An integrated population pharmacokinetic meta-analysis of propofol in morbidly obese and nonobese adults, adolescents, and children

Vancomycin Clearance in Obese Adults is not Predictive of Clearance in Obese Adolescents

BACKGROUND AND OBJECTIVE

Contradictory pharmacokinetic (PK) results have been observed between obese adults and obese adolescents, with absolute clearance (CL) reported to be either unaltered, lower, or higher in obese adolescents compared to obese adults. This study investigates the PK of vancomycin in adolescents and adults who are overweight or obese.

METHODS

Data from 125 overweight and obese adolescents (aged 10-18 years, weight 28.3-188 kg) and 81 overweight and obese adults (aged 29-88 years, weight 66.7-143 kg) were analysed using population PK modelling. In addition to age, sex, renal function estimates, and regular weight descriptors, we evaluated standard weight (WT_standard, defined as weight for length, age, and sex in adolescents and weight for length in adults) and excess weight (WT_excess, defined as total body weight (TBW) minus WT_standard) as covariates in order to distinguish between weight resulting from length versus weight resulting from obesity.

RESULTS

Analyzing adolescents and adults together, vancomycin CL was found to increase with TBW and decrease with increasing age (p < 0.001). A covariate analysis investigating adolescents and adults separately found that vancomycin CL increased with WT_standard in adolescents and adults, albeit with different functions, with adolescents having a higher CL per WT_standard than adults. Moreover, in this separate model, adolescent males had 21% higher CL than adolescent females of the same WT_standard, while in adults, CL decreased with increasing age (p < 0.001).

CONCLUSION

There are apparent differences in vancomycin CL in overweight and obese adults versus overweight and obese adolescents, implying that dosing of vancomycin cannot be directly extrapolated between these populations.

Drug pharmacokinetics in the obese population: challenging common assumptions on predictors of obesity-related parameter changes

INTRODUCTION

Obesity is associated with many physiological changes. We review available evidence regarding five commonly accepted assumptions to a priori predict the impact of obesity on drug pharmacokinetics (PK).

AREAS COVERED

The investigated assumptions are: 1) lean body weight is the preferred descriptor of clearance and dose adjustments; 2) volume of distribution increases for lipophilic, but not for hydrophilic drugs; 3) CYP-3A4 activity is suppressed and UGT activity is increased, implying decreased and increased dose requirements for substrates of these enzyme systems, respectively; 4) glomerular filtration rate is enhanced, necessitating higher doses for drugs cleared through glomerular filtration; 5) drug dosing information from obese adults can be extrapolated to obese adolescents.

EXPERT OPINION

Available literature contradicts, or at least limits the generalizability, of all five assumptions. Clinical studies should focus on quantifying the impact of duration and severity of obesity on drug PK in adults and adolescents, and also include oral bioavailability and pharmacodynamics in these studies. Physiologically-based PK approaches can be used to predict PK changes for individual drugs, but can also be used to define in general terms based on patient characteristics and drug properties, when certain assumptions can or cannot be expected to be systematically accurate.

Pharmacokinetics and Pharmacodynamics of Drugs in Obese Pediatric Patients: How to Map Uncharted Clinical Territories

Clinicians are increasingly faced with challenges regarding the pharmacological treatment of obese pediatric patients. To provide guidance for these treatments, a better understanding of the impact of obesity on pharmacological processes in children is needed. Results on pharmacological studies in adults show however ambiguous patterns regarding the impact of obesity on ADME processes or on drug pharmacodynamics. Additionally, based on the limited research performed in obese pediatric patients, it becomes clear that findings from obese adults cannot be expected to always translate directly to similar findings in obese children. To improve knowledge on drug pharmacology in obese pediatric patients, studies should focus on quantifying the impact of maturation, obesity, and other relevant variables on primary pharmacological parameters and on disentangling systemic (renal and/or hepatic) and presystemic (gut and/or first-pass hepatic) clearance. For this, data is required from well-designed clinical trials that include patients with not only a wide range in age but also a range in excess body weight, upon oral and intravenous dosing. Population modelling approaches are ideally suitable for this purpose and can also be used to link the pharmacokinetics to pharmacodynamics and to derive drug dosing regimens. Generalizability of research findings can be achieved by including mechanistic aspects in the data analysis, for instance, using either extrapolation approaches in population modelling or by applying physiologically based modelling principles. It is imperative that more and smarter studies are performed in obese pediatric patients to provide safe and effective treatment for this special patient population.

