Population pharmacokinetic and pharmacodynamic modeling of etanercept using logistic regression analysis

OBJECTIVE

Our objective was to develop a population pharmacokinetic and pharmacodynamic model of etanercept in patients with rheumatoid arthritis, with the American College of Rheumatology response criterion of 20% improvement (ACR20) used as a binary clinical outcome variable.

METHODS

Concentration-time profiles from 25 subjects, administered 25 mg subcutaneous etanercept twice weekly for 24 weeks, were pooled with data from 77 subjects, enrolled in a 24-week, randomized, double-blind study comparing 25 mg and 50 mg subcutaneous etanercept twice weekly. The cumulative area under the concentration-time curve (AUC) was used as the exposure variable, and ACR20 was the binomial clinical outcome. ACR20 data from another 80 placebo-treated patients enrolled in a randomized, double-blind phase III study were used to describe the placebo time course of ACR20. A logistic regression analysis with NONMEM was applied to describe the exposure-response relationship, and the 95% confidence intervals (95% CIs) were constructed by bootstrapping 1000 times.

RESULTS

The population mean apparent clearance was 0.117 L/h (95% CI, 0.108-0.130 L/h) for white female patients and 0.138 L/h (95% CI, 0.118-0.163 L/h) for white male patients. Interindividual variability and interoccasion variability were 41.1% and 27.6%, respectively. The mean absorption half-life was 20.9 hours, and the elimination half-life was 95.4 hours. An improved response profile in male patients was shown, but the multiplicative factor between slope on cumulative AUC between male and female patients was not statistically significant (1.69; 95% CI, 0.37-9.99). The model-predicted percentage of patients achieving ACR20 at 6 months after dosing of 25 mg subcutaneously twice weekly was 54.9%, comparable to the observed 52.9%.

CONCLUSION

The population pharmacokinetic analysis confirmed that etanercept is slowly absorbed and eliminated after subcutaneous administration. The logistic model linking cumulative AUC with ACR20 adequately characterized the time course of clinical improvement in patients with rheumatoid arthritis receiving etanercept.

Forces resisting jaw displacement in relaxed humans: a predominantly viscous phenomenon

Forces opening the relaxed human jaw are resisted by intrinsic restraints, including passive tensions in the jaw-closing muscles. These muscle tensions have been modelled as viscoelastic elements, and static measurements suggest their elastic portions contribute approximately a total of 5 N resistance at wide gape. As the viscous damping properties of muscles which affect the jaw's dynamic behaviour are unknown, we measured the jaw opening force required to reach maximum gape during fast and slow opening in six relaxed subjects. These data were then incorporated in a dynamic mathematical jaw model to determine the damping properties of the masticatory system. During the 3 and 8 s opening trials, forces increased with gape (6.7 +/- 3.3 and 3.9 +/- 2.3 N, respectively, at 50% gape) and reached their maxima at wide gape (19.9 +/- 4.5 and 13.2 +/- 4.4 N, respectively). The muscle damping constant needed by the model to emulate these results was 150 Nsm(-1), approximately 25% lower than the calculated critical damping constant. This study suggests low forces are required to open the jaw in relaxed humans, and that jaw viscosity, not elasticity, provides the major resistance to motion.

Implant angulation: a measurement technique, implant overdenture maintenance, and the influence of surgical experience

PURPOSE

The purposes of this study were to develop a technique to measure the angulation between two implants and between each implant and reference planes, to analyze the relationship between the maintenance (adjustments and repairs) of ball-attachment mandibular implant overdentures and implant angulation, and to see if there is any correlation between surgeon experience and implant orientation.

MATERIALS AND METHODS

Final casts of 41 patients who had received two-implant ball-attachment mandibular overdentures were used to measure implant angulations using digital photographs and plane geometry. The measured angles were compared with the number of adjustments and repairs of the prostheses and analyzed by surgeon experience for any trends.

RESULTS

No significant relationships were found between number of adjustments and repairs and the interimplant angles. However, there was a significantly higher number of repairs when the lingual inclination of an implant was > or = 6.0 degrees (P = .033) or if the facial inclination was < 6.5 degrees (P = .036). Less experienced surgeons had a significantly greater tendency to place implants that diverged from each other in the frontal plane (P = .045) and with a facial or lingual inclination in the sagittal plane (P = .035).

