Relationships among liver and kidney volumes, lean body mass and drug clearance

An Anatomically Complicated Living Donor Kidney Transplantation from Hepatitis B Surface Antigen-Positive Donor to Negative Recipient With Size Discrepancy

The deficiency of organ donors remains a barrier to kidney transplantation. Living donor kidney transplantation (LDKT) can overcome graft shortage, resulting in better outcomes. Many efforts are being made to expand the donor pool, such as hepatitis B surface antigen (HBsAg)-positive donors to negative recipients and anatomically complicated donor kidneys with size discrepancies. We report a case in which we overcame various problems in LDKT. The recipient was a 56-year-old, 106-kg, HBsAg negative male with diabetic nephropathy. The donor was a 63-year-old female, 56-kg, hepatitis B virus (HBV) carrier with dual renal arteries. Preoperative antiviral medication was provided to the donor for negative conversion of HBV-DNA. The recipient was given HBV vaccination (antihepatitis B antibody: 2.25-36.16 mIU/mL). Anti-HBV immunoglobulin was intraoperatively administered to prevent transmission. The donor and recipient had an absolute weight difference (50 kg). In addition, the donor's kidney had a main and an accessory artery in the upper pole, which were anastomosed to the recipient's right external iliac and inferior epigastric artery, respectively. Follow-up serum creatinine levels decreased. Doppler ultrasonography showed good vascular flow within the reference range of the resistive index. The recipient's follow-up HBV-DNA titer was negative with antiviral medication. We successfully performed LDKT from an HBV-positive donor to a negative recipient by perioperative antiviral treatment and overcame a significant size discrepancy and anatomic challenges by preserving even a small portion of the kidney graft.

Lean Body Mass and Total Body Weight Versus Body Surface Area as a Determinant of Docetaxel Pharmacokinetics and Toxicity

AIM

This study examined whether anthropometric and body composition parameters such as body surface area (BSA), lean body mass (LBM), and total body weight (TBW) are correlated with docetaxel clearance and exposure by analyzing area under the curve. In addition, LBM, TBW, and a fixed dose were compared with BSA as dosing parameters for dose individualization of docetaxel.

METHODS

Thirty-six patients receiving docetaxel chemotherapy for breast or metastatic castration-resistant prostate carcinoma were included. Before treatment, LBM was measured using a dual-energy X-ray absorptiometry scanner. Blood samples were collected up to 180 minutes after dosing to analyze docetaxel concentrations and determine individual pharmacokinetic parameters.

RESULTS

No significant correlations were found between docetaxel clearance and the anthropometric and body composition variables (BSA, LBM, and TBW). The area under the curve was significantly but poorly correlated with BSA [r = 0.452 ( P = 0.016)] and TBW [r = 0.476 ( P = 0.011)]. The mean absolute percentage error and mean error of simulated dosing based on LBM and fixed dosing were not significantly different from those of BSA. For TBW, only mean absolute percentage error was significantly higher compared with dosing based on BSA (24.1 versus 17.1, P = 0.001).

CONCLUSIONS

There was no clinically relevant correlation between docetaxel pharmacokinetics and the anthropometric and body composition variables BSA, LBM, and TBW. Therefore, dose individualization of docetaxel based on LBM, TBW, or fixed dosing cannot be recommended over BSA-based dosing.

Use of Real-World Data and Physiologically-Based Pharmacokinetic Modeling to Characterize Enoxaparin Disposition in Children With Obesity

Dosing guidance for children with obesity is often unknown despite the fact that nearly 20% of US children are classified as obese. Enoxaparin, a commonly prescribed low-molecular-weight heparin, is dosed based on body weight irrespective of obesity status to achieve maximum concentration within a narrow therapeutic or prophylactic target range. However, whether children with and without obesity experience equivalent enoxaparin exposure remains unclear. To address this clinical question, 2,825 anti-activated factor X (anti-Xa) surrogate concentrations were collected from the electronic health records of 596 children, including those with obesity. Using linear mixed-effects regression models, we observed that 4-hour anti-Xa concentrations were statistically significantly different in children with and without obesity, even for children with the same absolute dose (P = 0.004). To further mechanistically explore obesity-associated differences in anti-Xa concentration, a pediatric physiologically-based pharmacokinetic (PBPK) model was developed in adults, and then scaled to children with and without obesity. This PBPK model incorporated binding of enoxaparin to antithrombin to form anti-Xa and elimination via heparinase-mediated metabolism and glomerular filtration. Following scaling, the PBPK model predicted real-world pediatric concentrations well, with an average fold error (standard deviation of the fold error) of 0.82 (0.23) and 0.87 (0.26) in children with and without obesity, respectively. PBPK model simulations revealed that children with obesity have at most 20% higher 4-hour anti-Xa concentrations under recommended, total body weight-based dosing compared to children without obesity owing to reduced weight-normalized clearance. Enoxaparin exposure was better matched across age groups and obesity status using fat-free mass weight-based dosing.

Characterizing Pharmacokinetics in Children With Obesity-Physiological, Drug, Patient, and Methodological Considerations

Childhood obesity is an alarming public health problem. The pediatric obesity rate has quadrupled in the past 30 years, and currently nearly 20% of United States children and 9% of children worldwide are classified as obese. Drug distribution and elimination processes, which determine drug exposure (and thus dosing), can vary significantly between patients with and without obesity. Obesity-related physiological changes, such as increased tissue volume and perfusion, altered blood protein concentrations, and tissue composition can greatly affect a drug's volume of distribution, which might necessitate adjustment in loading doses. Obesity-related changes in the drug eliminating organs, such as altered enzyme activity in the liver and glomerular filtration rate, can affect the rate of drug elimination, which may warrant an adjustment in the maintenance dosing rate. Although weight-based dosing (i.e., in mg/kg) is commonly practiced in pediatrics, choice of the right body size metric (e.g., total body weight, lean body weight, body surface area, etc.) for dosing children with obesity still remains a question. To address this gap, the interplay between obesity-related physiological changes (e.g., altered organ size, composition, and function), and drug-specific properties (e.g., lipophilicity and elimination pathway) needs to be characterized in a quantitative framework. Additionally, methodological considerations, such as adequate sample size and optimal sampling scheme, should also be considered to ensure accurate and precise top-down covariate selection, particularly when designing opportunistic studies in pediatric drug development. Further factors affecting dosing, including existing dosing recommendations, target therapeutic ranges, dose capping, and formulations constraints, are also important to consider when undergoing dose selection for children with obesity. Opportunities to bridge the dosing knowledge gap in children with obesity include modeling and simulating techniques (i.e., population pharmacokinetic and physiologically-based pharmacokinetic [PBPK] modeling), opportunistic clinical data, and real world data. In this review, key considerations related to physiology, drug parameters, patient factors, and methodology that need to be accounted for while studying the influence of obesity on pharmacokinetics in children are highlighted and discussed. Future studies will need to leverage these modeling opportunities to better describe drug exposure in children with obesity as the childhood obesity epidemic continues.