Propofol Sedation for Intragastric Balloon Removal: Looking for the Optimal Body Weight Descriptor

AIM

Sedation is considered as a prerequisite for the safe and effective conclusion of Bioenterics Intragastric Balloon (BIB) removal (our aim was to ascertain the most appropriate body size scalars for propofol dosing and assess the efficacy and safety of a sedative approach involving the infusion of propofol for BIB removal.

METHOD

Retrospective analysis of prospectively collected data of 414 adults scheduled to undergo BIB removal. Our primary end-point was to delineate the relationship between propofol dosing and body size descriptors namely body mass index, total body weight, ideal body weight, lean body weight (LBW) and normalized LBW. Sedative efficacy of this practice, anesthesia or procedural-related adverse events and patients' satisfaction level served as secondary outcome parameters.

RESULTS

Propofol dose (mg/kg/min) was positively related to all body weight descriptors in an important manner (p < 0.001). Among them, LBW was singled out as the body size descriptor to best capture the appropriate needs of propofol (R2 = 0.432; p = 0.000). Hypoxemia, hemodynamic compromise, gastroesophageal reflux or moderate movement occurred rarely; all of them were readily reversed. The majority of participants had no recollection of the noxious phase of the procedure or declared at least adequately satisfied from the experience (84% and 95%, respectively).

CONCLUSION

LBW could serve as relatively more accurate dosing scalar compared to actual or ideal body weight descriptors, in obese individuals undergoing BIB removal under propofol sedation. The conscious/deep sedation based on propofol infusion emerges as a feasible and efficacious sedative approach for this procedure.

Drug Dose Selection in Pediatric Obesity: Available Information for the Most Commonly Prescribed Drugs to Children

Obesity rates continue to rise in children, and little guidance exists regarding the need for adjustment away from total body weight-based doses for those prescribing drugs to this population of children. A majority of drugs prescribed to children with obesity result in either sub-therapeutic or supra-therapeutic concentrations, placing these children at risk for treatment failure and drug toxicities. In this review, we highlight available obesity-specific pharmacokinetic and dosing information for the most frequently prescribed drugs to children in the inpatient and outpatient clinical settings. We also comment on available dosing recommendations for drugs prescribed to treat common pediatric obesity-related comorbidities. This review highlights that there is no safe or proven 'rule of thumb,' for dosing drugs for children with obesity, and a striking lack of pharmacokinetic data to support the creation of dosing guidelines for children with obesity for the most commonly prescribed drugs. It is important that those prescribing for children with obesity are aware of these gaps in knowledge and of potential drug treatment failure or adverse events related to drug toxicity as a result of these knowledge gaps. Until more data are available, we recommend close monitoring of drug response and adverse events in children with obesity receiving commonly prescribed drugs.

Higher Midazolam Clearance in Obese Adolescents Compared with Morbidly Obese Adults

BACKGROUND

The clearance of cytochrome P450 (CYP) 3A substrates is reported to be reduced with lower age, inflammation and obesity. As it is unknown what the overall influence is of these factors in the case of obese adolescents vs. morbidly obese adults, we studied covariates influencing the clearance of the CYP3A substrate midazolam in a combined analysis of data from obese adolescents and morbidly obese adults.

METHODS

Data from 19 obese adolescents [102.7 kg (62-149.5 kg)] and 20 morbidly obese adults [144 kg (112-186 kg)] receiving intravenous midazolam were analysed, using population pharmacokinetic modelling (NONMEM 7.2). In the covariate analysis, the influence of study group, age, total body weight (TBW), developmental weight (WTfor age and length) and excess body weight (WTexcess = TBW - WTfor age and length) was evaluated.

