Effect of obesity on the pharmacokinetics of drugs in humans

Doripenem Treatment during Continuous Renal Replacement Therapy

Doripenem is a broad-spectrum parenteral carbapenem with enhanced activity against Pseudomonas aeruginosa. While the initial dosing recommendation for renally competent patients and patients undergoing continuous renal replacement therapy (cRRT) was 500 mg every 8 h (q8h), the dose for renally competent patients was updated to 1 g q8h in June 2012. There are no updated data for the dosing of patients on continuous renal replacement therapy. The original dosing regimen for cRRT patients was based on nonseptic patients, while newer publications chose comparatively low target concentrations for a carbapenem. Thus, there is an urgent need for updated recommendations for dosing during cRRT. In the trial presented here, we included 13 oliguric septic patients undergoing cRRT in an intensive care setting. Five patients each were treated with hemodiafiltration or hemodialysis, while three patients received hemofiltration treatment. All patients received 1 g doripenem every 8 h. Doripenem concentrations in the plasma and ultrafiltrate were measured over 48 h. The mean hemofilter clearance was 36.53 ml/min, and the mean volume of distribution was 59.26 liters. The steady-state trough levels were found at 8.5 mg/liter, with no considerable accumulation. Based on pharmacokinetic and pharmacodynamic considerations, we propose a regimen of 1 g q8h, which may be combined with a loading dose of 1.5 to 2 g for critically ill patients. (This study has been registered with EudraCT under registration no. 2009-018010-18 and at ClinicalTrials.gov under registration no. NCT02018939.).

Pharmacokinetics and safety of posaconazole delayed-release tablets for invasive fungal infections

Posaconazole is a broad-spectrum triazole antifungal agent with potent activity against various pathogenic fungi, including yeast and moulds. Clinical studies have demonstrated that this agent is efficacious as prophylaxis against invasive fungal infections in patients at high risk, and may also be useful as salvage therapy against invasive aspergillosis and mucormycosis. However, the bioavailability of posaconazole following administration by oral suspension, which was the only formulation clinically available for many years, is highly variable and negatively influenced by several factors. Because of this, many patients had subtherapeutic or undetectable posaconazole levels when the oral suspension was used. To overcome this limitation, a delayed-release tablet was developed and is now available for clinical use. Hot-melt extrusion technology is used to combine a pH-sensitive polymer with posaconazole to produce a formulation that releases the drug in the elevated pH of the intestine where absorption occurs rather than in the low-pH environment of the stomach. This results in enhanced bioavailability and increased posaconazole exposure. Studies in healthy volunteers have demonstrated significantly higher and more consistent exposures with the tablet formulation compared to the oral suspension. In addition, pharmacokinetic parameters following administration of the tablets were not significantly affected by medications that raise gastric pH or increase gastric motility, and the tablets could also be administered without regard to food. Similar results have also been found in patients at high risk for invasive fungal infections who have received posaconazole tablets. The tablet formulation also appears to be well tolerated to date, although data regarding clinical efficacy are needed.

Obesity Is Common in Axial Spondyloarthritis and Is Associated with Poor Clinical Outcome

OBJECTIVE

To assess the prevalence of overweight and obesity in a large cohort of patients with axial spondyloarthritis (axSpA) in comparison with the general population. To explore the relationship of body mass index (BMI) with clinical outcome in axSpA.

METHODS

Patients from the Groningen Leeuwarden Axial SpA cohort who visited the outpatient clinic in 2011/2012 were included in this cross-sectional analysis. Body weight, height, disease activity, physical function, and quality of life (QoL) were assessed. Patients were divided into normal weight (BMI < 25 kg/m(2)), overweight (BMI ≥ 25 to < 30 kg/m(2)), and obese (BMI ≥ 30 kg/m(2)). BMI data for the general population in the same demographic region, matched for age and sex, were obtained from the LifeLines Cohort Study.

RESULTS

Of the 461 patients with axSpA, 37% were overweight and 22% were obese. In the LifeLines cohort (n = 136,577), 43% were overweight and 15% were obese. Overweight and obese patients were older, had longer symptom duration, and had more comorbidities, especially hypertension. Further, obese patients had significantly higher disease activity, worse physical function, and worse QoL than overweight and normal weight patients (mean Bath Ankylosing Spondylitis Disease Activity Index 4.5, 3.5, 3.8; mean Ankylosing Spondylitis Disease Activity Score 2.8, 2.2, 2.3; median C-reactive protein 5, 3, 3 mg/l; median erythrocyte sedimentation rate 13, 8, 8 mm/h; median Bath Ankylosing Spondylitis Functional Index 5.2, 2.9, 2.9; median Ankylosing Spondylitis QoL Questionnaire 8, 4, 5, respectively). After adjustment for potential confounders, obesity proved to be an independent predictor of worse clinical outcome.

CONCLUSION

In this large observational cohort study, obesity is more common in axSpA than in the general population and it is associated with worse clinical outcome.

Visceral adipose tissue is prognostic for survival of diffuse large B cell lymphoma treated with frontline R-CHOP

The potential role of visceral adipose tissue (VAT) as a prognostic factor in patients with diffuse large B cell lymphoma (DLBCL) treated with frontline rituximab, cyclophosphamide, doxorubicin, vincristine, and prednisolone (R-CHOP) immunochemotherapy was explored. Total adipose tissue and VAT were measured by analyzing positron emission tomography (PET)/computed tomography (CT) images obtained during the initial staging of patients with DLBCL. The VAT ratio was calculated as follows: VAT ratio = VAT area/total adipose tissue area. Body mass index (BMI), sex, and International Prognostic Index (IPI) were also incorporated as co-variates in the final model of multivariate Cox regression analysis for survival. A total of 156 patients with DLBCL, who were treated with frontline R-CHOP, were enrolled in our study. The median patient age was 61 years, and 81 patients were male (51.9 %). The median cycle of R-CHOP was six. The IPI risk group was a strong prognostic factor for progression-free survival (PFS) and overall survival (OS) (p < 0.001). Obese BMIs were an independent prognostic factor for PFS, but not for OS in multivariate analyses, compared to patients with normal BMIs (HR = 0.43, 95 % CI = 0.19-0.98, and p = 0.046 for PFS). A high VAT ratio (third tertile) was an independent adverse prognostic factor for PFS and OS in multivariate analyses (HR = 2.87 and 2.66, 95 % CI = 1.30-6.32 and 1.30-5.44, and p = 0.009 and 0.007 for PFS and OS, respectively). VAT ratio was an independent prognostic factor for patients with DLBCL treated with first-line R-CHOP; thus, additional large prospective studies are warranted.

