An approach for dose finding of drugs in infants: sedation by midazolam studied using the continual reassessment method

Characterization of Pediatric Rectal Absorption, Drug Disposition, and Sedation Level for Midazolam Gel Using Physiologically Based Pharmacokinetic/Pharmacodynamic Modeling

This study aims to explore and characterize the role of pediatric sedation via rectal route. A pediatric physiologically based pharmacokinetic-pharmacodynamic (PBPK/PD) model of midazolam gel was built and validated to support dose selection for pediatric clinical trials. Before developing the rectal PBPK model, an intravenous PBPK model was developed to determine drug disposition, specifically by describing the ontogeny model of the metabolic enzyme. Pediatric rectal absorption was developed based on the rectal PBPK model of adults. The improved Weibull function with permeability, surface area, and fluid volume parameters was used to extrapolate pediatric rectal absorption. A logistic regression model was used to characterize the relationship between the free concentrations of midazolam and the probability of sedation. All models successfully described the PK profiles with absolute average fold error (AAFE) < 2, especially our intravenous PBPK model that extended the predicted age to preterm. The simulation results of the PD model showed that when the free concentrations of midazolam ranged from 3.9 to 18.4 ng/mL, the probability of "Sedation" was greater than that of "Not-sedation" states. Combined with the rectal PBPK model, the recommended sedation doses were in the ranges of 0.44-2.08 mg/kg for children aged 2-3 years, 0.35-1.65 mg/kg for children aged 4-7 years, 0.24-1.27 mg/kg for children aged 8-12 years, and 0.20-1.10 mg/kg for adolescents aged 13-18 years. Overall, this model mechanistically quantified drug disposition and effect of midazolam gel in the pediatric population, accurately predicted the observed clinical data, and simulated the drug exposure for sedation that will inform dose selection for following pediatric clinical trials.

Application of Midazolam Injection in Patients with Intraoperative Nerve Block Anesthesia and Sedation Assisted by Imaging Guidance

OBJECTIVE

In the present study, we explored the clinical effect of midazolam as an adjuvant analgesic and tranquilizer after brachial plexus block anesthesia with the aid of imaging guidance.

METHODS

We selected 106 patients who had undergone elective unilateral upper extremity surgery from January 2017 to December 2019 and randomly divided them into groups A and B, with 53 cases in each group. All the patients had undergone brachial plexus block anesthesia. Group A received imidazole-assisted sedation, and group B received fentanyl plus midazolam-assisted sedation. Under ultrasound-guided intermuscular sulcus brachial plexus block, we observed and recorded the ultrasound anatomical images before injection, including the distance from the lower edge of the upper, middle, and lower trunk of the forearm brachial plexus to the skin. We also recorded the anesthesia and operation times, effects of the anesthetic block, and incidence of adverse reactions.

RESULTS

The distance from the lower edge of each nerve trunk to the skin averaged 1.002 cm for the upper stem, 1.598 cm for the middle stem, and 2.26 cm for the lower stem. The average anesthesia procedure time was 3 minutes, 56 seconds and was within 3-5 minutes for 92% of the procedures. The anesthesia effect was excellent, good, and poor in 81%, 11%, and 6%, respectively, and ineffective for 2% and effective for 92%.

CONCLUSIONS

The ultrasound-guided inferior intermuscular sulcus approach for brachial plexus block is suitable for unilateral upper extremity radial hand surgery. For surgery involving the upper extremity ulnar hand side, a larger dose (concentration) of local anesthetic should be used within a safe range and/or an additional ulnar nerve block might be necessary. Midazolam adjuvant medication can have a good sedative and amnestic effect in brachial plexus block anesthesia, helping to reduce pain and inhibit the increase in stress levels.

Copula-Based Abrupt Variations Detection in the Relationship of Seasonal Vegetation-Climate in the Jing River Basin, China