The Relationship between Initial Tacrolimus Metabolism Rate and Recipients Body Composition in Kidney Transplantation

There are several premises that the body composition of kidney transplant recipients may play a role in tacrolimus metabolism early after transplantation. The present study aimed at analyzing the relationship between the body composition parameters assessed by bioimpedance analysis (BIA) and initial tacrolimus metabolism. Immediately prior to transplantation, BIA using InBody 770 device was performed in 122 subjects. Tacrolimus concentration-to-dose (C/D) ratio was calculated based on the first blood trough level measurement. There was no difference in phase angle, visceral fat area, lean body mass index (LBMI) and the proportion of lean mass as a percentage of total body mass between the subgroups of slow and fast metabolizers. However, subjects with LBMI ≥ median value of 18.7 kg/m², despite similar initial tacrolimus dose per kg of body weight, were characterized by a significantly lower tacrolimus C/D ratio (median 1.39 vs. 1.67, respectively; p < 0.05) in comparison with the subgroup of lower LBMI. Multivariate regression analysis confirmed that age (r_partial = 0.322; p < 0.001) and LBMI (r_partial = −0.254; p < 0.01) independently influenced the tacrolimus C/D ratio. A LBMI assessed by BIA may influence the tacrolimus metabolism in the early post-transplant period and can be a useful in the optimization of initial tacrolimus dosing.

Biotransformation of soluble-insoluble lanthanum species and its induced NLRP3 inflammasome activation and chronic fibrosis

Soluble lanthanum (La)(Ⅲ) species that have been extensively used as fertilizers in agriculture can potentially get into the human body through foods and environment. Most soluble La(Ⅲ) species can rapidly transform into insoluble La(Ⅲ) species under physiological conditions, however, their potential biological behavior and chronic toxicity are rarely investigated. In the present study, insoluble La(Ⅲ) species formed under physiological condition were identified as nanoscale or microscale particles, and their major components were found to experience biotransformation process upon contact with cells. Insoluble La(Ⅲ) species could adhere to extracellular membrane or be internalized into cells, capable of activating a nucleotide-binding domain and leucine-rich repeat protein 3 (NLRP3) inflammasome. The underlying mechanism could be ascribed to K⁺ efflux and lysosomal rupture because these insoluble La(Ⅲ) species locating at extracellular membrane could reduce the unsaturated fatty acids of cell membrane, leading to potassium (K⁺) efflux, and those internalized into cells could consume the phospholipids of lysosomal membrane, leading to lysosomal rupture. Mice daily drinking soluble La(Ⅲ) species to mimic drinking tea process for 90 days were found to present NLRP3 inflammasome activation in liver and kidney, as a result of chronic fibrosis, which is potentially correlated to insoluble La(Ⅲ) species formation.

Influence of the Obesity Phenotype on the Adequacy of Antibiotic Prophylaxis with Cefoxitin for Obese Patients Undergoing Bariatric Surgery: Lessons Learnt and Future Considerations

BACKGROUND AND OBJECTIVES

A high inter-individual variability in pharmacokinetic parameters in obese patients is observed. The objective of this study was to evaluate the effect of obesity parameters on the pharmacokinetics of cefoxitin administered for antibiotic prophylaxis during bariatric surgery.

METHODS

This a secondary analysis of a pharmacokinetic study involving 174 obese patients scheduled for bariatric surgery and receiving a 4-g dose of cefoxitin. Blood samples were collected at incision and wound closure. The total plasma concentrations were assessed utilising a validated high-performance liquid chromatography-tandem mass spectrometry method. The pharmacokinetic and pharmacodynamic target was defined as an estimated free concentration of cefoxitin at the time of wound closure >8 mg/L. Specific evaluated obesity parameters were fat body mass, fat body mass/height², lean body mass, lean body mass/height², visceral adipose tissue and presence of a metabolic syndrome.

RESULTS

A total of 174 patients (median age 47 years) with a majority of women (75.3%) and a median BMI of 44 kg/m² were analysed. The percentage of patients who met the pharmacokinetic and pharmacodynamic target was 85.1%. In the whole population, a tendency to fail to reach the target was observed with a higher lean mass over height² [OR = 0.79; 95% CI (0.62-1.01); P = 0.060]. In the female subgroup, higher lean mass over height² [OR = 0.63; 95% CI (0.41-0.97); P = 0.037] and the presence of a metabolic syndrome [OR = 0.17; 95% CI (0.03-0.83); P = 0.030] were associated with failure to reach the pharmacokinetic and pharmacodynamic target.

CONCLUSION

Obese patients with a higher lean mass and a metabolic syndrome could constitute a subgroup at risk for cefoxitin under-dosage.

Tacrolimus Impairs Kupffer Cell Capacity to Control Bacteremia: Why Transplant Recipients Are Susceptible to Infection

BACKGROUND AND AIMS

Kupffer cells (KCs) are the resident intravascular phagocyte population of the liver and critical to the capture and killing of bacteria. Calcineurin/nuclear factor of activated T cells (NFAT) inhibitors (CNIs) such as tacrolimus are used to prevent rejection in solid organ transplant recipients. Although their effect on lymphocytes has been studied extensively, there are limited experimental data about if and how CNIs shape innate immunity, and whether this contributes to the higher rates of infection observed in patients taking CNIs.

APPROACH AND RESULTS

Here, we investigated the impact of tacrolimus treatment on innate immunity and, more specifically, on the capability of Kupffer cells (KCs) to fight infections. Retrospective analysis of data of >2,700 liver transplant recipients showed that taking calcineurin inhibitors such as tacrolimus significantly increased the likelihood of Staphylococcus aureus infection. Using a mouse model of acute methicillin-resistant S. aureus (MRSA) bacteremia, most bacteria were sequestered in the liver and we found that bacteria were more likely to disseminate and kill the host in tacrolimus-treated mice. Using imaging, we unveiled the mechanism underlying this observation: the reduced capability of KCs to capture, phagocytose, and destroy bacteria in tacrolimus-treated animals. Furthermore, in a gene expression analysis of infected KCs, the triggering receptor expressed on myeloid cells 1 (TREM1) pathway was the one with the most significant down-regulation after tacrolimus treatment. TREM1 inhibition likewise inhibited KC bacteria capture. TREM1 levels on neutrophils as well as the overall neutrophil response after infection were unaffected by tacrolimus treatment.

CONCLUSIONS

Our results indicate that tacrolimus treatment has a significant impact directly on KCs and on TREM1, thereby compromising their capacity to fend off infections.

Donor Age, Donor-Recipient Size Mismatch, and Kidney Graft Survival

BACKGROUND AND OBJECTIVES

Small donor and/or kidney sizes relative to recipient size are associated with a higher risk of kidney allograft failure. Donor and recipient ages are associated with graft survival and may modulate the relationship between size mismatch and the latter. The aim of this study was to determine whether the association between donor-recipient size mismatch and graft survival differs by donor and recipient age.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENT

We performed a retrospective cohort study of first adult deceased donor kidney transplantations performed between 2000 and 2018 recorded in the Scientific Registry of Transplant Recipients. We used multivariable Cox proportional hazards models to assess the association between donor-recipient body surface area ratio and death-censored graft survival, defined as return to dialysis or retransplantation. We considered interactions between donor-recipient body surface area ratio and each of recipient and donor age.

RESULTS

Among the 136,321 kidney transplant recipients included in this study, 23,614 (17%) experienced death-censored graft loss over a median follow-up of 4.3 years (interquartile range, 1.9-7.8 years). The three-way donor-recipient body surface area ratio by donor age by recipient age interaction was statistically significant (P=0.04). The magnitude of the association between severe size mismatch (donor-recipient body surface area ratio <0.80 versus ≥1.00) and death-censored graft survival was stronger with older donor age and recipient age. In all recipient age categories except the youngest (18-30 years), 5- and 10-year graft survival rates were similar or better with a size-mismatched donor aged <40 years than a nonsize-mismatched donor aged 40 years or older.

