Acetaminophen pharmacokinetics in severely obese adolescents and young adults

Management of Pain Medication in Patients With a History of Bariatric Surgery: A Systematic Review

CONTEXT

Obesity prevalence is persistently increasing worldwide. Among surgical therapeutic procedures, bypass surgery and sleeve gastrectomy have shown the best results regarding weight loss, prevention, and treatment of secondary complications. However, these surgeries are associated with an increased risk of malabsorption and metabolic changes that could further affect the pharmacokinetics of drugs. On the other hand, patients with a history of such surgeries are more likely to experience pain and request analgesic initiation or adaptation. The question of how to manage pain medication in these patients is challenging due to their narrow therapeutic indexes.

OBJECTIVES

To summarize the current literature on the impact of bariatric surgery on the subsequent pharmacokinetics of analgesics and propose a multidisciplinary therapeutic attitude to optimize pain management in these patients.

METHODS

We conducted a systematic review that included all pharmacological studies published after 2000.

RESULTS

Unexpectedly, these surgeries seem to increase the bioavailability of drugs by long-term improvement of hepatic function. Yet, the medical community drastically lacks robust guidelines for pain management in those patients. This systematic review aims to bring together pharmacological studies related to the use of pain treatments in patients who underwent bypass surgery or sleeve gastrectomy.

CONCLUSIONS

Caution should be exercised regarding the risk of overdose in every circumstance: treatment initiation, change of doses, or change of molecule. More prospective trials comparing the pharmacokinetics of medications in obese patients with and without prior bariatric surgery are needed.

A Quality Initiative to Improve Appropriate Medication Dosing in Pediatric Patients with Obesity

Introduction

Emerging evidence supports the use of alternative dosing weights for medications in patients with obesity. Pediatric obesity presents a particular challenge because most medications are dosed based on patient weight. Additionally, building system-wide pediatric obesity safeguards is difficult due to pediatric obesity definitions of body mass index-percentile-for-age via the Center for Disease Control growth charts. We describe a quality initiative to increase appropriate medication dosing in inpatients with obesity. The specific aim was to increase appropriate dosing for 7 high-risk medications in inpatients with obesity ≥2 years old from 37% to >74% and to sustain for 1 year.

Methods

The Institute for Healthcare Improvement model for improvement was used to plan interventions and track outcomes progress. Interventions included a literature review to establish internal dosing guidance, electronic health record (EHR) functionality to identify pediatric patients with obesity, a default selection for medication weight with an opt-out, and obtaining patient heights in the emergency department.

Results

Appropriate dosing weight use in medication ordered for patients with obesity increased from 37% to 83.4% and was sustained above the goal of 74% for 12 months.

Conclusions

Implementation of EHR-based clinical decision support has increased appropriate evidence-based dosing of medications in pediatric and adult inpatients with obesity. Future studies should investigate the clinical and safety implications of using alternative dosing weights in pediatric patients.

Pharmacokinetic pharmacodynamic modeling of analgesics and sedatives in children

Pharmacokinetic pharmacodynamic modeling is an important tool which uses statistical methodology to provide a better understanding of the relationship between concentration and effect of drugs such as analgesics and sedatives. Pharmacokinetic pharmacodynamic models also describe between-subject variability that allows identification of subgroups and dose adjustment for optimal pain management in individual patients. This approach is particularly useful in the pediatric population, where most drugs have received limited evaluation and dosing is extrapolated from adult practice. In children, the covariates of weight and age are used to describe size- and maturation-related changes in pharmacokinetics. It is important to consider both size and maturation in order to develop an accurate model and determine the optimal dose for different age groups. An adequate assessment of analgesic and sedative effect using pain scales or brain activity measures is essential to build reliable pharmacokinetic pharmacodynamic models. This is often challenging in children due to the multidimensional nature of pain and the limited sensitivity and specificity of some measurement tools. This review provides a summary of the pharmacokinetic and pharmacodynamic methodology used to describe the dose-concentration-effect relationship of analgesics and sedation in children, with a focus on the different pharmacodynamic endpoints and the challenges of pharmacodynamic modeling.