Understanding the changing relationships between vegetation coverage and precipitation/temperature (P/T) and then exploring their potential drivers are highly necessary for ecosystem management under the backdrop of a changing environment. The Jing River Basin (JRB), a typical eco-environmentally vulnerable region of the Loess Plateau, was chosen to identify abrupt variations of the relationships between seasonal Normalized Difference Vegetation Index (NDVI) and P/T through a copula-based method. By considering the climatic/large-scale atmospheric circulation patterns and human activities, the potential causes of the non-stationarity of the relationship between NDVI and P/T were revealed. Results indicated that (1) the copula-based framework introduced in this study is more reasonable and reliable than the traditional double-mass curves method in detecting change points of vegetation and climate relationships; (2) generally, no significant change points were identified during 1982–2010 at the 95% confidence level, implying the overall stationary relationship still exists, while the relationships between spring NDVI and P/T, autumn NDVI and P have slightly changed; (3) teleconnection factors (including Arctic Oscillation (AO), Pacific Decadal Oscillation (PDO), Niño 3.4, and sunspots) have a more significant influence on the relationship between seasonal NDVI and P/T than local climatic factors (including potential evapotranspiration and soil moisture); (4) negative human activities (expansion of farmland and urban areas) and positive human activities (“Grain For Green” program) were also potential factors affecting the relationship between NDVI and P/T. This study provides a new and reliable insight into detecting the non-stationarity of the relationship between NDVI and P/T, which will be beneficial for further revealing the connection between the atmosphere and ecosystems.

Comparison of oral dexmedetomidine and midazolam for premedication and emergence delirium in children after dental procedures under general anesthesia: a retrospective study

Background

Premedication is the most common way to minimize distress in children entering the operating room and to facilitate the smooth induction of anesthesia and is accomplished using various sedative drugs before the children are being transferred to the operating room. The aim of this study was to compare the effect of oral dexmedetomidine (DEX) and oral midazolam (MID) on preoperative cooperation and emergence delirium (ED) among children who underwent dental procedures at our hospital between 2016 and 2017.

Patients and methods

The medical records of 52 children, who were American Society of Anesthesiologists I, aged between 3 and 7 years, and who underwent full-mouth dental rehabilitation under general anesthesia (GA), were evaluated. Twenty-six patients were given 2 µg/kg of DEX, while another 26 patients were given 0.5 mg/kg of MID in apple juice as premedication agents. The patients’ scores on the Ramsay Sedation Scale (RSS), Parental Separation Anxiety Scale (PSAS), Mask Acceptance Scale, Pediatric Anesthesia Emergence Delirium Scale (PAEDS), and hemodynamic parameters were recorded from patients’ files. The level of sedation of children had been observed just before premedication and at 15, 30, and 45 min after premedication. The data were analyzed using a chi-square test, Fisher’s exact test, Student’s t-test, and analysis of variance in SPSS.

Results

The Mask Acceptance Scale and PSAS scores and RSS scores at 15, 30, and 45 min after premedication were not statistically different (p>0.05) in both groups, whereas the PAEDS scores were significantly lower in the DEX group (p<0.05).

Conclusion

Oral DEX provided satisfactory sedation levels, ease of parental separation, and mask acceptance in children in a manner similar to MID. Moreover, children premedicated with DEX experienced lesser ED than those premedicated with MID.

Effective concentration of levobupivacaine and ropivacaine in 80% of patients receiving epidural analgesia (EC80) in the first stage of labour: A study using the Continual Reassessment Method

BACKGROUND

A comparison of the effective dose in 50% of patients (ED50) has suggested that the potency of levobupivacaine lies between that of bupivacaine and ropivacaine. However, for clinical purposes, knowledge and use of doses close to the ED95 are more relevant. This study was designed to determine the EC80 (effective concentration) for both epidural levobupivacaine and ropivacaine using the Continual Reassessment Method (CRM) during obstetric analgesia.

METHODS

In this double-blind randomised study, term parturients were included by cohorts of 6 if cervical dilatation was≤5cm and visual analogue pain score (VAPS)>30mm. Efficacy was defined by a decrease of VAPS to a value≤10, thirty minutes after epidural injection of 20mL of levobupivacaine or ropivacaine. The first cohort received the lowest dose. Every next cohort received a dose according to the response's probability calculated using a Bayesian method, incorporating data from all consecutive previous patients. In addition, a logistic equation was fitted a posteriori to the whole data set to determine the whole dose-probability curve.

RESULTS

Fifty-four patients were enrolled. Levobupivacaine 0.17% and ropivacaine 0.2% gave probabilities of success of 82% and 72% respectively. By fitting the logistic model to the data, the concentration leading to a probability of 0.8 (EC80) was 0.14% for levobupivacaine and 0.24% for ropivacaine while the EC50 were 0.09% for levobupivacaine and 0.17% for ropivacaine, respectively.

CONCLUSION

This study suggests that epidural levobupivacaine used as the sole drug for labour analgesia has an EC80 lower than that of ropivacaine.