CONCLUSIONS

The association of donor-recipient size mismatch on long-term graft survival is modulated by recipient and donor age. Size-mismatched kidneys yield excellent graft survival when the donor is young. Donor age was more strongly associated with graft survival than size mismatch.

Population Pharmacokinetic Modeling of Cyclosporine Among Malaysian Renal Transplant Patients: An Evaluation of Methods to Handle Missing Doses in Conventional Drug-Monitoring Data

Cyclosporine is a primary drug in transplant immunosuppression regimens. It has a narrow therapeutic index and variable pharmacokinetic behavior. This study aimed to develop a population pharmacokinetic model of cyclosporine in Malaysian renal transplant recipients as well as to evaluate the performances of different methodsfor handling missing doses. A total of 2804 concentrationts predose and 2 hours after doses were collected retrospectively from 113 renal transplant patients on cyclosporine in Penang General Hospital. Model structure and pharmacokinetic parameters were estimated using nonlinear mixed-effects modeling software. Missing doses were handled using different methods to evaluate their performance. Covariate analysis was performed using stepwise forward addition (P < .05) followed by backward elimination (P < .001). Prediction-corrected visual predictive check and sampling-importance resampling methods were used to validate the final model. A 1-compartment model with first-order absorption and elimination best fitted the data. All methods to handle missing doses performed well with the missing dose method being superior to other methods and thus was applied in the final model. Cyclosporine clearance (CL/F) was estimated as 15.1 L/h, and volume of distribution (V/F) was 108 L. Postoperative time, sex, and calcium channel blockers were identified as significant covariates on CL/F, whereas sex and cholesterol level were identified as significant covariates on V/F. This is the first population pharmacokinetic model developed in Malaysian renal transplant patients using a large sample with an evaluation of different methods to handle missing doses in less informative conventional therapeutic drug-monitoring data.

Evaluating Lean Liver Volume as a Potential Scaler for In Vitro-In Vivo Extrapolation of Drug Clearance in Obesity Using the Model Drug Antipyrine

BACKGROUND

In vitro-in vivo extrapolation (IVIVE) of hepatic drug clearance (CL) involves the scaling of hepatic intrinsic clearance (CL_int,uH) by functional liver size, which is approximated by total liver volume (LV) as per the convention. However, in most overweight and obese patients, LV includes abnormal liver fat, which is not thought to contribute to drug elimination, thus overestimating drug CL. Therefore, lean liver volume (LLV) might be a more appropriate scaler of CL_int,uH.

OBJECTIVE

The objective of this work was to assess the application of LLV in CL extrapolation in overweight and obese patients (BMI >25 kg/m2) using a model drug antipyrine.

METHODS

Recently, a model to predict LLV from patient sex, weight, and height was developed and evaluated. In order to assess the LLV model's use in IVIVE, a correlation-based analysis was conducted using antipyrine as an example drug.

RESULTS

In the overweight group (BMI >25 kg/m2), LLV could describe 36% of the variation in antipyrine CL (R² = 0.36), which was >2-fold higher than that was explained by LV (R² = 0.17). In the normal-weight group (BMI ≤25 kg/m2), the coefficients of determination were 58% (R² = 0.58) and 43% (R²= 0.43) for LLV and LV, respectively.

CONCLUSION

The analysis indicates that LLV is potentially a more appropriate descriptor of functional liver size than LV, particularly in overweight individuals. Therefore, LLV has a potential application in IVIVE of CL in obesity.

Clinical Characteristics of 162 Patients with Drug-Induced Liver and/or Kidney Injury

Context

Drug-induced liver and kidney injuries are the most common adverse drug reactions in the clinic, and they have similar pathogeneses.

Aims

To analyze the clinical characteristics of patients with drug-induced liver and/or kidney injury.

Settings and Design

This was a retrospective study.

Methods and Materials

We analyzed data from 162 patients with drug-induced liver and/or kidney injury from 2008 to 2018 at the Chinese Rocket Force Characteristic Medical Center. Univariate and multivariate logistic analyses were performed on the drugs used, sex, age, weight, complications, and laboratory test results. Statistical analysis was performed using SPSS 25.0 statistical software.

Results

(1) The most common drugs causing organ injury in this study were antineoplastic drugs, antibiotics, traditional Chinese medicine, lipid-lowering drugs, and nonsteroidal anti-inflammatory drugs. (2) Among 22 patients with drug-induced liver and kidney injuries, 68.18% had a hepatocellular pattern, 13.64% had a mixed pattern, and 18.18% had a cholestatic pattern. Among the three groups, the P value for creatinine was 0.002. (3) The P value for urinary protein between the isolated kidney injury group and the liver and kidney injury group was 0.028. (4) Multivariate analysis showed that, among the drug-induced renal injury patients and all injury patients, those with a higher neutrophil percentage had a lower risk of liver injury (OR = 0.574, 95% CI: 0.390–0.846; OR = 0.545, 95% CI: 0.396–0.749).

Conclusions

(1) The serum creatinine level was higher in liver injury patients with the cholestatic pattern than in those with the hepatocellular or mixed pattern. (2) There was a significant difference in urinary protein between the isolated kidney and the liver and kidney injury groups. (3) Among patients with drug-induced organ injury, those with a higher neutrophils percentage had a lower risk of liver injury.

Impact of Baseline Nutrition and Exercise Status on Toxicity and Outcomes in Phase I and II Oncology Clinical Trial Participants

BACKGROUND

Malnutrition and physical inactivity are common in patients with advanced cancer and are associated with poor outcomes. There are increasing data that altered body composition is related to the pharmacokinetic properties of cancer therapies. These adverse conditions may impact outcomes in early-phase oncology clinical trials.

MATERIALS AND METHODS

We aimed to understand the relationships between baseline nutrition and exercise status with important trial endpoints including treatment-related toxicity and survival. Baseline assessments of nutrition and exercise status were conducted in patients prior to initiation of phase I and II oncology clinical trials. Patients were followed prospectively for the onset of adverse events. Tumor response and survival data were also obtained. Fisher's exact test and chi-square analysis were used to determine statistical significance. Kaplan-Meier curves were used to compare patient duration on study and survival.

RESULTS

One hundred patients were recruited, of whom 87 were initiating a phase I trial. Sixty percent were initiating trials studying immunotherapeutic agents. Critical malnutrition was found in 39% of patients, and 52% were sedentary. Patients who were malnourished had significantly increased rates of grade ≥ 3 toxicity (p = .001), hospitalizations (p = .001), and inferior disease control rate (p = .019). Six-month overall survival was significantly reduced in malnourished patients versus nonmalnourished patients (47% vs. 84%; p = .0003), as was median duration on study (48 days vs. 105 days; p = .047). Being sedentary at baseline was associated with decreased duration on study (57 days vs. 105 days; p = .019).

CONCLUSION

Malnutrition and sedentary lifestyle are highly prevalent in patients enrolling on early-phase oncology clinical trials and are associated with poor outcomes. The quality of data from these studies may be compromised as a result of these pre-existing conditions.

IMPLICATIONS FOR PRACTICE

Phase I and II trials are critical steps in the development of effective cancer therapeutics, yet only a small percentage of agents are ultimately approved for human cancer care. Despite increasing awareness of the interactions between malnutrition, sarcopenia, and treatment-related outcomes such as toxicity and response, these factors are not commonly incorporated into therapeutic decision making at the time of clinical trial consideration. Nutritional status and physical performance may be key biomarkers of mechanisms mediating treatment-related toxicity, dose modifications, risk of hospitalizations, and success of novel agents. This study advocates that a baseline nutritional assessment and early nutritional support may improve tolerability and response to experimental therapies.

