Individualized Dosing Algorithms and Therapeutic Monitoring for Antiepileptic Drugs.

Pharmacokinetic (PK) models exist for most antiepileptic drugs (AEDs). Yet their use in clinical practice to assess interindividual differences and derive individualized doses has been limited. Here we show how model-based dosing algorithms can be used to ensure attainment of target exposure and improve treatment response in patients. Using simulations, different treatment scenarios were explored for 11 commonly used AEDs. For each drug, five scenarios were considered: 1) all patients receive the same dose. 2) Individual clearance (CL), as predicted by population PK models, is used to personalize treatment. 3-5) Individual CL, obtained by therapeutic drug monitoring (TDM) according to different sampling schemes, is used to personalize treatment. Attainment of steady-state target exposure was used as the performance criterion to rank each scenario. In contrast to current clinical guidelines, our results show that patient demographic and clinical characteristics should be used in conjunction with TDM to personalize the treatment of seizures.

Dose optimization of piperacillin/tazobactam in critically ill children.

Objectives: To characterize the population pharmacokinetics of piperacillin and tazobactam in critically ill infants and children, in order to develop an evidence-based dosing regimen. Patients and methods: This pharmacokinetic study enrolled patients admitted to the paediatric ICU for whom intravenous piperacillin/tazobactam (8:1 ratio) was indicated (75 mg/kg every 6 h based on piperacillin). Piperacillin/tazobactam concentrations were measured by an LC-MS/MS method. Pharmacokinetic data were analysed using non-linear mixed effects modelling. Results: Piperacillin and tazobactam blood samples were collected from 47 patients (median age 2.83 years; range 2 months to 15 years). Piperacillin and tazobactam disposition was best described by a two-compartment model that included allometric scaling and a maturation function to account for the effect of growth and age. Mean clearance estimates for piperacillin and tazobactam were 4.00 and 3.01 L/h for a child of 14 kg. Monte Carlo simulations showed that an intermittent infusion of 75 mg/kg (based on piperacillin) every 4 h over 2 h, 100 mg/kg every 4 h given over 1 h or a loading dose of 75 mg/kg followed by a continuous infusion of 300 mg/kg/24 h were the minimal requirements to achieve the therapeutic targets for piperacillin (60% f T >MIC >16 mg/L). Conclusions: Standard intermittent dosing regimens do not ensure optimal piperacillin/tazobactam exposure in critically ill patients, thereby risking treatment failure. The use of a loading dose followed by a continuous infusion is recommended for treatment of severe infections in children >2 months of age.

Integration of pharmacogenetics and pharmacogenomics in drug development: implications for regulatory and medical decision making in pediatric diseases.

This article aims to provide an overview of the current situation regarding pharmacogenetic and pharmacogenomic (PG) studies in pediatrics, with a special focus on the role of PG data in the regulatory decision-making process. Despite the gap in pharmacogenetic research due to the lack of translational studies in adults and children, several technologies exist in drug development and biomarkers validation, which could supply valuable information concerning labeling and dosing recommendations. If performed under strict good clinical practice quality criteria, such findings could be included in the submission package of new chemical entities and used as additional information for prescribers, supporting further evaluation and understanding of the efficacy and safety profile of new medicines. Even though regulatory authorities may be aware of the potential role of PG in medical practice and guidances are available about the integration of PG in drug development, most data obtained from PG studies are not used by prescribers. The challenge is to better understand whether PG markers can be used to assess potential differences in drug response during the clinical program, so PG data can be integrated into the regulatory decision-making process, enabling the introduction of labeling information that promotes optimal dosing in the pediatric population.

Impact of chronic inflammation on the pharmacokinetic-pharmacodynamic relationship of naproxen.

OBJECTIVES: The use of biomarkers for predicting the clinical doses of analgesic drugs relies on the understanding of the relationship between drug exposure and response under disease conditions. In this study, we demonstrate the relevance of such a relationship for COX-inhibitors by modelling the effect of naproxen on prostaglandin E2 (PGE(2)) and thromboxane B2 (TXB(2)) in a chronic inflammation model in rats. METHODS: Rats were treated with Freund's complete adjuvant (FCA) by intraplantar injection. On post-inoculation days (PID) 7-21, animals received single or chronic (qd until day 21) doses of naproxen (10mg/kg). Blood samples were collected at various intervals after dosing to characterise naproxen pharmacokinetics and its effects on PGE(2) and TXB(2) production. PK-PD modelling was performed using nonlinear mixed effects in NONMEM. RESULTS: The inhibition of PGE(2) and TXB(2) could be described by a sigmoid E(max) model. A decrease in the potency estimates of both biomarkers was observed under chronic inflammation, as compared to healthy animals. IC(50) values for PGE(2) inhibition showed a shift from 2840+/-510 to 4000+/-677ng/ml(mean+/-SD), whilst IC(50) values for TXB(2) inhibition increased from 1180+/-323 to 3360+/-453ng/ml in healthy and FCA-inoculated animals, respectively. CONCLUSIONS: Our results show that chronic inflammation causes a significant change in the potency estimates for COX-inhibition. These findings illustrate the implications of pathophysiological processes on pharmacodynamics and consequently on the required exposure levels for achieving response during chronic treatment.

