Mara Medeiros

Methods of assessing renal function

Accurate assessment of renal function is critical for appropriate drug dosing of renally excreted compounds. Glomerular filtration rate (GFR) is considered the best marker of kidney function. Inulin clearance forms the gold standard for measuring GFR, both in adults and in children. The method is invasive, cumbersome, and smaller children require urinary catheterization for accurate timed urine collections. Nuclear medicine methods replaced inulin clearance in the 1970s after 51Cr EDTA clearance was introduced. Inulin has no plasma protein binding, whereas all commonly used radioisotopes have a small amount of plasma protein binding that leads to lower values. Only iohexol does not have significant plasma protein binding. The underestimation due to plasma protein binding is partially offset by overestimation due to the use of non-compartmental pharmacokinetic modeling of the plasma disappearance of the radioisotope. The problem could be overcome with a urinary nuclear medicine clearance method, but these have not been validated in children. Endogenous markers of GFR include serum creatinine and low molecular weight proteins such as cystatin C and beta-trace protein. Of these, estimation of GFR using cystatin C appears to be the most promising, although its accuracy in pregnancy and in the neonatal period may be limited.

Self-Management and Transition Readiness Assessment: Development, Reliability, and Factor Structure of the STARx Questionnaire

INTRODUCTION The Self-Management and Transition to Adulthood with Rx=Treatment (STARx) Questionnaire was developed to collect information on self-management and health care transition (HCT) skills, via self-report, in a broad population of adolescents and young adults (AYAs) with chronic conditions. METHODS Over several iterations, the STARx questionnaire was created with AYA, family, and health provider input. The development and pilot testing of the STARx Questionnaire took place with the assistance of 1219 AYAs with different chronic health conditions, in multiple institutions and settings over three phases: item development, pilot testing, reliability and factor structuring. RESULTS The three development phases resulted in a final version of the STARx Questionnaire. The exploratory factor analysis of the third version of the 18-item STARx identified six factors that accounted for about 65% of the variance: Medication management, Provider communication, Engagement during appointments, Disease knowledge, Adult health responsibilities, and Resource utilization. Reliability estimates revealed good internal consistency and temporal stability, with the alpha coefficient for the overall scale being .80. The STARx was developmentally sensitive, with older patients scoring significantly higher on nearly every factor than younger patients. CONCLUSION The STARx Questionnaire is a reliable, self-report tool with adequate internal consistency, temporal stability, and a strong, multidimensional factor structure. It provides another assessment strategy to measure self-management and transition skills in AYAs with chronic conditions.

Self-Management and Transition Readiness Assessment: Concurrent, Predictive and Discriminant Validation of the STARx Questionnaire

INTRODUCTION The STARx Questionnaire was designed with patient and provider input, to measure self-management and transition skills in adolescents and young adults (AYA) with chronic health conditions. With proven reliability and an empirically-based factor structure, the self-report STARx Questionnaire requires further validation to demonstrate its clinical and research utility. In this study we examine the concurrent, predictive, and discriminant validity of the STARx Questionnaire. METHODS To examine concurrent validity, the STARx Questionnaire was compared to two other published transition readiness tools. Predictive validity was examined using linear regressions between the STARx Total Score and literacy, medication adherence, quality of life, and health services use. Discriminant validity was examined by comparing the performance of three chronic illness conditions on the STARx Total Score and associated subscales. RESULTS The STARx Questionnaire and its subscales positively correlated with the scores for both transition readiness tools reflecting strong concurrent validity. The STARx Questionnaire also correlated positively with the literacy, self-efficacy, and adherence measures indicating strong predictive validity; however, it did not correlate with either quality of life or health care utilization. The performance of AYA across three different clinical conditions was not significant, indicating the clinical utility of this HCT tool for a variety of chronic health conditions. CONCLUSION The strong validity of the STARx Questionnaire, in tandem with its strong reliability, indicated adequate psychometric properties for this generic self-report measure. These strong psychometric properties should contribute to the STARx being a viable measure of health care transition for both research and clinical purposes.

CYP3A5 polymorphism in Mexican renal transplant recipients and its association with tacrolimus dosing.

BACKGROUND AND AIMS Variability in CYP3A5 expression associated with differences in tacrolimus bioavailability has been documented. The wild-type allele CYP3A5*1 expresses the functional protein, whereas the CYP3A5*3 allele is a splice variant with a premature stop codon and encodes a truncated nonfunctional protein. The aim of the study was to determine the frequency of CYP3A5*1 and CYP3A5*3 in 291 (124 adults, 167 pediatric) Mexican renal transplant recipients, evaluate the tacrolimus dose requirements by genotype and compare genotype frequency data with that of other populations. METHODS We carried out a multicenter study. Patients were recruited from three institutions located in Mexico City. Genotyping of the CYP3A5*1 and CYP3A5*3 alleles was performed by direct DNA sequencing. RESULTS Eighteen patients (6.2%) were CYP3A5*1*1 homozygous carriers or functional protein expresser homozygous, 121 patients (41.6 %) were CYP3A5*1*3 were heterozygous carriers or heterozygous expressers, and 152 patients (52.2%) were CYP3A5*3*3 homozygous carriers or homozygous nonexpressers. There was a statistically significant difference in frequency of the functional and nonfunctional expresser phenotypes from those reported for Black and Caucasian, but not for South Asian populations. The CYP3A5 phenotype had a significant impact in tacrolimus bioavailability, as wild-type carriers required higher dosing compared to mutated carriers to achieve similar drug trough levels. Patients with CYP3A5*1*1 genotype had a median dose requirement of 0.16 mg/kg/day, CYP3A5*1*3 patients had a median tacrolimus dose of 0.13 mg/kg/day and CYP3A5*3*3 had a median dose of 0.07 mg/kg/day (Kruskal-Wallis, p <0.0001). CONCLUSIONS Of the Mexican transplant recipients, 52.2% were CYP3A5*3*3 and required significantly lower tacrolimus dose than those with CYP3A5*1 allele.