A Pilot Study of Prediction of Creatinine Clearance by Ellipsoid Volumetry of Kidney Using Noncontrast Computed Tomography

Introduction

Aging is associated with a decline in kidney volume and function. The purpose of this study is to investigate a direct relationship between kidney volume and function in the elderly population and to challenge whether kidney function could be predictable by using the kidney volume.

Methods

We conducted a chart review of 366 patients who underwent abdominal computed tomography (CT) and renal function measurement prior to gastrointestinal surgery. The kidney volume was calculated by the ellipsoid method using a coronal section of noncontrast CT images.

Results

The patients were 72.2 ± 13.2 years of age, and 39.0% were female. Their average measured creatinine clearance (mCCr) was 72.0 ± 21.5 mL/min. The average kidney volume was 100.3 ± 27.6 cm³ in the right kidney and 109.3 ± 30.9 cm³ in the left. There was a significant positive correlation between the total kidney volume and mCCr. Multivariate regression analysis showed that age, diabetes mellitus, and total kidney volume were dependent variables with which to predict mCCr. The use of total kidney volume predicted mCCr of ≥50 mL/min with moderate accuracy (area under the curve = 0.782; 95% confidence interval = 0.692-0.871).

Conclusions

These results indicate a direct relationship between kidney volume and function in the elderly and might provide a pilot method which estimates the renal function using kidney morphology obtained from pre-existing CT images.

Population pharmacokinetics of cyclosporine A in Japanese renal transplant patients: comprehensive analysis in a single center

PURPOSE

Cyclosporine A (CyA), a potent immunosuppressive agent used in renal transplantation, has a narrow therapeutic window and a large variability in blood concentrations. This study aimed to develop a population pharmacokinetic (PPK) model of CyA in living-donor renal transplant patients at a single center and identify factors influencing CyA pharmacokinetics (PK).

METHODS

A total of 660 points (preoperative) and 4785 points (postoperative) of blood concentration data from 98 patients who underwent renal transplantation were used. Pre- and postoperative CyA model structure and PPK parameters were separately estimated with a non-linear mixed-effect model, and subsequently, covariate analysis of postoperative data were comprehensively estimated, including preoperative PK parameters.

RESULTS

A two-compartment model with first-order absorption and absorption lag time was selected in this study. Aspartate aminotransferase, body surface area (BSA), pretransplant area under the whole blood concentration-time curve/dose, and postoperative days were identified as the covariates on oral clearance. BSA was selected as a covariate of the distribution volume of the central compartment. In addition, diabetes mellitus was selected as a covariate of the first-order absorption rate.

CONCLUSIONS

This PPK study used the largest number of blood concentration data among previous reports of living-donor renal transplant patients. Moreover, all patients received the same immunosuppressive regimen in a single center. Therefore, the validity of the selected covariates is reliable with high precision. The developed PPK model and selected covariates provide useful information about factors influencing CyA PK and greatly contributes to the identification of the most suitable dosing regimen for CyA.

[Impact of cancer muscle mass loss on anticancer treatment toxicities]

Administration of targeted therapies as a flat dose and administration of chemotherapy based on body surface area do not take into account several important sources of inter-individual variation. These variations could be responsible partially for the occurrence of toxicity. Furthermore, the availability of high-resolution CT images in the record of cancer patients, from which key body composition information may be derived, allows us to study the relationship between body composition and toxicity. If many studies have highlighted this relationship, the mechanisms are not completely understood. There are some arguments for a pharmacokinetic hypothesis: low muscle mass i.e. sarcopenia, is associated with high drug plasma concentration which in turn is associated with an increase in the incidence of toxicity. The other hypothesis is that sarcopenic patients have a higher susceptibility to medical events leading to an increase in chemotherapy toxicity. This concept of frailty was widely described in studies in the elderly. This body composition analysis opened a huge area of research and many questions still need to be resolved. Defining the cut-offs values for low muscle mass is important since in most of the studies, the cut-offs values used were defined using survival studies. What could be the physiological link between cut-off values defined by survival studies and chemotherapy toxicities? Authors also used the median values, the level which predicted the occurrence of toxicity most accurately and sometimes the measure of the psoas. The final and crucial question is the capacity of reducing toxicity by body composition based dosing.

Comparative Toxicity by Sex Among Children Treated for Acute Lymphoblastic Leukemia: A Report From the Children's Oncology Group

BACKGROUND

Epidemiologic studies find sex-based differences in incidence, survival, and long-term outcomes for children with cancer. The purpose of this study was to determine whether male and female patients differ with regard to acute treatment-related toxicities.

PROCEDURES

We reviewed data collected on the Children's cancer group (CCG) high-risk acute lymphoblastic leukemia (ALL-HR) study (CCG-1961), and compared male and female patients' toxicity incidence and related variables in the first four phases of treatment. Similar analyses were performed with standard-risk ALL (ALL-SR) patients enrolled in CCG-1991.

RESULTS

Among ALL-HR patients, females had significantly more hospital days, delays in therapy, grade 3 or 4 toxicities (e.g., gastrointestinal, liver), and supportive care interventions (e.g., transfusions, intravenous antibiotics) than males. Females were significantly more likely to have died of treatment-related causes than males (Hazard ratio = 2.8, 95%CI = 1.5-5.3, P = 0.002). Five months after beginning the treatment, the cumulative incidence of treatment-related deaths was 2.6% for females and 1.2% for males. Similar disparities were found among ALL-SR patients, with females experiencing significantly more hospital days and treatment-related toxicities than males.

CONCLUSIONS

This study complements cancer survivorship studies that also report an increase in treatment-related late effects among females. Risk profiles appear to be different for male and female patients, with females having greater risk of developing both acute and long-term treatment-related toxicities. The underlying biological mechanisms for these sex differences are poorly understood and warrant further study in order to determine how sex-based outcome disparities can be addressed in future clinical trials and practice.

Verification of relationships between anthropometric variables among ureteral stents recipients and ureteric lengths: a challenge for Vitruvian-da Vinci theory

Objective

To determine and verify how anthropometric variables correlate to ureteric lengths and how well statistical models approximate the actual ureteric lengths.

Materials and methods

In this work, 129 charts of endourological patients (71 females and 58 males) were studied retrospectively. Data were gathered from various research centers from North and South America. Continuous data were studied using descriptive statistics. Anthropometric variables (age, body surface area, body weight, obesity, and stature) were utilized as predictors of ureteric lengths. Linear regressions and correlations were used for studying relationships between the predictors and the outcome variables (ureteric lengths); P-value was set at 0.05. To assess how well statistical models were capable of predicting the actual ureteric lengths, percentages (or ratios of matched to mismatched results) were employed.

Results

The results of the study show that anthropometric variables do not correlate well to ureteric lengths. Statistical models can partially estimate ureteric lengths. Out of the five anthropometric variables studied, three of them: body frame, stature, and weight, each with a P<0.0001, were significant. Two of the variables: age (R²=0.01; P=0.20) and obesity (R²=0.03; P=0.06), were found to be poor estimators of ureteric lengths. None of the predictors reached the expected (match:above:below) ratio of 1:0:0 to qualify as reliable predictors of ureteric lengths.

Conclusion

There is not sufficient evidence to conclude that anthropometric variables can reliably predict ureteric lengths. These variables appear to lack adequate specificity as they failed to reach the expected (match:above:below) ratio of 1:0:0. Consequently, selections of ureteral stents continue to remain a challenge. However, height (R²=0.68) with the (match:above:below) ratio of 3:3:4 appears suited for use as estimator, but on the basis of decision rule. Additional research is recommended for stent improvements and ureteric length determinations.

