A predictive pharmacokinetic/pharmacodynamic model of fentanyl for analgesia/sedation in neonates based on a semi-physiologic approach

Exploring the thermally-controlled fentanyl transdermal therapy to provide constant drug delivery by physics-based digital twins

Transdermal drug delivery is suitable for low-molecular-weight drugs with specific lipophilicity, like fentanyl, which is widely used for cancer-induced pain management. However, fentanyl's transdermal therapy displays high intra-individual variability. Factors like skin characteristics at application sites and ambient temperature contribute to this variation. In this study, we developed a physics-based digital twin of the human body to cope with this variability and propose better adapted setups. This twin includes an in-silico skin model for drug penetration, a pharmacokinetic model, and a pharmacodynamic model. Based on the results of our simulations, applying the patch on the flank (side abdominal area) showed a 15.3 % higher maximum fentanyl concentration in the plasma than on the chest. Additionally, the time to reach this maximum concentration when delivered through the flank was 19.8 h, which was 10.3 h earlier than via the upper arm. Finally, this variation led to an 18 % lower minimum pain intensity for delivery via the flank than the chest. Moreover, the impact of seasonal changes on ambient temperature and skin temperature by considering the activity level was investigated. Based on our result, the fentanyl uptake flux by capillaries increased by up to 11.8 % from an inactive state in winter to an active state in summer. We also evaluated the effect of controlling fentanyl delivery by adjusting the temperature of the patch to alleviate the pain to reach a mild pain intensity (rated three on the VAS scale). By implementing this strategy, the average pain intensity decreased by 1.1 points, and the standard deviation for fentanyl concentration in plasma and average pain intensity reduced by 37.5 % and 33.3 %, respectively. Therefore, our digital twin demonstrated the efficacy of controlled drug release through temperature regulation, ensuring the therapy toward the intended target outcome and reducing therapy outcome variability. This holds promise as a potentially useful tool for physicians.

Fentanyl dosage for preterm infants suggested by a pharmacokinetic, -dynamic, and -genetic model

BACKGROUND

Fentanyl is commonly administered for procedural pain management in preterm infants, but target concentrations have not yet been defined.

METHODS

To investigate pharmacokinetics (PK), -dynamics (PD), and -genetics (PG), 25 infants (gestational age 23.3-34.1 weeks) received a fentanyl dose before a skin-breaking procedure (0.5 µg/kg) or tracheal intubation (2 µg/kg). Four pain scales were used as a PD endpoint to evaluate efficacy. The impact of polymorphism in genes encoding enzymes (UGT2B7, CYP3A7, CYP3A4, COMT, CYP2D6, KCNJ6), transporters (SLC22A1, ABCC1, ABCC3) and receptor (OPRM1) on PK parameters was explored.

RESULTS

A two-compartment PK model adequately described the fentanyl concentration. The effects of weight and maturity on the clearance were included as covariates in the model. One genetic variant encoding the ABCC1 transporter (rs111517339 T/TA) and two encoding the ABCC3 transporter (rs11079921 T/C and rs8077268 C/T) had a significant effect on fentanyl elimination that explained 15% of the interindividual variability on the clearance. A proportional odds PK/PD model was used to describe the concentration-effect relationship of fentanyl using the Échelle de douleur et d'inconfort du nouveau-né (EDIN) pain score.

CONCLUSION

The simulations suggest that an intravenous dose of 2 µg/kg would be appropriate in preterm infants for a clearly painful procedure, such as an intubation.

IMPACT

Design of personalized analgesia with fentanyl for newborn infants should consider maturation and genetic variants of opioid transporters affecting drug elimination. The results indicate that an intravenous dose of 2 μg/kg fentanyl would be suitable before a clearly painful procedure in preterm infants. Genetic variants encoding ABCC1 and ABCC3 transporters increase the clearance of fentanyl, which is a novel finding.

