Effect of obesity on the pharmacokinetics of drugs in humans

Influence of obesity on efficacy and toxicity of induction chemotherapy in patients with newly diagnosed acute myeloid leukemia

Increased body mass index (BMI) is associated with increased risk of treatment-related complications and inferior overall survival in patients with acute myeloid leukemia (AML). We retrospectively evaluated the association between percentage of ideal body weight (IBW) and complete remission (CR) among 63 newly diagnosed, previously untreated patients with AML. The median percentage of ideal body weight was 121% (range 86-246%). Thirty-three percent of patients were obese (≥ 130% IBW). In multivariate analysis, obesity was not associated with CR (odds ratio [OR] = 0.97, p = 0.88), overall survival (hazard ratio = 0.48, p = 0.52), platelet recovery by 30 days (OR = 1.14, p = 0.52) or neutrophil recovery by 30 days (OR = 1.12, p = 0.60). Obesity was also not associated with any differences in non-hematologic toxicity. CR rates were not significantly different comparing patients not dose-adjusted to patients with obesity-related adjustments (CR = 86% vs. 67%, p = 0.55). Empiric dose reductions based on obesity did not result in significantly different CR rates.

Population pharmacokinetics and pharmacodynamics of propofol in morbidly obese patients

BACKGROUND AND OBJECTIVES

In view of the increasing prevalence of morbidly obese patients, the influence of excessive total bodyweight (TBW) on the pharmacokinetics and pharmacodynamics of propofol was characterized in this study using bispectral index (BIS) values as a pharmacodynamic endpoint.

METHODS

A population pharmacokinetic and pharmacodynamic model was developed with the nonlinear mixed-effects modelling software NONMEM VI, on the basis of 491 blood samples from 20 morbidly obese patients (TBW range 98-167 kg) and 725 blood samples from 44 lean patients (TBW range 55-98 kg) from previously published studies. In addition, 2246 BIS values from the 20 morbidly obese patients were available for pharmacodynamic analysis.

RESULTS

In a three-compartment pharmacokinetic model, TBW proved to be the most predictive covariate for clearance from the central compartment (CL) in the 20 morbidly obese patients (CL 2.33 L/min × [TBW/70]^[0.72]). Similar results were obtained when the morbidly obese patients and the 44 lean patients were analysed together (CL 2.22 L/min × [TBW/70]^[0.67]). No covariates were identified for other pharmacokinetic parameters. The depth of anaesthesia in the morbidly obese patients was adequately described by a two-compartment biophase-distribution model with a sigmoid maximum possible effect (E(max)) pharmacodynamic model (concentration at half-maximum effect [EC(50)] 2.12 mg/L) without covariates.

CONCLUSION

We developed a pharmacokinetic and pharmacodynamic model of propofol in morbidly obese patients, in which TBW proved to be the major determinant of clearance, using an allometric function with an exponent of 0.72. For the other pharmacokinetic and pharmacodynamic parameters, no covariates could be identified. Trial registration number (clinicaltrials.gov): NCT00395681.

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.

Estimation of body weight in hospitalized patients

AIM

To examine the bias and precision of different methods of estimating body mass and height in hospitalized adult patients.

METHODS

Patients were enrolled at the Alfred and Caulfield hospitals, Melbourne, Australia following verbal consent. Estimates were made using the Lorenz formula (that utilizes height, waist and hip circumference), the Crandell formula (that utilizes height and arm circumference) and visual estimation of weight based on the average results obtained by two pharmacy interns. Statistical error was calculated as the ratio of estimated to actual weight; bias was assessed as the mean error and precision as the proportion of estimates within 10 and 20% of measured weight and standard deviation of the error.

RESULTS

In a 5-week period July to August 2010, 198 patients were enrolled. The median age was 64 years (range 19-91) and 52% were female. Thirty-four (17%) patients were obese (BMI >30 kg/m(2)) and 8 (4%) were underweight (BMI <18 kg/m(2)). With the Lorenz formula an estimate within 10% was obtained for 56% of patients; with the Crandell formula prediction was poor. Documentation of body weight in notes and patient self-reporting were both accurate. Seventy-two patients (43%) were prescribed one or more drugs for which dosing potentially should be adjusted for body weight.

CONCLUSION

In adult hospitalized patients, the estimation of body weight by anthropomorphic measures is not accurate. This supports the need for equipment to be made widely available to accurately weigh patients directly in hospital, including in unconscious and immobile patients.

Features of cancer management in obese patients

There is worldwide increased in obesity prevalence and statistical almost half of United-States, including children, could be obese by 2050. Obesity in cancer patients is a major issue in oncology because weight gain and obesity account for approximately 20% of all cancer cases. Indeed, increased obesity is linked with higher risk of various types of cancer and a poorer survival. Although biological mechanisms underlying how obesity causes an increased risk of cancer are suggested, overweight as a putative direct cause of death is still debated. Numerous confounding factors may impact on survival, including comorbidities and imaging limitations. Moreover, difficulties to achieve the standard oncologic care with surgery, chemotherapy and/or radiation may also be concerned. Herein, we examined the specific features and potential adaptation of the cancer management in overweighed patients. Then, we reviewed how implicated molecular pathways may provide new strategies to decrease cancer risk and predict toxicities in an increasingly obese population.

