Drug disposition in obese humans. An update

Comparison of Weight-Based Valproic Acid Dosing in Treatment of Mental Illness Among Obese and Nonobese Patients

PURPOSE/BACKGROUND

A weight-based dosing approach of 20-30 mg/kg per day of valproic acid (VPA) has been shown to achieve rapid attainment of mood symptom control. Due to interindividual pharmacokinetic variability, therapeutic drug monitoring may be a useful tool to avoid VPA toxicity. Limited research exists on the impact of patient body weight on VPA pharmacokinetic profiles. This analysis aims to explore the correlation between steady-state serum levels of VPA and weight-based dosing strategies, including total body weight (TBW), ideal body weight (IBW), and adjusted body weight (AdjBW), between obese and nonobese patients.

METHODS/PROCEDURES

This single-center, retrospective, observational cohort analysis evaluated weight-based dosing of VPA in obese and nonobese patients admitted to inpatient psychiatry at a large academic medical center between July 1, 2017, and July 1, 2022.

FINDINGS/RESULTS

This analysis included 93 obese and 93 nonobese patients. No significant difference in median VPA serum concentrations was observed between groups ( P = 0.82). However, the obese group received a lower median weight-based dose (15.6 mg/kg) compared with the nonobese group (19.5 mg/kg, P < 0.001). A stronger correlation was found between VPA dose and therapeutic serum levels in the obese group compared with the nonobese group regardless of weight-based dosing strategy. Dosing with AdjBW in obese patients most closely approximated dosing with TBW in nonobese patients.

IMPLICATIONS/CONCLUSIONS

In obese patients, our analysis suggests dosing VPA using AdjBW may be considered as the preferred dosing strategy over IBW or TBW to minimize toxicity risk. Further research is needed with larger sample sizes and diverse patient populations to confirm these findings.

Estimation of Absolute and Relative Body Fat Content Using Noninvasive Surrogates: Can DXA Be Bypassed?

Dual-energy x-ray absorptiometry (DXA) scanning is used for objective determination of body composition, but instrumentation is expensive and not generally available in customary clinical practice. Anthropometric surrogates are often substituted as anticipated correlates of absolute and relative body fat content in the clinical management of obesity and its associated medical risks. DXA and anthropometric data from a cohort of 9230 randomly selected American subjects, available through the ongoing National Health and Nutrition Examination Survey, was used to evaluate combinations of surrogates (age, height, total weight, waist circumference) as predictors of DXA-determined absolute and relative body fat content. Multiple regression analysis yielded linear combinations of the 4 surrogates that were closely predictive of DXA-determined absolute fat content (R2  = 0.93 and 0.96 for male and female subjects). Accuracy of the new algorithm was improved over customary surrogate-based predictors such as body mass index. However prediction of relative body fat was less robust (R2  less than 0.75), probably due to the nonlinear relation between degree of obesity (based on body mass index) and relative body fat. The paradigm was validated using an independent cohort from the National Health and Nutrition Examination Survey, as well as two independent external subject groups. The described regression-based algorithm is likely to be a sufficiently accurate predictor of absolute body fat (but not relative body fat) to substitute for DXA scanning in many clinical situations. Further work is needed to assess algorithm validity for subgroups of individuals with "atypical" body construction.

Pharmacokinetics of obese adults: Not only an increase in weight

Obesity is a pathophysiological state defined by a body mass index > 30 kg/m2 and characterized by an adipose tissue accumulation leading to an important weight increased. Several pathologies named comorbidities such as cardiovascular disease, type 2 diabetes and cancer make obesity the fifth cause of death in the world. Physiological changes impact the four main phases of pharmacokinetics of some drugs and leads to an inappropriate drug-dose. For absorption, the gastrointestinal transit is accelerated, and the gastric empty time is shortened, that can reduce the solubilization and absorption of some oral drugs. The drug distribution is probably the most impacted by the obesity-related changes because the fat mass (FM) increases at the expense of the lean body weight (LBW), leading to an important increase of the volume of distribution for lipophilic drugs and a low or moderately increase of this parameter for hydrophilic drugs. This modification of the distribution may require drug-dose adjustments. By various mechanisms, the metabolism and elimination of drugs are impacted by obesity and should be considered as similar or lower than that non-obese patients. To better understand the necessary drug-dose adjustments in obese patients, a narrative review of the literature was conducted to highlight the main elements to consider in the therapeutic management of adult obese patients.

Physiologically Based Pharmacokinetic Modelling to Identify Physiological and Drug Parameters Driving Pharmacokinetics in Obese Individuals

BACKGROUND

Obese individuals are often underrepresented in clinical trials, leading to a lack of dosing guidance.

OBJECTIVE

This study aimed to investigate which physiological parameters and drug properties determine drug disposition changes in obese using our physiologically based pharmacokinetic (PBPK) framework, informed with obese population characteristics.

METHODS

Simulations were performed for ten drugs with clinical data in obese (i.e., midazolam, triazolam, caffeine, chlorzoxazone, acetaminophen, lorazepam, propranolol, amikacin, tobramycin, and glimepiride). PBPK drug models were developed and verified first against clinical data in non-obese (body mass index (BMI) ≤ 30 kg/m²) and subsequently in obese (BMI ≥ 30 kg/m²) without changing any drug parameters. Additionally, the PBPK model was used to study the effect of obesity on the pharmacokinetic parameters by simulating drug disposition across BMI, starting from 20 up to 60 kg/m².

RESULTS

Predicted pharmacokinetic parameters were within 1.25-fold (71.5%), 1.5-fold (21.5%) and twofold (7%) of clinical data. On average, clearance increased by 1.6% per BMI unit up to 64% for a BMI of 60 kg/m², which was explained by the increased hepatic and renal blood flows. Volume of distribution increased for all drugs up to threefold for a BMI of 60 kg/m²; this change was driven by pK_a for ionized drugs and logP for neutral and unionized drugs. C_max decreased similarly across all drugs while t_max remained unchanged.