Implementing physics-based digital patient twins to tailor the switch of oral morphine to transdermal fentanyl patches based on patient physiology

Fentanyl transdermal patches are widely implemented for cancer-induced pain treatment due to the high potency of fentanyl and gradual drug release. However, transdermal fentanyl up-titration for opioid-naïve patients is difficult, which is why opioid treatment is often started with oral/iv morphine. Based on the daily dose of morphine, the initial dose of the fentanyl patch is decided upon. After reaching a stable level of pain, the switch is made from oral/iv morphine to transdermal fentanyl. There are standard calculation tools for transferring from oral/iv morphine to transdermal fentanyl, which is the same for all patients. By considering the variations in the physiology of the patients, a unique switching strategy cannot meet the needs of different patients. This study explores the outcome in terms of pain relief and minute ventilation during opioid therapy. For this, we used physics-based simulations on a virtually-generated population of patients, and we applied the same therapy to all patients. We could show that patients' physiology, such as gender, age, and weight, greatly impact the outcome of the therapy; as such, the correlation coefficient between pain intensity and age is 0.89, and the correlation coefficient between patient's weight and maximum plasma concentration of morphine and fentanyl is -0.98 and -0.97. Additionally, a different combination of the duration of overlap between morphine and fentanyl therapy with different doses of fentanyl was considered for the virtual patients to find the best opioid-switching strategy for each patient. We explored the impact of combining physiological features to determine the best-suited strategy for virtual patients. Our findings suggest that tailoring morphine and fentanyl therapy only based on a limited number of features is insufficient, and increasing the number of impactful physiological features positively influences the outcome of the therapy.

An individualized digital twin of a patient for transdermal fentanyl therapy for chronic pain management

Fentanyl transdermal therapy is a suitable treatment for moderate-to-severe cancer-related pain. The inter-individual variability of the patients leads to different therapy responses. This study aims to determine the effect of physiological features on the achieved pain relief. Therefore, a set of virtual patients was developed by using Markov chain Monte Carlo (MCMC) based on actual patient data. The members of this virtual population differ by age, weight, gender, and height. Tailored digital twins were developed using these correlated, individualized parameters to propose a personalized therapy for each patient. It was shown that patients of different ages, weights, and gender have significantly different fentanyl blood uptake, plasma fentanyl concentration, pain relief, and ventilation rate. In the digital twins, we included the virtual patients' response to the treatment, namely, pain relief. Therefore, the digital twin was able to adjust the therapy in silico to have more efficient pain relief. By implementing digital-twin-assisted therapy, the average pain intensity decreased by 16% compared to conventional therapy. The median time without pain increased by 23 h over 72 h. Therefore, the digital twin can be successfully used in individual control of transdermal therapy to reach higher pain relief and maintain steady pain relief. (Created with BioRender.com).

Physiologically-based pharmacokinetic modelling and dosing evaluation of gentamicin in neonates using PhysPK

Each year, infections caused around the 25% of neonatal deaths. Early empirical treatments help to reduce this mortality, although optimized dosing regimens are still lacking. The aims were to develop and validate a gentamicin physiologically-based pharmacokinetic (PBPK) model and then potentially explore dosing regimens in neonates using pharmacokinetic and pharmacodynamic criteria. The PBPK model developed consisted of 2 flow-limited tissues: kidney and other tissues. It has been implemented on a new tool called PhysPK, which allows structure reusability and evolution as predictive engine in Model-Informed Precision Dosing (MIPD). Retrospective pharmacokinetic information based on serum levels data from 47 neonates with gestational age between 32 and 39 weeks and younger than one-week postnatal age were used for model validation. The minimal PBPK model developed adequately described the gentamicin serum concentration-time profile with an average fold error nearly 1. Extended interval gentamicin dosing regimens (6 mg/kg q36h and 6 mg/kg q48h for term and preterm neonates, respectively) showed efficacy higher than 99% with toxicity lower than 10% through Monte Carlo simulation evaluations. The gentamicin minimal PBPK model developed in PhysPK from literature information, and validated in preterm and term neonates, presents adequate predictive performance and could be useful for MIPD strategies in neonates.