The recovery of platelet cyclooxygenase activity explains interindividual variability in responsiveness to low-dose aspirin in patients with and without diabetes

BACKGROUND

Interindividual variability in response to aspirin has been popularized as 'resistance'. We hypothesized that faster recovery of platelet cyclooxygenase-1 activity may explain incomplete thromboxane (TX) inhibition during the 24-h dosing interval.

OBJECTIVE

To characterize the kinetics and determinants of platelet cyclooxygenase-1 recovery in aspirin-treated diabetic and non-diabetic patients.

PATIENTS/METHODS

One hundred type 2 diabetic and 73 non-diabetic patients on chronic aspirin 100 mg daily were studied. Serum TXB(2) was measured every 3 h, between 12 and 24 h after a witnessed aspirin intake, to characterize the kinetics of platelet cyclooxygenase-1 recovery. Patients with the fastest TXB(2) recovery were randomized to aspirin 100 mg once daily, 200 mg once daily or 100 mg twice daily, for 28 days and TXB(2) recovery was reassessed.

RESULTS AND CONCLUSIONS

Platelet TXB(2) production was profoundly suppressed at 12 h in both groups. Serum TXB(2) recovered linearly, with a large interindividual variability in slope. Diabetic patients in the third tertile of recovery slopes (≥ 0.10 ng mL(-1) h(-1) ) showed significantly higher mean platelet volume and body mass index, and younger age. Higher body weight was the only independent predictor of a faster recovery in non-diabetics. Aspirin 100 mg twice daily completely reversed the abnormal TXB(2) recovery in both groups. Interindividual variability in the recovery of platelet cyclooxygenase activity during the dosing interval may limit the duration of the antiplatelet effect of low-dose aspirin in patients with and without diabetes. Inadequate thromboxane inhibition can be easily measured and corrected by a twice daily regimen.

Body mass index influences the response to infliximab in ankylosing spondylitis

INTRODUCTION

The excess of adipose tissue in obese individuals may have immunomodulating properties and pharmacokinetic consequences. The aim of this study was to determine whether body mass index (BMI) affects response to infliximab (IFX) in ankylosing spondylitis (AS) patients.

METHODS

In 155 patients retrospectively included with active AS, the BMI was calculated before initiation of IFX treatment (5 mg/kg intravenously). After 6 months of treatment, changes from baseline in BASDAI, Visual Analogue Scale (VAS) pain, C-reactive protein (CRP) level, and total dose of nonsteroidal antiinflammatory drug (NSAID) were dichotomized with a threshold corresponding to a decrease of 50% of initial level of the measure, into binary variables assessing response to IFX (BASDAI50, VAS50, CRP50, NSAID50). Whether the BMI was predictive of the response to IFX therapy according to these definitions was assessed with logistic regression.

RESULTS

Multivariate analysis found that a higher BMI was associated with a lower response for BASDAI50 (P = 0.0003; OR, 0.87; 95% CI (0.81 to 0.94)), VAS50 (P < 0.0001; OR, 0.87; 95% CI (0.80 to 0.93)); CRP50 (P = 0.0279; OR, 0.93; 95% CI (0.88 to 0.99)), and NSAID50 (P = 0.0077; OR, 0.91; 95% CI (0.85 to 0.97)), criteria. According to the three WHO BMI categories, similar results were found for BASDAI50 (77.6%, 48.9%, and 26.5%; P < 0.0001), VAS50 (72.6%, 40.4%, and 16.7%; P < 0.0001); CRP50 (87.5%, 65.7%, and 38.5%; P = 0.0001), and NSAID50 (63.2%, 51.5%, and 34.6%; P = 0.06).

CONCLUSIONS

This study provides the first evidence that a high BMI negatively influences the response to IFX in AS. Further prospective studies, including assessment of the fat mass, pharmacokinetics, and adipokines dosages are mandatory to elucidate the role of obesity in AS IFX response.

Gender-specific reduction of hepatic Mrp2 expression by high-fat diet protects female mice from ANIT toxicity

Emerging evidence suggests that feeding a high-fat diet (HFD) to rodents affects the expression of genes involved in drug transport. However, gender-specific effects of HFD on drug transport are not known. The multidrug resistance-associated protein 2 (Mrp2, Abcc2) is a transporter highly expressed in the hepatocyte canalicular membrane and is important for biliary excretion of glutathione-conjugated chemicals. The current study showed that hepatic Mrp2 expression was reduced by HFD feeding only in female, but not male, C57BL/6J mice. In order to determine whether down-regulation of Mrp2 in female mice altered chemical disposition and toxicity, the biliary excretion and hepatotoxicity of the Mrp2 substrate, α-naphthylisothiocyanate (ANIT), were assessed in male and female mice fed control diet or HFD for 4weeks. ANIT-induced biliary injury is a commonly used model of experimental cholestasis and has been shown to be dependent upon Mrp2-mediated efflux of an ANIT glutathione conjugate that selectively injures biliary epithelial cells. Interestingly, HFD feeding significantly reduced early-phase biliary ANIT excretion in female mice and largely protected against ANIT-induced liver injury. In summary, the current study showed that, at least in mice, HFD feeding can differentially regulate Mrp2 expression and function and depending upon the chemical exposure may enhance or reduce susceptibility to toxicity. Taken together, these data provide a novel interaction between diet and gender in regulating hepatobiliary excretion and susceptibility to injury.