Low-Molecular-Weight Heparin Prophylaxis Dosing

Objective. To evaluate the pharmacokinetic, safety, and effectiveness data of dosing low-molecular-weight heparins (LMWHs) for prophylaxis of venous thromboembolic events (VTEs) in obese people. Data Sources. A PubMed search (1966 to September 2015) was performed of published English articles using the following keywords: low-molecular-weight heparin, prophylaxis, and obesity. Study Selection and Data Extraction. In all, a total of 11 articles were included in this review. The search was conducted to identify pharmacokinetic studies, clinical trials (phases I-IV), or retrospective evaluations of the impact of weight and/or obesity on anti-Xa levels as well as the safety and effectiveness of LMWHs used for VTE prophylaxis. Data Synthesis. The vast majority of the available data focus on enoxaparin. Pharmacokinetic, effectiveness, and safety data all support increased enoxaparin dosing in obese patients. However, the optimal adjustment remains uncertain. For now, we recommend using 40 mg twice daily as the data for effectiveness use this regimen. Dalteparin dosing should not be adjusted in class I-II obese (body mass index 30.0-39.9 kg/m2) patients. Data regarding the impact of class III obesity (body mass index ≥40 kg/m2) on dalteparin effectiveness is needed. Total body weight dosing of tinzaparin can be used to optimize anti-Xa levels, but safety and effectiveness data are needed before weight-based tinzaparin dosing is routine medical practice for obese patients. Conclusions. The data regarding dosing of LMWHs for VTE prophylaxis are quite limited. High-quality studies are needed to help optimize dosing for obese adults requiring LMWH prophylaxis.

The Impact of Body Mass Index on the Surgical Outcomes of Patients With Gastric Cancer: A 10-Year, Single-Institution Cohort Study

This study aimed to investigate the impact of body mass index (BMI) on the short-term and long-term results of a large cohort of gastric cancer (GC) patients undergoing gastrectomy.Recently, the "obesity paradox" has been proposed, referring to the paradoxically "better" outcomes of overweight and obese patients compared with nonoverweight patients. The associations between BMI and surgical outcomes among patients with GC remain controversial.A single-institution cohort of 1249 GC patients undergoing gastrectomy between 2000 and 2010 were categorized to low-BMI (<18.49 kg/m), normal-BMI (18.50-24.99 kg/m), and high-BMI (≥25.00 kg/m) groups. The postoperative complications were classified according to the Clavien-Dindo system, and their severity was assessed by using the Comprehensive Complication Index (CCI). The impact of BMI on the postoperative complications and overall survival was analyzed.There were 908, 158, and 182 patients in the normal-BMI, low-BMI, and high-BMI groups, respectively. The overall morbidity in the high-BMI group (24.7%) was higher than that in either the low-BMI or the normal-BMI group (20.9% and 15.5%, respectively; P = 0.006), but the mean CCI in the low-BMI group was significantly higher (8.32 ± 19.97) than the mean CCI in the normal-BMI and high-BMI groups (3.76 ± 11.98 and 5.58 ± 13.07, respectively; P < 0.001). The Kaplan-Meier curve and the log-rank test demonstrated that the low-BMI group exhibited the worst survival outcomes compared with the normal-BMI group, whereas the high-BMI group exhibited the best survival outcomes (P < 0.001). In multivariate analysis, BMI was identified as an independent prognostic factor. In the stage-specific subgroup analysis, a low BMI was associated with poorer survival in the cases of stage III-IV diseases.Low BMI was associated with more severe postoperative complications and poorer prognosis. Despite a higher risk of mild postoperative complications, the high-BMI patients exhibited paradoxically "superior" survival outcomes compared with the normal-BMI patients. These findings confirm the "obesity paradox" in GC patients undergoing gastrectomy.

Drug disposition in obesity: toward evidence-based dosing

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

A Review of the Toxicologic Implications of Obesity

The increasing prevalence of obesity in developed nations has far-reaching implications for medical toxicology. The management of obese patients is complicated by comorbid illnesses, changes in cardiovascular and respiratory physiology, alterations in pharmacokinetics, and a lack of studies to identify appropriate dosing for current therapeutics and antidotes. In this review article, we examine obesity-associated physiologic and pharmacokinetic changes that may increase the vulnerability of obese patients to overdose. Further research is needed to characterize the relationship between drug toxicity and obesity.

Gaps in Drug Dosing for Obese Children: A Systematic Review of Commonly Prescribed Emergency Care Medications

PURPOSE

Approximately 1 of 6 children in the United States is obese. This has important implications for drug dosing and safety because pharmacokinetic (PK) changes are known to occur in obesity due to altered body composition and physiologic mechanisms. Inappropriate drug dosing in an emergency setting can limit therapeutic efficacy and increase drug-related toxic effects for obese children. Few systematic reviews examining PK properties and drug dosing in obese children have been performed.

METHODS

We identified 25 emergency care drugs from the Strategic National Stockpile and Acute Care Supportive Drugs List and performed a systematic review for each drug in 3 study populations: obese children (2-18 years of age), normal weight children, and obese adults (aged >18 years). For each study population, we first reviewed a drug's Food and Drug Administration label and then performed a systematic literature review. From the literature, we extracted drug PK data, biochemical properties, and dosing information. We then reviewed data in 3 age subpopulations (2-7 years, 8-12 years, and 13-18 years) for obese and normal weight children and by route of drug administration (intramuscular, intravenous, oral, and inhaled). If sufficient PK data were not available by age and route of administration, a data gap was identified.

FINDINGS

Only 2 of 25 emergency care drugs (8%) contained dosing information on the Food and Drug Administration label for obese children and adults compared with 22 of 25 (88%) for normal weight children. We found no sufficient PK data in the literature for any of the emergency care drugs in obese children. Sufficient PK data were found for 7 of 25 emergency care drugs (28%) in normal weight children and 3 of 25 (12%) in obese adults.