Analgesic Patterns and Opioid Administration in Children Hospitalized With Acute Pancreatitis

BACKGROUND

Pain is the most common symptom of acute pancreatitis (AP), and opioids have been utilized as the cornerstone of treatment. Despite the adverse effects of opioids, data on effective analgesia in children with AP is lacking. We aimed to evaluate analgesia prescribing patterns in pediatric AP, identify factors associated with opioid administration, and test the associations between opioid administration and hospital length of stay (LOS).

METHODS

This is a retrospective cohort study of pediatric AP hospitalizations in a single institution from 2010 to 2020. Opioid administration was calculated for the first 48 hours of admission (morphine milligram equivalent; MME48). Data on multimodal analgesia [defined as the administration of acetaminophen and nonsteroidal anti-inflammatory drugs (NSAIDs)] during hospitalization was captured.

RESULTS

The sample included 224 patients, mean age 12.0 years (standard deviation = 4.9) and 58.9% female. Median LOS was 4 days (interquartile range 2-9). Most patients (71.4%) were prescribed opioids, 77.7% acetaminophen, 40.2% NSAIDs, and 37.5% multimodal analgesia. Opioid administration decreased over the study period; in contrast, there was an increase in multimodal analgesia administration. Opioid administration did not differ by sex, age, biliary versus non-biliary etiology, or race/ethnicity. In a multivariate regression model, lower albumin values ( P < 0.01) and younger age ( P < 0.05) were significant predictors of increased LOS, while MME48 was not associated with increased LOS.

CONCLUSIONS

Opioids were commonly administered; only 37.5% of children were administered multimodal analgesia during their hospitalization for AP. Opioid administration was not associated with increased LOS. Prospective studies are needed to determine optimal pain management for pediatric AP.

Perioperative Acetaminophen Dosing in Obese Children

Acetaminophen is a commonly used perioperative analgesic drug in children. The use of a preoperative loading dose achieves a target concentration of 10 mg/L associated with a target analgesic effect that is 2.6 pain units (visual analogue scale 1–10). Postoperative maintenance dosing is used to keep this effect at a steady-state concentration. The loading dose in children is commonly prescribed per kilogram. That dose is consistent with the linear relationship between the volume of distribution and total body weight. Total body weight is made up of both fat and fat-free mass. The fat mass has little influence on the volume of distribution of acetaminophen but fat mass should be considered for maintenance dosing that is determined by clearance. The relationship between the pharmacokinetic parameter, clearance, and size is not linear. A number of size metrics (e.g., fat-free and normal fat mass, ideal body weight and lean body weight) have been proposed to scale clearance and all consequent dosing schedules recognize curvilinear relationships between clearance and size. This relationship can be described using allometric theory. Fat mass also has an indirect influence on clearance that is independent of its effects due to increased body mass. Normal fat mass, used in conjunction with allometry, has proven a useful size metric for acetaminophen; it is calculated using fat-free mass and a fraction (Ffat) of the additional mass contributing to total body weight. However, the Ffat for acetaminophen is large (Ffat = 0.82), pharmacokinetic and pharmacodynamic parameter variability high, and the concentration–response slope gentle at the target concentration. Consequently, total body weight with allometry is acceptable for the calculation of maintenance dose. The dose of acetaminophen is tempered by concerns about adverse effects, notably hepatotoxicity associated with use after 2–3 days at doses greater than 90 mg/kg/day.

Intravenous Acetaminophen Overdose in an Infant With Toxicokinetic Data

CASE REPORT

A 12-month-old (former 24 week gestational age), 8.7 kg male was hospitalized after an uneventful colostomy reversal. In the postoperative unit, the patient unintentionally received 1000 mg IV (114.9 mg/kg) acetaminophen instead of the intended 100 mg IV. Serial acetaminophen concentrations were drawn. The patient received IV Nacetylcysteine and ultimately had no adverse outcomes.