CONCLUSION

Both physiological changes and drug properties impact drug pharmacokinetics in obese subjects. Clearance increases due to enhanced hepatic and renal blood flows. Volume of distribution is higher for all drugs, with differences among drugs depending on their pK_a/logP.

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.

Drug Disposition in Subjects with Obesity: The Research Work of Darrell R. Abernethy

In 1979, the late Dr. Darrell R. Abernethy and colleagues began a series of clinical studies aimed at understanding the pertinent determinants of drug distribution, elimination, and clearance in obesity, and how those variables are interconnected. The studies confirmed that volume of distribution (Vd) and clearance are the principal independent biological variables, which conjointly determine elimination half-life as a dependent variable. For drugs distributed by passive diffusion, their pharmacokinetic Vd - after correcting for plasma protein binding - was increased in obesity, depending in part on the physicochemical lipophilicity of the individual drugs, and the quantitative extent of obesity in overweight individuals. Across all studies, the ratio of mean clearance in obese divided by control groups had an overall median value of 1.21 (range: 0.75 to 3.11), indicating a small and variable effect of obesity on clearance, without clear directionality. Since drug clearance was not clearly related to lipophilicity or degree of obesity, the prolonged half-life of lipophilic drugs in obese patients was largely explained by the increased Vd. Dr. Abernethy further identified delayed attainment of steady-state after initiation of multiple-dose treatment, and delayed washout after termination of dosage, as potential clinical consequences of the extended half-life in obese persons. These consequences for specific drugs have been recently emphasized in contemporary studies of chronic dosage in subjects with obesity. Without data identifying an obesity-related change in clearance for a specific drug, maintenance doses (in milligrams) should be based on ideal weight rather than adjusted upward based on total weight. This article is protected by copyright. All rights reserved.

Pharmacokinetic Pharmacodynamic Modelling Contributions to Improve Paediatric Anaesthesia Practice

The use of pharmacokinetic-pharmacodynamic models has improved anaesthesia practice in children through a better understanding of dose-concentration-response relationships, developmental pharmacokinetic changes, quantification of drug interactions and insights into how covariates (e.g., age, size, organ dysfunction, pharmacogenomics) impact drug prescription. Simulation using information from these models has enabled the prediction and learning of beneficial and adverse effects and decision-making around clinical scenarios. Covariate information, including the use of allometric size scaling, age and consideration of fat mass, has reduced population parameter variability. The target concentration approach has rationalised dose calculation. Paediatric pharmacokinetic-pharmacodynamic insights have led to better drug delivery systems for total intravenous anaesthesia and an expectation about drug offset when delivery is stopped. Understanding concentration-dependent adverse effects have tempered dose regimens. Quantification of drug interactions has improved the understanding of the effects of drug combinations. Repurposed drugs (e.g., antiviral drugs used for COVID-19) within the community can have important effects on drugs used in paediatric anaesthesia, and the use of simulation educates about these drug vagaries.

Development and Evaluation of a Virtual Population of Children with Obesity for Physiologically Based Pharmacokinetic Modeling

BACKGROUND AND OBJECTIVE

While one in five children in the USA are now obese, and more than three-quarters receive at least one drug during childhood, there is limited dosing guidance for this vulnerable patient population. Physiologically based pharmacokinetic modeling can bridge the gap in the understanding of how pharmacokinetics, including drug distribution and clearance, changes with obesity by incorporating known obesity-related physiological changes in children. The objective of this study was to develop a virtual population of children with obesity to enable physiologically based pharmacokinetic modeling, then use the novel virtual population in conjunction with previously developed models of clindamycin and trimethoprim/sulfamethoxazole to better understand dosing of these drugs in children with obesity.

METHODS

To enable physiologically based pharmacokinetic modeling, a virtual population of children with obesity was developed using national survey, electronic health record, and clinical trial data, as well as data extracted from the literature. The virtual population accounts for key obesity-related changes in physiology relevant to pharmacokinetics, including increased body size, body composition, organ size and blood flow, plasma protein concentrations, and glomerular filtration rate. The virtual population was then used to predict the pharmacokinetics of clindamycin and trimethoprim/sulfamethoxazole in children with obesity using previously developed physiologically based pharmacokinetic models.

RESULTS

Model simulations predicted observed concentrations well, with an overall average fold error of 1.09, 1.24, and 1.53 for clindamycin, trimethoprim, and sulfamethoxazole, respectively. Relative to children without obesity, children with obesity experienced decreased clindamycin and trimethoprim/sulfamethoxazole weight-normalized clearance and volume of distribution, and higher absolute doses under recommended pediatric weight-based dosing regimens.

CONCLUSIONS

Model simulations support current recommended weight-based dosing in children with obesity for clindamycin and trimethoprim/sulfamethoxazole, as they met target exposure despite these changes in clearance and volume of distribution.

Interactions between Food and Drugs, and Nutritional Status in Renal Patients: A Narrative Review

Drugs and food interact mutually: drugs may affect the nutritional status of the body, acting on senses, appetite, resting energy expenditure, and food intake; conversely, food or one of its components may affect bioavailability and half-life, circulating plasma concentrations of drugs resulting in an increased risk of toxicity and its adverse effects, or therapeutic failure. Therefore, the knowledge of these possible interactions is fundamental for the implementation of a nutritional treatment in the presence of a pharmacological therapy. This is the case of chronic kidney disease (CKD), for which the medication burden could be a problem, and nutritional therapy plays an important role in the patient’s treatment. The aim of this paper was to review the interactions that take place between drugs and foods that can potentially be used in renal patients, and the changes in nutritional status induced by drugs. A proper definition of the amount of food/nutrient intake, an adequate definition of the timing of meal consumption, and a proper adjustment of the drug dosing schedule may avoid these interactions, safeguarding the quality of life of the patients and guaranteeing the effectiveness of drug therapy. Hence, a close collaboration between the nephrologist, the renal dietitian, and the patient is crucial. Dietitians should consider that food may interact with drugs and that drugs may affect nutritional status, in order to provide the patient with proper dietary suggestions, and to allow the maximum effectiveness and safety of drug therapy, while preserving/correcting the nutritional status.