Dose-Finding Study of Omeprazole on Gastric pH in Neonates with Gastro-Esophageal Acid Reflux Using a Bayesian Sequential Approach

Objective

Proton pump inhibitors are frequently administered on clinical symptoms in neonates but benefit remains controversial. Clinical trials validating omeprazole dosage in neonates are limited. The objective of this trial was to determine the minimum effective dose (MED) of omeprazole to treat pathological acid reflux in neonates using reflux index as surrogate marker.

Design

Double blind dose-finding trial with continual reassessment method of individual dose administration using a Bayesian approach, aiming to select drug dose as close as possible to the predefined target level of efficacy (with a credibility interval of 95%).

Setting

Neonatal Intensive Care unit of the Robert Debré University Hospital in Paris, France.

Patients

Neonates with a postmenstrual age ≥ 35 weeks and a pathologic 24-hour intra-esophageal pH monitoring defined by a reflux index ≥ 5% over 24 hours were considered for participation. Recruitment was stratified to 3 groups according to gestational age at birth.

Intervention

Five preselected doses of oral omeprazole from 1 to 3 mg/kg/day.

Main outcome measures

Primary outcome, measured at 35 weeks postmenstrual age or more, was a reflux index <5% during the 24-h pH monitoring registered 72±24 hours after omeprazole initiation.

Results

Fifty-four neonates with a reflux index ranging from 5.06 to 27.7% were included. Median age was 37.5 days and median postmenstrual age was 36 weeks. In neonates born at less than 32 weeks of GA (n = 30), the MED was 2.5mg/kg/day with an estimated mean posterior probability of success of 97.7% (95% credibility interval: 90.3–99.7%). The MED was 1mg/kg/day for neonates born at more than 32 GA (n = 24).

Conclusions

Omeprazole is extensively prescribed on clinical symptoms but efficacy is not demonstrated while safety concerns do exist. When treatment is required, the daily dose needs to be validated in preterm and term neonates. Optimal doses of omeprazole to increase gastric pH and decrease reflux index below 5% over 24 hours, determined using an adaptive Bayesian design differ among neonates. Both gestational and postnatal ages account for these differences but their differential impact on omeprazole doses remains to be determined.

Response-adaptive clinical trials: case studies in the medical literature

The past 15 years has seen many pharmaceutical sponsors consider and implement adaptive designs (AD) across all phases of drug development. Given their arrival at the turn of the millennium, we might think that they are a recent invention. That is not the case. The earliest idea of an AD predates Bradford Hill's MRC tuberculosis study, appearing in Biometrika in 1933. In this paper, we trace the development of response-ADs, designs in which the allocation to intervention arms depends on the responses of subjects already treated. We describe some statistical details underlying the designs, but our main focus is to describe and comment on ADs from the medical research literature. Copyright © 2016 John Wiley & Sons, Ltd.

Determination of the 90% effective dose (ED90) of phenylephrine for hypotension during elective cesarean delivery using a continual reassessment method

OBJECTIVE

The purpose of this study was to determine, by continual reassessment, the 90% effective dose (ED90) of phenylephrine for hypotension after combined spinal-epidural anesthesia.

STUDY DESIGN

Term pregnant women scheduled for elective cesarean delivery received combined spinal epidural anesthesia. Subjects received phenylephrine at one of 6 incremental doses ranging from 60 to 160μg (n=3 for each dose). While the first cohort received a conservative, predetermined dose of 60μg, subsequent cohorts received phenylephrine doses determined using Bayesian-based software. One of the predetermined bolus doses of phenylephrine was given in the event of both hypotension [defined as systolic blood pressure (SBP)<80% of baseline or below 100mmHg] and tachycardia [defined as heart rate >120% of baseline or >100beatsmin(-1)]. Treatment was considered successful if SBP returned to within 80% of the baseline or ≥100mmHg within 2min.

RESULTS

Twenty-four subjects with hypotension and tachycardia were included. T6 block was achieved within 15min in 20 patients and after additional epidural chloroprocaine in the remaining four. The estimated ED90 was 100μg, with a response probability of 90.7% (95% CI 74.1-99.5%). Treatment was successful in 20 patients. Probability of success at each bolus dose (in μg) was as follows: 60, 58.9%; 80, 80.3%; 100, 90.7%; 120, 95.5%; 140, 98.3%; and 160, 99.2%.

CONCLUSIONS

The ED90 of a phenylephrine bolus dose for hypotension in term pregnant women is approximately 100μg, based on continual reassessment.

