Niclas Jonsson | PubMed Health

PubMed2005

Non-linear mixed-effects models with stochastic differential equations: implementation of an estimation algorithm.

Pharmacokinetic/pharmacodynamic modelling is most often performed using non-linear mixed-effects models based on ordinary differential equations with uncorrelated intra-individual residuals. More sophisticated residual error models as e.g. stochastic differential equations (SDEs) with measurement noise can in many cases provide a better description of the variations, which could be useful in various aspects of modelling. This general approach enables a decomposition of the intra-individual residual variation epsilon into system noise w and measurement noise e. The present work describes implementation of SDEs in a non-linear mixed-effects model, where parameter estimation was performed by a novel approximation of the likelihood function. This approximation is constructed by combining the First-Order Conditional Estimation (FOCE) method used in non-linear mixed-effects modelling with the Extended Kalman Filter used in models with SDEs. Fundamental issues concerning the proposed model and estimation algorithm are addressed by simulation studies, concluding that system noise can successfully be separated from measurement noise and inter-individual variability.

Algorithms↗

PubMed2005

PsN-Toolkit--a collection of computer intensive statistical methods for non-linear mixed effect modeling using NONMEM.

PsN-Toolkit is a collection of statistical tools for pharmacometric data analysis using the non-linear mixed effect modeling software NONMEM. The toolkit is object oriented and written in the programming language Perl using the programming library Perl-speaks-NONMEM (PsN). Five methods: the Bootstrap, the Jackknife, Log-likelihood Profiling, Case-deletion Diagnostics and Stepwise Covariate Model building are included as separate classes and may be used in user-written Perl scripts or through stand-alone command line applications. The tools are designed with the ability to cooperate and with an emphasis on common structures for workflow and result handling. Parallel execution of independent tool sections is supported on shared memory multiprocessor (SMP) computers, Mosix/openMosix clusters and distributed computing environments following the NorduGrid standard. In conclusion, PsN-Toolkit makes it easier to use the Bootstrap, the Jackknife, Log-likelihood Profiling, Case-deletion Diagnostics and Stepwise Covariate Model building in pharmacometric data analysis.

Cluster Analysis↗

PubMed2002

Treatment of acute ischaemic stroke with the low-affinity, use-dependent NMDA antagonist AR-R15896AR. A safety and tolerability study.

BACKGROUND AND PURPOSE: A low-affinity, use-dependent N-Methyl-D-Aspartate (NMDA) antagonist AR-R15896AR has neuroprotective properties in animal models of ischaemic stroke. The aim of the present study was to examine the safety and tolerability of a new and higher dosage regimen that would enable acute stroke patients to achieve and maintain neuroprotective plasma concentrations. METHODS: A randomised, multi-centre, double-blind, placebo-controlled, parallel group study was carried out at 19 centres in France, Germany and the Netherlands in patients with a clinical diagnosis of acute ischaemic stroke, and onset of symptoms within 12 hours before start of study drug administration. Two loading doses of 3.5 mg/kg of AR-R15896AR over 60 minutes, followed by a 2.5 mg/kg infusion over the next 120 minutes were given. Eight hours after the start of the loading dose infusion, the first maintenance dose (120 mg) was administered over 60 minutes. Eight further maintenance infusions were administered at intervals of 8 hours over a total treatment period of 3 days. Main variables were safety, tolerability and pharmacokinetics. Follow-up assessments also included the Barthel Index (BI) and the NIH Stroke Scale (NIHSS) at 4-7 days after the end of the last infusion and at 30 days after the onset of stroke. RESULTS: 103 patients with acute ischaemic stroke were randomised to either treatment with AR-R15896AR (70 patients) or placebo (33 patients). Mortality was not significantly different in the AR-R15896AR group compared with the placebo group (10 % vs. 6 %). Serious adverse events during treatment due to psychiatric conditions were associated with AR-R15896AR (3 vs. 0). Other side effects were more common in the group treated with AR-R15896AR: vomiting (29 % vs. 9 %), nausea (23 % vs. 12 %), fever (17 % vs. 12 %), agitation (7 % vs. 3 %), dizziness (7 % vs. 0 %), and hallucinations (6 % vs. 0 %). No significant difference between the two groups (with respect to the proportions of patients with favourable outcome) was detected in either the analysis of the BI or the NIHSS. Pharmacokinetic data showed that plasma concentrations of AR-R15896AR were in the expected neuroprotective range. CONCLUSION: In most of the patients with acute stroke receiving AR-R15896AR the intended high plasma levels were reached within a short time period. However, active treatment produced more side effects than placebo, thus indicating safety concerns and tolerability issues for use in high doses in an acute stroke population.

Acute Disease↗