Appropriate chemotherapy dosing for obese adult patients with cancer: American Society of Clinical Oncology clinical practice guideline

PURPOSE

To provide recommendations for appropriate cytotoxic chemotherapy dosing for obese adult patients with cancer.

METHODS

The American Society of Clinical Oncology convened a Panel of experts in medical and gynecologic oncology, clinical pharmacology, pharmacokinetics and pharmacogenetics, and biostatistics and a patient representative. MEDLINE searches identified studies published in English between 1996 and 2010, and a systematic review of the literature was conducted. A majority of studies involved breast, ovarian, colon, and lung cancers. This guideline does not address dosing for novel targeted agents.

RESULTS

Practice pattern studies demonstrate that up to 40% of obese patients receive limited chemotherapy doses that are not based on actual body weight. Concerns about toxicity or overdosing in obese patients with cancer, based on the use of actual body weight, are unfounded.

RECOMMENDATIONS

The Panel recommends that full weight-based cytotoxic chemotherapy doses be used to treat obese patients with cancer, particularly when the goal of treatment is cure. There is no evidence that short- or long-term toxicity is increased among obese patients receiving full weight-based doses. Most data indicate that myelosuppression is the same or less pronounced among the obese than the non-obese who are administered full weight-based doses. Clinicians should respond to all treatment-related toxicities in obese patients in the same ways they do for non-obese patients. The use of fixed-dose chemotherapy is rarely justified, but the Panel does recommend fixed dosing for a few select agents. The Panel recommends further research into the role of pharmacokinetics and pharmacogenetics to guide appropriate dosing of obese patients with cancer.

The influence of fatty acids on theophylline binding to human serum albumin. Comparative fluorescence study

Theophylline, popular diuretic, is used to treat asthma and bronchospasm. In blood it forms complexes with albumin, which is also the main transporter of fatty acids. The aim of the present study was to describe the influence of fatty acids (FA) on binding of theophylline (Th) to human serum albumin (HSA) in the high affinity binding sites. Binding parameters have been obtained on the basis of the fluorescence analysis. The data obtained for the complex of Th and natural human serum albumin (nHSA) obtained from blood of obese patients qualified for surgical removal of stomach was compared with our previous studies on the influence of FA on the complex of Th and commercially available defatted human serum albumin (dHSA).

The impact of obesity on the immune response to infection

There is strong evidence indicating that excess adiposity negatively impacts immune function and host defence in obese individuals. This is a review of research findings concerning the impact of obesity on the immune response to infection, including a discussion of possible mechanisms. Obesity is characterised by a state of low-grade, chronic inflammation in addition to disturbed levels of circulating nutrients and metabolic hormones. The impact of these metabolic abnormalities on obesity-related comorbidities has undergone intense scrutiny over the past decade. However, relatively little is known of how the immune system and host defence are influenced by the pro-inflammatory and excess energy milieu of the obese. Epidemiological data suggest obese human subjects are at greater risk for nosocomial infections, especially following surgery. Additionally, the significance of altered immunity in obese human subjects is emphasised by recent studies reporting obesity to be an independent risk factor for increased morbidity and mortality following infection with the 2009 pandemic influenza A (H1N1) virus. Rodent models offer important insight into how metabolic abnormalities associated with excess body weight can impair immunity. However, more research is necessary to understand the specific aspects of immunity that are impaired and what factors are contributing to reduced immunocompetence in the obese. Additionally, special consideration of how infection in this at-risk population is managed is required, given that this population may not respond optimally to antimicrobial drugs and vaccination. Obesity impacts millions globally, and greater understanding of its associated physiological disturbances is a key public health concern.

Application of a systems approach to the bottom-up assessment of pharmacokinetics in obese patients: expected variations in clearance

BACKGROUND AND OBJECTIVES

The maintenance dose of a drug is dependent on drug clearance, and thus any biochemical and physiological changes in obesity that affect parameters such as cardiac output, renal function, expression of drug-metabolizing enzymes and protein binding may result in altered clearance compared with that observed in normal-weight subjects (corrected or uncorrected for body weight). Because of the increasing worldwide incidence of obesity, there is a need for more information regarding the optimal dosing of drug therapy to be made available to prescribers. This is usually provided via clinical studies in obese people; however, such studies are not available for all drugs that might be used in obese subjects. Incorporation of the relevant physiological and biochemical changes into predictive bottom-up pharmacokinetic models in order to optimize dosage regimens may offer a logical way forward for the cases where no clinical data exist. The aims of the current report are to apply such a 'systems approach' to identify the likelihood of observing variations in the clearance of drugs in obesity and morbid obesity for a set of compounds for which clinical data, as well as the necessary in vitro information, are available, and to provide a framework for assessing other drugs in the future.