Using the continual reassessment method to estimate the minimum effective dose in phase II dose-finding studies: a case study

Background

The Continual Reassessment Method typically is presented as the method of choice for the purpose of dose-finding based on a toxicity scale in phase I clinical trials. However, this adaptive statistical approach also can be applied easily to dose-finding experiments in phase II trials.

Purpose

To provide a case study from a real clinical trial to illustrate the use of the Continual Reassessment Method in the context of phase II dose finding.

Methods

The Continual Reassessment Method was used to model the dose-failure relationship in order to estimate the minimal effective dose. This approach was retrospectively used to determine the minimal effective dose of granulocyte colony-stimulating factor for peripheral blood stem cell collection in allografted patients following chemotherapy.

Results

After the inclusion of 25 patients, the minimal effective dose was estimated to be the third dose level tested in the study.

Limitations

The main limitation of the Continual Reassessment Method, which is not specific to the method but to the dose-finding setting, is that the empirical choice of the dose range can be either under or over-estimated. The method requires a calibration study prior to trial onset.

Conclusions

Assuming that a dose-effect relationship is monotonically increasing, the use of the Continual Reassessment Method in phase II dose-finding studies allows the estimation of the minimum effective dose for further studies. Modeling the dose-failure relationship allows the direct use of available software developed for the Continual Reassessment Method in the context of phase I clinical trials.

Adaptive designs for dose-finding in non-cancer phase II trials: influence of early unexpected outcomes

BACKGROUND

In non-cancer phase II trials, dose-finding trials are usually carried out using fixed designs, in which several doses including a placebo are randomly distributed to patients. However, in certain vulnerable populations, such as neonates or infants, there is an heightened requirement for safety, precluding randomization.

PURPOSE

To estimate the minimum effective dose of a new drug from a non-cancer phase II trial, we propose the use of adaptive designs like the Continual Reassessment Method (CRM). This approach estimates the dose closest to some target response, and has been shown to be unbiased and efficient in cancer phase I trials.

METHODS

Based on a motivating example, we point out the individual influence of first outliers in this setting. A weighted version of the CRM is proposed as a theoretical benchmark to control for these outliers. Using simulations, we illustrate how this approach provides further insight into the behavior of the CRM.

RESULTS

When dealing with low targets like a 10% failure rate, the CRM appears unable to rapidly overcome an early unexpected outcome. This behavior persisted despite changing the inference (Bayesian or likelihood), underlying dose-response model (though slightly improved using the power model), and the number of patients enrolled at each dose level.

LIMITATIONS

The choices for initial guesses of failure rates, the vague prior for the model parameter, and the log-log shape of weights can appear somewhat arbitrary.

CONCLUSIONS

In phase II dose-finding studies in which failure targets are below 20%, the CRM appears quite sensitive to first unexpected outcomes. Using a power model for dose-response improves some behavior if the trial is started at the first dose level and includes at least three to five patients at the starting dose before applying the CRM allocation rule.

Effective dose of nefopam in 80% of patients (ED80): a study using the continual reassessment method

AIMS

The effective dose in 50% of patients (ED(50)) is far from being relevant for clinical purposes. We used the continual reassessment method (CRM) to determine the effective dose of nefopam in 80% of the patients suffering from moderate pain in the postoperative period (ED(80)).

METHODS

Patients with a pain intensity >3 on a 1-10 numerical pain score (NPS) received increasing or decreasing doses of nefopam (20, 30, 40, 60, 80 mg) postoperatively. The criterion of success was a NPS <or=3, 30 min after the beginning of infusion. The initial dose was 20 mg and the subsequent doses were determined by the continuous reassessment method (CRM). The data were also fitted a posteriori with the maximum likelihood technique.

RESULTS

Twenty-four patients were enrolled. Nefopam 60 mg gave a probability of success of 0.818 (95% credibility interval 0.606-0.941). Using the maximum likelihood technique, we determined an ED(50) of 27.3 mg and a dose leading to a probability of 0.8 (ED(80)) of 74.4 mg. We did not observe a high incidence of side-effects.

CONCLUSIONS

The ED(80) of nefopam, close to 60 mg is higher than the usual dose of 20 mg. The CRM allowed us to determine the ED(80) of nefopam with reasonable accuracy in a small number of patients as compared with the classical dose-probability curve fitting. We did not observe an increased incidence of side-effects when compared with the literature or to our previous studies.

