Biomedical subjects

Leon Aarons

Publications and source records attributed to Leon Aarons.

27 records · Page 2Linked to original sources

PubMed2004

Modelling and simulation in the development and use of anti-cancer agents: an underused tool?

To help identify the role of modelling and simulation in the development of anti-cancer agents, their main advantages and the obstacles to their rational use, an expert meeting was organized by COST B15. This manuscript presents a synthesis of views expressed at that meeting and indicates future directions. The manuscript also shows some examples where modelling and simulation have proven to be of relevant value in the drug development process for anti-cancer agents.

Antineoplastic Agents↗

PubMed2004

Population pharmacokinetics of artemether and dihydroartemisinin following single intramuscular dosing of artemether in African children with severe falciparum malaria.

AIMS: To determine the population pharmacokinetics of artemether and dihydroartemisinin in African children with severe malaria and acidosis associated with respiratory distress following an intramuscular injection of artemether. METHODS: Following a single intramuscular (i.m.) injection of 3.2 mg kg-1 artemether, blood samples were withdrawn at various times over 24 h after the dose. Plasma was assayed for artemether and dihydroartemisinin by gas chromatography-mass spectrometry. The software program NONMEM was used to fit the concentration-time data and investigate the influence of a range of clinical characteristics (respiratory distress and metabolic acidosis, demographic features and disease) on the pharmacokinetics of artemether and dihydroartemisinin. RESULTS: A total of 100 children with a median age of 36.4 (range 5-108) months were recruited into the study and data from 90 of these children (30 with respiratory distress and 60 with no respiratory distress) were used in the population pharmacokinetic analysis. The best model to describe the disposition of artemether was a one-compartment model with first-order absorption and elimination. The population estimate of clearance (clearance/bioavailability, CL/F) was 14.3 l h-1 with 53% intersubject variability and that of the terminal half-life was 18.5 h. If it was assumed that artemisin displays "flip-flop" kinetics, the elimination half-life was estimated to be 21 min and the corresponding volume of distribution was 8.44 l, with an intersubject variability of 104%. None of the covariates could be identified as having any influence on the disposition of artemether. The disposition of dihydroartemisinin was fitted separately using a one-compartment linear model in which the volume of distribution was fixed to the same value as that of artemether. Assuming that artemether is completely converted to dihydroartemisinin, the estimated value of CL/F for dihydroartemisinin was 93.5 l h-1, with an intersubject variability of 90.2%. The clearance of dihydroartemisinin was formation rate limited. CONCLUSIONS: Administration of a single 3.2 mg kg-1 i.m. dose of artemether to African children with severe malaria and acidosis is characterized by variable absorption kinetics, probably related to drug formulation characteristics rather than to pathophysiological factors. Use of i.m. artemether in such children needs to be reconsidered.

Acidosis, Respiratory↗

PubMed2004

Retrospective population pharmacokinetic analysis of cetirizine in children aged 6 months to 12 years.

AIMS: To evaluate retrospectively the population pharmacokinetics of cetirizine, a second-generation antihistamine, in children. METHODS: Data were pooled from six clinical trials, in which cetirizine was administered orally in various formulations and in single and multiple dosage regimens. The population consisted of 112 children (33 female and 79 male) aged 6 months to 12 years. A one-compartment open model with first-order absorption and elimination was fitted to the plasma concentration-time profiles using nonlinear mixed effects modelling with first-order estimation. RESULTS: A linear association was found between apparent clearance (CL/F) and age with the former increasing by 0.12 l h(-1) per year. The intercept of the relationship was slightly lower for female children (0.59 vs. 0.77 l h(-1) in male). The population estimate of CL/F for an average age of 7 years was 1.61 and 1.43 l h(-1) for male and female children, respectively. A linear association was found between apparent volume of distribution (V/F) and age with the former increasing by 1.4 l year(-1), with an intercept of 4.0 l. The population estimate of V/F for an average age of 7 years was 13.9 l. The magnitudes of interpatient variability were 35.6% for CL/F and 19.7% for V/F. The magnitude of residual variability in cetirizine concentrations was 26.9%. CONCLUSIONS: Population analysis predicts a linear increase in cetirizine CL/F and V/F with age, with CL/F being slightly lower in female children, relative to males of the same age. However, this gender difference probably has no clinical consequences. Since V/F increased more rapidly with age than CL/F, a nonlinear increase in half-life was seen, from < 4 h in infants to near the adult value at 12 years of age. The current recommended dosing regimens that younger children should receive lower but more frequent doses, are confirmed by the present analysis.