METHODS

The population-specific changes in demographic, physiological and biochemical parameters that are known to be relevant to obese and morbidly obese subjects were collated and incorporated into two separate population libraries. These libraries, together with mechanistic in vitro-in vivo extrapolations (IVIVE) within the Simcyp Population-based Simulator™, were used to predict the clearance of oral alprazolam, oral caffeine, oral chlorzoxazone, oral ciclosporin, intravenous and oral midazolam, intravenous phenytoin, oral theophylline and oral triazolam. The design of the simulated studies was matched as closely as possible with that of the clinical studies. Outcome was measured by the predicted ratio of the clearance of the drug in obese and lean subjects ± its 90% confidence interval, compared with observed values. The overall statistical measures of the performance of the model to detect differences in compound clearance between obese and lean populations were investigated by measuring sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV). A power calculation was carried out to investigate the impact of the sample size on the overall outcome of clinical studies.

RESULTS

The model was successful in predicting clearance in obese subjects, with the degree to which simulations could mimic the outcome of in vivo studies being greater than 60% for six of the eight drugs. A clear difference in the clearance of chlorzoxazone was correctly picked up via simulation. The overall statistical measures of the performance of the Simcyp Simulator were 100% sensitivity, 66% specificity, 60% PPV and 100% NPV. Studies designed on the basis of the ratio of the absolute values required substantial numbers of participants in order to detect a significant difference, except for phenytoin and chlorzoxazone, where the ratios of the weight-normalized clearances generally showed statistically significant differences with a smaller number of subjects.

CONCLUSION

Extension of a mechanistic predictive pharmacokinetic model to accommodate physiological and biochemical changes associated with obesity and morbid obesity allowed prediction of changes in drug clearance on the basis of in vitro data, with reasonable accuracy across a range of compounds that are metabolized by different enzymes. Prediction of the effects of obesity on drug clearance, normalized by various body size scalars, is of potential value in the design of clinical studies during drug development and in the introduction of dosage adjustments that are likely to be needed in clinical practice.

The effect of gastric bypass on the pharmacokinetics of serotonin reuptake inhibitors

OBJECTIVE

Morbidly obese patients frequently present with mood and anxiety disorders, which are often treated with serotonin reuptake inhibitors (SRIs). Having observed that patients treated with SRIs frequently relapse after Roux-en-Y gastric bypass surgery, the authors sought to assess whether SRI bioavailability is reduced postoperatively.

METHOD

Twelve gastric bypass candidates treated with an SRI for primary mood or anxiety disorders were studied prospectively. Timed blood samples for SRI plasma levels were drawn for pharmacokinetic studies before surgery and 1, 6, and 12 months afterward. Maximum concentration, time to maximum concentration, and area under the concentration/time curve (AUC) were determined.

RESULTS

In eight of the 12 patients, AUC values 1 month after surgery dropped to an average of 54% (SD=18) of preoperative levels (range=36%-80%); in six of these patients, AUC values returned to baseline levels (or greater) by 6 months. Four patients had an exacerbation of depressive symptoms, which resolved by 12 months in three of them. Three of the four patients had a reduced AUC level at 1 month and either gained weight or failed to lose weight between 6 and 12 months. Normalization of the AUC was associated with improvement in symptom scores.

CONCLUSIONS

Patients taking SRIs in this study were at risk for reduced drug bioavailability 1 month after Roux-en-Y gastric bypass. The authors recommend close psychiatric monitoring after surgery.

Predictors of dose escalation of adalimumab in a prospective cohort of Crohn's disease patients

BACKGROUND

Adalimumab is effective for the induction and maintenance of remission in Crohn's disease (CD)-patients.

AIM

To find predictors for adalimumab dose escalation at initiation of adalimumab.

METHODS

Crohn's disease patients in a single tertiary referral centre who started adalimumab between July 2007 and March 2010 at an induction dose (week 0 160 mg subcutaneously (sc), week 2 80 mg sc) and maintenance dose of 40 mg sc thereafter every other week were followed prospectively. Patients on adalimumab for at least 3 months were included. The number of patients needing dose escalation was assessed. Patients that needed dose escalation were compared with patients that did not need dose escalation.

RESULTS

Of 199 CD patients treated with adalimumab and followed prospectively, 122 patients (M/F 54/68, median age 35 years, range 18-66 years, median CDAI 164, range 6-468) were treated for 3 months. In total 38% of these patients (46/122) needed a dose escalation within a median time of 21 weeks after adalimumab introduction (range 4-105). Body mass index (BMI) (P < 0.03) and secondary non-response to infliximab (IFX) (P < 0.06) were identified as predictors for dose escalation. Concomitant use of immunomodulators at initiation of adalimumab and the presence of autoantibodies to IFX did not predict dose escalation.

CONCLUSIONS

Over one-third adalimumab-treated patients are dose escalated within a median of 5 months. Higher BMI and secondary non-response to IFX treatment are predictive for a dose escalation during adalimumab treatment.