DISCUSSION

This case report adds to the existing literature regarding toxicokinetics of IV APAP in infants. Our patient had a calculated ke of 0.263 h-1, correlating with a half-life of 2.63 hours. Based on current available data, the half-life of IV APAP in infants varies (2.6 to 4.9 hours). The reason for this variation is unknown and further research is needed in this area.

Application of a Volumetric Absorptive Microsampling (VAMS)-Based Method for the Determination of Paracetamol and Four of its Metabolites as a Tool for Pharmacokinetic Studies in Obese and Non-Obese Patients

BACKGROUND

The pharmacokinetic (PK) profile of a drug is influenced by several factors, which can lead to a suboptimal dosing regimen in specific patient populations. As obesity becomes increasingly prevalent, it is important that optimized dosing schemes are available for these patients. To set up such dosing schemes, PK studies should be performed in this population. Regarding paracetamol (acetaminophen [APAP]), obese patients would benefit from a tailored dosing scheme, as both the volume of distribution and metabolism are increased compared with non-obese patients. This includes metabolism by cytochrome P450 2E1, which is involved in APAP-associated hepatotoxicity. To decrease the burden for patients in these PK studies, finger-prick sampling could be used.

OBJECTIVE

The aim of this study was to compare the quantitative determination of APAP and four metabolites in different blood-based matrices and to determine if capillary dried blood samples, collected directly following finger-prick, could serve as a tool to investigate APAP PK in obese and non-obese patients.

METHODS

In this study, we performed a clinical validation of methods for the determination of APAP and four of its metabolites (APAP-glucuronide, APAP-sulfate, APAP-mercapturate, and APAP-cysteine) in blood, plasma, and dried blood. The latter was obtained by volumetric absorptive microsampling (VAMS), either starting from the venous blood or collected directly following a finger-prick. Results were compared between the different matrices and, in addition, blood:plasma (B:P) ratios were determined for the different analytes.

RESULTS

Liquid and dried venous blood results were in good agreement. Furthermore, differences between capillary (finger-prick) and venous VAMS blood samples remained limited for most analytes. However, for APAP-cysteine, caution should be paid to the interpretation of concentrations in (dried) blood. With the exception of APAP, concentrations were higher in plasma compared with blood, with B:P ratios ranging between 0.52 and 0.65. A time-dependent change in median B:P ratio was observed for APAP and APAP-cysteine. Additionally, a time-dependent trend was seen for APAP, as well as for APAP-glucuronide and APAP-mercapturate, for the distribution between capillary and venous blood.

CONCLUSIONS

We demonstrated that finger-prick sampling is a viable alternative to conventional venous blood sampling to investigate the PK of APAP and its metabolites in obese and non-obese patients.

Medication Errors in Overweight and Obese Pediatric Patients: A Narrative Review

BACKGROUND

The childhood obesity epidemic in the United States has increased utilization of health care and prescribing of medications in overweight and obese children, yet it is unclear whether this has led to more medication errors. The objective of this study was to review all available literature on incidence and types of medication errors in overweight and obese children.

METHODS

A search of MEDLINE, Embase, and Scopus databases was conducted for all studies and oral abstracts through December 2020 reporting medication errors in overweight or obese children aged ≤ 18 years. All studies were identified and extracted via a Covidence database. Two reviewers independently reviewed studies and rated the methodologic quality of those included per GRADE (Grading of Recommendations, Assessment, Development and Evaluations) criteria.

RESULTS

The search identified 1,016 abstracts from databases. Following review, full text was obtained for 146 articles, of which 141 were excluded. A total of 5 studies met criteria for inclusion and described dosing errors of antimicrobials, anesthetics, and paracetamol in overweight and obese pediatric patients. Two of the 5 studies compared medication errors in obese to nonobese children, and both found that medication errors (both over- and underdosing) were generally more common among obese children. The identified reasons for medication errors included incorrect dosing weight, incorrect dosing strategy, over- and underdosing with weight-based and flat-fixed dosing, and inapposite use of age-based dosing schemas.

CONCLUSION

There is a paucity of patient safety evidence available evaluating medication use in overweight and obese children and associated medication errors. Overweight and obese children may be at increased risk of medication errors, although the clinical significance of this is unknown.