Differences in the sensitivity of behavioural measures of pain to the selectivity of cyclo-oxygenase inhibitors.

OBJECTIVES: Freund's complete adjuvant (FCA) is an animal model of inflammatory pain commonly used in the screening of COX-inhibitors. However, there is little understanding of how behavioural measures of the anti-inflammatory effect in the FCA model correlate to differences in mechanism of action and whether such endpoints equally reflect drug activity in humans. In the current investigation we evaluate the time course of the analgesic effect for different endpoints after treatment with drugs with varying degrees of selectivity for COX-1 and COX-2. We also assess prostaglandin (PGE(2)) and thromboxane (TXB(2)) inhibition to establish the correlation between behavioural measures and the degree of selectivity for COX-1 and COX-2. METHODS: Sprague-Dawley rats were treated with FCA by intra-plantar injection. On post-inoculation day (PID) 7, rats received a single oral dose of naproxen, diclofenac, ketorolac or rofecoxib. Drug treatment continued until PID 21. A control group received placebo only. Behavioural endpoints for inflammatory pain and blood samples for biomarkers were obtained at various time points before and after dosing to characterise the time course of drug effect and disease progression. RESULTS: COX-inhibitors showed no effect on the dynamic plantar test. In contrast, full analgesia was observed after drug administration for weight bearing capacity (WBC) and paw pressure (PP), with varying duration of the effect for each of the endpoints. No tolerance to drug effect was observed up to 14 days of chronic treatment. Rofecoxib showed an increase in baseline pain threshold values after chronic treatment, which may be related to its pharmacokinetic characteristics. CONCLUSIONS: Changes in paw pressure threshold seem to best reflect the anti-hyperalgesic properties of COX-inhibitors with enough sensitivity to enable estimation of the dose-exposure-response curve.

Fit-for-purpose pharmacogenomic biomarkers in drug development: a project team case study with 'what-ifs'.

Over the past four years, the annual US FDA-DIA pharmacogenomic workshops have brought together attendees with wide-ranging expertise spanning industry, regulatory authorities and academia. This special report summarizes a breakout session using a novel, interactive case format as a way to engage participants, raise awareness and share diverse learnings via 'real life' decisions that project teams might face in developing a new medicine. This case was situated just prior to approval by a Regulatory Authority as a project team is finalizing a new medicine label. To effectively integrate new biomarkers such as pharmacogenomics into developing new medicines, this session highlighted the importance in considering medical practice implications as relevant (or not) to information or actions by a prescriber; progressing validation beyond assay to clinical; and fitting pharmacogenomics into context with other evidence often built over decades during a drug's development. All converge onto a label that must communicate evidence-based use of a new medicine that is effective and safe.

Mechanism-based pharmacokinetic-pharmacodynamic (PK-PD) modeling in translational drug research.

The use of pharmacokinetic-pharmacodynamic (PK-PD) modeling in translational drug research is a promising approach that provides better understanding of drug efficacy and safety. It is applied to predict efficacy and safety in humans using in vitro bioassay and/or in vivo animal data. Current research in PK-PD modeling focuses on the development of mechanism-based models with improved extrapolation and prediction properties. A key element in mechanism-based PK-PD modeling is the explicit distinction between parameters for describing (i) drug-specific properties and (ii) biological system-specific properties. Mechanism-based PK-PD models contain specific expressions for the characterization of processes on the causal path between drug exposure and drug response. The different terms represent: target-site distribution, target binding and activation and transduction. Ultimately, mechanism-based PK-PD models will also characterize the interaction of the drug effect with disease processes and disease progression. In this review, the principles of mechanism-based PK-PD modeling are described and illustrated by recent applications.

Efficacy of pulmonary insulin delivery in diabetic rats: use of a model-based approach in the evaluation of insulin powder formulations.