Impact of obesity on sepsis mortality: A systematic review

PURPOSE

Sepsis and severe sepsis are the most common cause of death among critically ill patients admitted in medical intensive care units. As more than one-third of the adult population of the United States is obese; we undertook a systematic review of the association between obesity and mortality among patients admitted with sepsis, severe sepsis, or septic shock.

MATERIALS AND METHODS

A systematic review was conducted to identify pertinent studies using a comprehensive search strategy. Studies reporting mortality in obese patients admitted with sepsis were identified.

RESULTS

Our initial search identified 183 studies of which 7 studies met our inclusion criteria. Three studies reported no significant association between obesity and mortality, 1 study observed increased mortality among obese patients, whereas 3 studies found lower mortality among obese patients.

CONCLUSION

Our review of the current clinical evidence of association of obesity with sepsis mortality revealed mixed results. Clinicians are faced with a number of challenges while managing obese patients with sepsis and should be mindful of the impact of obesity on antibiotics administration, fluid resuscitation, and ventilator management. Further studies are needed to elicit the impact of obesity on mortality in patients with sepsis.

Impact of sarcopenia on the prognosis and treatment toxicities in patients diagnosed with cancer

PURPOSE OF REVIEW

High-resolution computed tomography (CT) imaging routinely performed for cancer follow-up provides valuable information on body composition. The influence of body composition on outcomes and the occurrence of toxicities can therefore be explored in cancer patients. This review describes recent findings regarding the prognostic impact of skeletal muscle mass (SMM) on chemotherapy toxicity.

RECENT FINDINGS

The higher risk of toxicity associated with low SMM (i.e. sarcopenia) was first described for 5-fluorouracil-based chemotherapy toxicity in colon cancer patients before being increasingly studied, not only in the case of body surface area-adapted chemotherapy in breast cancer but also in various cancers treated with targeted therapies. The underlying mechanisms are still being debated; sarcopenia could act on pharmacokinetic parameters and/or sarcopenic patients could be more susceptible to adverse medical events including chemotherapy toxicity.

SUMMARY

Evidence for a strong link between sarcopenia and chemotherapy toxicity is increasing. SMM may not be the only body composition parameter involved. Muscle function assessed by measuring muscle density and the BMI could be of interest. The ultimate purpose is to better identify patients at higher risk of toxicity and to reduce toxicity through body composition-based dosing.

Low skeletal muscle is associated with toxicity in patients included in phase I trials

BACKGROUND

Low muscle mass has been associated with chemotherapy toxicity. We conducted this prospective study to evaluate the effects of body composition on the occurrence of toxicity in phase I trials.

PATIENTS AND METHODS

Patients were consecutively enrolled irrespective of the type of tumor or the type of drug. The Skeletal Muscle Index (SMIndex) and visceral and subcutaneous adipose tissue were assessed with computed tomography imaging by measuring cross-sectional areas of the tissues (cm(2)/m(2)). Dose-limiting toxicity (DLT) corresponded to toxicities occurring during the 1(st) cycle that necessitated dose reduction, postponement or interruption of drug administration and severe toxicity events (STE) corresponded to DLT or permanent treatment withdrawal due to toxicity.

RESULTS

93 patients were evaluated. Ten percent of patients experienced DLT and had a lower SMIndex: 40.8 ± 4.6 vs. 48.1 ± 9.6 cm(2)/m(2) (p = 0.01). STE occurred in 14 % of the patients. The only factor associated with STE was a low SMIndex: 42.4 ± 5.8 vs. 48.4 ± 9.7 cm(2)/m(2) (p = 0.02). STE were observed in 25.5 % of the patients when the SMIndex was below the median value compared to 6.5 % of patients with a high SMIndex (p = 0.02).

CONCLUSION

Muscle mass is a critical predictor of severe toxicity events in phase I patients, suggesting that sarcopenia may be considered in assessing patients for eligibility of phase-1 studies.

Pharmacokinetics of drugs in cachectic patients: a systematic review

Cachexia is a weight-loss process caused by an underlying chronic disease such as cancer, chronic heart failure, chronic obstructive pulmonary disease, or rheumatoid arthritis. It leads to changes in body structure and function that may influence the pharmacokinetics of drugs. Changes in gut function and decreased subcutaneous tissue may influence the absorption of orally and transdermally applied drugs. Altered body composition and plasma protein concentration may affect drug distribution. Changes in the expression and function of metabolic enzymes could influence the metabolism of drugs, and their renal excretion could be affected by possible reduction in kidney function. Because no general guidelines exist for drug dose adjustments in cachectic patients, we conducted a systematic search to identify articles that investigated the pharmacokinetics of drugs in cachectic patients.

Body composition in chemotherapy: the promising role of CT scans

PURPOSE OF REVIEW

Reducing cancer-treatment toxicity was a largely ignored research agenda, which is now emerging as an active area of investigation. Studies of human body composition using computerized tomography scans have provided proof-of-concept that variability in drug disposition and toxicity profiles may be partially explained by different features in body composition.

RECENT FINDINGS

Collectively, studies suggest that skeletal muscle depletion (regardless of body weight) is an independent predictor of severe toxicity, affecting cancer treatment and its outcomes. Although precise mechanisms are unknown, pharmacokinetic parameters such as variations in volume of distribution and increased drug exposure may explain such findings.

SUMMARY

Computerized tomography scans are readily available in clinical databases of diagnostic images and provide feasible, reliable, and highly differentiated measurements of body composition. These images should be used to optimize screening and management of patients in order to prevent severe toxicity, and to improve the efficacy and cost-efficiency of chemotherapy treatments.

Defining sarcopenia: the impact of different diagnostic criteria on the prevalence of sarcopenia in a large middle aged cohort

Sarcopenia, low muscle mass, is an increasing problem in our ageing society. The prevalence of sarcopenia varies extremely between elderly cohorts ranging from 7% to over 50%. Without consensus on the definition of sarcopenia, a variety of diagnostic criteria are being used. We assessed the degree of agreement between seven different diagnostic criteria for sarcopenia based on muscle mass and handgrip strength, described in literature. In this cross-sectional study, we included men (n=0325) and women (n=0329) with complete measurements of handgrip strength and body composition values as measured by bioimpedance analysis within the Leiden Longevity Study. Prevalence of sarcopenia was stratified by gender and age. In men (mean age 64.5 years), the prevalence of sarcopenia with the different diagnostic criteria ranged from 0% to 20.8% in the lowest age category (below 60 years), from 0%to 31.2% in the middle (60 to 69 years) and from 0% to 45.2% in the highest age category (above 70 years). In women (mean age 61.8 years), the prevalence of sarcopenia ranged from 0% to 15.6%, 0% to 21.8% and 0% to 25.8% in the lowest, middle and highest age category, respectively. Only one participant (0.2%) was identified having sarcopenia according to all diagnostic criteria that marked prevalence above 0%. We conclude that the prevalence of sarcopenia is highly dependent on the applied diagnostic criteria. It is necessary to reach a consensus on the definition of sarcopenia in order to make studies comparable and for implementation in clinical care.

Pharmacokinetics of Antimicrobials in Obese Children

INTRODUCTION

Childhood obesity is common and results in substantial morbidity. The most commonly prescribed drugs in obese children are antibiotics. However, physiologic changes associated with childhood obesity can alter antibiotic pharmacokinetics and optimal body size measures to guide dosing in his population are ill defined. This combination can result in therapeutic failures or drug-related toxicities. This review summarizes pharmacokinetic information for antibiotics in obese children and implications for dosing.

