Application of Item Response Theory to Model Disease Progression and Agomelatine Effect in Patients with Major Depressive Disorder.

INTRODUCTION: In this paper, we studied the effect over time of agomelatine, an antidepressant drug administered in patient with major depressive disorder, through item response theory (IRT), taking into account a strong placebo effect and missing not at random. We also assessed the informativeness of the HAMD-17 scale's item. MATERIALS AND METHODS: The data includes five phase III clinical trials sponsored by Servier Institute, totalling 1549 patients followed during a maximum of 1 year. At each observation, individual scores for the 17 items of the HAMD scale were recorded. The probability for each score was modelled with IRT. A non-linear mixed effects model was used to describe the evolution of the disease and was coupled with a time to event model to predict dropout. Clinical trial simulations were then used to compare placebo and active treatment. Informativeness of each item was evaluated using the Fisher information theory. RESULTS: The best model combined an IRT model, a longitudinal model for underlying depression which describes the remission and then a possible relapse, and a hazard model for dropout depending on the evolution from baseline. The drug effect was best modelled as an effect on the remission and the relapse phases. The median predicted drop in HAMD between baseline and 6 weeks was 8.8 (90% PI, 8.3-9.2) when on placebo and 13.1 (90% PI, 12.8-13.4) when treated. Nine items were found to be the most informative. CONCLUSION: The IRT framework allowed to characterise the evolution of depression with time and estimate the effect of agomelatine, as well as the link between symptoms and disease.

Population Pharmacokinetics of Stiripentol in Paediatric Patients with Dravet Syndrome Treated with Stiripentol, Valproate and Clobazam Combination Therapy.

AIM: The aim of this study was to describe the pharmacokinetics of stiripentol in children with Dravet syndrome and to determine the concentrations of stiripentol achieved in this population for the usual 25 mg/kg twice-daily dose. METHODS: Thirty-five children with epilepsy were included in a prospective population pharmacokinetic study (using MONOLIX software). Four blood samples were drawn per patient. Stiripentol area under the plasma concentration-time curve (AUC) values and trough concentrations were simulated for 7000 theoretical children weighing between 10 and 70 kg for the 25 mg/kg twice-daily dose. RESULTS: The pharmacokinetics of stiripentol was described using a one-compartment model with zero-order absorption and first-order elimination. The apparent clearance (CL/F) and apparent volume of distribution (V d/F) of stiripentol were related to body weight by allometric equations. A dose-dependent non-linearity was also observed with an allometric model relating CL/F to the weight-normalised dose. Mean population estimates (% inter-individual variability) were 4.2 L/h (21%) for CL/F and 82 L (25%) for V d/F. The AUC of stiripentol increased by 300% when body weight increased from 10 to 70 kg. CONCLUSION: This population pharmacokinetic model of stiripentol in children with Dravet syndrome confirmed the dose-dependent non-linearity that has been evidenced in adults. It also supported that a 25 mg/kg twice-daily dose might lead to excessive exposure in children >30 kg, suggesting an eventual dose adjustment during adolescence. CLINICAL TRIAL IDENTIFIER: This study is part of the STIPOP study (EUDRACT number: 2007-001784-30).

Model-based approaches for ivabradine development in paediatric population, part I: study preparation assessment.

The main objective was to help design a paediatric study for ivabradine, a compound already marketed in adults, focusing on: the paediatric formulation evaluation, the doses to be administered, the sampling design and the sampling technique. A secondary objective was to perform a comparison of the prediction of ivabradine pharmacokinetics (PK) in children using a physiologically-based pharmacokinetic (PBPK) approach and allometric scaling of a population pharmacokinetic (PPK) model. A study was conducted in order to assess the relative bioavailability (Frel) of the paediatric formulation and a similar Frel was observed between the paediatric formulation and the adult marketed tablet. PBPK modelling was used to predict initial doses to be administered in the paediatric study and to select the most appropriate sample time collections. The dried blood spot technique was recommended in the clinical trial in children. Simulations obtained by both the PBPK approach and allometric scaling of a PPK model were compared a posteriori to the paediatric study observations. Both PPK and PBPK approaches allowed an adequate prediction of the PK of ivabradine and its metabolite in children.

Model-based approaches for ivabradine development in paediatric population, part II: PK and PK/PD assessment.

The objectives of this work were first to describe the pharmacokinetic (PK) of ivabradine and its active metabolite in a paediatric patient population after repeated oral administration of ivabradine using a population PK approach, and secondly to assess whether the blood/plasma ratio and the pharmacokinetic/pharmacodynamic (PK/PD) relationship are preserved in the paediatric population in comparison to adult. PK data for 70 patients were obtained after blood sampling using dried blood spot and one plasma sample in order to assess the relationship between blood and plasma concentration. In order to describe ivabradine and its metabolite blood concentrations in children, a joint population PK model was developed taking into account weight & age effects on PK parameters. Plasma PK exposure parameters were calculated in children using plasma PK profiles. In order to assess the PK/PD relationship in children, an adult PK/PD model was used. The relationship between blood and plasma concentrations was described using linear mixed effect models. Two and one-compartment models best described parent and metabolite dispositions. Weight effects were fixed to the allometric values of ¾ on clearance (CL) and 1 on volume. A maturation function was added on metabolite formation clearance (CL PM ) reflecting enzyme maturation. Plasma exposure comparison indicated that higher dose/kg were necessary to achieve a similar exposure between younger and older children. No differences between age classes were observed in terms of range of exposure at the maintenance dose. The PK/PD relationship in adult patients is conserved in children.

Reassessment of stiripentol pharmacokinetics in healthy adult volunteers.

Because children who have been receiving stiripentol for the treatment of Dravet syndrome for more than 10 years are now becoming young adults, it is important to accurately characterize stiripentol pharmacokinetics in this age range. A double-blind placebo-controlled dose ranging study was therefore conducted to investigate the pharmacokinetics and tolerability of stiripentol in 12 healthy volunteers. Each subject received 3 single doses of stiripentol (500, 1000, and 2000 mg) separated by a wash-out period of 1 week. Pharmacokinetics of stiripentol was analyzed for each dose by non-compartmental analysis. Median area under the curve (AUC), terminal elimination half-life (t1/2,z) and maximal concentration (Cmax) were calculated for between-dose comparison. Safety was evaluated based on both clinical and biological criteria. Oppositely to previous results, there was no concentration rebounds in the elimination phase, which could be the consequence of the food intake. A more than proportional increase in the AUC was observed, associated with a significant increase in the t1/2,z, for increasing doses (median AUC of 8.3, 31 and 88 mgh/L, and median t1/2,z of 2, 7.7 and 10h for the 500, 1000, and 2000 mg doses respectively), which confirmed the Michaelis-Menten pharmacokinetics of Stiripentol. However, dose-normalized Cmax did not significantly vary between doses. Median Michaelis-Menten parameters were 117 mg/h for Vmax and 1.9 mg/L for Km. No safety concern was observed during the study. The present study allowed a better characterization of the disposition phase of stiripentol and confirmed its non-linear pharmacokinetic behaviour. Further pharmacokinetic/pharmacodynamic studies would be useful to determine the optimal dose of stiripentol for the treatment of Dravet patients in adulthood.