Impact of Obesity on Brexpiprazole Pharmacokinetics: Proposal for Improved Initiation of Treatment

Brexpiprazole is an oral antipsychotic agent indicated for use in patients with schizophrenia or as adjunctive treatment for major depressive disorder. As obesity (body mass index ≥35 kg/m² ) has the potential to affect drug pharmacokinetics and is a common comorbidity of both schizophrenia and major depressive disorder, it is important to understand changes in brexpiprazole disposition in this population. This study uses a whole-body physiologically based pharmacokinetic model to compare the pharmacokinetics of brexpiprazole in obese and normal-weight (body mass index 18-25 kg/m² ) individuals known to be cytochrome P450 2D6 extensive metabolizers (EMs) and poor metabolizers (PMs). The physiologically based pharmacokinetic simulations demonstrated significant differences in the time to effective concentrations between obese and normal-weight individuals within metabolizer groups according to the label-recommended titration. Simulations using an alternative dosing strategy of 1 week of twice-daily dosing in obese EMs or 2 weeks of twice-daily dosing in obese poor metabolizers, followed by a return to once-daily dosing, yielded more consistent plasma concentrations between normal-weight and obese patients without exceeding the area under the plasma concentration-time curve observed in the normal-weight EMs. These alternative dosing strategies reduce the time to effective concentrations in obese patients and may improve clinical response to brexpiprazole.

Effect of obesity on gastrointestinal transit, pressure and pH using a wireless motility capsule

BACKGROUND

Despite the increasing prevalence and medical burden of obesity, the understanding of gastrointestinal physiology in obesity is scarce, which hampers drug development.

AIM

To investigate the effect of obesity and food intake on gastrointestinal transit, pressure and pH.

MATERIAL AND METHODS

An exploratory cross-sectional study using a wireless motility capsule (SmartPill©) was performed in 11 participants with obesity and 11 age- and gender-matched participants with normal weight (group) in fasted and fed state (visit). During the first visit, the capsule was ingested after an overnight fast. During a second visit, the capsule was ingested after a nutritional drink to simulate fed state. Linear mixed models were constructed to compare segmental gastrointestinal transit, pressure and pH between groups (obesity or control) and within every group (fasted or fed).

RESULTS

Food intake slowed gastric emptying in both groups (both P < 0.0001), though food-induced gastric contractility was higher in participants with obesity compared to controls (P = 0.02). In the small intestine, a higher contractility (P = 0.001), shorter transit (P = 0.04) and lower median pH (P = 0.002) was observed in participants with obesity compared to controls. No differences were observed for colonic measurements.

CONCLUSION

Obesity has a profound impact on gastrointestinal physiology, which should be taken into account for drug development.

Effect of lipophilicity on drug distribution and elimination: Influence of obesity

AIMS

For a given passively-distributed lipophilic drug, the extent of in vivo distribution (pharmacokinetic volume of distribution, V_d ) in obese individuals increases in relation to the degree of obesity. The present study had the objective of evaluating drug distribution in relation to in vitro lipophilicity, and the relative increase in V_d associated with obesity across a series of drugs.

METHODS

Cohorts of normal-weight control and obese subjects received single doses of drugs ranging from hydrophilic (acetaminophen, salicylate) to lipophilic (imipramine, verapamil). Lipid solubility was measured by the log-transformed values of the high-pressure liquid chromatographic (HPLC) retention index (Log₁₀ (HPLC)), and the octanol-water partition coefficient (LogP).

RESULTS

Among normal-weight controls, V_d normalized for protein binding was highly correlated with Log₁₀ (HPLC) (R² = .65) and with LogP (R² = .78). V_d of all drugs was increased in the obese cohort, but the relative increase (compared to controls) for individual drugs was disproportionately greater as lipid solubility increased. Since clearance was unrelated to lipophilicity, the increased V_d produced a parallel disproportionate increase in elimination half-life in the obese cohort that was associated with Log₁₀ (HPLC) (R² = .62).

CONCLUSION

Lipophilicity is a principal correlate of in vivo V_d , as well as the increased V_d of drugs in obese patients. The consequent prolongation of half-life in obesity has clinical safety implications in terms of delayed drug accumulation and washout during and after chronic dosage. The magnitude and importance of this effect for a given drug depends on the degree of obesity, as well as the lipid-solubility of the specific drug.

Effect of Body Mass Index on Postoperative Nausea and Vomiting: Propensity Analysis

The impact of body mass index (BMI) on postoperative nausea and vomiting (PONV) is controversial, and few studies have focused on their relationship. We investigated the effects of BMI on PONV, taking into account other PONV risk factors. We analyzed adults over the age of 18 years who received general anesthesia between 2015 and 2019, using propensity score matching. Before propensity score matching, odds ratios (ORs) for PONV were lower for overweight (OR, 0.91; 95% confidence interval (CI), 0.87–0.96; p < 0.0001) or obese patients (OR, 0.77; 95% CI, 0.71–0.84; p < 0.0001) than for normal-BMI patients. After matching, the ORs for PONV of overweight (OR, 0.89; 95% CI, 0.80–0.98; p = 0.016) and obese patients (OR, 0.71; 95% CI, 0.63–0.79; p < 0.0001) were low. However, the ORs of underweight patients did not differ from those of normal-BMI patients, irrespective of matching. Therefore, the incidence of PONV may be lower among adults with a higher-than-normal BMI.

