Assessment of Interspecies Differences in Drug-Induced QTc Interval Prolongation in Cynomolgus Monkeys, Dogs and Humans.

BACKGROUND AND PURPOSE: The selection of the most suitable animal species and subsequent translation of the concentration-effect relationship to humans are critical steps for accurate assessment of the pro-arrhythmic risk of candidate molecules. The objective of this investigation was to assess quantitatively the differences in the QTc prolonging effects of moxifloxacin between cynomolgus monkeys, dogs and humans. The impact of interspecies differences is also illustrated for a new candidate molecule. EXPERIMENTAL APPROACH: Pharmacokinetic data and ECG recordings from pre-clinical protocols in monkeys and dogs and from a phase I trial in healthy subjects were identified for the purpose of this analysis. A previously established Bayesian model describing the combined effect of heart rate, circadian variation and drug effect on the QT interval was used to describe the pharmacokinetic-pharmacodynamic relationships. The probability of a ≥ 10 ms increase in QT was derived as measure of the pro-arrhythmic effect. KEY RESULTS: For moxifloxacin, the concentrations associated with a 50% probability of QT prolongation ≥ 10 ms (Cp50) varied from 20.3 to 6.4 and 2.6 µM in dogs, monkeys and humans, respectively. For NCE05, these values were 0.4 µM vs 2.0 µM for monkeys and humans, respectively. CONCLUSIONS AND IMPLICATIONS: Our findings reveal significant interspecies differences in the QT-prolonging effect of moxifloxacin. In addition to the dissimilarity in pharmacokinetics across species, it is likely that differences in pharmacodynamics also play an important role. It appears that, regardless of the animal model used, a translation function is needed to predict concentration-effect relationships in humans.

Prospective Evaluation of a Model-Based Dosing Regimen for Amikacin in Preterm and Term Neonates in Clinical Practice.

Based on a previously derived population pharmacokinetic model, a novel neonatal amikacin dosing regimen was developed. The aim of the current study was to prospectively evaluate this dosing regimen. First, early (before and after second dose) therapeutic drug monitoring (TDM) observations were evaluated for achieving target trough (<3 mg/liter) and peak (>24 mg/liter) levels. Second, all observed TDM concentrations were compared with model-predicted concentrations, whereby the results of a normalized prediction distribution error (NPDE) were considered. Subsequently, Monte Carlo simulations were performed. Finally, remaining causes limiting amikacin predictability (i.e., prescription errors and disease characteristics of outliers) were explored. In 579 neonates (median birth body weight, 2,285 [range, 420 to 4,850] g; postnatal age 2 days [range, 1 to 30 days]; gestational age, 34 weeks [range, 24 to 41 weeks]), 90.5% of the observed early peak levels reached 24 mg/liter, and 60.2% of the trough levels were <3 mg/liter (93.4% ≤5 mg/liter). Observations were accurately predicted by the model without bias, which was confirmed by the NPDE. Monte Carlo simulations showed that peak concentrations of >24 mg/liter were reached at steady state in almost all patients. Trough values of <3 mg/liter at steady state were documented in 78% to 100% and 45% to 96% of simulated cases with and without ibuprofen coadministration, respectively; suboptimal trough levels were found in patients with postnatal age <14 days and current weight of >2,000 g. Prospective evaluation of a model-based neonatal amikacin dosing regimen resulted in optimized peak and trough concentrations in almost all patients. Slightly adapted dosing for patient subgroups with suboptimal trough levels was proposed. This model-based approach improves neonatal dosing individualization.

Analysis of the relationship between age and treatment response in migraine.