METHODS

We conducted a comprehensive literature search of PubMed, EMBASE, and International Pharmaceutical Abstracts to identify pharmacokinetic studies of antimicrobial agents in obese children. We included the following search terms: obesity, pharmacokinetics, pharmacodynamics, drug toxicity, dosing, anti-infective agents, antiviral agents, and antifungal agents.

RESULTS

We identified four pharmacokinetic studies of antibiotics in obese children: one for cefazolin and tobramycin, one for gentamicin, and two for vancomycin. Only the cefazolin/tobramycin trial was prospective. The drugs studied differ in their tissue and body water distribution characteristics. Two of the studies (tobramycin and gentamicin) reported pharmacokinetic differences and required dosing modifications in obese children.

DISCUSSION

The lack of pharmacokinetic studies in obese children is pronounced. The scarcity of pharmacokinetic data limits the ability to predict drug disposition using drug physicochemical properties and impedes a rational approach to selection of appropriate body size measures for dosing. Given this knowledge gap, additional trials in obese children are urgently needed and is a public health concern.

CONCLUSION

Pharmacokinetic studies of antimicrobials in obese children are desperately needed to guide dosing and avoid therapeutic failures or unwanted toxicities.

Pharmacokinetics of tacrolimus according to body composition in recipients of kidney transplants

Background

Currently, the dosage of tacrolimus used after transplantation is based on the patient's body weight. However, there is a low correlation between body weight and body composition in kidney transplant recipients. In this study, we evaluate the pharmacokinetics of tacrolimus according to body composition in 18 Korean kidney transplant recipients with stable graft function.

Methods

Body composition parameters were calculated using bioelectrical impedance analysis. Pharmacokinetic profiles were determined 0, 1, 2, 3, and 4 hours after treatment with tacrolimus and were compared between high- and low-level median body composition groups. The values of C₀, C₁, C₂, C₃, and C₄ were used in determining an abbreviated area under the curve (AUC) for tacrolimus.

Results

The mean body mass index (BMI) and body composition values were as follows: BMI, 24.3 kg/m²; lean mass, 49.8 kg; and fat mass, 17.4 kg. There were no statistical differences in pharmacokinetic profiles between groups with different BMIs. However, the C₀ and C₄ in the high-fat group were significantly elevated compared with those of the low-fat group (P=0.024 and 0.031, respectively). Furthermore, the C₀, C₂, C₃, and C₄ and the AUC were significantly different between the two lean mass groups (P=0.007, 0.038, 0.047, 0.015, and 0.015, respectively). Other variables, such as waist circumference and arm muscle circumference, did not differentiate between the pharmacokinetic profiles of tacrolimus.

Conclusion

Taken together, these data suggest that tacrolimus dose monitoring based on body composition may provide adequate dosage leading to favorable long-term outcomes.

Determinants and functional significance of renal parenchymal volume in adults

BACKGROUND AND OBJECTIVES

The significance of renal parenchymal volume and the factors that influence it are poorly understood.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Renal parenchymal volume (RPV) was measured on contrast-enhanced CT scans after exclusion of sinus fat and vessels in 224 healthy subjects evaluated as kidney donors and in a separate cohort of 22 severely obese individuals before and after 6 months of weight loss. GFR was measured by iohexol clearance in 76 of the transplant donors. RPV was correlated with age, GFR, and various anthropometric parameters.

RESULTS

In potential transplant donors, RPV correlated with body surface area (BSA; r = 0.68) and was 7% larger in men but did not vary with age or race. Gender and body size were independent determinants of RPV. RPV correlated well with GFR (r = 0.62) and accounted for almost all of the variability in a model of GFR that included age, race, gender, and body surface area. GFR correlated more strongly with RPV than with creatinine-based equations. The same relationship between RPV and BSA was observed in obesity, and RPV decreased with weight loss.

CONCLUSIONS

In healthy adults younger than 65 years, renal parenchymal volume is governed by body size and gender but not age or race and is strongly correlated with GFR. This indicates that renal parenchymal volume varies to meet metabolic demand and is closely linked to renal function.

Drug disposition in obesity and protein–energy malnutrition

Clinical response to medication can differ between patients. Among the known sources of variability is an individual's nutrition status. This review defines some pharmacokinetic terms, provides relevant body size metrics and describes the physiologic influences of protein–energy malnutrition and obesity on drug disposition. Weight-based drug dosing, which presumes a healthy BMI, can be problematic in the protein–energy malnourished or obese patient. The use of total body weight, lean body weight, or an adjusted body weight depends on the drug and how it is differently handled in malnutrition or obesity. Most of the recognized influences are seen in drug distribution and drug elimination as a result of altered body composition and function. Distribution characteristics of each drug are determined by several drug-related factors (e.g. tissue affinity) in combination with body-related factors (e.g. composition). Drug elimination occurs through metabolic and excretory pathways that can also vary with body composition. The current data are limited to select drugs that have been reported in small studies or case reports. In the meantime, a rational approach to evaluate the potential influences of malnutrition and obesity can be used clinically based on available information. Antimicrobials are discussed as a useful example of this approach. Further advancement in this field would require collaboration between experts in body composition and those in drug disposition. Until more data are available, routine monitoring by the clinician of the protein–energy malnourished or obese patient receiving weight-based drug regimens is necessary.

An exploratory study of body composition as a determinant of epirubicin pharmacokinetics and toxicity

PURPOSE

Although body composition has emerged as an important predictor of drug efficacy and toxicity, explanations for this association are unclear. Our goal was to investigate relationships between lean body mass (LBM), liver size/function and epirubicin pharmacokinetics (PK) and toxicity.

METHODS

Data from a clinical study (n = 24) of patients with breast cancer receiving adjuvant intravenous FE(100)C chemotherapy were used to examine relationships between LBM, liver size, and epirubicin clearance. Muscle tissue and liver mass were measured by analysis of computerized tomography cross-sectional images, and an extrapolation of muscle mass to total LBM compartment was employed. Population PK analysis of epirubicin was undertaken to test effects of body composition on epirubicin clearance and area under the curve (AUC).

RESULTS

Estimated LBM was extremely variable in this cohort ranging from 32.9 to 67.3 kg. LBM was associated with neutrophil nadir (r = 0.5, P = 0.023), and mean LBM was lower for patients presenting with toxicity compared to those where toxicity was absent (41.6 vs. 56.2 kg, P = 0.002); 33% of variance in clearance was explained by LBM and aspartate aminotransferase (AST). Liver mass was not related to epirubicin clearance likely due to larger livers presenting with larger fat content, but liver attenuation (degree of fat infiltration) and AST were associated with AUC.

CONCLUSION

To our knowledge, this is the first study to examine relationships between LBM, liver mass/function and epirubicin PK and toxicity. This exploratory work investigates the notion of organs and tissues having distinctive contributions to the distribution and metabolism of antineoplastic drugs.