Obesity and atrial fibrillation: making inroads through fat

The global prevalence of obesity has reached epidemic proportions, paralleled by a rise in cases of atrial fibrillation (AF). Data from epidemiological cohorts support the role of obesity as an independent risk factor for AF. Increasing evidence indicates that obesity may contribute to the AF substrate through a number of pathways including by altering epicardial adipose tissue biology, inflammatory pathways, structural cardiac remodelling, and inducing atrial fibrosis. Due to changes in pharmacokinetics and pharmacodynamics, specific therapeutic considerations are required to guide management of patients with AF including anticoagulation and rhythm control. Also, weight loss in patients with AF has been associated with reduced progression from paroxysmal to persistent AF and indeed regression from persistent to proximal AF. However, the role of dietary intervention in AF control remains to be fully elucidated and hard prospective outcome data to support weight loss are required in AF to determine its role as part of a comprehensive risk factor management strategy for AF in obese patients.

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.

Opioid and Benzodiazepine Requirements in Obese Adult Patients Receiving Extracorporeal Membrane Oxygenation

Background: The use of extracorporeal membrane oxygenation (ECMO) sometimes requires deep levels of sedation (Richmond Agitation Sedation Scale [RASS] −5) in patients with acute respiratory distress syndrome (ARDS). The role of obesity in opioid and sedative requirements remains unclear in patients receiving ECMO. Objective: This study sought to determine whether obesity increases midazolam and opioid requirements in patients receiving venovenous (vv)-ECMO up to the first 7 days after initiation. Methods: This was a retrospective cohort study of adult patients with ARDS managed with vv-ECMO. Results: The obese (n = 38) and nonobese (n = 43) groups had similar baseline characteristics. Fentanyl equivalents were significantly higher on day 3 in the obese group ( P = 0.02) despite similar RASS scores with no differences in midazolam requirements. There were no differences in duration of ECMO, length of stay, or mortality. Conclusion and Relevance: Daily midazolam requirements were not significantly different, and opioid requirements were only significantly higher in the obese group on day 3 despite similar levels of sedation. The impact of obesity with the addition of ECMO and how to adapt doses of medications remains elusive.

Glucocorticoids dosing in obese subjects: A systematic review

Glucocorticoids (GCs) are amongst the most widely used and effective treatments to control inflammatory and autoimmune diseases. In obese subjects, drug dosing adjusted by body weight is problematic, all the more so as patients are at higher risk of GC metabolic side effects. We propose here to describe the determinants of drug pharmacokinetics (PK) in obese subjects and GC pharmacology, and to identify the existing PK studies that may help discussing the best size descriptor for GC dosing in obese subjects. A clinician and a pharmacist screened PubMed using the MeSH Terms: "glucocorticoids" OR "steroidal agents" AND "pharmacokinetics" AND "obesity" OR "overweight". The search was limited to the publications written in English language and to those performed in humans. A systematic search using the MeSH terms was performed until August 31st, 2017. Only three such PK studies have been published so far that compare dexamethasone, prednisolone and methylprednisolone in obese and normal weight subjects. The studies concur that GC partially distribute in the excess of body weight and that adjustment by total body weight (TBW) or by body weight (BW) excess would increase the initial plasma GC concentration after a loading dose and would thus be inappropriate. Contradictory results are observed regarding GC exposure or clearance according to the GC studied. Behind this overwhelming lack of conclusive evidence for adjusting GC by body weight, further PK studies are clearly needed for guiding their dosing. Furthermore, studies demonstrated an increased sensibility to GC, even when GC exposure was reduced, suggesting that adjustment by body weight may not only be unnecessary but also dangerous.

Effects of obesity on burn resuscitation

The effects of obesity on resuscitation after severe burn are not well understood. Formulas to calculate 24-h resuscitation volumes incorporate body weight, which in obese patients often leads to excessive fluid administration and potential complications such as pulmonary edema, extremity or abdominal compartment syndrome, and longer mechanical ventilation. We evaluated the impact of obesity on 24-h fluid resuscitation after severe burn using a cohort of 145 adults admitted to the burn ICU from January 2014 to March 2017 with >20% total body surface area burns. Patients were divided into four groups based on body mass index: normal weight (index of <25), overweight (25-29.9), obese (30-39.9), and morbidly obese (>40). Median total body surface area burn was 39.4% (interquartile range: 23.5%-49.5%). Patients were 74.5% male and demographics and injury characteristics were similar across groups. Resuscitation volumes exceeded the predicted Parkland formula volume in the normal and overweight groups but were less than predicted in the obese and morbidly obese categories (p<0.001). No difference was found in 24-h urine output between groups (p=0.08). Increasing body mass index was not associated with increased use of renal replacement therapy. Only total body surface area burned, and age were independent predictors of hospital mortality (p<0.001). We conclude that using body weight to calculate resuscitation in obese patients results in a predicted fluid volume that is higher than the volume actually given, which can lead to over-resuscitation if rates are not titrated regularly to address fluid responsiveness.

Sustained Impairment of Lurasidone Clearance After Discontinuation of Posaconazole: Impact of Obesity, and Implications for Patient Safety

PURPOSE/BACKGROUND

The antipsychotic agent lurasidone (Latuda®) is metabolized by Cytochrome P450-3A (CYP3A) enzymes. Coadministration with strong CYP3A inhibitors (such as ketoconazole, posaconazole, and ritonavir) is contraindicated due to the risk of sedation and movement disorders from high levels of lurasidone. This study evaluated the time-course of recovery from the posaconazole drug interaction, and the effect of obesity on the recovery process.

METHODS/PROCEDURES

Healthy normal-weight volunteers (n = 11, mean body mass index, BMI, = 23.1 kg/m) and otherwise healthy obese subjects (n = 13, mean BMI = 49.3 kg/m) received single doses of lurasidone in the baseline control condition, again during coadministration of posaconazole, and at 4 additional time points during the 2 weeks after posaconazole discontinuation.

