned by sponsors. However, all drugs that prolong the QT interval do not increase risk of TdP. Researchers in regulatory agencies, academia and industry are working to find better biomarkers of drug‐induced TdP which could prevent many useful drugs from being prematurely abandoned. Drug‐induced TdP is a rare occurrence. With fewer drugs that prolong QT interval reaching the licensing stage, knowing which of these drugs are torsadogenic is proving to be elusive. Thus, paradoxically, the effectiveness of the E14 guidance itself has made prospective validation of new biomarkers difficult.

Are women more susceptible than men to drug-induced QT prolongation? Concentration-QTc modelling in a phase 1 study with oral rac-sotalol.

AIMnTo study the differences in QTc interval on ECG in response to a single oral dose of rac-sotalol in men and women.nnnMETHODSnContinuous 12-lead ECGs were recorded in 28 men and 11 women on a separate baseline day and following a single oral dose of 160u2009mg rac-sotalol on the following day. ECGs were extracted at prespecified time points and upsampled to 1000u2009Hz and analyzed manually in a central ECG laboratory on the superimposed median beat. Concentration-QTc analyses were performed using a linear mixed effects model.nnnRESULTSnRac-sotalol produced a significant reduction in heart rate in men and in women. An individual correction method (QTc I) most effectively removed the heart rate dependency of the QTc interval. Mean QTc I was 10 to 15 ms longer in women at all time points on the baseline day. Rac-sotalol significantly prolonged QTc I in both genders. The largest mean change in QTc I (ΔQTc I) was greater in females (68 ms (95% confidence interval (CI) 59, 76 ms) vs. 27 ms (95% CI 22, 32 ms) in males). Peak rac-sotalol plasma concentration was higher in women than in men (mean Cmax 1.8u2009μgu2009ml(-1) (range 1.1-2.8) vs. 1.4u2009μgu2009ml(-1) (range 0.9-1.9), P = 0.0009). The slope of the concentration-ΔQTc I relationship was steeper in women (30u2009ms per μgu2009ml(-1) vs. 23u2009ms per μgu2009ml(-1) in men; P = 0.0135).nnnCONCLUSIONSnThe study provides evidence for a greater intrinsic sensitivity to rac-sotalol in women than in men for drug-induced delay in cardiac repolarization.

Intra- and interreader variability in QT interval measurement by tangent and threshold methods in a central electrocardiogram laboratory

BACKGROUNDnThe QT interval can be measured by tangent (QT(Tan)) and threshold (QT(Thr)) methods; the better method is the one with lower reader variability.nnnMETHODSnQT(Tan) and QT(Thr) were measured twice in 100 digital electrocardiograms (ECGs) by 8 experienced readers in a central laboratory. For QT(Thr), the end of the T wave was the point where the T wave reached the isoelectric baseline; for QT(Tan), it was the point where a line from the peak of the T wave through the steepest part of the descending limb intercepted the isoelectric baseline.nnnRESULTSnThe average absolute intrareader variability ranged from 3.4 to 6.9 milliseconds for QT(Tan) and from 3.5 to 5.2 milliseconds for QT(Thr). By analysis of variance, intrareader SD of QT(Tan) was 7.0 and 7.5 milliseconds for QT(Thr); interreader SD was 13.1 milliseconds for QT(Tan) and 11.9 milliseconds for QT(Thr). QT(Tan) was shorter than QT(Thr) in 96 of the 100 ECGs, it exceeded QT(Thr) in 4 ECGs, which had prominent U waves.nnnCONCLUSIONSnFor trained readers in a central ECG laboratory using sophisticated on-screen tools for QT measurement in high-quality digital ECGs, between- and within-reader variability are comparable for QT(Tan) and QT(Thr). However, QT(Tan) is consistently shorter than QT(Thr) by up to 10 milliseconds.

Probable resistance to parenteral artemether in Plasmodium falciparum : case reports from Mumbai (Bombay), India