Application of fixed exponent 0.75 to the prediction of human drug clearance: an inaccurate and misleading concept

Considering the controversy surrounding the exponent of 0.75 for the prediction of human drug clearance and lack of any systematic evaluation of the aforementioned proposal, the objective of this study was to determine whether the exponent 0.75 is indeed the most suitable exponent for the prediction of human drug clearance as compared to allometric scaling using the rule of exponents (ROE). Three methods were used to predict human drug clearance. Besides evaluating the exponent of 0.75, an arbitrarily selected exponent of 0.65 was also tested. ROE was also used to predict human drug clearance, and predicted values by all three methods were compared with observed human drug clearance. The results indicate that the exponent 0.75 is not the best approach for the prediction of human drug clearance. Both exponents 0.75 and 0.65 predicted human drug clearance with uncertainty, although on average the prediction of human drug clearance by 0.65 was better than the exponent 0.75. ROE provided far more accurate prediction of human drug clearance than either of the exponents. Although exponent 0.75 occasionally provided a good prediction of human drug clearance for a given drug for a given species, overall, the method is highly erratic and unreliable.

Assessment of the optimal temporal window for intravenous CT cholangiography

The optimal temporal window of intravenous (IV) computed tomography (CT) cholangiography was prospectively determined. Fifteen volunteers (eight women, seven men; mean age, 38 years) underwent dynamic CT cholangiography. Two unenhanced images were acquired at the porta hepatis. Starting 5 min after initiation of IV contrast infusion (20 ml iodipamide meglumine 52%), 15 pairs of images at 5-min intervals were obtained. Attenuation of the extrahepatic bile duct (EBD) and the liver parenchyma was measured. Two readers graded visualization of the higher-order biliary branches. The first biliary opacification in the EBD occurred between 15 and 25 min (mean, 22.3 min +/- 3.2) after initiation of the contrast agent. Biliary attenuation plateaued between the 35- and the 75-min time points. Maximum hepatic parenchymal enhancement was 18.5 HU +/- 2.7. Twelve subjects demonstrated poor or non-visualization of higher-order biliary branches; three showed good or excellent visualization. Body weight and both biliary attenuation and visualization of the higher-order biliary branches correlated significantly (P<0.05). For peak enhancement of the biliary tree, CT cholangiography should be performed no earlier than 35 min after initiation of IV infusion. For a fixed contrast dose, superior visualization of the biliary system is achieved in subjects with lower body weight.

Prediction of Drug Clearance in Children: Impact of Allometric Exponents, Body Weight, and Age

In recent years, with the advent of pediatric exclusivity and requirements for conducting clinical studies involving children, emphasis has been placed on finding safe and efficacious doses of drugs for children. It has been suggested that one can predict the clearance (CL) of a drug in children according to this equation: CL in the child = Adult CL * (Weight of the child/70)0.75. In light of the controversy surrounding the exponent of 0.75 for the prediction of clearance, the objectives of the study were as follows: (1) to develop allometric equations based on body weight or age to predict clearance of a drug in children; (2) to determine if the fixed exponent of 0.75 is a suitable exponent for the prediction of clearance in children from adult data, as compared with the allometric exponent generated for individual drugs; (3) to determine if the allometric equation generated on the basis of age predicts clearance in children better or worse than the allometric equation generated on the basis of body weight; and (4) to propose a new approach based on the findings of the current evaluation. Five methods were used to predict drug clearance in children. Six drugs were used in the evaluation, and drug clearance in each child was predicted for a given drug. Besides evaluating the exponent of 0.75, allometric equations were developed using double log plots of clearance versus body weight or age. The exponents of the allometric equations were then used to predict drug clearance by replacement of 0.75 in the aforementioned equation. The results of the study indicate that 0.75 is not the best exponent for prediction of drug clearance in children, and a more suitable approach is to develop an allometric relationship for a given drug in children. For all 6 drugs, there were 77 children in whom the clearance was predicted. There were 48 observations for which error in the predicted clearance was 50% or more with use of the exponent 0.75, whereas there were only 13 observations with prediction error > or = 50% when 0.75 was replaced by an allometric exponent developed for a given drug. In order to predict drug clearance in children with reasonable accuracy, an allometric equation should be developed for every drug and the exponent 0.75 should be replaced by the exponent of the allometric equation developed for that drug.

Prediction of drug clearance in children from adults: a comparison of several allometric methods

AIMS

In recent years with the advent of paediatric exclusivity and requirements to conduct clinical studies in children, the current emphasis is to find a safe and efficacious dose of a drug in children. It has been suggested that one can predict the clearance of a drug in children according to the equation: CL in the child=adult CLx(weight of the child/70)0.75. Considering the controversy surrounding the exponent of 0.75 for the prediction of clearance and lack of any systematic evaluation of the aforementioned proposal, the objectives of the study were as follows: (i) to determine if indeed the exponent 0.75 is the most suitable exponent for the prediction of clearance in children from adult data; (ii) to explore and search for other exponents that are more accurate or as good as 0.75; and (iii) to propose a new approach (if any) based on the findings of the current evaluation.

METHODS

Six methods were used to predict clearance of drugs in children from adult data. Besides evaluating the exponent of 0.75, exponents of 0.80, 0.85 and 1.0 were also evaluated. An empirical approach based on kidney and liver weights was also examined. Based on the results of five methods, a sixth method was introduced.

RESULTS

The results of the study indicate that no single method is suitable for all drugs or for all age groups. The exponents 0.75, 0.80, and 0.85 provided the same degree of accuracy or error in the prediction of clearance in children.

CONCLUSIONS

Since no single method is suitable for all drugs or for all age groups. A combination of approaches is suggested which may help in improving the prediction of clearance in children from adult data.

AGE AND LEAN BODY WEIGHT RELATED GROWTH CURVES OF KIDNEYS USING REAL-TIME 3-DIMENSIONAL ULTRASOUND IN PEDIATRIC UROLOGY

PURPOSE

Kidney volume and growth are important parameters for evaluating and monitoring several diseases in pediatric urology. Studies have shown the significant relationship of kidney volume and function. Until now normal values of kidney size and growth have been based on 2-dimensional measurements combined with arithmetic formulas for the ellipsoid. Real-time 3-dimensional (RT3D) ultrasound is a new imaging modality. Moreover, corresponding software allows RT3D imaging within a short time exposure. We created nomograms of kidney volumes for routine diagnostics that could serve as a standard for pediatric renal growth assessment, decreasing the need for invasive tests.

MATERIALS AND METHODS

RT3D volumetry of a total of 620 kidneys in 310 children with a homogeneous age distribution (range newborn to 10 years) and without any evidence of renal impairment was performed using a Voluson 730 (Kretztechnik, Ultrasound, Zipf, Austria) system. Polynomial regression analysis was applied for the prediction and estimation of growth variables of kidney volumes as a function of gender, age, body mass index or lean body weight.

RESULTS

Stepwise multiple regression analysis incorporating the different independent variables indicated with significant correlation that age and lean body weight were the strongest predictors of kidney volumes in children.

CONCLUSIONS

This study shows that RT3D ultrasound is particularly qualified for evaluating kidney volume in pediatric urology. RT3D volumetry is suitable for monitoring renal growth, reflecting kidney function. Furthermore, this methodology is feasible in screening programs assessing congenital urogenital diseases.

The effects of renal impairment on the pharmacokinetics and safety of fosfluconazole and fluconazole following a single intravenous bolus injection of fosfluconazole

AIMS

Fosfluconazole is a phosphate prodrug of fluconazole (FLCZ). This study was conducted to investigate the effect of renal impairment on the pharmacokinetics of fosfluconazole and FLCZ, and to assess the safety and toleration of fosfluconazole following a single intravenous bolus injection of fosfluconazole in subjects with normal and impaired renal function.