Predicting transdermal fentanyl delivery using physics-based simulations for tailored therapy based on the age

Transdermal fentanyl patches are an effective alternative to the sustained release of oral morphine for chronic pain management. Due to the narrow therapeutic range of fentanyl, the concentration of fentanyl in the blood needs to be carefully monitored. Only then can effective pain relief be achieved while avoiding adverse effects such as respiratory depression. This study developed a physics-based digital twin of a patient by implementing drug uptake, pharmacokinetics, and pharmacodynamics models. The twin was employed to predict the in-silico effect of conventional fentanyl transdermal in a 20–80-year-old virtual patient. The results show that, with increasing age, the maximum transdermal fentanyl flux and maximum concentration of fentanyl in the blood decreased by 11.4% and 7.0%, respectively. However, the results also show that as the patient's age increases, the pain relief increases by 45.2%. Furthermore, the digital twin was used to propose a tailored therapy based on the patient's age. This predesigned therapy customized the duration of applying the commercialized fentanyl patches. According to this therapy, a 20-year-old patient needs to change the patch 2.1 times more frequently than conventional therapy, which leads to 30% more pain relief and 315% more time without pain. In addition, the digital twin was updated by the patient's pain intensity feedback. Such therapy increased the patient's breathing rate while providing effective pain relief, so a safer treatment. We quantified the added value of a patient's physics-based digital twin and sketched the future roadmap for implementing such twin-assisted treatment into the clinics.

Development of a Virtual Chinese Pediatric Population Physiological Model Targeting Specific Metabolism and Kidney Elimination Pathways

Background: Physiologically based pharmacokinetic (PBPK) modeling and simulating may be a powerful tool in predicting drug behaviors in specific populations. It is a mathematical model that relates the pharmacokinetic (PK) profile of a compound with human anatomical characteristics, physiological characteristics, and biochemical parameters. Predictions using PBPK models offer a promising way to guide drug development and can be used to optimize clinical dosing regimens. However, PK data of new drugs in the pediatric population are too limited to guide clinical therapy, which may lead to frequent adverse events or insufficient efficacy for pediatric patients, particularly in neonates and infants.

Objective: The objective of this study was to establish a virtual Chinese pediatric population based on the physiological parameters of Chinese children that could be utilized in PBPK models.

Methods: A Chinese pediatric PBPK model was developed in Simcyp Simulator by collecting published Chinese pediatric physiological and anthropometric data to use as system parameters. This pediatric population model was then evaluated in the Chinese pediatric population by predicting the pharmacokinetic characteristics of four probe drugs: theophylline (major CYP1A2 substrate), fentanyl (major CYP3A4 substrate), vancomycin, and ceftazidime (renal-eliminated).

Results: The predicted maximum concentration (C_max), area under the curve of concentration-time (AUC), and clearance (CL) for theophylline (CYP1A2 metabolism pathway) and fentanyl (CYP3A4 metabolism pathway) were within two folds of the observed data. For drugs mainly eliminated by renal clearance (vancomycin and ceftazidime) in the Chinese pediatric population, the ratio of prediction to observation for major PK parameters was within a 2-fold error range.

Conclusion: The model is a supplement to the previous Chinese population PBPK model. We anticipate the model to be a better representative of the pediatric Chinese population for drugs PK, offering greater clinical precision for medication given to the pediatric population, ultimately advancing clinical development of pediatric drugs. We can refine this model further by collecting more physiological parameters of Chinese children.

Factors Contributing to Fentanyl Pharmacokinetic Variability Among Diagnostically Diverse Critically Ill Children

OBJECTIVE

The objective of this study was to characterize the population pharmacokinetics of fentanyl and identify factors that contribute to exposure variability in critically ill pediatric patients.