FINDINGS/RESULTS

With posaconazole coadministration, lurasidone area under the concentration curve (AUC) increased by an arithmetic mean factor of 6.2 in normals, and by 4.9 in obese subjects. Post-treatment washout of posaconazole was slow in normals (mean half-life 31 hours), and further prolonged in obese subjects (53 hours). Recovery of lurasidone AUC toward baseline was correspondingly slow, and was incomplete. AUC remained significantly elevated above baseline both in normals (factor of 2.1) and obese subjects (factor of 3.4) even at 2 weeks after stopping posaconazole.

IMPLICATIONS/CONCLUSIONS

Product labeling does not address the necessary delay after discontinuation of a strong CYP3A inhibitor before lurasidone can be safely administered. We recommend requiring normal-weight and obese patients to limit the dosage of lurasidone, or undergo a washout period, for two and three weeks, respectively, after discontinuation of posaconazole.

Vortioxetine Disposition in Obesity: Potential Implications for Patient Safety

BACKGROUND

Obesity and depression are common comorbid conditions. The objective of the study was to evaluate the effect of obesity on the pharmacokinetics of the serotonergic antidepressant vortioxetine.

METHODS

Vortioxetine pharmacokinetics were evaluated in 16 otherwise healthy obese volunteers (mean weight, 119 kg; mean body mass index (BMI) 41.8 kg/m) and in 14 normal-weight subjects (mean weight, 68 kg; mean BMI, 23.0 kg/m) matched for age. All subjects received a single 5-mg oral dose of vortioxetine once daily for 29 days. Pre-dose plasma vortioxetine concentrations were measured during the 29 days of dosing, and during a 4-week washout period after the last dose. Full 24-hour profiles were obtained after the first and last doses.

RESULTS

Vortioxetine accumulated extensively over the 29 days; the accumulation ratio was not significantly different between obese and control groups (means: 5.24 and 4.46, respectively). Steady-state concentration (Css) and steady-state clearance also did not differ between groups. However mean washout half-life (T1/2) was significantly prolonged in obese vs. control subjects (3.26 days vs. 2.21 days, P < 0.01). Up to 89% of the individual variability in T1/2 was explained by the product of Css and numeric indicators of the degree of obesity.

CONCLUSIONS

The half-life of vortioxetine washout after discontinuation of therapy is significantly prolonged in obese individuals compared to normal weight controls. To avoid a potential risk of serotonin syndrome, obese patients who plan to change their medication from vortioxetine to a monoamine oxidase inhibitor (MAOI) should extend the time between vortioxetine discontinuation and MAOI initiation beyond what is recommended in the product label.

Advances in pharmacokinetic modeling: target controlled infusions in the obese

PURPOSE OF REVIEW

The use of conventional pharmacokinetic parameters sets 'models' derived from nonobese patients has proven inadequate to administer intravenous anesthetics in the obese population and is commonly associated with higher than anticipated plasma propofol concentrations when used with target (plasma or effect site) controlled infusion pumps. In this review we will describe recent modeling strategies to characterize the disposition of intravenous anesthetics in the obese patient and will show clinically relevant aspects of new model's performance in the obese population.

RECENT FINDINGS

Because clearance of a drug increases in a nonlinear manner with weight, nonlinear relationships better scale infusion rates between lean and obese individuals. Allometric concepts have been successfully used to describe size-related nonlinear changes in clearances. Other nonlinear scaling options include the use of descriptors such as body surface area, lean body weight, fat-free mass, and normal fat mass. Newer pharmacokinetic models, determined from obese patient data, have been developed for propofol and remifentanil using allometric concepts and comprehensive size descriptors.

SUMMARY

Pharmacokinetic models to perform target-controlled infusion in the obese population should incorporate descriptors that reflect with greater precision the influence of body composition in volumes and clearances of each drug. It is our hope that commercially available pumps will soon incorporate these new models to improve the performance of this technique in the obese population.

Effect of equipotent doses of bupivacaine and ropivacaine in high-fat diet fed neonatal rodent model

OBJECTIVES

The increase in the prevalence of obesity presents a significant health and economic problem. Obesity has been reported to be a major contributor to variety of chronic diseases. Childhood obesity has been rising over the past decades leading to various complications in health. Millions of infants and children undergo surgery every year on various health grounds. The present investigation was undertaken to evaluate the effect of spinal anesthesia of equipotent doses of ropivacaine and bupivacaine on over-weight neonatal rats.

METHODS

The Sprague-Dawley rat pups were overfed on high fat diet to induce obesity. Behavioral assessments for sensory and motor blockade was made by evaluating thermal and mechanical withdrawal latencies at various time intervals following intrathecal injections of bupivacaine (5.0mg·kg^-1) and ropivacaine (7.5mg·kg^-1) in P14 rats. Spinal tissue was analyzed for apoptosis by determination of activated caspase-3 using monoclonal anti-activated caspase-3 and Fluoro-Jade C staining. Long-term spinal function in P30 rat pups was evaluated.

RESULTS

Exposure to intrathecal anesthesia in P14 increased thermal and mechanical latencies and was observed to increase apoptosis as presented by increase in activated caspase-3 and Fluro-Jade C positive cells. Significant alterations in spinal function were observed in high fat diet-fed pups as against non-obese control pups that were on standard diet. Bupivacaine produced more pronounced apoptotic effects on P14 pups; ropivacaine however produced long lasting effects as evidenced in motor function tests at P30.

CONCLUSION

Ropivacaine and bupivacaine induced spinal toxicity that was more pronounced in over-fed rat pups as against normal controls.

IV fosphenytoin in obese patients: Dosing strategies, safety, and efficacy

Background

Previous studies evaluated the disposition of IV phenytoin loading doses and found that obese patients had increased drug distribution into excess body weight, larger volumes of distribution, and longer half-lives when compared to their nonobese counterparts. We assess the safety and efficacy of fosphenytoin loading doses in patients with different body mass indices (BMIs).