METHODS

In an open, parallel-group, two-centre study, subjects with normal and impaired renal function received a single 1000-mg bolus intravenous injection of fosfluconazole. Subjects were categorized as Normal (> 80 ml min(-1)), Mild (51-80 ml min(-1)), Moderate (30-50 ml min(-1)) or Severe (< 30 ml min(-1)) impairment group according to their Cockcroft and Gault creatinine clearance (CLcr) values. Concentrations of fosfluconazole and FLCZ were determined in plasma and urine samples taken up to 240 h and 48 h postdose, respectively.

RESULTS

Fosfluconazole plasma concentrations were very similar across the four groups, and there was no apparent relationship between any of the fosfluconazole pharmacokinetic parameters with increasing renal impairment. The conversion of fosfluconazole to FLCZ was unaffected by the degree of renal impairment. Only small amounts of fosfluconazole were excreted in the urine suggesting almost complete conversion to FLCZ. FLCZ concentrations were still detected in plasma after 240 h postdose and remained higher at the later sampling times in subjects in the Moderate and Severe groups. The area under the plasma concentration vs. time curve between time zero and infinity (AUC), the terminal elimination phase half-life (t(1/2)) and the mean residence time (MRT) of FLCZ all increased with the degree of renal impairment. The ratios (95% confidence interval) for AUC (Renal impairment group/Normal group) were 112.8% (89.5, 142.1), 240.6% (128.2, 451.4) and 355.1% (259.3, 486.3) for the Mild, Moderate and Severe impairment groups, respectively. There was a linear relationship between CLcr with AUC, t(1/2), MRT and the total plasma clearance of FLCZ (CL/F). Both the amount excreted over 48 h in the urine and the renal clearance of FLCZ decreased with an increase in renal impairment. The adverse events reported were mild to moderate in intensity, and there was no observed relationship with impairment group. There were no severe or serious adverse events, and in general fosfluconazole was well tolerated.

CONCLUSIONS

The pharmacokinetics of fosfluconazole, including its efficient conversion into FLCZ, were unaffected by renal impairment. For FLCZ, there was a significant linear relationship between CLcr and AUC, t(1/2), MRT and CL/F, with AUC, t(1/2) and MRT increasing and CL/F decreasing as renal impairment increased. The dose adjustment used for FLCZ (half normal dose for patients with CLcr at <or= 50 ml min(-1)) can be applied to fosfluconazole as well. There were no safety concerns for any subject in this study, and fosfluconazole and FLCZ were well tolerated by all the treatment groups.

Dosing of medications in morbidly obese patients in the intensive care unit setting

OBJECTIVE

To derive recommendations for the dosing of commonly used medications in the morbidly obese patient in the ICU.

DATA SOURCES

Articles were obtained through computerized searches involving MEDLINE. The bibliographies of retrieved publications and textbooks were reviewed for additional references.

STUDY SELECTION

All studies involving the pharmacokinetics or pharmacodynamics of medications in obese subjects or patients.

DATA EXTRACTION

The emphasis was on studies involving morbidly obese patients but, in the absence of such data, investigations involving lesser forms of obesity were extracted.

DATA SYNTHESIS

There is a paucity of data upon which to make recommendations for dosing commonly used medications in the morbidly obese patient in the ICU, although recommendations were provided based on the available information.

CONCLUSIONS

There is clearly a need for more investigations involving dosing regimens of medications in the morbidly obese population. Until such studies are available, the clinician must try to derive the best dosing regimens for medications based on the limited pharmacokinetic data available for some agents and clinical judgement.

Body surface area as a determinant of pharmacokinetics and drug dosing

Body surface area (BSA) was introduced into medical oncology in order to derive a safe starting dose for phase I studies of anticancer drugs from preclinical animal toxicology data. It is not clear however, as to why dosing by BSA was extended to the routine dosing of antineoplastic agents. Several formulas exist to estimate BSA, but the formula derived by DuBois and DuBois is the one used in adult medical oncology. This formula was derived based on data from only nine patients; subsequent attempts to validate the formula have found the DuBois formula to either over or underestimate the actual determined BSA. While cardiac output does correlate with BSA, the relationship between BSA and other physiologic measures relevant for drug metabolism and disposition, such as, renal and hepatic function, is weak or nonexistent. Further only epirubicin, etoposide, and carboplatin have been studied to determine if dosing by BSA would reduce interpatient variability, and none of these drugs were found to have significant relationships between their pharmacokinetics and BSA. Future clinical trials of new agents should not presume that dosing based on BSA reduces interpatient variability. Studies should examine the role, if any, BSA has in dosing new chemotherapeutic agents in initial phase I studies.

Pharmacokinetics of phenylbutazone and its metabolite oxyphenbutazone in miniature donkeys

OBJECTIVE

To describe the pharmacokinetics of phenylbutazone and oxyphenbutazone after IV administration in miniature donkeys.

ANIMALS

6 clinically normal miniature donkeys.

PROCEDURE

Blood samples were collected before and 5, 10, 20, 30, 45, 60, 90, 120, 180, 240, 300, 360, and 480 minutes after IV administration of phenylbutazone (4.4 mg/kg of body weight). Serum was analyzed in triplicate by use of high-performance liquid chromatography for determination of phenylbutazone and oxyphenbutazone concentrations. The serum concentration-time curve for each donkey was analyzed separately to estimate model-independent pharmacokinetic variables.

RESULTS

Serum concentrations decreased rapidly after IV administration of phenylbutazone, and they reached undetectable concentrations within 4 hours. Values for mean residence time ranged from 0.5 to 3.0 hours (median, 1.1 hour), whereas total body clearance ranged from 4.2 to 7.5 ml/kg/min (mean, 5.8 ml/kg/min). Oxyphenbutazone appeared rapidly in the serum; time to peak concentration ranged from 13 to 41 minutes (mean, 26.4 minutes), and peak concentration in serum ranged from 2.8 to 4.0 mg/ml (mean, 3.5 microg/ml).

CONCLUSION AND CLINICAL RELEVANCE

Clearance of phenylbutazone in miniature donkeys after injection of a single dose (4.4 mg/kg, IV) is rapid. Compared with horses, miniature donkeys may require more frequent administration of phenylbutazone to achieve therapeutic efficacy.

Pharmacokinetics of recombinant factor IX in relation to age of the patient: implications for dosing in prophylaxis

The aims of this study were to investigate possible age-related changes in the disposition of factor IX procoagulant activity (FIX:C) after administration of recombinant factor IX (rFIX) and to translate the pharmacokinetic findings into suggestions for dosing of rFIX during prophylactic treatment of haemophilia B. Pharmacokinetic data were available from a previous study on 56 patients, aged 4-56 years (one of whom was excluded from analysis). FIX:C curves during prophylactic dosing were computer-simulated from the single-dose data. Clearance and volume of distribution at steady state of FIX:C increased linearly with body weight of the patients, consequently increasing during childhood and adolescence but remaining fairly constant during adulthood. The terminal half-life of FIX:C showed no correlation with age, while in vivo recovery (in U dL(-1) per U kg(-1) given) tended to increase. Computer-predicted trough levels of exogenous FIX:C during repeated doses of rFIX (50 U kg(-1)) and, conversely, doses (in U kg(-1)) needed to maintain a 1-U dL(-1) trough level showed little or no dependence on age. There was considerable interindividual variation in disposition and required doses of rFIX, emphasizing the need for individual dose titration. Dosing of rFIX according to lean body mass instead of body weight did not reduce this variability. During prophylaxis a 1-U dL(-1) trough level can normally be maintained by dosing every 2-3 days, the former schedule resulting in, on average, a 45% lower consumption of rFIX.