IMPLICATIONS

Insufficient information exists to guide dosing in obese children for any of the emergency care drugs reviewed. This knowledge gap is alarming, given the known PK changes that occur in the setting of obesity. Future clinical trials examining the PK properties of emergency care medications in obese children should be prioritized.

Prediction of drug disposition in diabetic patients by means of a physiologically based pharmacokinetic model

BACKGROUND AND OBJECTIVE

Accumulating evidence has shown that diabetes mellitus may affect the pharmacokinetics of some drugs, leading to alteration of pharmacodynamics and/or toxic effects. The aim of this study was to develop a novel physiologically based pharmacokinetic (PBPK) model for predicting drug pharmacokinetics in patients with type 2 diabetes mellitus quantitatively.

METHODS

Contributions of diabetes-induced alteration of physiological parameters including gastric emptying rates, intestinal transit time, drug metabolism in liver and kidney functions were incorporated into the model. Plasma concentration-time profiles and pharmacokinetic parameters of seven drugs (antipyrine, nisoldipine, repaglinide, glibenclamide, glimepiride, chlorzoxazone, and metformin) in non-diabetic and diabetic patients were predicted using the developed model. The PBPK model coupled with a Monte-Carlo simulation was also used to predict the means and variability of pharmacokinetic parameters.

RESULTS

The predicted area under the plasma concentration-time curve (AUC) and maximum (peak) concentration (C max) were reasonably consistent (<2-fold errors) with the reported values. Sensitivity analysis showed that gut transit time, hepatic enzyme activity, and renal function affected the pharmacokinetic characteristics of these drugs. Shortened gut transit time only decreased the AUC of controlled-released drugs and drugs with low absorption rates. Impairment of renal function markedly altered pharmacokinetics of drugs mainly eliminated via the kidneys.

CONCLUSION

All of these results indicate that the developed PBPK model can quantitatively predict pharmacokinetic alterations induced by diabetes.

Vitamin paradox in obesity: Deficiency or excess?

Since synthetic vitamins were used to fortify food and as supplements in the late 1930s, vitamin intake has significantly increased. This has been accompanied by an increased prevalence of obesity, a condition associated with diabetes, hypertension, cardiovascular disease, asthma and cancer. Paradoxically, obesity is often associated with low levels of fasting serum vitamins, such as folate and vitamin D. Recent studies on folic acid fortification have revealed another paradoxical phenomenon: obesity exhibits low fasting serum but high erythrocyte folate concentrations, with high levels of serum folate oxidation products. High erythrocyte folate status is known to reflect long-term excess folic acid intake, while increased folate oxidation products suggest an increased folate degradation because obesity shows an increased activity of cytochrome P450 2E1, a monooxygenase enzyme that can use folic acid as a substrate. There is also evidence that obesity increases niacin degradation, manifested by increased activity/expression of niacin-degrading enzymes and high levels of niacin metabolites. Moreover, obesity most commonly occurs in those with a low excretory reserve capacity (e.g., due to low birth weight/preterm birth) and/or a low sweat gland activity (black race and physical inactivity). These lines of evidence raise the possibility that low fasting serum vitamin status in obesity may be a compensatory response to chronic excess vitamin intake, rather than vitamin deficiency, and that obesity could be one of the manifestations of chronic vitamin poisoning. In this article, we discuss vitamin paradox in obesity from the perspective of vitamin homeostasis.

Body Mass Index and Smoking Affect Thioguanine Nucleotide Levels in Inflammatory Bowel Disease

INTRODUCTION

Optimal levels of the thiopurine metabolite, 6-thioguanine nucleotides [6-TGN] correlate with remission of inflammatory bowel disease [IBD]. Apart from variations in the thiopurine methyl transferase [TPMT] gene, little is known about other predictors of 6-TGN levels. Obesity adversely affects response to infliximab and adalimumab and clinical course in IBD, but little is known about the interaction of thiopurines and obesity. We investigated the relationship between body mass index [BMI] and 6-TGN levels and sought to examine other predictors of 6-TGN levels.

METHODS

This retrospective cohort study included patients with concurrent measurements of 6-TGN and BMI. The association between 6-TGN and clinical variables including BMI was estimated using a multivariable linear regression model.

RESULTS

Of 132 observations, 77 [58%] had Crohn's disease and 55 [42%] ulcerative colitis. BMI, smoking, and TPMT levels were associated with 6-TGN levels in multivariable analysis. Every 5kg/m(2) increase in BMI was associated with an 8% decrease in 6-TGN (0.92; 95% confidence interval [CI] 0.87-0.98; p = 0.009). Smokers had higher 6-TGN levels in comparison with non-/ex-smokers [1.43; 95% CI 1.02-2.02; p = 0.041]. Patients with intermediate TPMT had higher 6-TGN compared to those with normal levels [2.13; 95% CI 1.62-2.80; p < 0.001]. Obese patients were more likely to have sub-therapeutic 6-TGN levels and a higher methyl mercaptopurine nucleotide [MMPN/TGN] ratio despite a similar dose of thiopurines.

CONCLUSIONS

Active smoking and intermediate TPMT values were associated with higher 6-TGN levels but increasing BMI resulted in lower 6-TGN and higher MMPN levels. This may explain the worse outcome that has been reported previously in obese IBD subjects.

Resistance to cancer chemotherapy: failure in drug response from ADME to P-gp

Cancer chemotherapy resistance (MDR) is the innate and/or acquired ability of cancer cells to evade the effects of chemotherapeutics and is one of the most pressing major dilemmas in cancer therapy. Chemotherapy resistance can arise due to several host or tumor-related factors. However, most current research is focused on tumor-specific factors and specifically genes that handle expression of pumps that efflux accumulated drugs inside malignantly transformed types of cells. In this work, we suggest a wider and alternative perspective that sets the stage for a future platform in modifying drug resistance with respect to the treatment of cancer.

Peri-operative management of the obese surgical patient 2015: Association of Anaesthetists of Great Britain and Ireland Society for Obesity and Bariatric Anaesthesia

Guidelines are presented for the organisational and clinical peri-operative management of anaesthesia and surgery for patients who are obese, along with a summary of the problems that obesity may cause peri-operatively. The advice presented is based on previously published advice, clinical studies and expert opinion.