Methods

A retrospective chart review was conducted in 410 patients who received fosphenytoin. Patients were divided into 2 groups: BMI <30 (nonobese) and BMI ≥30 (obese). Patient demographics, fosphenytoin dose administered in mg/kg body weight, renal and liver function tests, fosphenytoin drug levels, and pre- and post-fosphenytoin administration vital signs were collected to assess for adverse events. Necessity of additional antiepileptic loading doses was used as a surrogate for clinical efficacy.

Results

The median dose of fosphenytoin administered was 19 mg/kg (interquartile range 15-20). The most frequently encountered adverse event was hypotension, which occurred in 39% of the cohort. Using a Bonferroni adjustment for multiple comparisons, there were no differences in adverse events between the 2 groups. The need for additional antiepileptic loading doses was not different between the 2 groups (p = 0.07).

Conclusions

The incidence of adverse events and the need for repeat loading antiepileptic medications was similar between the 2 groups. From our findings, the patients in our study did not receive empiric loading dose adjustments and the current method of loading fosphenytoin achieves similar outcomes, regardless of the patient's BMI.

[Effect of equipotent doses of bupivacaine and ropivacaine in high-fat diet fed neonatal rodent model]

OBJECTIVES

The increase in the prevalence of obesity presents a significant health and economic problem. Obesity has been reported to be a major contributor to variety of chronic diseases. Childhood obesity has been rising over the past decades leading to various complications in health. Millions of infants and children undergo surgery every year on various health grounds. The present investigation was undertaken to evaluate the effect of spinal anesthesia of equipotent doses of ropivacaine and bupivacaine on over-weight neonatal rats.

METHODS

The Sprague-Dawley rat pups were overfed on high fat diet to induce obesity. Behavioral assessments for sensory and motor blockade was made by evaluating thermal and mechanical withdrawal latencies at various time intervals following intrathecal injections of bupivacaine (5.0mg·kg^-1) and ropivacaine (7.5mg·kg^-1) in P14 rats. Spinal tissue was analyzed for apoptosis by determination of activated caspase-3 using monoclonal anti-activated caspase-3 and Fluoro-Jade C staining. Long-term spinal function in P30 rat pups was evaluated.

RESULTS

Exposure to intrathecal anesthesia in P14 increased thermal and mechanical latencies and was observed to increase apoptosis as presented by increase in activated caspase-3 and Fluro-Jade C positive cells. Significant alterations in spinal function were observed in high fat diet-fed pups as against non-obese control pups that were on standard diet. Bupivacaine produced more pronounced apoptotic effects on P14 pups; ropivacaine however produced long lasting effects as evidenced in motor function tests at P30.

CONCLUSION

Ropivacaine and bupivacaine induced spinal toxicity that was more pronounced in over-fed rat pups as against normal controls.

ANTIBIOTIC PROPHYLAXIS IN BARIATRIC SURGERY: a continuous infusion of cefazolin versus ampicillin/sulbactam and ertapenem

Background The incidence of surgical site infection in bariatric patients is significant and the current recommendations for antibiotic prophylaxis are sometimes inadequate. Objective The aim of this study was to analyze the effect of three prophylactic antibiotic regimens on the incidence of surgical site infection. Methods A prospective, cross-sectional study was conducted between January 2009 and January 2013 in which 896 Roux-en-Y gastric bypasses were performed to treat obesity. The study compared three groups of patients according to the perioperative antibiotic prophylaxis administered intravenously and beginning at anesthesia induction: Group I consisting of 194 patients treated with two 3-g doses of ampicillin/sulbactam; Group II with 303 patients treated with a single 1-g dose of ertapenem; and Group III with 399 patients treated with a 2-g dose of cefazolin at anesthesia induction followed by a continuous infusion of cefazolin 1g throughout the surgical procedure. The rate of surgical site infection was analyzed, as well as its association with age, sex, preoperative weight, body mass index and comorbidities. Results The rates of surgical site infection were 4.16% in the group treated prophylactically with ampicillin/sulbactam, 1.98% in the ertapenem group and 1.55% in the continuous cefazolin group. Conclusion The prophylactic use of continuous cefazolin in surgeries for morbid obesity shows very promising results. These findings suggest that some prophylactic regimens need to be reconsidered and even substituted by more effective therapies for the prevention of surgical site infections in bariatric patients.

The role of adipose tissue and obesity in causing treatment resistance of acute lymphoblastic leukemia

Obesity is responsible for ~90,000 cancer deaths/year, increasing cancer incidence and impairing its treatment. Obesity has also been shown to impact hematological malignancies, through as yet unknown mechanisms. Adipocytes are present in bone marrow and the microenvironments of many types of cancer, and have been found to promote cancer cell survival. In this review, we explore several ways in which obesity might cause leukemia treatment resistance. Obese patients may be at a treatment disadvantage due to altered pharmacokinetics of chemotherapy and dosage "capping" based on ideal body weight. The adipose tissue provides fuel to cancer cells in the form of amino acids and free fatty acids. Adipocytes have been shown to cause cancer cells to resist chemotherapy-induced apoptosis. In addition, obese adipose tissue is phenotypically altered, producing a milieu of pro-inflammatory adipokines and cytokines, some of which have been linked to cancer progression. Given the prevalence of obesity, understanding its role and adipose tissue in acute lymphoblastic leukemia treatment is necessary for evaluating current treatment regimen and revealing new therapeutic targets.

Effect of caloric restriction and AMPK activation on hepatic nuclear receptor, biotransformation enzyme, and transporter expression in lean and obese mice

PURPOSE

Fatty liver alters liver transporter expression. Caloric restriction (CR), the recommended therapy to reverse fatty liver, increases Sirtuin1 deacetylase activity in liver. This study evaluated whether CR and CR mimetics reversed obesity-induced transporter expression in liver and hepatocytes.

METHODS

mRNA and protein expression was determined in adult lean (lean) and leptin-deficient obese (OB) mice fed ad libitum or placed on 40% (kCal) reduced diet. Hepatocytes were isolated from lean and OB mice, treated with AMP Kinase activators, and gene expression was determined.