Optimal meropenem concentrations to treat multidrug-resistant Pseudomonas aeruginosa septic shock

A patient with septic shock due to extensively drug resistant (XDR) Pseudomonas aeruginosa was cured by optimizing the meropenem (MEM) regimen to obtain at least 40% of the time between two administrations in which drug levels were four times higher than the MIC of the pathogen. As the standard drug dose did not achieve these optimal concentrations, the MEM regimen was progressively increased up to 12 g/day (3 g every 6 h in a 3-h extended infusion), which eventually resulted in sepsis resolution. High MEM dosage may represent a valuable therapeutic option for infection due to multidrug-resistant (MDR) strains, and drug monitoring would allow rapid regimen adjustment in clinical practice.

Variability in the responsiveness to low-dose aspirin: pharmacological and disease-related mechanisms

The main pharmacological aspects of pharmacodynamics (PD) and pharmacokinetics (PK) of aspirin as antiplatelet agent were unravelled between the late sixties and the eighties, and low-dose aspirin given once daily has been shown to be a mainstay in the current treatment and prevention of cardiovascular disorders. Nevertheless, several PD and PK aspects of aspirin in selected clinical conditions have recently emerged and deserve future clinical attention. In 1994, the term "aspirin resistance" was used for the first time, but, until now, no consensus exists on definition, standardized assay, underlying mechanisms, clinical impact, and possible efficacy of alternative therapeutic interventions. At variance with an undefined aspirin-resistant status, in the last 5 years, the concept of variability in response to aspirin due to specific pathophysiological mechanisms and based on PK and/or PD of the drug has emerged. This growing evidence highlights the existence and possible clinical relevance of an interindividual variability of pharmacological aspirin response and calls for new, large studies to test new low-dose aspirin-based regimens which may ameliorate platelet acetylation, reduce variability in drug responsiveness, and improve clinical efficacy on selected populations.

Appropriate antibiotic dosage levels in the treatment of severe sepsis and septic shock

Antibiotic treatment of critically ill patients remains a significant challenge. Optimal antibacterial strategy should achieve therapeutic drug concentration in the blood as well as the infected site. Achieving therapeutic drug concentrations is particularly difficult when infections are caused by some pathogens, such as Pseudomonas aeruginosa, methicillin-resistant Staphylococcus aureus (MRSA) and Gram-negative rods, because of their low susceptibility to antimicrobials. In sepsis, pharmacokinetics (PKs) of antibiotics are profoundly altered and may result in inadequate drug concentrations, even when recommended regimens are used, which potentially contribute to increased mortality and spread of resistance. The wide inter-individual PK variability observed in septic patients strongly limits the a priori prediction of the optimal dose that should be administered. Higher than standard dosages are necessary for the drugs, such as β-lactams, aminoglycosides, and glycopeptides, that are commonly used as first-line therapy in these patients to maximize their antibacterial activity. However, the benefit of reaching adequate drug concentrations on clinical outcome needs to be further determined.

Endocrine disrupting chemicals and other substances of concern in food contact materials: an updated review of exposure, effect and risk assessment

Food contact materials (FCM) are an underestimated source of chemical food contaminants and a potentially relevant route of human exposure to endocrine disrupting chemicals (EDCs). Quantifying the exposure of the general population to substances from FCM relies on estimates of food consumption and leaching into food. Recent studies using polycarbonate plastics show that food simulants do not always predict worst-case leaching of bisphenol A, a common FCM substance. Also, exposure of children to FCM substances is not always realistically predicted using the common conventions and thus possibly misjudged. Further, the exposure of the whole population to substances leaching into dry foods is underestimated. Consumers are exposed to low levels of substances from FCM across their entire lives. Effects of these compounds currently are assessed with a focus on mutagenicity and genotoxicity. This approach however neglects integrating recent new toxicological findings, like endocrine disruption, mixture toxicity, and developmental toxicity. According to these new toxicology paradigms women of childbearing age and during pregnancy are a new sensitive population group requiring more attention. Furthermore, in overweight and obese persons a change in the metabolism of xenobiotics is observed, possibly implying that this group of consumers is insufficiently protected by current risk assessment practice. Innovations in FCM risk assessment should therefore include routine testing for EDCs and an assessment of the whole migrate toxicity of a food packaging, taking into account all sensitive population groups. In this article I focus on recent issues of interest concerning either exposure to or effects of FCM-related substances. Further, I review the use of benzophenones and organotins, two groups of known or suspected EDCs, in FCM authorized in the US and EU.

Does BMI affect the clinical efficacy of proton pump inhibitor therapy in GERD? The case for rabeprazole

BACKGROUND

Increased BMI is associated with a higher risk of gastroesophageal reflux disease.

AIMS

To investigate whether overweight/obesity (BMI≥25 kg/m(2)) affects rabeprazole clinical efficacy versus omeprazole in patients with erosive esophagitis (EE).

PATIENTS AND METHODS

Post-hoc analysis of EE healing rate and symptom response stratified by patient BMI was performed on data from a multicenter, double-blind, randomized, 4-to-8-week trial comparing EE healing with rabeprazole (20 mg daily) and omeprazole (20 mg daily). Analysis of variance, two-sample t-test, Blackwelder's test for equivalence, log-rank, and Cochran-Mantel-Haenszel tests were used to analyze comparisons.