Cetirizine↗

PubMed2003

A population pharmacokinetic model for doxorubicin and doxorubicinol in the presence of a novel MDR modulator, zosuquidar trihydrochloride (LY335979).

PURPOSE: To develop a population pharmacokinetic model for doxorubicin and doxorubicinol in the presence of zosuquidar.3HCl, a potent P-glycoprotein inhibitor. METHODS: The population approach was used (implemented with NONMEM) to analyse doxorubicin-doxorubicinol pharmacokinetic data from 40 patients who had received zosuquidar.3HCl and doxorubicin intravenously (separately in cycle 1 and concomitantly in cycle 2 over 48 h and 0.5 h, respectively). RESULTS: A five-compartment pharmacokinetic model (including three compartments for doxorubicin pharmacokinetics with two pathways for doxorubicinol formation) best described the doxorubicin-doxorubicinol pharmacokinetics in the presence of zosuquidar.3HCl. Doxorubicin clearance (CL), peripheral volume of distribution (V2) and doxorubicinol apparent clearance (CLm/fm) and apparent volume of distribution (Vm/fm) were 62.3 l/h, 2360 l, 143 l/h and 3150 l, respectively, in the absence or presence of low doses of zosuquidar.3HCl (<500 mg). In the presence of high doses of zosuquidar.3HCl (>or=500 mg), these values decreased by 25%, 26%, 48% and 73%, respectively, and doxorubicinol pharmacokinetics were characterized by a delayed t(max) (24 h versus 4 h), which led to the inclusion of the parallel pathways. A decrease in the objective function ( P<0.005) was observed when the impact of zosuquidar.3HCl was accounted for. CONCLUSIONS: This integrated parent-metabolite population pharmacokinetic model accurately characterized the increase in doxorubicin and doxorubicinol exposure (1.33- and 2-fold, respectively) in the presence of zosuquidar.3HCl (>or=500 mg) and provided insights into the pharmacokinetic interaction, which may be useful in designing future clinical trials.

Adult↗

PubMed2003

A population pharmacokinetic model for paclitaxel in the presence of a novel P-gp modulator, Zosuquidar Trihydrochloride (LY335979).

AIMS: To develop a population pharmacokinetic model for paclitaxel in the presence of a MDR modulator, zosuquidar 3HCl. METHODS: The population approach was used (implemented with NONMEM) to analyse paclitaxel pharmacokinetic data from 43 patients who received a 3-h intravenous infusion of paclitaxel (175 mg x m(-2) or 225 mg x m(-2)) alone in cycle 2 or concomitantly with the oral administration of zosuquidar 3HCl in cycle 1. RESULTS: The structural pharmacokinetic model for paclitaxel, accounting for the Cremophor ELTM impact, was a three-compartment model with a nonlinear model for paclitaxel plasma clearance (CL), involving a linear decrease in this parameter during the infusion and a sigmoidal increase with time after the infusion. The final model described the effect of Zosuquidar 3HCl on paclitaxel CL by a categorical relationship. A 25% decrease in paclitaxel CL was observed, corresponding to an 1.3-fold increase in paclitaxel AUC (from 14829 microg x l(-1) x h to 19115 microg x l(-1) x h following paclitaxel 175 mg x m(-2)) when zosuquidar Cmax was greater than 350 microg x l(-1). This cut-off concentration closely corresponded to the IC50 of a sigmoidal Emax relationship (328 microg x l(-1)). A standard dose of 175 mg x m(-2) of paclitaxel could be safely combined with doses of zosuquidar 3HCl resulting in plasma concentrations known, from previous studies, to result in maximal P-gp inhibition. CONCLUSIONS: This analysis provides a model which accurately characterized the increase in paclitaxel exposure, which is most likely to be due to P-gp inhibition in the bile canaliculi, in the presence of zosuquidar 3HCl (Cmax > 350 microg x l(-1)) and is predictive of paclitaxel pharmacokinetics following a 3 h infusion. Hence the model could be useful in guiding therapy for paclitaxel alone and also for paclitaxel administered concomitantly with a P-gp inhibitor, and in designing further clinical trials.

ATP Binding Cassette Transporter, Subfamily B, Mem↗

PubMed2003

A Bayesian method based on clotting factor activity for the prediction of maintenance warfarin dosage regimens.

A Bayesian algorithm, employing a population pharmacokinetic-pharmacodynamic model, for the effective and rapid prediction of warfarin maintenance dosing requirements was developed. The algorithm was evaluated prospectively in five healthy volunteers who were given a 15-mg single dose of racemic warfarin. Based on previous population pharmacokinetic and pharmacodynamic parameters and factor VII response measurements taken during the first 48 hours, dosage regimens to achieve a subtherapeutic degree of anticoagulation (50% of normal) were determined. Three factor VII response measurements were sufficient to determine dosing requirements in the five volunteers. The advantage of the algorithm is that it does not require warfarin concentration measurements and uses non-steady-state data.