RESULTS

CR decreased Oatp1a1, Oatp1b2, and Abcb11 mRNA expression in lean, but not OB mice. CR increased Abcc2 mRNA OB livers, whereas protein expression increased in both genotypes. CR increased Abcc3 protein expression increased in OB livers. CR did not alter Abcc1, 4 and 5 mRNA expression in lean mice but decreased expression in livers of OB mice. CR increased Abcc4 protein in lean, but not OB mice.

CONCLUSIONS

CR restriction reversed the expression of some, but not all transporters in livers of OB mice. Overall, these data indicate a potential for CR to restore some hepatic transporter changes in OB mice, but suggest a functional leptin axis is needed for reversal of expression for some transporters.

Hemodynamics and early recovery characteristics of desflurane versus sevoflurane in bariatric surgery

Context:

Morbidly obese patients are prone for intraoperative hemodynamic disturbances and postoperative airway complications.

Aim:

Comparison of intraoperative hemodynamics and postoperative recovery characteristics of desflurane versus sevoflurane in morbidly obese patients undergoing laparoscopic bariatric surgery.

Settings and Design:

Randomized controlled trial

Materials and Methods:

After institutional ethics committee approval and written informed consent, 40 morbidly obese patients (BMI > 35 kg/m²) were randomized to receive desflurane or sevoflurane as part of a standardized general anesthesia technique. Volatile anesthetic concentration was titrated to maintain electroencephalographic bispectral index score (BIS) in the range of 40-60. Mean arterial pressure (MAP) and heart rate (HR) were recorded preoperatively, at induction and intubation, then at regular intervals. After extubation, early recovery was recorded by time to emergence and orientation to time and place. In post anesthesia care unit, intermediate recovery was assessed by modified Aldrete Score and Digit Symbol Substitution Test (DSST).

Results:

Intraoperative MAP and HR did not differ between the two groups (P > 0.05). The time to response to painful stimuli, obeying verbal commands and spontaneous eye opening was shorter (P = 0.001) and modified Aldrete Score was higher after desflurane anesthesia than after sevoflurane anesthesia (P = 0.049). DSST also returned towards normal faster after desflurane (28.50 ± 6.30 min vs. 35.0 ± 5.62 min, P = 0.03).

Conclusions:

Both desflurane and sevoflurane produce similar hemodynamic changes but the immediate and intermediate recovery was significantly faster after desflurane thus contributing to fast tracking and early discharge of patients.

Effect of diabetes mellitus on pharmacokinetic and pharmacodynamic properties of drugs

The effects of diabetes mellitus on the pharmacokinetics and pharmacodynamics of drugs have been well described in experimental animal models; however, only minimal data exist for humans and the current knowledge regarding the effects of diabetes on these properties remains unclear. Nevertheless, it has been observed that the pharmacokinetics and pharmacodynamics of drugs are changed in subjects with diabetes. It has been reported that diabetes may affect the pharmacokinetics of various drugs by affecting (i) absorption, due to changes in subcutaneous adipose blood flow, muscle blood flow and gastric emptying; (ii) distribution, due to non-enzymatic glycation of albumin; (iii) biotransformation, due to regulation of enzymes/transporters involved in drug biotransformation; and (iv) excretion, due to nephropathy. Previously published data also suggest that diabetes-mediated changes in the pharmacokinetics of a particular drug cannot be translated to others. Although clinical studies exploring the effect of diabetes on pharmacodynamics are still very limited, there is evidence that disease-mediated effects are not limited only to pharmacokinetics but also alter pharmacodynamics. However, for many drugs it remains unclear whether these influences reflect diabetes-mediated changes in pharmacokinetics rather than pharmacodynamics. In addition, even though diabetes-mediated pharmacokinetics and pharmacodynamics might be anticipated, it is important to study the effect on each drug and not generalize from observed data. The available data indicate that there is a significant variability in drug response in diabetic subjects. The discrepancies between individual clinical studies as well as between ex vivo and clinical studies are probably due to (i) the restricted and focused population of subjects in clinical studies; (ii) failure to consider type, severity and duration of the disease; (iii) histopathological characteristics generally being missing; and (iv) other factors such as varying medication use, dietary protein intake, age, sex and obesity. The obesity epidemic in the developed world has also inadvertently influenced the directions of pharmacological research. This review attempts to map new information gained since Gwilt published his paper in Clinical Pharmacokinetics in 1991. Although a large body of research has been conducted and significant progress has been made, we still have to conclude that the available information regarding the effect of diabetes on pharmacokinetics and pharmacodynamics remains unclear and further clinical studies are required before we can understand the clinical significance of the effect. An understanding of diabetes-mediated changes as well as of the source of the variability should lead to the improvement of the medical management and clinical outcomes in patients with this widespread disease.

Impact of obesity on drug metabolism and elimination in adults and children

The prevalence of obesity in adults and children is rapidly increasing across the world. Several general (patho)physiological alterations associated with obesity have been described, but the specific impact of these alterations on drug metabolism and elimination and its consequences for drug dosing remains largely unknown. In order to broaden our knowledge of this area, we have reviewed and summarized clinical studies that reported clearance values of drugs in both obese and non-obese patients. Studies were classified according to their most important metabolic or elimination pathway. This resulted in a structured review of the impact of obesity on metabolic and elimination processes, including phase I metabolism, phase II metabolism, liver blood flow, glomerular filtration and tubular processes. This literature study shows that the influence of obesity on drug metabolism and elimination greatly differs per specific metabolic or elimination pathway. Clearance of cytochrome P450 (CYP) 3A4 substrates is lower in obese as compared with non-obese patients. In contrast, clearance of drugs primarily metabolized by uridine diphosphate glucuronosyltransferase (UGT), glomerular filtration and/or tubular-mediated mechanisms, xanthine oxidase, N-acetyltransferase or CYP2E1 appears higher in obese versus non-obese patients. Additionally, in obese patients, trends indicating higher clearance values were seen for drugs metabolized via CYP1A2, CYP2C9, CYP2C19 and CYP2D6, while studies on high-extraction-ratio drugs showed somewhat inconclusive results. Very limited information is available in obese children, which prevents a direct comparison between data obtained in obese children and obese adults. Future clinical studies, especially in children, adolescents and morbidly obese individuals, are needed to extend our knowledge in this clinically important area of adult and paediatric clinical pharmacology.