METHODS

We conducted a single-center, retrospective cohort study using electronic record data and remnant blood samples in the setting of a mixed medical/surgical intensive care unit (ICU) at a quaternary children's hospital. Children with a predicted ICU length of stay of at least 3 days and presence of an indwelling central venous or arterial line were included. Serum fentanyl measurements were performed for 278 unique remnant samples from 66 patients. Both one- and two-compartment models were evaluated to describe fentanyl disposition. Covariates were introduced into the model in a forward/backward, stepwise approach and included age, sex, race, weight, cytochrome P450 (CYP) 3A5 genotype, and the presence of CYP3A4 or CYP3A5 inducers or inhibitors. Simulations were performed using the successful model to depict the influence of inducers on fentanyl concentrations.

RESULTS

A two-compartment base model best described the data. There was good agreement between observed and predicted concentrations in the final model. The typical fentanyl clearance for 70 kg (reference weight) and 20.1 kg (median weight) patients were 34.6 and 13.6 L/h, respectively. The magnitude of the unexplained random inter-individual variability was high for both clearance (60.7%) and apparent volume of the central compartment (V₁) (107.2%). Coadministration of the known CYP3A4/5 inducers fosphenytoin and/or phenobarbital was associated with significantly increased fentanyl clearance. Simulations demonstrate that the effect of inducer administration was most pronounced following discontinuation of a fentanyl infusion.

CONCLUSIONS

In this study we show the feasibility and utility of using electronic record data and remnant blood samples to successfully construct population pharmacokinetic models for a heterogeneous cohort of critically ill children. A clinically relevant effect of concomitant CYP3A4/5 inducers was identified. Scaling this population pharmacokinetic approach is necessary to craft precision approaches to fentanyl administration for critically ill children.

Rapidly maturing fentanyl clearance in preterm neonates

BACKGROUND

Fentanyl is frequently used off-label in preterm newborns. Due to very limited pharmacokinetic and pharmacodynamic data, fentanyl dosing is mostly based on bodyweight. This study describes the maturation of the pharmacokinetics in preterm neonates born before 32 weeks of gestation.

METHODS

442 plasma samples from 98 preterm neonates (median gestational age: 26.9 (range 23.9-31.9) weeks, postnatal age: 3 (range 0-68) days, bodyweight 1.00 (range 0.39-2.37) kg) were collected in an opportunistic trial and fentanyl plasma levels were determined. NONMEM V.7.3 was used to develop a population pharmacokinetic model and to perform simulations.

RESULTS

Fentanyl pharmacokinetics was best described by a two-compartment model. A pronounced non-linear influence of postnatal and gestational age on clearance was identified. Clearance (L/hour/kg) increased threefold, 1.3-fold and 1.01-fold in the first, second and third weeks of life, respectively. In addition, clearance (L/hour/kg) was 1.4-fold and 1.7-fold higher in case of a gestational age of 28 and 31 weeks, respectively, compared with 25 weeks. Volume of distribution changed linearly with bodyweight and was 8.7 L/kg. To achieve similar exposure across the entire population, a continuous infusion (µg/kg/hour) dose should be reduced by 50% and 25% in preterm neonates with a postnatal age of 0-4 days and 5-9 days in comparison to 10 days and older.

CONCLUSION

Because of low clearance, bodyweight-based dosages may result in fentanyl accumulation in neonates with the lowest postnatal and gestational ages which may require dose reduction. Together with additional information on the pharmacodynamics, the results of this study can be used to guide dosing.

Model Informed Pediatric Development Applied to Bilastine: Ontogenic PK Model Development, Dose Selection for First Time in Children and PK Study Design

PURPOSE

Bilastine is an H₁ antagonist whose pharmacokinetics (PK) and pharmacodynamics (PD) have been resolved in adults with a therapeutic oral dose of 20 mg/day. Bilastine has favorable characteristics for use in pediatrics but the PK/PD and the optimal dose in children had yet to be clinically explored. The purpose is to: (1) Develop an ontogenic predictive model of bilastine PK linked to the PD in adults by integrating current knowledge; (2) Use the model to design a PK study in children; (3) Confirm the selected dose and the study design through the evaluation of model predictability in the first recruited children; (4) Consider for inclusion the group of younger children (< 6 years).