CONCLUSION

While interimplant angulation did not appear to affect prosthesis maintenance, individual implants with a lingual inclination > or = 6 degrees and a facial inclination < 6.5 degrees were associated with significantly more prosthesis repairs. There was a tendency for implants placed by less experienced surgeons to demonstrate greater inclination.

Prediction of the outcome of a phase 3 clinical trial of an antischizophrenic agent (quetiapine fumarate) by simulation with a population pharmacokinetic and pharmacodynamic model

A completed phase 3 trial result was simulated 100 times on the basis of a simulation model of quetiapine fumarate (Seroquel), an antischizophrenic agent. The simulation was executed by analysts who were completely blinded from results of the actual trial until after the simulations were submitted to the holder of the trial results. Data from two clinical investigations of quetiapine in patients with schizophrenia were analyzed by use of nonlinear mixed effects modeling to derive a population pharmacokinetic- and pharmacodynamic-based simulation model. The time course of quetiapine concentrations was described by use of a one-compartment open linear pharmacokinetic model with first-order absorption and elimination. The combination of an inhibitory maximum effect pharmacodynamic model for the active treatment effect and a linear function of time for the placebo effect characterized the observed time course of change in the Brief Psychiatric Rating Scale. Simulation results were compared with those in the actual trial to evaluate how well the simulations predicted the outcome. The actual trial results for all doses except the placebo group fell within the predicted Brief Psychiatric Rating Scale scores +/- 1 SE. Unlike the phase 2 trial, from which the pharmacokinetic/pharmacodynamic model was developed, the placebo group in the actual phase 3 trial showed deterioration of Brief Psychiatric Rating Scale scores with time. We conclude that variable placebo responses observed in short-term studies of schizophrenia provide an inadequate basis for the modeling and simulation of placebo subjects in clinical trials. Knowledge of the range of placebo response observed in other studies may have provided an improved basis for the placebo effect model. The model for active drug produced adequate predictions of the actual trial outcomes.

Dynamic simulation of muscle and articular properties during human wide jaw opening

Human mandibular function is determined in part by masticatory muscle tensions and morphological restraints within the craniomandibular system. As only limited information about their interactions can be obtained in vivo, mathematical modeling is a useful alternative. It allows simulation of causal relations between structure and function and the demonstration of hypothetical events in functional or dysfunctional systems. Here, the external force required to reach maximum jaw gape was determined in five relaxed participants, and this information used, with other musculoskeletal data, to construct a dynamic, muscle-driven, three-dimensional mathematical model of the craniomandibular system. The model was programmed to express relations between muscle tensions and articular morphology during wide jaw opening. It was found that a downward force of 5 N could produce wide gape in vivo. When the model's passive jaw-closing muscle tensions were adjusted to permit this, the jaw's resting posture was lower than that normally observed in alert individuals, and low-level active tone was needed in the closer muscles to maintain a typical rest position. Plausible jaw opening to wide gape was possible when activity in the opener muscles increased incrementally over time. When the model was altered structurally by decreasing its angles of condylar guidance, jaw opening required less activity in these muscles. Plausible asymmetrical jaw opening occurred with deactivation of the ipsilateral lateral pterygoid actuator. The model's lateral deviation was limited by passive tensions in the ipsilateral medial pterygoid, which forced the jaw to return towards the midline as opening continued. For all motions, the temporomandibular joint (TMJ) components were maintained in continual apposition and displayed stable pathways despite the absence of constraining ligaments. Compressive TMJ forces were presented in all the cases and increased to maximum at wide gape. Dynamic mathematical modeling appears a useful way to study such events, which as yet are unrecordable in the human craniomandibular system.