The potential of N-trimethyl chitosan (TMC) with two degrees of quaternization (DQ), TMC20 (DQ 20%, as a mucoadhesive) and TMC60 (DQ 60%, as a mucoadhesive and a permeation enhancer), and dextran (as a non-mucoadhesive and non-permeation enhancer) microparticles as carriers for pulmonary delivery of insulin was studied in diabetic rats. The impact of the powder formulation on insulin bioavailability and its pharmacological effect was evaluated using a population pharmacokinetic-pharmacodynamic (PKPD) model. Insulin-loaded microparticles were prepared by a supercritical fluid (SCF) drying technique. They had a median volume diameter and median volume aerodynamic diameter of about 6-10 microm and 4 microm, respectively. The PK of insulin in the diabetic rats was analyzed by a one-compartment disposition model and the PD was described by the minimal model of glucose disappearance. The bioavailability of the pulmonarily administered dextran-, TMC20- and TMC60-insulin microparticles relative to subcutaneously (SC) administered insulin, was 0.48, 0.59 and 0.95, respectively. Histological examinations of the rats' lungs did not show any local adverse reactions after single administration of insulin powders. The pharmacodynamic model could describe the insulin-glucose relationship and pharmacodynamic efficiency of insulin formulations, which was about 0.6(*)10(-5) ml/microU, irrespective of the formulations. The current findings suggest that TMC microparticles are a promising vehicle for pulmonary delivery of insulin.

Relevance of absorption rate and lag time to the onset of action in migraine.

OBJECTIVE: The objective of this analysis was to simulate the performance of oral triptan formulations with varying absorption characteristics and their impact on the onset and magnitude of the antimigraine effect using a Markov model for migraine attacks. ANALYSIS: Sumatriptan pharmacokinetic data were obtained from clinical pharmacology studies in which marketed solid formulations were administered. Based on a population pharmacokinetic model, mean concentration-time profiles were generated by varying the absorption rate constant and lag time. Subsequently, the simulated profiles were evaluated in a disease model of migraine to predict the onset and duration of the effect (the pain-free, pain-relief response). RESULTS: Based on a therapeutic dose of 50 mg of sumatriptan, a maximum gain in the pain-free response of 12% was achieved with an increased absorption rate. This gain in the response was reached approximately 0.5 hours after administration. A decrease only in the lag time with respect to the currently available formulations (i.e. 0.24 hours) resulted in a maximum gain of 5% in the pain-free response, which in contrast may not be interpreted as clinically relevant. CONCLUSION: Model-based predictions suggest that increases in the absorption rate of the currently marketed oral formulation of sumatriptan result in a gain in the pain-free response that is both clinically and statistically relevant.

Pharmacogenetics and paediatric drug development: issues and consequences to labelling and dosing recommendations.

The area of pharmacogenetics (PGt) is evolving rapidly. However, ongoing efforts in this field are not aligned with the requirements for the inclusion of clinically relevant findings into the label, especially with reference to paediatric indications. Clinical research in children poses unique issues from a practical and technical perspective, but many challenges can be overcome by applying advanced study design and data analysis methods. When investigating the role of PGt factors on treatment effect, all features that influence drug response must be taken into account. Yet, PGt often has a privileged status in research protocols, with PGt factors evaluated independently from other determinants of response, instead of being regarded as other demographic or clinical covariates (e.g., age, renal function). At present, guidelines to incorporate PGt findings into label statements are lacking in part because this is a new and incompletely understood area. This situation is no longer acceptable. To achieve the potential that PGt can offer to drug development and ultimately to drug prescription, academia, industry and regulatory agencies need to pool resources on the revision of study design and data analysis requisites, bringing in model-based methodologies to enable accurate interpretation of results and provide appropriate labelling recommendations.

Markers of exacerbation severity in chronic obstructive pulmonary disease.

BACKGROUND: Patients with chronic obstructive pulmonary disease (COPD) can experience 'exacerbations' of their conditions. An exacerbation is an event defined in terms of subjective descriptors or symptoms, namely dyspnoea, cough and sputum that worsen sufficiently to warrant a change in medical management. There is a need for reliable markers that reflect the pathological mechanisms that underlie exacerbation severity and that can be used as a surrogate to assess treatment effects in clinical studies. Little is known as to how existing study variables and suggested markers change in both the stable and exacerbation phases of COPD. In an attempt to find the best surrogates for exacerbations, we have reviewed the literature to identify which of these markers change in a consistent manner with the severity of the exacerbation event. METHODS: We have searched standard databases between 1966 to July 2004 using major keywords and terms. Studies that provided demographics, spirometry, potential markers, and clear eligibility criteria were included in this study. Central tendencies and dispersions for all the variables and markers reported and collected by us were first tabulated according to sample size and ATS/ERS 2004 Exacerbation Severity Levels I to III criteria. Due to the possible similarity of patients in Levels II and III, the data was also redefined into categories of exacerbations, namely out-patient (Level I) and in-patient (Levels II & III combined). For both approaches, we performed a fixed effect meta-analysis on each of the reported variables. RESULTS: We included a total of 268 studies reported between 1979 to July 2004. These studies investigated 142,407 patients with COPD. Arterial carbon dioxide tension and breathing rate were statistically different between all levels of exacerbation severity and between in out- and in-patient settings. Most other measures showed weak relationships with either level or setting, or they had insufficient data to permit meta-analysis. CONCLUSION: Arterial carbon dioxide and breathing rate varied in a consistent manner with exacerbation severity and patient setting. Many other measures showed weak correlations that should be further explored in future longitudinal studies or assessed using suggested mathematical modelling techniques.