Adequacy of high-dose cefepime regimen in febrile neutropenic patients with hematological malignancies

While guidelines recommend empirical cefepime therapy in febrile neutropenia, the mortality benefit of cefepime has been controversial. In light of this, recent reports on pharmacokinetic changes for several antibiotics in febrile neutropenia and the consequent suboptimal exposure call for a pharmacokinetic/pharmacodynamic evaluation of current dosing. This study aimed to assess pharmacokinetic/pharmacodynamic target attainment from a 2-g intravenous (i.v.) every 8 h (q8h) cefepime regimen in febrile neutropenic patients with hematological malignancies. Cefepime plasma concentrations were measured in the 3rd, 6th, and 9th dosing intervals at 60% of the interval and/or trough point. The selected pharmacokinetic/pharmacodynamic targets were the proportion of the dosing interval (60% and 100%) for which the free drug concentration remains above the MIC (fT>MIC). Target attainment was assessed in reference to the MIC of isolated organisms if available or empirical breakpoints if not. The percentage of fT>MIC was also estimated by log-linear regression analysis. All patients achieved >60% fT>MIC in the 3rd and 6th dosing intervals. A 100% fT>MIC was not attained in 6/12, 4/10, and 4/9 patients in the 3rd, 6th, and 9th dose intervals, respectively, or in 14/31 (45%) of the dosing intervals investigated. On the other hand, 29/31 (94%) of trough concentrations were at or above 4 mg/liter. In conclusion, for patients with normal renal function, a high-dose 2-g i.v. q8h cefepime regimen appears to provide appropriate exposure if the MIC of the organism is ≤4 mg/liter but may fail to cover less susceptible organisms.

The potential for nutritional components of food items used for enrichment of research animals to act as confounding variables in toxicology studies

Produce and other non-certified foods may be provided to laboratory animals for enrichment, but this practice can generate scientific concerns, particularly if these food items contain nutrients that are pharmacologically active or affect animals' consumption of the basal diet. The author reviews information on potential for a number of nutritional components of food items to affect study data. On the basis of published effect levels, he proposes an upper limit for the consumption of each component in enrichment items relative to the amount present in a standard basal diet. He then assesses the amounts of these nutritional components in a broad range of food enrichment items and proposes a maximum serving size for each item for several common laboratory animals. Total caloric content and sugar content are the limiting components for many enrichment food items, but most items may be used as enrichment for laboratory animals without affecting study results, as long as the amounts of the items provided are managed.

Determinants of reduced antiplatelet effect of aspirin in patients with stable coronary artery disease

Background

Aspirin is a cornerstone in management of coronary artery disease (CAD). However, considerable variability in the antiplatelet effect of aspirin has been reported.

Aim

To investigate independent determinants of reduced antiplatelet effect of aspirin in stable CAD patients.

Methods

We performed a cross-sectional study including 900 stable, high-risk CAD patients. Among these, 795 (88%) had prior myocardial infarction, 250 (28%) had type 2 diabetes, and 170 (19%) had both. All patients received 75 mg aspirin daily as mono antiplatelet therapy. The antiplatelet effect of aspirin was assessed by measurement of platelet aggregation employing 1) multiple electrode aggregometry (MEA, Multiplate Analyzer) in whole blood anticoagulated with citrate or hirudin using arachidonic acid (AA) or collagen as agonists, and 2) VerifyNow Aspirin Assay. Compliance was assessed by measurement of serum thromboxane B₂.

Results

Platelet count, prior myocardial infarction, type 2 diabetes and body mass index were independent determinants of increased AA-induced MEA platelet aggregation in citrate and hirudin anticoagulated blood (p-values ≤ 0.045). Similar results were found with VerifyNow. Prior coronary artery bypass grafting, age, smoking (MEA, AA/citrate) and female gender (MEA, AA/hirudin) were also independent determinants of increased platelet aggregation (p-values ≤ 0.038). Compliance was confirmed by low serum thromboxane B₂ levels in all patients (median [25%;75%]: 0.97 [0.52;1.97], range 0.02-26.44 ng/ml).

Conclusion

Platelet count, prior myocardial infarction, type 2 diabetes and body mass index were independent determinants of increased platelet aggregation, indicating that these characteristics may be key factors in reduced antiplatelet effect of aspirin in stable CAD patients.

Response to Chemotherapy in Overweight/Obese Patients With Low-Risk Gestational Trophoblastic Neoplasia

Objective

Despite rising global obesity rates, the impact of obesity on gestational trophoblastic neoplasia (GTN) remains uninvestigated. This study aimed at investigating whether overweight/obesity relates to response to chemotherapy in low-risk GTN patients.

Methods

This nonconcurrent cohort study included 300 patients with International Federation of Gynecology and Obstetrics–defined postmolar low-risk GTN treated with a single-agent chemotherapy—methotrexate or actinomycin-D (actD)—between 1973 and 2012 at the New England Trophoblastic Disease Center. Chemotherapy dosing was based on actual body weight regardless of obesity status, except for 5-day courses or pulse regimens of actD. Patients were classified as overweight/obese (body mass index [BMI] ≥25 kg/m2) or non-overweight/obese (BMI <25 kg/m2). Information on patient characteristics and response to chemotherapy (need for second-line chemotherapy, reason for changing to an alternative chemotherapy, number of cycles, need for combination chemotherapy, and time to human chorionic gonadotropin remission) was obtained.

Results

Of 300 low-risk GTN patients, 81 (27%) were overweight/obese. Overweight/obese patients were older than the non-overweight/obese patients (median age: 30 vs 28 years, P = 0.004). First-line therapy using actD was more frequent in overweight/obese patients (6.2% vs 1.4%, P = 0.036). Resistance and toxicity were similar between groups. No significant difference in the number of chemotherapy cycles needed for remission or time required to achieve remission was found between groups.

Conclusions

No association between overweight/obesity and low-risk GTN outcomes was found. Current chemotherapy dosing using BMI seems to be appropriate for overweight/obese patients with low-risk GTN.