Practical Challenges-Use of Paracetamol in Children and Youth Who are Overweight or Obese: A Narrative Review

Worldwide, > 380 million children and adolescents are overweight or obese, including 41 million children aged < 5 years. Obesity can change the pharmacokinetic properties of drugs by altering their distribution, metabolism, and elimination. Thus, children who are overweight or obese are at increased risk for receiving inappropriate doses of commonly used drugs, which can result in treatment failure, adverse events, and/or drug toxicity. This review analyzes available data on paracetamol dosing for pain and fever in children and adolescents who are overweight or obese to identify gaps and challenges in optimal dosing strategies. Literature searches using Medline, Embase, and ClinicalTrials.gov were conducted to identify English-language articles reporting paracetamol pharmacokinetics, dosing practices, and guidelines in children and adolescents who are overweight or obese. Of 24 relevant studies identified, 20 were specific to overweight/obese individuals and 15 were specific to children and/or adolescents. Data on paracetamol pharmacokinetics in children and adolescents who are overweight or obese are lacking, and there is no high-quality evidence to guide paracetamol prescribing practices in these patients. Adult data have been extrapolated to pediatric populations; however, extrapolation does not address differences in paracetamol metabolism in adults versus children; the efficacy and safety effects of such differences are unknown. Given the growing worldwide prevalence of obesity in children and adolescents and the likelihood that paracetamol use in this population will increase accordingly, obesity-specific pediatric dosing guidelines for paracetamol are urgently needed. High-quality research is necessary to inform such guidelines.

Dosing Common Medications in Hospitalized Pediatric Patients with Obesity: A Review

Medication management in children and adolescents with obesity is challenging because both developmental and pathophysiological changes may impact drug disposition and response. Evidence to date indicates an effect of obesity on drug disposition for certain drugs used in this population. This work identified published studies evaluating drug dosing, pharmacokinetics (PK), and effect in pediatric patients with obesity, focusing on 70 common medications used in a pediatric network of 42 US medical centers. A PubMed search revealed 33 studies providing PK and/or effectiveness data for 23% (16 of 70) of medications, 44% of which have just one study and can be considered exploratory. This work appraising 4 decades of literature shows several promising approaches: greater use of PK models applied to prospective clinical studies, dosing recommendations derived from both PK and safety, and multiyear effectiveness data on drugs for chronic conditions (e.g., asthma). Most studies make dose recommendations but are weakened by retrospective study design, small study populations, and no controls or historic controls. Dosing decisions continue to rely on extrapolating knowledge, including targeting systemic drug exposure typically achieved in adults. Optimal weight-based dosing strategies vary by drug and warrant prospective, controlled studies incorporating PK and modeling and simulation to complement clinical assessment.

Pharmacokinetic and pharmacodynamic considerations of general anesthesia in pediatric subjects

Introduction: The target concentration strategy uses PKPD information for dose determination. Models have also quantified exposure-response relationships, improved understanding of developmental pharmacokinetics, rationalized dose prescription, provided insight into the importance of covariate information, explained drug interactions and driven decision-making and learning during drug development.Areas covered: The prime PKPD consideration is parameter estimation and quantification of variability. The main sources of variability in children are age (maturation) and weight (size). Model use is mostly confined to pharmacokinetics, partly because anesthesia effect models in the young are imprecise. Exploration of PK and PD covariates and their variability hold potential to better individualize treatment.Expert opinion: The ability to model drugs using computer-based technology is hindered because covariate data required to individualize treatment using these programs remain lacking. Target concentration intervention strategies remain incomplete because covariate information that might better predict individualization of dose is absent. Pharmacogenomics appear a valuable area for investigation for pharmacodynamics and pharmacodynamics. Effect measures in the very young are imprecise. Assessment of the analgesic component of anesthesia is crude. While neuromuscular monitoring is satisfactory, depth of anaesthesia EEG interpretation is inadequate. Closed loop anesthesia is possible with better understanding of EEG changes.