RESULTS

In the two BMI groups (<25 kg/m(2) and ≥25 kg/m(2) respectively), rabeprazole and omeprazole were equally effective for mucosal healing regardless of patient's BMI (N=542, P>0.05). However, in overweight/obese patients, rabeprazole was significantly faster than omeprazole in inducing heartburn relief during the first treatment week (P<0.0001).

CONCLUSIONS

Results of this study show that the clinical efficacy of rabeprazole is maintained in overweight/obese patients with gastroesophageal reflux disease and suggest that this subgroup of patients may derive, from rabeprazole, even greater benefit than lean patients.

Oseltamivir and oseltamivir carboxylate pharmacokinetics in obese adults: dose modification for weight is not necessary

Obesity is an independent risk factor for mortality in patients infected with pandemic influenza A virus (H1N1). Given the poor outcomes observed among adult obese patients with H1N1, the dosing of antiviral agents in this population has been questioned, and use of twice the standard oseltamivir dose has been suggested. However, studies evaluating the disposition of oseltamivir and oseltamivir carboxylate (the active metabolite) in the obese population are scant. We evaluated the single-dose and steady-state pharmacokinetics of oseltamivir (75 mg by mouth twice daily) in a cohort of 21 healthy adult volunteers with class III obesity (body mass index [BMI], ≥ 40 kg/m(2)). The median (minimum, maximum) age, weight, and BMI were 36 (19, 50) years, 122 (106, 159) kg, and 43.7 (40.0, 54.4) kg/m(2), respectively. The population pharmacokinetic exposure profiles of oseltamivir carboxylate (the active metabolite) were comparable between class III obese subjects and nonobese adults (healthy and infected). Similar to previous pharmacokinetic analyses in nonobese subjects, the mean (percent covariance [CV]) area under the concentration-time curve for the dosing interval (AUC(0-τ)) was 2,621 ng · h/ml (17) for oseltamivir carboxylate. Body size was significantly (P < 0.05) associated with oseltamivir and oseltamivir carboxylate apparent clearance, but the correlation coefficient was poor (R(2) ≤ 0.3). Creatinine clearance estimated by the Cockcroft-Gault method and lean body weight were also significantly (P < 0.05) but poorly (R(2) = 0.17) correlated with oseltamivir carboxylate apparent clearance. Since the systemic exposure of oseltamivir carboxylate is not reduced in class III obese adults with standard doses, a dose increment of oseltamivir is likely to be unnecessary.

Innovative clinical trial design for pediatric therapeutics

Until approximately 15 years ago, sponsors rarely included children in the development of therapeutics. US and European legislation has resulted in an increase in the number of pediatric trials and specific label changes and dosing recommendations, although infants remain an understudied group. The lack of clinical trials in children is partly due to specific challenges in conducting trials in this patient population. Therapeutics in special populations, including premature infants, obese children and children receiving extracorporeal life support, are even less studied. National research networks in Europe and the USA are beginning to address some of the gaps in pediatric therapeutics using novel clinical trial designs. Recent innovations in pediatric clinical trial design, including sparse and scavenged sampling, population pharmacokinetic analyses and 'opportunistic' studies, have addressed some of the historical challenges associated with clinical trials in children.

Oseltamivir pharmacokinetics in morbid obesity (OPTIMO trial)

BACKGROUND

Detailed pharmacokinetics to guide oseltamivir (Tamiflu®) dosing in morbidly obese patients is lacking.

METHODS

The OPTIMO trial was a single-centre, non-randomized, open-label pharmacokinetic study of single-dose and steady-state oral oseltamivir phosphate and its carboxylate metabolite in healthy, morbidly obese [body mass index (BMI) >  40)] and healthy, non-obese (BMI  <  30) subjects.

RESULTS

In the morbidly obese versus control subjects, respectively, the single-dose median oseltamivir oral clearance (CL/F) [840 (range 720-1640) L/h versus 580 (470-1800) L/h] was higher, the area under the curve from time zero to infinity (AUC(0-∞)) [89 (46-104) ng·h/mL versus 132 (42-160) ng·h/mL] was lower and the volume of distribution (V/F) [2320 (900-8210) L versus 1670 (700-7290) L] was unchanged. In the morbidly obese versus control subjects, respectively, the single-dose median oseltamivir carboxylate CL/F [22 (17-40) L/h versus 23 (12-33) L/h], AUC(0-∞) [3100 (1700-4100) ng·h/mL versus 3000 (2100-5900) ng·h/mL] and V/F [200 (130-370) L versus 260 (150-430) L] were similar. Similar results for oseltamivir and oseltamivir carboxylate CL/F, AUC₀₋₁₂ and V/F values were observed in the multiple-dose study.

CONCLUSIONS

With single and multiple dosing, the systemic exposure to oseltamivir is decreased but that of oseltamivir carboxylate is largely unchanged. Based on these pharmacokinetic data, an oseltamivir dose adjustment for body weight would not be needed in morbidly obese individuals.

Implications of obesity for drug therapy: limitations and challenges

Obesity has become a worldwide challenge with significant health and socioeconomic implications. One of the major implications is its impact on drug therapy. In order to gain a better understanding of this impact, we surveyed the regulatory guidances, the newly approved molecular entity drug products, and drug product labels in the Physician's Desk Reference. This review summarizes the findings of the survey along with the existing knowledge on pharmacokinetic and pharmacodynamic changes associated with obesity.