RESULTS

The population mean midazolam clearance was significantly higher in obese adolescents than in morbidly obese adults [0.71 (7%) vs. 0.44 (11%) L/min; p < 0.01]. Moreover, clearance in obese adolescents increased with TBW (p < 0.01), which seemed mainly explained by WTexcess, and for which a so-called 'excess weight' model scaling WTfor age and length to the power of 0.75 and a separate function for WTexcess was proposed.

DISCUSSION

We hypothesise that higher midazolam clearance in obese adolescents is explained by less obesity-induced suppression of CYP3A activity, while the increase with WTexcess is explained by increased liver blood flow. The approach characterising the influence of obesity in the paediatric population we propose here may be of value for use in future studies in obese adolescents.

Obesity and drug pharmacology: a review of the influence of obesity on pharmacokinetic and pharmacodynamic parameters

INTRODUCTION

The rising prevalence of obesity confronts clinicians with dosing problems in the (extreme) overweight population. Obesity has a great impact on key organs that play a role in the pharmacokinetics (PK) and pharmacodynamics (PD) of drugs, however the ultimate impact of these changes on how to adapt the dose may not always be known. Areas covered: In this review, physiological changes associated with obesity are discussed. An overview is provided on the alterations in absorption, distribution, drug metabolism and clearance in (morbid) obesity focusing on general principles that can be extracted from pharmacokinetic studies. Also, relevant pharmacodynamic considerations in obesity are discussed. Expert opinion: Over the last two decades, increased knowledge is generated on PK and PD in obesity. Future research should focus on filling in the knowledge gaps that remain, especially in connecting obesity-related physiological changes with changes in PK and/or PD and vice versa. Ultimately, this knowledge can be used to develop physiologically based PK and PD models on the basis of quantitative systems pharmacology principles. Moreover, efforts should focus on thorough prospective evaluation of developed model-based doses with subsequent implementation of these dosing recommendations in clinical practice.

Drug Dosing in Obese Children: Challenges and Evidence-Based Strategies

With the alarming increase of obesity in children, pediatricians are increasingly being confronted with difficult dosing decisions. Many drug labels do not provide specific dosing instructions for children who are obese. In this article, we describe the physiologic parameters altered by obesity and their influences on drug disposition and effect. We review the principles of allometry, and the key pharmacokinetic parameters that can be used to derive age appropriate dosing regimens. Last, we illustrate how appropriate weight descriptors can be selected, and how important PK parameters can be extrapolated for dosing in obese children when pediatric pharmacokinetic information is available.

Information provision for antibacterial dosing in the obese patient: a sizeable absence?

BACKGROUND

Obesity is on course to overtake being underweight as a global disease burden. Obesity alters antibacterial pharmacokinetics (PK) and pharmacodynamics (PD). Historically, drug PK/PD parameters have not been studied in obese populations. This means dose recommendations risk being sub-therapeutic in a population at increased risk of infection. Suboptimal antibacterial prescribing is widely associated with treatment failure, worse clinical outcomes, unnecessary escalation to broad-spectrum therapy and the emergence of antimicrobial resistance (AMR).

OBJECTIVES

To analyse current information provided by pharmaceutical companies, for the most commonly prescribed antibacterial agents in the UK, for evidence of dosing guidance for obese adults.

METHODS

We analysed the manufacturers' Summary of Product Characteristics (SPC) for 42 of the most clinically important and frequently prescribed antibacterial agents dispensed across both primary and secondary care. The manufacturer's SPC was reviewed, and cross-referenced with the online British National Formulary, to assess dosing guidance for obese adults.

RESULTS

No advice was provided to guide dosing for obese adults in 35 (83%) of 42 of the most clinically important and frequently prescribed antibacterial agents in the UK. Seven (17%) antibacterial agents (tigecycline, vancomycin, daptomycin, amikacin, gentamicin, tobramycin and teicoplanin) provided variable levels of advice.