Postoperative pain management of the obese patient

In the obese patient, the goal of postoperative pain management is provision of comfort, early mobilisation and improved respiratory function without causing inadequate sedation and respiratory compromise. The pathophysiology of obesity, typical co-morbidities and the high prevalence of obstructive sleep apnoea (OSA) amongst obese patients make safe analgesic management difficult. In particular, pain control after bariatric surgery is a major challenge. Although several reviews covering anaesthesia and analgesia for obese patients are published, there is mainly expert opinion and a paucity of evidence-based recommendations. Advice on general management includes multimodal analgesic therapy, preference for regional techniques, avoidance of sedatives, non-invasive ventilation with supplemental oxygen, early mobilisation and elevation of the head of bed to 30 degrees. Finally, with regard to monitoring, sedation scoring is most relevant, but there should be a low threshold for continuous pulse oxymetry, arterial blood pressure measurement and placement in a high-dependency area for the postoperative period.

Tips and traps analyzing pediatric PK data

Pharmacokinetic (PK) and pharmacodynamic (PD) modeling has elucidated aspects of developmental pharmacology of value to the anesthetic community. The increasing sophistication of modeling techniques is associated with pitfalls that may not be readily apparent to readers or investigators. While size and age are considered primary covariates for PK models, the impact of birth on clearance maturation is poorly documented, dose in obese children is poorly investigated, pharmacologic implications of physiologic changes poorly portrayed, disease progression on drug response poorly depicted and the impact of metabolites on effect poorly illustrated. This review identifies some of these pitfalls and suggests ideas to circumvent or investigate these hazards.

The effect of bamboo extract on hepatic biotransforming enzymes--findings from an obese-diabetic mouse model

AIM OF THE STUDY

Bamboo leaves are used as a component in traditional Chinese medicine for the anti-inflammatory function. Our previous studies have demonstrated that an ethanol/water extract from Phyllostachys edulis ameliorated obesity-associated chronic systemic inflammation in mice, and therefore relieving the symptoms of type 2 diabetes. The aim of this project was to further investigate the effects of this bamboo extract on hepatic biotransformation enzymes in both lean and obese mice, as an initial step in the toxicological evaluation of using this traditional medicine in obese/diabetic population.

MATERIALS AND METHODS

Male C57BL/6J mice were randomized to 4 groups and fed standard (10% kcal from fat) diet with or without bamboo extract supplementation at a dose of 10 gram per kilogram diet (n=10 and n=9, respectively), or high fat (45% kcal from fat) diet with or without bamboo extract (n=8 and N=7, respectively). The dietary treatment lasted for 6 months. Subsequently, the activities and expression of the major Phase I and II hepatic biotransformation enzymes were assessed in subcellular fractions from murine livers.

RESULTS

Three groups of mice, lean bamboo extract-supplemented, obese/diabetic, and bamboo extract-supplemented obese/diabetic, showed greater activities of cytochromes P450 1a2 and 3a11 compared to control but no changes in the expression level of these proteins. For Phase II enzymes, bamboo extract supplementation in lean mice caused decreased glutathione-S-transferase activity (-12%) and greater uridine diphosphate glucuronosyltransferase activity (+46%), but had no effect on sulfotransferase activity. Conversely, the obese/diabetic condition itself increased glutathione-S-transferase and uridine diphosphate glucuronosyltransferase activities, but decreased total sulfotransferase activity and sulfotransferase 2a1 expression.

CONCLUSIONS

Bamboo extract and obesity/diabetes show significant independent effects on hepatic biotransformation as well as interaction effects in mice. These changes may alter the clearance of endo- and xenobiotics, including bamboo extract itself, hence this effect should be carefully considered in the medicinal application of bamboo extract as it has potential to alter its own metabolism and that of other medications concurrently administered to obese diabetic patients.

Influence of obesity on propofol pharmacokinetics: derivation of a pharmacokinetic model

BACKGROUND

The objective of this study was to develop a pharmacokinetic (PK) model to characterize the influence of obesity on propofol PK parameters.

METHODS

Nineteen obese ASA II patients undergoing bariatric surgery were studied. Patients received propofol 2 mg kg(-1) bolus dose followed by a 5-20-40-120 min, 10-8-6-5 mg kg(-1) h(-1) infusion. Arterial blood samples were withdrawn at 1, 3, 5 min after induction, every 10-20 min during propofol infusion, and every 10-30 min for 2 h after stopping the propofol infusion. Arterial samples were processed by high-performance liquid chromatography. Time-concentration data profiles from this study were pooled with data from two other propofol PK studies available at http://www.opentci.org. Population PK modelling was performed using non-linear mixed effects model.

RESULTS

The study involved 19 obese adults who contributed 163 observations. The pooled analysis involved 51 patients (weight 93 sd 24 kg, range 44-160 kg; age 46 sd 16 yr, range 25-81 yr; BMI 33 sd 9 kg m(-2), range 16-52 kg m(-2)). A three-compartment model was used to investigate propofol PK. An allometric size model using total body weight (TBW) was superior to all other models investigated (linear TBW, free fat mass, lean body weight, normal fat mass) for all clearance parameters. Variability in V2 and Q2 was reduced by a function showing a decrease in both parameters with age.

CONCLUSIONS

We have derived a population PK model using obese and non-obese data to characterize propofol PK over a wide range of body weights. An allometric model using TBW as the size descriptor of volumes and clearances was superior to other size descriptors to characterize propofol PK in obese patients.