Simulation of clinical trials

Computer simulation of clinical trials has evolved over the past two decades from a simple instructive game to "full" simulation models yielding pharmacologically sound, realistic trial outcomes. The need to make drug development more efficient and informative and the awareness that many industries make extensive use of simulation in product development have advanced considerably the use of simulation of clinical trials in pharmaceutical product development over the past decade. The structural and stochastic components of trial simulation models are explained as a prelude to a listing of representative simulation projects, reflecting investigative applications of statistical methods, trial design comparisons, and full simulation of new drugs being developed. Lessons learned from these projects are reviewed in the context of their current impact and potential for influencing the future of drug development.

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.

Optimizing the science of drug development: opportunities for better candidate selection and accelerated evaluation in humans

Two international meetings were convened in 1998 to review the current science of drug development and the potential opportunities to optimize the evaluation of new drugs in humans. This report represents a synopsis of these meetings, and focuses on the current state of knowledge pertaining to drug development, future scientific and technical needs, and the relative merits of various strategies intended to accelerate the clinical development of drugs.

Trajectories of condylar points during nonworking side and protrusive movements of the mandible

STATEMENT OF PROBLEM

During lateral excursive and protrusive jaw movements, condylar points are distant from any instantaneous rotational center. Therefore, it is likely that different condylar points would follow similar trajectories during these movements.

PURPOSE

This study evaluated the effect of changes in condylar point location on trajectories of condylar points on the nonworking side and during a protrusive jaw movement and compared these changes with the effects described for open-close and working-side condylar movements in the same group of subjects.

METHODS

The movements of 5 clinically determined condylar points were recorded in 44 subjects during a contralateral excursion and during protrusion (7 radiographically determined condylar points in 2 subjects).

RESULTS

During any single jaw movement, the trajectory of each condylar point was similar in form and dimension to the other condylar points within that subject.

CONCLUSION

Changes in condylar point location had little effect on the trajectories of condylar points on the nonworking side and during protrusive jaw movement.

Trajectories of condylar points during working-side excursive movements of the mandible

STATEMENT OF PROBLEM

Trajectories of different condylar points provide different interpretations of condylar movement during open-close jaw movements. Movement of the working-side condyle is often assessed clinically by recording the trajectory of a single arbitrary condylar point.

PURPOSE

This study examined the effect of the differences in condylar point location on condylar point movement trajectories during a working-side movement.

METHODS

Different points exhibited different trajectories during a single working-side movement in each of 44 subjects.

RESULTS

Up to 40% of a point's displacement could be attributed simply to the location of the point.

CONCLUSIONS

Interpretation of condylar movement on the working side within a subject depends on the point chosen.

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.

The variability of condylar point pathways in open-close jaw movements

STATEMENT OF PROBLEM

Clinical assessments of condylar movement often rely on the movement of a single clinically determined or average value condylar point.

PURPOSE

The aim of this investigation was to study the effect of differences in condylar point location on recorded movement trajectories with an open-close jaw movement.

METHODS

Recordings were made of the movements of various condylar points in 44 subjects. The points were identified clinically (average value points) and radiographically.

RESULTS

The trajectory of each condylar point, whether average value or radiographically determined, was different in form and dimension from any other condylar point within a subject for the same open-close jaw movement.

CONCLUSIONS

Depending on the point chosen in the vicinity of the condyle, quite different interpretations of condylar movement within a subject could be made. The data underscore the caution that must be exercised when interpreting condylar movement from the movement of a single condylar point.

Implementations, comparisons, and an investigation of heuristic techniques for cone-beam tomography

A novel cone-beam reconstruction method was proposed in 1985. The first objective of the work reported here is to implement this reconstruction method. The second objective is to compare it with the method developed by Feldkamp et al. (1984). Although the resulting reconstruction was not perfect, the proposed method did eliminate the axial distortion associated with Feldkamp's method. A second cone-beam reconstruction method was proposed in 1987. Two major challenges arise when this method is implemented. One is to minimize the error that results from violating an assumed condition on the distribution of the cones. The second is to minimize the error that results from the convolution of a discontinuous function which is introduced to compensate for the redundancy in the data set. The third objective of the work reported here was to investigate several heuristic techniques to minimize these errors. Techniques were found that did mitigate these errors and using these techniques resulted in images that are more accurate than those resulting from the 1985 method.