METHODS

A semi-mechanistic approach was applied to predict bilastine PK in children assuming the same PD as described in adults. The model was used to simulate the time evolution of plasma levels and wheal and flare effects after several doses and design an adaptive PK trial in children that was then confirmed using data from the first recruits by comparing observations with model predictions.

RESULTS

PK/PD simulations supported the selection of 10 mg/day in 2 to <12 year olds. Results from the first interim analysis confirmed the model predictions and design hence trial continuation.

CONCLUSION

The model successfully predicted bilastine PK in pediatrics and optimally assisted the selection of the dose and sampling scheme for the trial in children. The selected dose was considered suitable for younger children and the forthcoming safety study in children aged 2 to <12 years.

Pragmatic pharmacology: population pharmacokinetic analysis of fentanyl using remnant samples from children after cardiac surgery

AIMS

One barrier contributing to the lack of pharmacokinetic (PK) data in paediatric populations is the need for serial sampling. Analysis of clinically obtained specimens and data may overcome this barrier. To add evidence for the feasibility of this approach, we sought to determine PK parameters for fentanyl in children after cardiac surgery using specimens and data generated in the course of clinical care, without collecting additional blood samples.

METHODS

We measured fentanyl concentrations in plasma from leftover clinically-obtained specimens in 130 paediatric cardiac surgery patients and successfully generated a PK dataset using drug dosing data extracted from electronic medical records. Using a population PK approach, we estimated PK parameters for this population, assessed model goodness-of-fit and internal model validation, and performed subset data analyses. Through simulation studies, we compared predicted fentanyl concentrations using model-driven weight-adjusted per kg vs. fixed per kg fentanyl dosing.

RESULTS

Fentanyl clearance for a 6.4 kg child, the median weight in our cohort, is 5.7 l h(-1) (2.2-9.2 l h(-1) ), similar to values found in prior formal PK studies. Model assessment and subset analyses indicated the model adequately fit the data. Of the covariates studied, only weight significantly impacted fentanyl kinetics, but substantial inter-individual variability remained. In simulation studies, model-driven weight-adjusted per kg fentanyl dosing led to more consistent therapeutic fentanyl concentrations than fixed per kg dosing.

CONCLUSIONS

We show here that population PK modelling using sparse remnant samples and electronic medical records data provides a powerful tool for assessment of drug kinetics and generation of individualized dosing regimens.

Neonatal paracetamol treatment reduces long-term nociceptive behaviour after neonatal procedural pain in rats

BACKGROUND

Pain from skin penetrating procedures (procedural pain) during infancy in the neonatal intensive care unit (NICU) may result in changes of nociceptive sensitivity in later life. This supports the need for pain management during such vulnerable periods in life. This study, therefore, analyses the short- and long-term consequences of neonatal paracetamol (acetaminophen) treatment on pain behaviour in an experimental rat model of neonatal procedural pain.

METHODS

A repetitive needle-prick model was used, in which neonatal rats received four needle pricks into the left hind paw per day from postnatal day 0 to day 7 (P0-P7). Paracetamol (50 mg/kg/day s.c.) was administered daily (P0-P7), and sensitivity to mechanical stimuli was compared with a needle-prick/saline-treated group and to a tactile control group. At 8 weeks of age, all animals underwent an ipsilateral paw-incision, modelling postoperative pain, and the duration of hypersensitivity was assessed.

RESULTS

Neonatal paracetamol administration had no effect upon short-term mechanical hypersensitivity during the first postnatal week or upon long-term baseline sensitivity from 3 to 8 weeks. However, neonatal paracetamol administration significantly reduced the postoperative mechanical hypersensitivity in young adults, caused by repetitive needle pricking.

CONCLUSION

Paracetamol administration during neonatal procedural pain does not alter short-term or long-term effects on mechanical sensitivity, but does reduce the duration of increased postoperative mechanical hypersensitivity in a clinically relevant neonatal procedural pain model.