Algorithms↗

PubMed2002

Pharmacokinetics of controlled-release verapamil in healthy volunteers and patients with hypertension or angina.

AIMS: To study the dose-ranging population pharmacokinetics of controlled release verapamil in healthy subjects and patients with angina or hypertension. To characterize the pharmacodynamics of controlled-release verapamil in patients with hypertension. METHODS: Dose-ranging studies were conducted in healthy volunteers and patients with hypertension and angina. Subjects received doses of 120, 180, 360, or 540 mg racemic verapamil as an osmotic controlled-release formulation. A population pharmacokinetic model involving zero-order release of verapamil into the gastrointestinal tract with first-order absorption and elimination was used to describe the steady-state plasma concentration profile for R- and S-verapamil. A population sigmoid E(max) pharmacodynamic model was used to describe the effect of R- and S-verapamil on mean arterial blood pressure. RESULTS: S-verapamil had an approximate 4-fold greater apparent clearance than R-verapamil in both healthy volunteers and patients. The apparent plasma clearance of R- and S-verapamil in healthy volunteers decreased over the dose range of 120-540 mg. A similar dose-dependent decrease in apparent plasma clearance was also noted in patients. None of the patient demographic variables examined (age, total body weight, lean body weight, body mass index, and height) explained the variability in verapamil pharmacokinetics. The pharmacodynamic model describing the relationship between verapamil plasma concentration and mean arterial blood pressure indicated that the S-verapamil had a 3.6-fold lower estimated EC(50) compared to R-verapamil. CONCLUSIONS: The results from this dose-ranging pharmacokinetic investigation in healthy volunteers and patients are consistent with previous reports in healthy subjects. S-verapamil is cleared more rapidly than R-verapamil and the estimated EC(50) for S-verapamil was 3.6-fold lower than for R-verapamil. Estimated EC(50) values for R- and S-verapamil decreased with increasing age and decreasing weight.

Adult↗

PubMed2002

Determination of an optimal dosage regimen using a Bayesian decision analysis of efficacy and adverse effect data.

One of the aims of Phase II clinical trials is to determine the dosage regimen(s) that will be investigated during a confirmatory Phase III clinical trial. During Phase II, pharmacodynamic data are collected that enables the efficacy and safety of the drug to be assessed. It is proposed in this paper to use Bayesian decision analysis to determine the optimal dosage regimen based on efficacy and toxicity of the drug oxybutynin used in the treatment of urinary urge incontinence. Such an approach results in a general framework allowing modeling, inference and decision making to be carried out. For oxybutynin, the repeated measurement efficacy and toxicity data were modeled using nonlinear hierarchical models and inferences were based on posterior probabilities. The optimal decision in this problem was to determine the dosage regimen that maximized the posterior expected utility given the prior information on the model parameters and the patient response data. The utility function was defined using clinical opinion on the satisfactory levels of efficacy and toxicity and then combined by weighting the relative importance of each pharmacodynamic response. Markov chain Monte Carlo (MCMC) methodology implemented in Win-BUGS 1.3 was used to obtain posterior estimates of the model parameters, probabilities and utilities.

Aged↗

PubMedDate not supplied

Estimation of population pharmacokinetic parameters of free-phenytoin in adult epileptic patients.

BACKGROUND: Serum concentrations of free-phenytoin (F-PHT) obtained in adult epileptic patients receiving PHT in monotherapy were analyzed to estimate the Michaelis-Menten pharmacokinetic parameters. METHODS: Steady-state F-PHT serum concentrations, PHT dosing history, and associated information were collected prospectively. The maximum metabolic rate (Vm) and Michaelis-Menten constant (Km) of F-PHT and their interindividual variability data were estimated using nonlinear mixed effects modeling (NONMEM). RESULTS: Twenty-nine patients with two or more available steady-state F-PHT serum concentrations (total of 63 dose/serum concentration pairs) met the inclusion criteria. Patients were taking PHT (100-500 mg/day) in monotherapy. The population estimates of F-PHT for Vm and Km were 9.1 mg/kg/day and 7.3 mg/L, respectively. The model was prospectively evaluated in a small group (seven) of additional patients. CONCLUSIONS: The recommended daily dose in this population to achieve a F-PHT concentration of 1.5 mg/L is 6.1 mg/kg.

Adolescent↗