Applications of physiologically based pharmacokinetic modeling for the optimization of anti-infective therapies

INTRODUCTION

The pharmacokinetic properties of anti-infective drugs are a determinant part of treatment success. Pathogen replication is inhibited if adequate drug levels are achieved in target sites, whereas excessive drug concentrations linked to toxicity are to be avoided. Anti-infective distribution can be predicted by integrating in vitro drug properties and mathematical descriptions of human anatomy in physiologically based pharmacokinetic models. This method reduces the need for animal and human studies and is used increasingly in drug development and simulation of clinical scenario such as, for instance, drug-drug interactions, dose optimization, novel formulations and pharmacokinetics in special populations.

AREAS COVERED

We have assessed the relevance of physiologically based pharmacokinetic modeling in the anti-infective research field, giving an overview of mechanisms involved in model design and have suggested strategies for future applications of physiologically based pharmacokinetic models.

EXPERT OPINION

Physiologically based pharmacokinetic modeling provides a powerful tool in anti-infective optimization, and there is now no doubt that both industry and regulatory bodies have recognized the importance of this technology. It should be acknowledged, however, that major challenges remain to be addressed and that information detailing disease group physiology and anti-infective pharmacodynamics is required if a personalized medicine approach is to be achieved.

Impact of obesity on chemotherapy management and outcomes in women with gynecologic malignancies

OBJECTIVE

To describe the effects of obesity on the pharmacokinetics and dosing of chemotherapies and provide recommendations for chemotherapy management in obese women with gynecologic malignancies.

METHODS

PubMEd and MEDLINE databases were searched for articles published before June 2014. Only English-language articles were considered. 84 manuscripts were reviewed and 66 were included. Search terms included: obesity, overweight, body mass index, body surface area, glomerular filtration rate, chemotherapy, ovarian cancer, endometrial cancer, inflammation, and pharmacokinetics,

RESULTS

Obese cancer patients have worse clinical outcomes, compared with non-obese patients. This may be because of differences in pharmacokinetics, metabolic dysregulation, or physicians' decisions to reduce chemotherapy dose-intensity during treatment to minimize toxicities. A 2012 American Society of Clinical Oncology Clinical Practice Guideline recommends using actual body weight for chemotherapy dosing in all patients treated with curative intent, irrespective of obesity, to avoid compromising clinical outcomes, including progression free survival (PFS) and overall survival (OS). In women with gynecologic cancers most studies demonstrate no difference in PFS or OS when obese patients receive the same chemotherapy dose intensity as non-obese patients, except perhaps with bevacizumab.

CONCLUSIONS

Chemotherapy dose-intensity is a critical determinant of cancer outcomes and should be maintained in all patients, irrespective of obesity. Future studies should prospectively examine the impact of obesity on clinical outcomes (adverse events, survival) to improve the care of this growing population of patients who are at risk for inferior clinical outcomes.

Association of body composition with outcome of docetaxel chemotherapy in metastatic prostate cancer: a retrospective review

Background

Docetaxel, a lipophilic drug, is indicated for castration-resistant metastatic prostate cancer. Most men with such disease would have had androgen-deprivation therapy, which decreases muscle and increases body fat. Obesity and body composition changes may influence the outcomes of docetaxel therapy.

Methods

We conducted a retrospective review of 333 patients with metastatic prostate cancer treated with docetaxel at a comprehensive cancer center between October 7, 2004 and December 31, 2012. Body composition parameters were measured based on the areas of muscle and adipose tissues in the visceral and subcutaneous compartments on CT images at L3-4 levels. Dose calculations, toxicity and adverse reaction profiles, and overall survival were analyzed.

Results

Obese patients were younger at the diagnosis of prostate cancer and had a shorter duration from diagnosis to docetaxel therapy. Analysis of body composition found that a high visceral fat-to-subcutaneous fat area ratio (VSR) was associated with poor prognosis but a high visceral fat-to-muscle area ratio (VMR) and high body mass index were associated with increased duration from starting docetaxel to death, allowing such men to catch up with patients with normal body mass index in overall survival from cancer diagnosis to death. Cox proportional hazard regression showed that age ≥65 years, high VSR, abnormal serum alkaline phosphatase, and >10% reduction of initial dosage were significant predictors of shorter time between starting docetaxel and death, and that high VMR, obesity, and weekly regimens were significant predictors of longer survival after docetaxel.

Conclusion

Obese and overweight patients may benefit more from weekly docetaxel regimens using the reference dosage of 35 mg/m² without empirical dosage reduction.

Nonalcoholic steatohepatitis in precision medicine: Unraveling the factors that contribute to individual variability

There are numerous factors in individual variability that make the development and implementation of precision medicine a challenge in the clinic. One of the main goals of precision medicine is to identify the correct dose for each individual in order to maximize therapeutic effect and minimize the occurrence of adverse drug reactions. Many promising advances have been made in identifying and understanding how factors such as genetic polymorphisms can influence drug pharmacokinetics (PK) and contribute to variable drug response (VDR), but it is clear that there remain many unidentified variables. Underlying liver diseases such as nonalcoholic steatohepatitis (NASH) alter absorption, distribution, metabolism, and excretion (ADME) processes and must be considered in the implementation of precision medicine. There is still a profound need for clinical investigation into how NASH-associated changes in ADME mediators, such as metabolism enzymes and transporters, affect the pharmacokinetics of individual drugs known to rely on these pathways for elimination. This review summarizes the key PK factors in individual variability and VDR and highlights NASH as an essential underlying factor that must be considered as the development of precision medicine advances. A multifactorial approach to precision medicine that considers the combination of two or more risk factors (e.g. genetics and NASH) will be required in our effort to provide a new era of benefit for patients.

Individualizing pharmacotherapy in patients with renal impairment: the validity of the Modification of Diet in Renal Disease formula in specific patient populations with a glomerular filtration rate below 60 ml/min. A systematic review

Background

The Modification of Diet in Renal Disease (MDRD) formula is widely used in clinical practice to assess the correct drug dose. This formula is based on serum creatinine levels which might be influenced by chronic diseases itself or the effects of the chronic diseases. We conducted a systematic review to determine the validity of the MDRD formula in specific patient populations with renal impairment: elderly, hospitalized and obese patients, patients with cardiovascular disease, cancer, chronic respiratory diseases, diabetes mellitus, liver cirrhosis and human immunodeficiency virus.