WHAT DOES THIS STUDY ADD

Paracetamol can be used safely in neonatal rats. Neonatal paracetamol treatment had no effect upon short-term mechanical hypersensitivity during the first postnatal week, nor upon long-term baseline sensitivity from 3 to 8 weeks. Paracetamol treatment during the first postnatal week significantly reduced the postoperative mechanical hypersensitivity in young adult rats.

Clinical pharmacology of fentanyl in preterm infants. A review

Fentanyl is a synthetic opioid that is very important in anesthetic practice because of its relatively short time to peak analgesic effect and the rapid termination of action after small bolus doses. The objective of this survey is to review the clinical pharmacology of fentanyl in preterm infants. The bibliographic search was performed using PubMed and EMBASE databases as search engines. In addition, the books Neofax: A manual of drugs used in neonatal care and Neonatal formulary were consulted. Fentanyl is N-dealkylated by CYP3A4 into the inactive norfentanyl. Fentanyl may be administered as bolus doses or as a continuous infusion. In neonates, there is a remarkable interindividual variability in the kinetic parameters. In neonates, fentanyl half-life ranges from 317 minutes to 1266 minutes and in adults it is 222 minutes. Respiratory depression occurs when fentanyl doses are >5 μg/kg. Chest wall rigidity may occur in neonates and occasionally is associated with laryngospasm. Tolerance to fentanyl may develop after prolonged use of this drug. Significant withdrawal symptoms have been reported in infants treated with continuous infusion for 5 days or longer. Fentanyl is an extremely potent analgesic and is the opioid analgesic most frequently used in the neonatal intensive care unit.

Quantitative determination of fentanyl in newborn pig plasma and cerebrospinal fluid samples by HPLC-MS/MS

In this study, a selective and sensitive high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) method requiring low sample volume (≤100 μL) was developed and validated for the quantitative determination of the opioid drug fentanyl in plasma and cerebrospinal fluid (CSF). A protein precipitation extraction with acetonitrile was used for plasma samples whereas CSF samples were injected directly on the HPLC column. Fentanyl and (13) C6 -fentanyl (Internal Standard) were analyzed in an electrospray ionization source in positive mode, with multiple reaction monitoring (MRM) of the transitions m/z 337.0/188.0 and m/z 337.0/105.0 for quantification and confirmation of fentanyl, and m/z 343.0/188.0 for (13) C6 -fentanyl. The respective lowest limits of quantification for plasma and CSF were 0.2 and 0.25 ng/mL. Intra- and inter-assay precision and accuracy did not exceed 15%, in accordance with bioanalytical validation guidelines. The described analytical method was proven to be robust and was successfully applied to the determination of fentanyl in plasma and CSF samples from a pharmacokinetic and pharmacodynamic study in newborn piglets receiving intravenous fentanyl (5 µg/kg bolus immediately followed by a 90-min infusion of 3 µg/kg/h).

Evaluation of fentanyl disposition and effects in newborn piglets as an experimental model for human neonates

Background

Fentanyl is widely used off-label in NICU. Our aim was to investigate its cerebral, cardiovascular and pulmonary effects as well as pharmacokinetics in an experimental model for neonates.

Methods

Fentanyl (5 µg/kg bolus immediately followed by a 90 minute infusion of 3 µg/kg/h) was administered to six mechanically ventilated newborn piglets. Cardiovascular, ventilation, pulmonary and oxygenation indexes as well as brain activity were monitored from T = 0 up to the end of experiments (T = 225–300 min). Also plasma samples for quantification of fentanyl were drawn.

Results

A “reliable degree of sedation” was observed up to T = 210–240 min, consistent with the selected dosing regimen and the observed fentanyl plasma levels. Unlike cardiovascular parameters, which were unmodified except for an increasing trend in heart rate, some of the ventilation and oxygenation indexes as well as brain activity were significantly altered. The pulmonary and brain effects of fentanyl were mostly recovered from T = 210 min to the end of experiment.

Conclusion

The newborn piglet was shown to be a suitable experimental model for studying fentanyl disposition as well as respiratory and cardiovascular effects in human neonates. Therefore, it could be extremely useful for further investigating the drug behaviour under pathophysiological conditions.