Modelling and clinical trials in paediatrics

Clinical trials are more difficult to conduct in children, but they are even more necessary than in adults their scarcity is an ethical scandal. Mathematical models can be built that can describe both the disease process and the mechanism of action of drugs. These models can then be used to simulate the outcome of clinical trials. Inspection of the simulated results then facilitates optimisation of the trial design and proposed methods of analysis. Validation is a crucial issue for the good practice of modelling and simulation. The participants of Round Table No. 6 recommend: (i) that modelling be systematically employed; (ii) that all the required professional personnel be involved, at all phases; (iii) that all data needed are made accessible; (iv) that clinicians be trained; (v) that specialists develop training tool kits; and (vi) that universities provide appropriate training.

Software to compute and conduct sequential Bayesian phase I or II dose-ranging clinical trials with stopping rules

The aim of dose-ranging phase I (resp. phase II) clinical trials is to rapidly identify the maximum tolerated dose (MTD) (resp., minimal effective dose (MED)) of a new drug or combination. For the conduct and analysis of such trials, Bayesian approaches such as the Continual Reassessment Method (CRM) have been proposed, based on a sequential design and analysis up to a completed fixed sample size. To optimize sample sizes, Zohar and Chevret have proposed stopping rules (Stat. Med. 20 (2001) 2827), the computation of which is not provided by available softwares. We present in this paper a user-friendly software for the design and analysis of these Bayesian Phase I (resp. phase II) dose-ranging Clinical Trials (BPCT). It allows to carry out the CRM with stopping rules or not, from the planning of the trial, with choice of model parameterization based on its operating characteristics, up to the sequential conduct and analysis of the trial, with estimation at stopping of the MTD (resp. MED) of the new drug or combination.

Phase I (or phase II) dose-ranging clinical trials: proposal of a two-stage Bayesian design

We propose a new design for phase I (or phase II) dose-ranging clinical trials aiming at determining a dose of an experimental treatment to satisfy safety (respectively efficacy) requirements, at treating a sufficiently large number of patients to estimate the toxicity (respectively failure) probability of the dose level with a given reliability, and at stopping the trial early if it is likely that no dose is safe (respectively efficacious). A two-stage design was derived from the Continual Reassessment Method (CRM), with implementation of Bayesian criteria to generate stopping rules. A simulation study was conducted to compare the operating characteristics of the proposed two-stage design to those reached by the traditional CRM. Finally, two applications to real data sets are provided.

The continual reassessment method: comparison of Bayesian stopping rules for dose-ranging studies

The continual reassessment method (CRM) provides a Bayesian estimation of the maximum tolerated dose (MTD) in phase I clinical trials and is also used to estimate the minimal efficacy dose (MED) in phase II clinical trials. In this paper we propose Bayesian stopping rules for the CRM, based on either posterior or predictive probability distributions that can be applied sequentially during the trial. These rules aim at early detection of either the mis-choice of dose range or a prefixed gain in the point estimate or accuracy of estimated probability of response associated with the MTD (or MED). They were compared through a simulation study under six situations that could represent the underlying unknown dose-response (either toxicity or failure) relationship, in terms of sample size, probability of correct selection and bias of the response probability associated to the MTD (or MED). Our results show that the stopping rules act correctly, with early stopping by using the two first rules based on the posterior distribution when the actual underlying dose-response relationship is far from that initially supposed, while the rules based on predictive gain functions provide a discontinuation of inclusions whatever the actual dose-response curve after 20 patients on average, that is, depending mostly on the accumulated data. The stopping rules were then applied to a data set from a dose-ranging phase II clinical trial aiming at estimating the MED dose of midazolam in the sedation of infants during cardiac catheterization. All these findings suggest the early use of the two first rules to detect a mis-choice of dose range, while they confirm the requirement of including at least 20 patients at the same dose to reach an accurate estimate of MTD (MED). A two-stage design is under study.

[What's new in pediatric pharmacology?]

Only a minority of the drugs administered to children and infants have a pediatric labeling and have been sufficiently tested for efficacy, safety and correct pediatric dosing, which cannot necessarily be extrapolated from adult data. This situation is scientifically and ethically unacceptable. To address this problem, the suggestion is being made in several countries that more formal legal requirements should be introduced. In the United States, in 1997, a new legislation encouraged pharmaceutical companies to study medicines in children (for example, by offering the financial incentive of a six-month extension to patent exclusivity). However, there are undeniable difficulties in pediatric and neonatal studies. To minimize the risks of clinical investigation in children, appropriate methodologies should be used. New in vitro and in vivo methods are now available, taking into account pediatric characteristics.