Malaria continues to kill approximately 0.5 million-2.5 million people each year in the tropics (Newton and White, 1999). Drug resistance among malarial parasites is rampant and is making treatment more and more difficult (White, 1998). Artemisinin (qinghaosu) and its derivatives, artemether and artesunate, arc currently the most rapidly acting antimalarial drugs, and are considered effective against all species and strains of the human parasites, including multidrug-resistant Plasmodium falciparum (De Vries and Dien, 1996). However, three cases of recrudescence among 37 patients who had each been given intramuscular artemether ( 480 mg, given over 5 days, as treatment for complicated malaria) raise the spectre of resistance even to this drug. These three cases, all seen at the Seth G.S. Medical College & K.E.M. Hospital, in Mumbai (Bombay), India, are described below. A 22-year-old male patient presented after having had fever, chills and rigors for 3 days. On examination, the patient was disoriented, semi-conscious and gave irrelevant answers to the questions asked. He had already been given chloroquine, though the dose could not be ascertained. Examination of smears of peripheral blood collected on the day of admission (day 1) revealed a parasitaemia of 5880 asexual parasites/ ftl, with 2.64% of the erythrocytes infected. Intramuscular artemethcr therapy was initiated (160 mg on day 1, and 80 mg on each of days 2, 3, 4, and 5) and the patient apparently responded rapidly, as no parasites could be detected on smears produced on days 2, 3 or 4. On day 5, however, just prior to the last dose of artemcther, the patient was found to be parasitaemic again (98 asexual parasites/ J.LI) although afebrile. On day 6 the patient had a similar parasitaemia and had become febrile. RII resistance was diagnosed and the patient was given sulfadoxine-pyrimethamine (three tablets, each containing 500 mg sulfadoxine and 25 mg pyrimethamine) and closely monitored. The patient responded, becoming afebrile and parasite-negative within 48 h, and remained aparasitaemic over the next 42 days of follow-up. Two other patients, both also adult males, who were found to have parasitaemias of 2.78% and 2.02% on presentation, were given the same treatment with artemether. Although both were smear-negative on days 5 and 6 (indicating parasitological cure), the patients subsequently returned, one on day 22 and the other on day 29, when they were smearpositive for the ring stages of P. falciparum and febrile. They were both diagnosed as cases of RI resistance and successfully treated, as the other case, with sulfadoxinepyrimethamine. Artemether has been in use in India for I year and the present reports are some of the results from one of the earliest clinical studies with the drug in India. All medication in the present study was supervised and documented. The two cases who were found to be parasitaemic again only after they had been discharged could both represent re-infections. However, the patient who became smearnegative and then smear-positive during his course of artemether probably represents a case of artemether resistance. The regimen of intramuscular artemether used in the present study has given cure rates of 100% (Bunang et al., 1991) or 90.3% (Bunang et al., 1993) against uncomplicated, falciparum malaria and of 65% against severe, falciparum malaria (Bunang et al., 1992). For India, a country that is presently witnessing dangerously escalating chloroquine resistance (Garg et al., 1999), the artemisinin derivatives represent valuable treatment options, particularly for complicated/ severe

Comparison of 5 methods of QT interval measurements on electrocardiograms from a thorough QT/QTc study: effect on assay sensitivity and categorical outliers

INTRODUCTIONnWe studied moxifloxacin-induced QT prolongation and proportion of categorical QTc outliers when 5 methods of QT measurement were used to analyze electrocardiograms (ECGs) from a thorough QT study.nnnMETHODSnQT interval was measured by the threshold, tangent, superimposed median beat, automated global median beat, and longest QT methods in a central ECG laboratory in 2730 digital ECGs from 39 subjects during placebo and moxifloxacin treatment.nnnRESULTSnAll 5 methods were able to demonstrate statistically significant moxifloxacin-induced QTcF prolongation. However, lower bound of 95% 1-sided confidence interval of QTcF prolongation did not exceed 5 milliseconds with the longest QT method. More QTcF outliers were observed with the longest QT and tangent methods, whereas the other 3 methods were comparable. QTcF values greater than 500 milliseconds were observed only with moxifloxacin by the tangent method, and with moxifloxacin and placebo by the longest QT method.nnnCONCLUSIONnThe method of QT measurement must be considered when interpreting individual thorough QT/QTc studies.

Early repolarization and short QT interval in healthy subjects.

BACKGROUNDnAn early repolarization (ER) pattern is common in ECGs from patients with ventricular fibrillation (VF). These patients with ER have shorter QT intervals. Morphological variants of the ER pattern also have been associated with idiopathic VF, but their prevalence in healthy subjects is unclear.nnnOBJECTIVEnThe purpose of this study was to study the prevalence of ER and its morphological variants, and its association with the QTc interval in healthy subjects.nnnMETHODSnDigital ECGs from 1886 healthy subjects from Phase I clinical trials were analyzed by a central ECG laboratory.nnnRESULTSnER, defined as J-point elevation ≥0.1 mV in ≥2 contiguous leads, was present in 514 subjects (27.3%), of whom 505 (98.2%) were males. The prevalence of ER declined progressively with increasing age. ER pattern was seen in lateral leads (I, aVL, V(4)-V(6)) in 26.1%, in inferior (II, III, aVF) or inferolateral leads in 8%, and was global in 1.9%. The terminal portion of the QRS complex was notched in 43.1% and slurred in 56.9%. Notching was common in inferior/lateral leads, and slurring was common in anterior leads. A non-ascending ST segment was seen in 71% of ECGs with a notched pattern but in only 12.3% of ECGs with a slurred pattern. The ER group had slower heart rates (9.3 ± 13.3 bpm [mean difference ± SD], P <.001) and shorter QTc intervals (QTcB = 20.2 ± 25.6 ms, QTcF = 11.0 ± 21.9 ms; P <.001). Four subjects in each group had a short QT interval (QTcF <350 ms).nnnCONCLUSIONnER and all of its variants are common in healthy young males with slower heart rates and slightly shorter QTc intervals. A short QT interval (QTcF <350 ms) is rare.