Methods and Findings

We searched for articles in Pubmed published from January 1999 through January 2014. Selection criteria were (1) patients with a glomerular filtration rate (GFR) < 60 ml/min (/1.73m²), (2) MDRD formula compared with a gold standard and (3) statistical analysis focused on bias, precision and/or accuracy. Data extraction was done by the first author and checked by a second author. A bias of 20% or less, a precision of 30% or less and an accuracy expressed as P₃₀% of 80% or higher were indicators of the validity of the MDRD formula. In total we included 27 studies. The number of patients included ranged from 8 to 1831. The gold standard and measurement method used varied across the studies. For none of the specific patient populations the studies provided sufficient evidence of validity of the MDRD formula regarding the three parameters. For patients with diabetes mellitus and liver cirrhosis, hospitalized patients and elderly with moderate to severe renal impairment we concluded that the MDRD formula is not valid. Limitations of the review are the lack of considering the method of measuring serum creatinine levels and the type of gold standard used.

Conclusion

In several specific patient populations with renal impairment the use of the MDRD formula is not valid or has uncertain validity.

Dapsone and body mass index in subjects with multibacillary leprosy

BACKGROUND

The physiological changes in obese subjects can modify the pharmacokinetic profiles of drugs influencing the therapeutic efficacy.

METHODS

In this study, the authors compare plasma dapsone trough levels of multibacillary leprosy subjects stratified by body mass index (BMI) to evaluate if obesity plays a significant role on drug levels. The relationship between drug levels and BMI was also determined. Dapsone was measured by high-performance liquid chromatography and BMI based on World Health Organization criteria.

RESULTS

At steady state, the median plasma dapsone trough level was significantly lower in obesity class 2 group, when compared with other groups, but they were similar between normal weight and preobesity groups. A weak association between drug levels and BMI was observed.

CONCLUSIONS

Obesity promotes a significant reduction in plasma dapsone trough levels of subjects with multibacillary leprosy with a weak association between drug levels and BMI.

Angiotensin Converting Enzyme Inhibitors (ACEI) and doxorubicin pharmacokinetics in women receiving adjuvant breast cancer treatment

Purpose

Doxorubicin (DOX) chemotherapy can cause cardiac complications. Angiotensin converting enzyme inhibitors (ACEI) may protect against these complications. We performed a pharmacokinetics (PK) study to determine whether DOX levels are altered in the presence of ACEI.

Methods

In this randomized, cross-over, single-blinded drug-drug interaction study, 19 women with breast cancer prescribed DOX and cyclophosphamide every 14 days received one cycle of DOX chemotherapy with ACEI enalapril 10 mg daily and another cycle of DOX with placebo. Blood samples for DOX and doxorubicinol were drawn at baseline, 0.5, 1.0, 2.0, 4.0, 24.0 and 48.0 hours after infusion with and without ACEI enalapril. Correlative laboratories were also obtained. PK data was analyzed using non compartmental methods and DOX and doxorubicinol area under the curve (AUC) 0 to infinity, Cmax and half-life were estimated. Paired t-tests were used to determine whether DOX and its metabolite were altered with the use of enalapril (P < 0.05).

Results

17 women (median age 45 years) received 60 mg/m2 DOX every two weeks for four cycles. Mean (SD) AUC0- ∞ for DOX and doxorubicinol with enalapril exposure was 1185.56 (44.64) hr*ng/ml and 1040 (80.6) hr*ng/ml, respectively. AUC0- ∞ for DOX and doxobubicinol without enalapril was 1167.73 (45.26) hr*ng/ml and 1056.32 (92.03) hr*ng/ml, respectively. There is no interaction between DOX and enalapril. Enalapril was tolerated (33% grade 1 dizziness).

Conclusion

ACEI, enalapril, does not appear to alter the PK of DOX. Ongoing efforts to determine the effectiveness of ACEI as a cardioprotective agent in women receiving DOX chemotherapy should be continued.

Body mass index and other anthropometric parameters in patients with diffuse large B-cell lymphoma: physiopathological significance and predictive value in the immunochemotherapy era

Diffuse large B-cell lymphoma (DLBCL) is the most common form of aggressive non-Hodgkin lymphoma, accounting for 30-40% of newly diagnosed cases. Obesity is a well-defined risk factor for DLBCL. However, the impact of body mass index (BMI) on DLBCL prognosis is controversial. Recent studies suggest that skeletal muscle wasting (sarcopenia) or loss of fat mass can be detected by computed tomography (CT) images and is useful for predicting the clinical outcome in several types of cancer including DLBCL. Several hypotheses have been proposed to explain the differences in DLBCL outcome according to BMI or weight that include tolerance to treatment, inflammatory background and chemotherapy or rituximab metabolism. In this review, we summarize the available literature, addressing the impact and physiopathological relevance of simple anthropometric tools including BMI and tissue distribution measurements. We also discuss their relationship with other nutritional parameters and their potential role in the management of patients with DLBCL.

Impact of body weight on virological and immunological responses to efavirenz-containing regimens in HIV-infected, treatment-naive adults

OBJECTIVE

The prevalence of overweight and obesity is increasing among HIV-infected patients. Whether standard antiretroviral drug dosage is adequate in heavy individuals remains unresolved. We assessed the virological and immunological responses to initial efavirenz (EFV)-containing regimens in heavy compared to normal-weight HIV-infected patients.

DESIGN

Observational European cohort collaboration study.

METHODS

Eligible patients were antiretroviral-naïve with documented weight prior to EFV start and follow-up viral loads after treatment initiation. Cox regression analyses evaluated the association between weight and time to first undetectable viral load (<50 copies/ml) after treatment initiation, and time to viral load rebound (two consecutive viral load >50 copies/ml) after initial suppression over 5 years of follow-up. Recovery of CD4 cell count was evaluated 6 and 12 months after EFV initiation. Analyses were stratified by weight (kg) group (I - <55; II - >55, <80 (reference); III - >80, <85; IV - >85, <90; V - >90, <95; VI - >95).