Antibiotic dosing in critical illness

Early and effective antibiotic therapy is essential in the management of infection in critical illness. The loading dose is probably the most important dose and is a function of the volume of distribution of the drug and the desired plasma concentration but independent of renal function. Antibiotics are classified in a number of ways that have implications for dosing. Doses of hydrophilic agents such as β-lactams should be increased in the early stages of sepsis as the extravascular space increases. For lipophilic agents such as macrolides, the inflammatory process is less important, although factors such as obesity will affect dosing. Classification can also be based on pharmacodynamic properties. Concentration-dependent antibiotics such as aminoglycosides should be administered by extended interval regimens, which maximize bactericidal effect, minimize nephrotoxicity and allow time between doses for the post-antibiotic effect. The critical factor for time-dependent agents, such as β-lactams, is time above the MIC. Ideally administration of these agents should be continuous, although vascular access availability can restrict infusion time to between 4 and 6 h, which is probably adequate. As well as antibiotic factors, patient factors such as hepatic and renal failure will affect dosing. Hepatic failure will affect antibiotic metabolism, although it is most important in end-stage failure. Renal failure and support will affect drug elimination. Knowledge of these factors is essential. Patient safety and prevention of unnecessary harm is a weighty consideration in critical illness. To ensure effective treatment and minimize adverse effects, therapy should be reviewed daily and adjusted in the light of changes in patient organ function and underlying pathology.

Anaesthesia for adults undergoing non-bariatric surgery

Obesity is a worldwide epidemic with increasing importance in both industrialised and developing countries. Anaesthesiologists will be increasingly challenged by the care for morbidly and super-obese patients. Prerequisites for an optimal perioperative care are a suitable and adapted environment both on the ward and in the operating theatre, the timely and comprehensive preoperative evaluation focussed on co-morbidities, such as diabetes, coronary artery disease and obstructive sleep apnoea syndrome and appropriate equipment for positioning, anaesthesia and surgery. To deliver an adequate standard of care, anaesthesiologists must consider the pharmacokinetic characteristics and pathophysiological sequelae of obesity. Careful preoxygenation, special positioning, adequate monitoring and adapted intra-operative ventilation are key issues for a successful perioperative care. While co-morbidities are frequent in the obese, overall morbidity and mortality up to a body mass index (BMI) < or = 40 kg m(-2) are not significantly increased compared with lean patients.

Physiologically-based pharmacokinetics in drug development and regulatory science

The application of physiologically-based pharmacokinetic (PBPK) modeling is coming of age in drug development and regulation, reflecting significant advances over the past 10 years in the predictability of key pharmacokinetic (PK) parameters from human in vitro data and in the availability of dedicated software platforms and associated databases. Specific advances and contemporary challenges with respect to predicting the processes of drug clearance, distribution, and absorption are reviewed, together with the ability to anticipate the quantitative extent of PK-based drug-drug interactions and the impact of age, genetics, disease, and formulation. The value of this capability in selecting and designing appropriate clinical studies, its implications for resource-sparing techniques, and a more holistic view of the application of PK across the preclinical/clinical divide are considered. Finally, some attention is given to the positioning of PBPK within the drug development and approval paradigm and its future application in truly personalized medicine.

Steady-state plasma pharmacokinetics of oral voriconazole in obese adults

Voriconazole is an antifungal agent that is currently used as primary therapy for invasive aspergillosis and as a potential treatment for systemic candidiasis. Data on the dosing of voriconazole in obese patients are not available, which is problematic given the increased prevalence of this special population. To address this limitation, we evaluated the steady-state plasma pharmacokinetics of voriconazole through a two-way, crossover design in a cohort of eight healthy volunteers with class II obesity or greater. The median (minimum, maximum) age, weight, and body mass index of obese subjects were 43 (22, 48) years, 133 (105, 155) kg, and 46.2 (38.4, 53.7) kg/m², respectively. The geometric mean ratios (90% confidence intervals) for the area under the curve from time zero to 12 h (dosing interval; AUC(0-τ)), maximum concentration (C(max)), minimum concentration at 12 h (C(min)), and time to C(max) (T(max)) of the 300-mg to 200-mg dosing regimens were 2.0 (1.5, 2.7), 1.8 (1.4, 2.2), 2.2 (1.6, 2.9), and 1.6 (1.0, 2.4) in obese subjects, respectively. The AUC(0-τ) values observed in obese subjects were comparable to those from a historical data set of nonobese subjects. Voriconazole dose-normalized AUC(0-τ) values had a modestly better correlation with lean body weight (r² = 0.42) than total body weight (r² = 0.14). An excellent linear relationship (r² = 0.96) was identified between C(min) values and AUC(0-τ) values. Adjustment of voriconazole doses in individuals with class II obesity or greater does not appear to be necessary on the basis of body weight.