Effect of Number of Replicate Electrocardiograms Recorded at Each Time Point in a Thorough QT Study on Sample Size and Study Cost

In a “thorough QT/QTc” (TQT) study, several replicate electrocardiograms (ECGs) are recorded at each time point to reduce within‐subject variability. This decreases the sample size but increases the cost of ECG analysis. To determine the most cost‐effective number of ECG replicates, the authors retrospectively analyzed data from the placebo and moxifloxacin arms of a TQT study with crossover design. Six replicate ECGs were recorded at 7 time points on day −1 (baseline day), day 1, and day 3 in 124 normal healthy volunteers who were randomized to receive moxifloxacin or placebo on day 1 and the other treatment on day 3. QT interval was corrected for heart rate by the Fridericia (QTcF) and individual subject‐specific (QTcI) formulas. Within‐subject and between‐subject standard deviations for QTcF obtained by repeated‐measures analysis of covariance were 9.5 and 13.3 milliseconds with 1 replicate; 7.8 and 12.7 milliseconds with 2 replicates; 7.3 and 12.3 milliseconds with 3 replicates; 6.9 and 12.2 milliseconds with 4 replicates; 6.8 and 11.9 milliseconds with 5 replicates; and 6.6 and 11.8 milliseconds with 6 replicates. Within‐ and between‐subject variance with QTcI also declined with increasing replicates. Sample size benefit based on these estimates was negligible beyond 4 replicates. The study cost was least with 3 or 4 replicates, depending on per‐ECG and per‐subject costs.

A prospective study evaluating the efficacy of a single, 45-mg dose of primaquine, as a gametocytocidal agent, in patients with Plasmodium falciparum malaria in Mumbai, India

Abstract The efficacy of a single dose of 45 mg primaquine, as a gametocytocidal agent, was assessed in Mumbai, India, among adults with uncomplicated or severe Plasmodium falciparum malaria. All the patients investigated had been found gametocytaemic, with at least 56 gametocytes/μl blood, within the first 72 h of their illness. Those with uncomplicated malaria, like those with severe malaria, were randomized to receive or not receive primaquine. All the patients were followed up for 29 days post-admission, for gametocytaemia and gametocyte viability (as determined by exflagellation). Among those with uncomplicated malaria, six (27.3%) of the 22 who did not receive primaquine but only one (4.2%) of the 24 who did receive the drug, on day 4, remained gametocytaemic on day 29 (P < 0.05). Similarly, seven (31.8%) of the 22 severe cases who did not receive primaquine but only two (9.5%) of the 21 severe cases who received the drug, on day 8, were found gametocytaemic on day 15 (P < 0.05). While the single, 45-mg dose of primaquine recommended by the World Health Organization was effective in clearing gametocytes from the blood of > 90% of the present cases of malaria, > 4% of the patients with uncomplicated malaria and > 9% of those with the severe disease continued to harbour gametocytes in their peripheral blood 29 and 15 days after taking the primaquine, respectively.

Z-score for benchmarking reader competence in a central ECG laboratory.

Background: ECGs from thorough QT studies must be read in a central laboratory by trained experts. Standards of expertise are not presently defined. We, therefore, studied the use of Z‐scores to define reader competence.

A pilot study of the association of pharmacokinetic and pharmacodynamic parameters of warfarin with the dose in patients on long-term anticoagulation

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECTnWarfarin is a widely used anticoagulant with a low therapeutic index. There is wide interindividual variation in the pharmacokinetics and pharmacodynamics of warfarin which is also reflected in the warfarin dose requirement. CYP2C9 and VKORC1 polymorphisms have been shown to affect warfarin dose requirement. However a large amount of the variation in warfarin dose remains unaccounted for.nnnWHAT THIS STUDY ADDSnOur findings suggest that in patients who are on long-term warfarin therapy, INR : plasma 7-hydroxywarfarin concentration correlates well with warfarin requirement and also accounts for a large amount of variation in warfarin dose.nnnAIMSnTo assess the correlation between plasma total warfarin concentration, plasma 7-hydroxywarfarin concentration and INR and the weekly doses of warfarin in patients on long-term anticoagulation.nnnMETHODSnTwenty-five patients on long-term anticoagulation with warfarin were studied. Plasma total warfarin and 7-hydroxywarfarin concentrations and INR were determined. Equations were derived with the weekly warfarin dose as the dependent variable and plasma total warfarin concentration : plasma 7-hydroxywarfarin concentration, INR : plasma total warfarin concentration and INR : plasma 7-hydroxywarfarin concentration as independent variables.nnnRESULTSnThere was a good correlation between INR : plasma total warfarin concentration and the weekly dose of warfarin (y = 46.73e(-0.30x), r(2) = 0.65). There was a better correlation between INR : plasma 7-hydroxywarfarin concentration and the weekly dose of warfarin (y = 156.52x(-0.63), r(2) = 0.74)nnnCONCLUSIONSnPharmacokinetic parameters along with INR seem to correlate with the weekly doses of warfarin in patients on long-term anticoagulation. These parameters may therefore be useful for predicting warfarin doses.