CONCLUSIONS

There is a paucity of advice and evidence in the UK to guide dosing common antibacterial agents in the obese. The literature on antibacterial PK/PD studies in obese populations remains scarce. In the face of the increasing risks of AMR combined with the global rise of obesity there is an urgent need to address this significant research gap.

Pain in Intellectually Disabled Children: Towards Evidence-Based Pharmacotherapy?

This critical opinion article deals with the challenges of finding the most effective pharmacotherapeutic options for the management of pain in intellectually disabled children and provides recommendations for clinical practice and research. Intellectual disability can be caused by a wide variety of underlying diseases and may be associated with congenital anomalies such as cardiac defects, small-bowel obstructions or limb abnormalities as well as with comorbidities such as scoliosis, gastro-esophageal reflux disease, spasticity, and epilepsy. These conditions themselves or any necessary surgical interventions are sources of pain. Epilepsy often requires chronic pharmacological treatment with antiepileptic drugs. These antiepileptic drugs can potentially cause drug-drug interactions with analgesic drugs. It is unfortunate that children with intellectual disabilities often cannot communicate pain to caregivers. Although these children are at high risk of experiencing pain, researchers nevertheless often have to exclude them from trials on pain management because of ethical considerations. We therefore make a plea for prescribers, researchers, patient organizations, pharmaceutical companies, and policy makers to study evidence-based, safe and effective pharmacotherapy in these children through properly designed studies. In the meantime, parents and clinicians must resort to validated pain assessment tools such as the revised FLACC scale.

Drug disposition in obesity: toward evidence-based dosing

Obesity and morbid obesity are associated with many physiological changes affecting pharmacokinetics, such as increased blood volume, cardiac output, splanchnic blood flow, and hepatic blood flow. In obesity, drug absorption appears unaltered, although recent evidence suggests that this conclusion may be premature. Volume of distribution may vary largely, but the magnitude and direction of changes seem difficult to predict, with extrapolation on the basis of total body weight being the best approach to date. Changes in clearance may be smaller than in distribution, whereas there is growing evidence that the influence of obesity on clearance can be predicted on the basis of reported changes in the metabolic or elimination pathways involved. For obese children, we propose two methods to distinguish between developmental and obesity-related changes. Future research should focus on the characterization of physiological concepts to predict the optimal dose for each drug in the obese population.

Propofol: a review of its role in pediatric anesthesia and sedation

Propofol is an intravenous agent used commonly for the induction and maintenance of anesthesia, procedural, and critical care sedation in children. The mechanisms of action on the central nervous system involve interactions at various neurotransmitter receptors, especially the gamma-aminobutyric acid A receptor. Approved for use in the USA by the Food and Drug Administration in 1989, its use for induction of anesthesia in children less than 3 years of age still remains off-label. Despite its wide use in pediatric anesthesia, there is conflicting literature about its safety and serious adverse effects in particular subsets of children. Particularly as children are not "little adults", in this review, we emphasize the maturational aspects of propofol pharmacokinetics. Despite the myriad of propofol pharmacokinetic-pharmacodynamic studies and the ability to use allometrical scaling to smooth out differences due to size and age, there is no optimal model that can be used in target controlled infusion pumps for providing closed loop total intravenous anesthesia in children. As the commercial formulation of propofol is a nutrient-rich emulsion, the risk for bacterial contamination exists despite the Food and Drug Administration mandating addition of antimicrobial preservative, calling for manufacturers' directions to discard open vials after 6 h. While propofol has advantages over inhalation anesthesia such as less postoperative nausea and emergence delirium in children, pain on injection remains a problem even with newer formulations. Propofol is known to depress mitochondrial function by its action as an uncoupling agent in oxidative phosphorylation. This has implications for children with mitochondrial diseases and the occurrence of propofol-related infusion syndrome, a rare but seriously life-threatening complication of propofol. At the time of this review, there is no direct evidence in humans for propofol-induced neurotoxicity to the infant brain; however, current concerns of neuroapoptosis in developing brains induced by propofol persist and continue to be a focus of research.