In migraine, headache severity varies with age. As a consequence, the effectiveness of medication may also depend on a patient's age. The purpose of this study was to assess the combined effect of age and drug treatment on headache characteristics. Using data from clinical trials of sumatriptan in adolescents and adults, we show how the interaction between age and drug exposure can be parameterised as a covariate on a Markov model that describes the decline of headache severity over three clinically defined stages (no relief, relief and pain-free status). The model explains important clinical observations: (i) the rates at which the pain relief and pain-free status were attained were found to be inversely related to age; (ii) in placebo-treated patients, the mean transit time from 'no relief' to 'relief' is 3 h for young adolescents and increases to 6 h for patients aged >or= 30 years; and (iii) sumatriptan reduces the transit time to 2 h, irrespective of age. These findings indicate that the therapeutic gain over placebo increases with age. Prospective studies of antimigraine drugs should take this relationship into account when extrapolating efficacy data from adults to adolescents.

Prediction of headache response in migraine treatment.

Triptans are efficacious for the acute treatment of migraine attacks. Yet, defining a concentration-effect relation for these compounds is difficult as the dynamics of the migraine attack are not thoroughly understood. The objective of this investigation was to develop a disease model to predict measures of headache in randomized placebo-controlled clinical trials investigating oral sumatriptan as a paradigm compound. A hidden Markov model based on the states of response (no relief, relief, and pain free) and headache scores (observed variable) was used in conjunction with population pharmacokinetics. Model parameters were capable of predicting the course of headache relief, pain-free status and headache recurrence. It was shown that sumatriptan shortens mean transit times between states by up to 5 h. The potency of sumatriptan (EC(50)) was 9 ng/ml. These findings demonstrate the value of combining pharmacokinetic and efficacy information to model disease and characterize time-independent drug properties in a population of migraineurs.

A pharmacodynamic Markov mixed-effects model for the effect of temazepam on sleep.

BACKGROUND: A hypnogram shows how sleep travels through its various stages in the course of a night. The sleep stage changes can be quantified to study sedative drug effects. METHODS: Hypnograms from 21 patients with primary insomnia were collected during a randomized, placebo-controlled crossover study of 20 mg temazepam. A separate daytime session was performed to determine the pharmacokinetics of 20 mg temazepam and its effect on saccadic eye movement and electroencephalogram. A first-order Markov model was developed to describe the probability of sleep stage changes as a function of time after drug intake and time after last sleep stage change. The influence of temazepam concentration on the probability to change sleep stage was incorporated into the model. RESULTS: Transitions between sleep stages were profoundly influenced by the time of the night and by the time since the last change of sleep stage. Temazepam reduced the time spent awake. This effect could be attributed to four mechanisms: (1) transition to "deeper" sleep was facilitated, (2) transition to "lighter" sleep was inhibited, (3) regardless of sleep stage, the transition to wake state was inhibited, and (4) return to sleep was facilitated. Daytime sensitivities to temazepam, measured with the surrogate markers saccadic peak velocity and electroencephalogram beta activity, each correlated with one of the transition probabilities influenced by temazepam. CONCLUSIONS: By the development of a Markov model for these non-ordered six categorical data, the effect of temazepam on the sleep-wake status could be interpreted in terms of known mechanisms for sleep generation and benzodiazepine pharmacology.

Pharmacokinetic-pharmacodynamic modelling of the EEG effect of alfentanil in rats: assessment of rapid functional adaptation.