Correlation between in vitro and in vivo concentration-effect relationships of naproxen in rats and healthy volunteers.

Understanding the mechanisms underlying the analgesic effect of new cyclooxygenase inhibitors is essential to identify dosing requirements in early stages of drug development. Accurate extrapolation to humans of in vitro and in vivo findings in preclinical species is needed to optimise dosing regimen in inflammatory conditions. The current investigation characterises the inhibition of prostaglandin E2 (PGE(2)) and thromboxane B2 (TXB(2)) by naproxen in vitro and in vivo in rat and human blood. The inhibition of PGE(2) in the absence or presence of increasing concentrations of naproxen (10(-8)-10(-1) M) was measured by ex vivo whole blood stimulation with LPS, whereas inhibition of TXB(2) was measured in serum following blood clotting. In further experiments, inhibition of PGE(2) and TXB(2) levels was also assessed ex vivo in animals treated with naproxen (2.5, 10, 25 mg kg(-1)). Subsequently, pharmacokinetic (PK)/pharmacodynamics (PD) modelling of in vitro and in vivo data was performed using nonlinear mixed effects in NONMEM (V). Inhibition of PGE(2) and TXB(2) was characterised by a sigmoid E(max) model. The exposure-response relationships in vitro and in vivo were of the same order of magnitude in both species. IC(80) estimates obtained in vitro were similar for PGE(2) inhibition (130.8 +/- 11 and 131.9 +/- 19 10(-6) M, mean +/- s.d. for humans and rats, respectively), but slightly different for TXB(2) inhibition (103.9+/-15 and 151.4 +/- 40 10(-6) M, mean +/- s.d. for humans and rats, respectively, P < 0.05). These differences, however, may not be biologically relevant. The results confirm the value of exposure-effect relationships determined in vitro as a means to predict the pharmacological activity in vivo. This analysis also highlights the need to parameterise concentration-effect relationships in early drug development, as indicated by the estimates of IC(80) for PGE(2) and TXB(2) inhibition.

Markers of disease severity in chronic obstructive pulmonary disease.

BACKGROUND AND OBJECTIVES: Diagnosis and assessment of treatment effect in chronic obstructive pulmonary disease (COPD) have relied primarily on the examination of a complex set of symptoms and the use of spirometry. However, these methods require long periods of assessment to determine whether patients show clinically relevant improvements after intervention. We therefore wanted to determine how existing clinical and laboratory measures change with COPD severity and identify disease markers that can serve as better endpoints for diagnosis and assessment of COPD progression and treatment effect. METHODS: Using standard COPD keywords and terms, we searched PubMed, ISI Web of Science, and Cochrane Review databases for retrospective and prospective clinical studies published since 1966. We identified 652 studies (n = 146,255) from 1978 to September 2003 based on the availability of spirometric and demographic data, investigation of possible markers, absence of acute exacerbations and co-morbidities, and the withdrawal of standard COPD medication. Central tendencies and dispersions of subject baseline measures were collected according to study sample size, smoking status, and mild, moderate and severe COPD stages. A fixed effect meta-analysis was then conducted on each measure at various disease stages. RESULTS: Arterial oxygen tension, sputum neutrophils and IL-8, and serum TNF-alpha and C-Reactive Protein showed a trend toward separation between COPD stages. Other measures such as pack-years and St George's Respiratory Questionnaire only distinguished between disease and disease-free states. CONCLUSIONS: We observed little separation between disease stages for many measures used in COPD diagnosis and clinical trials. This demonstrates the poor sensitivity of such endpoints to define a patient's clinical status and to quantify treatment effect. Therefore, we recommend that longitudinal studies and disease modelling be the primary methods for assessing whether potential markers of disease progression can be used for COPD diagnosis and clinical trials.