RESULTS

The study included 19,968 patients, of whom 9.1, 68.3, 9.1, 5.8, 3.5, and 4.3% were in weight groups I-VI, respectively. Overall, 81.1% patients attained virological suppression, of whom 34.1% subsequently experienced viral load rebound. After multiple adjustments, no statistical difference was observed in time to undetectable viral load and virological rebound for heavier individuals compared to their normal-weight counterparts. Although heaviest individuals had significantly higher CD4 cell count at baseline, CD4 cell recovery at 6 and 12 months after EFV initiation was comparable to normal-weight individuals.

CONCLUSION

Virological and immunological responses to initial EFV-containing regimens were not impaired in heavy individuals, suggesting that the standard 600 mg EFV dosage is appropriate across a wide weight range.

Measuring anti-factor xa activity to monitor low-molecular-weight heparin in obesity: a critical review

BACKGROUND

The choice of whether to monitor anti-factor Xa (anti-Xa) activity in patients who are obese and who are receiving low-molecular-weight heparin (LMWH) therapy is controversial. To the authors' knowledge, no systematic review of monitoring of anti-Xa activity in such patients has been published to date.

OBJECTIVE

To systematically ascertain the utility of monitoring anti-Xa concentrations for LMWH therapy in obese patients.

DATA SOURCES

MEDLINE (1946 to September 2014), the Cochrane Database of Systematic Reviews, Embase (1974 to September 2014), PubMed (1947 to September 2014), International Pharmaceutical Abstracts (1970 to September 2014), and Scopus were searched using the terms obesity, morbid obesity, thrombosis, venous thrombosis, embolism, venous thromboembolism, pulmonary embolism, low-molecular weight heparin, enoxaparin, dalteparin, tinzaparin, anti-factor Xa, anti-factor Xa monitoring, anti-factor Xa activity, and anti-factor Xa assay. The reference lists of retrieved articles were also reviewed.

STUDY SELECTION AND DATA EXTRACTION

English-language studies describing obese patients treated with LMWH or reporting anti-Xa activity were reviewed using a 9-step decision-making algorithm to determine whether monitoring of LMWH therapy by means of anti-Xa activity in obesity is warranted. Studies published in abstract form were excluded.

DATA SYNTHESIS

The analysis showed that anti-Xa concentrations are not strongly associated with thrombosis or hemorrhage. In clinical studies of LMWH for thromboprophylaxis in bariatric surgery, orthopedic surgery, general surgery, and medical patients, and for treatment of venous thrombo embolism and acute coronary syndrome, anti-Xa activity can be predicted from dose of LMWH and total body weight; no difference in clinical outcome was found between obese and non-obese participants.

CONCLUSIONS

Routinely determining anti-Xa concentrations in obese patients to monitor the clinical effectiveness of LMWH is not warranted on the basis of the current evidence. Circumstances where measurement of anti-Xa concentration may help in clinical decision-making in either obese or non-obese patients would be cases where elimination of LMWH is impaired or there is an unexpected clinical response, as well as to confirm compliance with therapy or to identify deviation from predicted pharmacokinetics.

Temocillin (6 g daily) in critically ill patients: continuous infusion versus three times daily administration

OBJECTIVES

The growing incidence of infections caused by Enterobacteriaceae producing ESBLs has led to increased use of carbapenems. Temocillin, which resists most β-lactamases, may be a useful alternative. The aim of this study was to assess the pharmacokinetics and target attainment rates of 6 g of temocillin daily divided into three administrations every 8 h (three times daily) or administered by continuous infusion in critically ill patients.

PATIENTS AND METHODS

This was a prospective, two-centre, randomized, controlled study in patients with intra-abdominal or lower respiratory tract infections caused by Enterobacteriaceae.

RESULTS

Thirty-two patients were included and analysed for clinical efficacy, and pharmacokinetics were measured in 29 of them. Four patients undergoing continuous veno-venous haemofiltration (CVVH) were analysed separately. Mean, median and range of percentages of the dosing interval during which the free drug concentration remained >16 mg/L were 76.4, 98 and 18.7-98.9 in patients treated three times daily and 98.9, 89.7 and 36.4-99.9 in patients with continuous infusion, respectively. Clinical cure rates were 79% and 93% in each of these groups, respectively (not significant). Patients with CVVH received a daily dose of 750 mg given by continuous infusion and had a mean free drug concentration of only 13.8 ± 1.9 mg/L. No adverse event attributable to temocillin was observed.

CONCLUSIONS

Temocillin (6 g daily) given by continuous infusion allows a larger proportion of critically ill patients to have free drug serum concentrations covering infections caused by Enterobacteriaceae with an MIC of 16 mg/L compared with administration three times daily. Clinical efficacy compared with carbapenems in documented severe infections needs to be further studied.

Influence of Body Mass Index on the Activated Clotting Time Under Weight-Based Heparin Dose

BACKGROUND

Activated clotting time (ACT) has been successfully applied during percutaneous coronary intervention (PCI) to monitor the extent of thrombin inhibition and anti-coagulation from unfractionated heparin (UFH) aiming to reduce the incidence of thrombotic adverse events and hemorrhagic complications. And this investigation was to explore the influence of body mass index (BMI) on ACT in patients received weight-based dose of UFH during PCI treatment.

METHODS

78 male patients undergoing coronary angiography or PCI treatment with a mean age of 63.86 ± 6.89 years were enrolled in this study. The patients were statistically divided into four quartiles according to their BMI. The ACT values were recorded as ACT0 , ACT5 , ACT10 , ACT30 and ACT60 , respectively. Taking the preoperative ACT0 as reference, and the differences of the other ACT values with ACT0 was indicated as ΔACTs. ACT values peaked at 5 min in 33.33% of the patients, 10 min in 51.33% of the patients and 30 min in 15.34% of the patients, respectively.

RESULTS

In addition, significant differences were found in overall maximum post-UFH ACT values among all BMI quartiles. UFH doses per blood volume were significantly different among the BMI quartiles, showing a positive association with BMI quartiles; further evidence revealed that the areas under the ΔACT-time curves increased gradually from quartile I to quartile IV. The proportions of ACT60 > 250 s and ACT60 > 300 s were found to be positively correlated with the increased BMI at 60 min after heparin loading.

CONCLUSIONS

The results of our study have shown that a standardized dosing nomogram that uses the actual body weight to calculate the heparin doses may result in UFH overdose for patients with higher BMI compared to patients with lower BMI.