1. The purpose of the present investigation was to quantify rapid functional adaptation in the concentration-pharmacological effect relationship of alfentanil in rats using quantitative EEG parameters as a pharmacodynamic endpoint. Three groups of 6-7 rats received in a randomized fashion two consecutive infusions of 2.00, 3.14, or 4.24 mg/kg(-1) of alfentanil in 20, 40 or 60 min, respectively. The EEG was continuously recorded and frequent arterial blood samples were collected for determination of the alfentanil concentration by gas chromatography. 2. The pharmacokinetics of alfentanil were most adequately described by a bi-exponential function. The values (mean+/-s.e., n=20) of clearance, volume of distribution at steady-state and terminal half-life were 45+/-3 ml x min(-1) x kg(-1), 0.91+/-0.09 l/kg(-1) and 23+/-1 min, respectively, and independent of the administered dose. 3. Increase in power in the 0.5-4.5 Hz (delta) frequency band of the EEG was used as the measure of the pharmacological response. By pharmacokinetic-pharmacodynamic modeling the individual concentration-EEG effect relationships of alfentanil were derived which were successfully quantified by the sigmoidal Emax pharmacodynamic model. When the results of the first of the two consecutive infusions were compared, no systematic differences in the pharmacodynamic parameters were observed for the different infusion rates. The averaged values of the pharmacodynamic parameters of alfentanil were (mean+/-s.e., n=20): E0=56+/-3 microV, Emax=93+/-8 microV, EC50=235+/-27 ng x ml(-1) and Hill factor=1.6+/-0.1, respectively. For the second of the two consecutive infusions a significantly higher value of the EC50 of 404+/-56 ng x ml(-1) was observed (P < 0.05), while the values of the other pharmacodynamic parameters were unchanged. Simulations according to a mechanism-based model indicated that the observed change in concentration effect relationship can be explained by a 40% loss of functional mu-opioid receptors. 4. The results of the present study show that upon the administration of a single intravenous dose, acute functional adaptation does not interfere with the assessment of the concentration-EEG effect relationship of alfentanil. Upon repeated administration however functional adaptation may be a complicating factor.

Pharmacodynamics of temazepam in primary insomnia: assessment of the value of quantitative electroencephalography and saccadic eye movements in predicting improvement of sleep.

BACKGROUND AND OBJECTIVE: Quantitative electroencephalographic parameters and saccadic eye movements are frequently used as pharmacodynamic measures of benzodiazepine effect. We investigated the relationship between these measures and the hypnotic effect. METHODS: The correlation between the pharmacodynamic measures and sleep quality was determined in 21 patients with primary insomnia. The pharmacokinetic-pharmacodynamic relationships were characterized after administration of 20 mg oral temazepam. The hypnotic effect was determined on the basis of polysomnographic sleep recordings and a subjective sleep evaluation questionnaire. Correlations between pharmacodynamic measures and the improvement of sleep were investigated. RESULTS: The pharmacokinetic-pharmacodynamic relationships for the parameters derived from electroencephalography and saccadic eye movements showed considerable interindividual variability. Administration of temazepam led to a significant improvement in the objective parameters sleep period efficiency, wake time after sleep onset, and sleep efficiency and in the subjective assessment of sleep quality. No significant correlations were observed between the pharmacokinetic-pharmacodynamic-derived parameters and the improvement in objective or subjective sleep parameters. CONCLUSION: In subjects with primary insomnia the administration of 20 mg oral temazepam results in changes in both the pharmacodynamic measures and in quality of sleep. No individual correlations between the pharmacodynamic measures and quality of sleep were observed. We concluded that the investigated pharmacodynamic measures are of value in the first assessment of clinical efficacy and for the selection of the dose(s) to be investigated in subsequent trials that aim at showing clinical efficacy. However, the conclusive quantification of clinical efficacy should be performed only on the basis of the clinical end point itself.

Assessment of the enantiomeric purity of R- and S-N6-phenylisopropyladenosine (PIA): implications for adenosine receptor subclassification.

A chiral column high-performance liquid chromatographic method was developed for the assessment of the enantiomeric purity of the stereoisomers of N6-phenylisopropyladenosine (PIA). The observed chiral purity of R-PIA was greater than 99.9%, whereas S-PIA was found to contain 4.4% of the R-enantiomer. In radioligand binding studies, the observed affinity of S-PIA for the adenosine A1 receptor (IC50 240 nM) could entirely be attributed to its content of R-PIA (IC50 7.8 nM). Calculation of a theoretical IC50 of pure S-PIA for the A2 receptor yielded a value of 6700 nM, which was 35-fold higher than for R-PIA (190 nM). Concludingly, the utilization of enantiomeric impure S-PIA in the definition of adenosine receptor subclasses is questionable.