Prevention of venous thromboembolism in obesity

Venous thromboembolism (VTE) is a significant cause of morbidity and mortality in hospitalized patients. Where appropriate, evidence-based methods of prophylaxis are implemented and the burden of VTE can be reduced substantially. Obesity, including morbid obesity, is associated with a high risk of VTE and, unfortunately, fixed doses of US FDA-approved anticoagulant regimens, including unfractionated heparins, low-molecular-weight heparins and factor Xa inhibitors, may not provide optimal VTE prophylaxis in these patients. Although the data are still limited, a rapidly growing body of literature and cumulative evidence suggests that anticoagulant dose adjustments in morbidly obese patients may optimize pharmacodynamic activity and reduce VTE risk. With the prevalence of morbid obesity continuing to rise, more high-quality clinical data are needed to better understand the pathobiology of VTE in obesity and provide effective, yet safe, prevention strategies.

On the accuracy of estimation of basic pharmacokinetic parameters by the traditional noncompartmental equations and the prediction of the steady-state volume of distribution in obese patients based upon data derived from normal subjects

The steady-state and terminal volumes of distribution, as well as the mean residence time of drug in the body (V(ss), V(β), and MRT) are the common pharmacokinetic parameters calculated using the drug plasma concentration-time profile C(p) (t) following intravenous (i.v. bolus or constant rate infusion) drug administration. These calculations are valid for the linear pharmacokinetic system with central elimination (i.e., elimination rate being proportional to drug concentration in plasma). Formally, the assumption of central elimination is not normally met because the rate of drug elimination is proportional to the unbound drug concentration at elimination site, although equilibration between systemic circulation and the site of clearance for majority of small molecule drugs is fast. Thus, the assumption of central elimination is practically quite adequate. It appears reasonable to estimate the extent of possible errors in determination of these pharmacokinetic parameters due to the absence of central elimination. The comparison of V(ss), V(β), and MRT calculated by exact equations and the commonly used ones was made considering a simplified physiologically based pharmacokinetic model. It was found that if the drug plasma concentration profile is detected accurately, determination of drug distribution volumes and MRT using the traditional noncompartmental calculations of these parameters from C(p) (t) yields the values very close to that obtained from exact equations. Though in practice, the accurate measurement of C(p) (t), especially its terminal phase, may not always be possible. This is particularly applicable for obtaining the distribution volumes of lipophilic compounds in obese subjects, when the possibility of late terminal phase at low drug concentration is quite likely, specifically for compounds with high clearance. An accurate determination of V(ss) is much needed in clinical practice because it is critical for the proper selection of drug treatment regimen. For that reason, we developed a convenient method for calculation of V(ss) in obese (or underweight) subjects. It is based on using the V(ss) values obtained from pharmacokinetic studies in normal subjects and the physicochemical properties of drug molecule. A simple criterion that determines either the increase or decrease of V(ss) (per unit body weight) due to obesity is obtained. The accurate determination of adipose tissue-plasma partition coefficient is crucial for the practical application of suggested method.

Clinical pharmacology profile of raltegravir, an HIV-1 integrase strand transfer inhibitor

Raltegravir is an HIV-1 integrase inhibitor approved to treat HIV infection in adults in combination with other antiretrovirals. Data from healthy volunteers demonstrate that raltegravir is rapidly absorbed with a mean half-life of approximately 7 to 12 hours, with steady state achieved in approximately 2 days. Raltegravir is characterized by both high intra- and interindividual variabilities, although neither gender, race, age, body mass index, food intake, nor renal or hepatic insufficiency has a clinically meaningful effect on raltegravir pharmacokinetics. Raltegravir lacks activity as a perpetrator of drug-drug interactions and demonstrates a low propensity to be subject to drug-drug interactions. Raltegravir is metabolized primarily by UGT1A1 and is not affected by P450 inhibitors or inducers. Inhibitors of UGT1A1 (eg, atazanavir) can increase plasma concentrations of raltegravir, although this increase has not been found to be clinically meaningful. Likewise, inducers of UGT1A1 (eg, rifampin) can reduce plasma concentrations of raltegravir, and the clinical significance of this reduction is being investigated in ongoing clinical studies. Raltegravir demonstrates favorable clinical pharmacology and a drug interaction profile that permits administration to a wide, demographically diverse patient population and coadministration with many other therapeutic agents, including antiretroviral agents and supportive medications, without restrictions or dose adjustment.

Measurement of glomerular filtration rate in obese patients: pitfalls and potential consequences on drug therapy

Epidemiological studies have shown that obesity is associated with chronic kidney disease and end stage renal disease. These studies have used creatinine derived equations to estimate glomerular filtration rate (GFR) and have indexed GFR to body surface area (BSA). However, the use of equations using creatinine as a surrogate marker of glomerular filtration and the indexation of GFR for BSA can be questioned in the obese population. First, these equations lack precision when they are compared to gold standard GFR measurements such as inulin clearances; secondly, the indexation of GFR for 1.73 m(2) of BSA leads to a systematic underestimation of GFR compared to absolute GFR in obese patients who have BSA that usually exceed 1.73 m(2). Obesity is also associated with pathophysiological changes that can affect the pharmacokinetics of drugs. The effect of obesity on both renal function and drug pharmacokinetics raises the issue of correct drug dosage in obese individuals. This may be particularly relevant for drugs known to have a narrow therapeutic range or excreted by the kidney.