Effects of type 2 diabetes mellitus on the population pharmacokinetics of rifampin in tuberculosis patients

Diabetes mellitus (DM) is a well-known risk factor to develop tuberculosis (TB). Some reports indicate the serum concentrations of anti-TB drugs are lower in patients with TB and DM than those with TB only. Therefore, we developed a nonlinear mixed-effects model (NONMEM) to determine the population PK parameters of rifampin and assessed the effects of DM status in patients with TB. One-compartment linear modeling with first-order absorption was evaluated using the 206 plasma samples of rifampin from 54 patients with DM. Based on the final model, DM affected the absorption rate constant (ka) and the volume of distribution (Vd) of rifampin. The body mass index (BMI) of the patients affected rifampin clearance (CL). The ka of rifampin in patients with TB and DM was greater than that in patients with TB only. Further, the predicted Vd in patients with DM was greater than that in patients without DM. As Vd is inversely correlated with plasma concentrations, the rifampin concentrations were predicted to be lower in the patients with DM. The authors recommend administering the greater doses of rifampin for the treatment of TB in patients with DM compared with the doses for the patients without DM to prevent treatment failure.

How can we improve oral contraceptive success in obese women?

A rapid increase in obesity rates worldwide further underscores the importance of better understanding the pharmacokinetic alterations in this sub-population and the subsequent effects on pharmacotherapeutics. Pharmacokinetics of contraceptive steroids is altered in obese oral contraceptive users, which may in turn impact efficacy. Our study has identified several dosing strategies that offset these pharmacokinetic changes and may improve effectiveness for obese oral contraception users.

Increase in body mass index from normal weight to overweight in a cross-sectional sample of healthy research volunteers

Current literature provides limited information about healthy volunteers serving as controls for biomedical research. This study describes trends in body mass index (BMI), a ratio of weight to height (kilograms per square meter), of the population of healthy volunteers at the National Institutes of Health Clinical Center (NIH CC) and compares these trends to a nationally representative sample, as reported by the National Health and Nutrition Examination Survey. We hypothesized that BMI trends at the NIH CC would follow those of the US population. This cross-sectional study examined the BMI of healthy volunteers at the NIH CC from 1976 to 1980, 1981 to 1987, 1988 to 1994, 1995 to 1998 and for all subsequent two-year periods onward until 2012. Study data were extracted from the NIH Biomedical Translational Research Information System. Subjects were selected based on a discharge code of "volunteer." Descriptive statistics of volunteers at the NIH CC were calculated for height, weight, age-adjusted BMI, age, and sex, and associations between categorical variables were analyzed using the χ2 test. Differences between BMI categories or periods for continuous independent variables were assessed using Kruskal-Wallis and post hoc Tamhane T2 tests. The 13 898 healthy volunteers with median age of 34 years were 53% female and primarily non-Hispanic whites. Mean BMI was within the normal category from 1976 to 1987. From 1988 on, mean BMI fluctuated but increased overall. The BMI of healthy volunteers at the NIH CC appears to follow national trends as described by National Health and Nutrition Examination Survey data of increasing body weight during the past three decades followed by a recent plateau.

Concentration of amoxicillin in maternal serum, cord blood, amniotic fluid and the placenta after vaginal administration

OBJECTIVE

The aim of this study was to assess the amoxicillin concentration in maternal serum, cord blood, amniotic fluid and the placenta, 2 h following vaginal administration and the factors influencing the drug level.

METHODS

Twenty-eight full-term pregnant women who qualified for elective cesarean delivery were included in the study. Vaginal suppositories containing 250 mg of amoxicillin were administered 2 h prior to the operation. Amoxicillin levels were determined using the diffusion microbial assay.

RESULTS

The amoxicillin level in amniotic fluid was significantly higher in comparison to that of maternal serum, cord blood or the placenta. Maternal age positively and gestational weight gain negatively correlated with the amoxicillin concentration in maternal serum. The maternal serum hemoglobin level and red blood cell count were positively correlated with amoxicillin concentration in the amniotic fluid. Neonatal birth weight was positively correlated with maternal serum and cord blood amoxicillin levels. Hypertensive women had significantly higher amoxicillin concentrations in amniotic fluid, and women with thrombocytopenia presented significantly higher cord blood amoxicillin concentrations.

CONCLUSIONS

Amoxicillin presented poor concentration in maternal-fetal compartments after vaginal administration, but the factors influencing the drug level in different compartments require further investigation.

Role of Kupffer cells in ischemic injury in alcoholic fatty liver

BACKGROUND

This study was designed to evaluate the role of Kupffer cells (KCs) in hepatic drug metabolizing dysfunction after hepatic ischemia-reperfusion (IR) in alcoholic fatty liver.

MATERIALS AND METHODS

Rats were fed the Lieber-DeCarli diet for 5 wk to develop alcoholic fatty liver, then were subjected to 90 min of hepatic ischemia and 5 h of reperfusion. For ablation of KCs, rats were pretreated with gadolinium chloride (GdCl3) 48 and 24 h before the IR procedure.

RESULTS

After the IR procedure, ethanol diet (ED)-fed rats had higher serum aminotransferase activity compared with the control diet-fed rats. These changes were attenuated by GdCl3. The ED-fed rats exhibited increased hepatic microsomal total cytochrome P450 (CYP) content and nicotinamide adenine dinucleotide phosphate-CYP reductase and CYP1A1, 1A2, 2B1, and 2E1 isozyme activity. After hepatic IR, these increases were reduced to lower levels than observed in the sham group, except CYP2E1 activity. Increases in CYP2E1 activity and its expression were augmented after hepatic IR in ED-fed animals, but were attenuated by GdCl3. Finally, toll-like receptor 4 and myeloid differentiation primary response gene 88 protein expression, nuclear translocation of nuclear factor-κB and activator protein 1, and levels of proinflammatory mediators were further increased in ED-fed animals compared with control diet-fed animals after IR. These increases were attenuated by GdCl3.

CONCLUSIONS

We suggest that KCs contribute to hepatic drug metabolizing dysfunction during hepatic IR in alcoholic fatty liver via the toll-like receptors 4-mediated inflammatory response.