Efficacy and safety of conversion of mycophenolate mofetil to enteric-coated mycophenolate sodium in Mexican renal transplant children.

Reyes H, Hernández AM, Valverde S, Cataneo A, Mendoza A, Barrera I, Ortíz L, García‐Roca P, Lopéz‐Martínez B, Castañeda‐Hernández G, Medeiros M. Efficacy and safety of conversion of mycophenolate mofetil to enteric‐coated mycophenolate sodium in Mexican renal transplant children.
Pediatr Transplantation 2010: 14:746–752.

Prevalence of metabolic syndrome and obesity in renal transplanted Mexican children

Abstract:  The purpose of the study was to evaluate the prevalence of MS and obesity in Mexican children with more than one yr post‐renal transplantation. Thirty‐two children transplanted between January 2004 and February 2006 were included in the study. The weight and height at the time of renal transplant were obtained. A fasting blood sample was drawn for serum creatinine, adiponectin, and complete lipid profile, and a three‐h glucose tolerance test was also taken. A complete nutritional evaluation was performed including anthropometry. There was a statistically significant increase in BMI at one yr post‐transplant that was maintained at two yr post‐transplant. Three patients exhibited obesity and were overweight. Seventeen patients had hypertension, 14 patients had low HDL, 12 patients had hypertriglyceridemia, all had normal fasting glucose, six of them had glucose intolerance, and two had waist circumference higher than 90%. Eight patients (25%) had MS. Patients with MS had higher proportion of deceased donor grafts, acute rejection episodes, and received more methylprednisolone pulses; also they had a statistically significant higher pretransplant BMI than patients without MS. There was a significant relationship between BMI at one yr post‐renal transplant and creatinine clearance estimated by Schwartz formula.

Latin American Registry of Pediatric Renal Transplantation 2004-2008

Latin American Pediatric Nephrology Association (ALANEPE) and Latin American Pediatric Renal Transplant Cooperative Study. Latin American Registry of Pediatric Renal Transplantation 2004–2008.
Pediatr Transplantation 2010: 14:701–708.

Cisplatin Nephrotoxicity and Longitudinal Growth in Children With Solid Tumors: A Retrospective Cohort Study

AbstractCisplatin, a major antineoplastic drug used in the treatment of solid tumors, is a known nephrotoxin. This retrospective cohort study evaluated the prevalence and severity of cisplatin nephrotoxicity in 54 children and its impact on height and weight.We recorded the weight, height, serum creatinine, and electrolytes in each cisplatin cycle and after 12 months of treatment. Nephrotoxicity was graded as follows: normal renal function (Grade 0); asymptomatic electrolyte disorders, including an increase in serum creatinine, up to 1.5 times baseline value (Grade 1); need for electrolyte supplementation <3 months and/or increase in serum creatinine 1.5 to 1.9 times from baseline (Grade 2); increase in serum creatinine 2 to 2.9 times from baseline or need for electrolyte supplementation for more than 3 months after treatment completion (Grade 3); and increase in serum creatinine ≥3 times from baseline or renal replacement therapy (Grade 4).Nephrotoxicity was observed in 41 subjects (75.9%). Grade 1 nephrotoxicity was observed in 18 patients (33.3%), Grade 2 in 5 patients (9.2%), and Grade 3 in 18 patients (33.3%). None had Grade 4 nephrotoxicity. Nephrotoxicity patients were younger and received higher cisplatin dose, they also had impairment in longitudinal growth manifested as statistically significant worsening on the height Z Score at 12 months after treatment. We used a multiple logistic regression model using the delta of height Z Score (baseline-12 months) as dependent variable in order to adjust for the main confounder variables such as: germ cell tumor, cisplatin total dose, serum magnesium levels at 12 months, gender, and nephrotoxicity grade. Patients with nephrotoxicity Grade 1 where at higher risk of not growing (OR 5.1, 95% CI 1.07–24.3, P = 0.04). The cisplatin total dose had a significant negative relationship with magnesium levels at 12 months (Spearman r = −0.527, P = <0.001).

Validation of the UNC TRxANSITION Scale™Version 3 Among Mexican Adolescents With Chronic Kidney Disease

BACKGROUND There is a lack of valid health care transition readiness (HCT) scales in Spanish. OBJECTIVE To provide initial validation of the UNC TRxANSITION Scale™ among Mexican adolescents and young adults (youth) with chronic kidney disease (CKD). METHODS We used the professionally translated/back translated, provider-administered UNC TRxANSITION Scale™ (Ferris et al., 2012). This 33-question scale measures HCT in ten sub-scales including knowledge about diagnosis or treatment, diet, reproductive health, school/work, insurance, ability to self-manage and looking for new health providers. Its maximum score is 10. We enrolled 163 Mexican adolescents (48.5% females) with CKD stage≥3, mean age of 15.1years (±2.1) and whose primary language is Spanish. There were 15 patients on hemodialysis (9.2%) and 30 transplant recipients (18.4%). Results were compared to those reported in adolescents with chronic conditions from the USA. RESULTS Our cohorts overall median total score was 5.9. Patients≥16years old had a median total score of 6.4, whereas younger patients had median score of 5.6 (p<0.05). Transplant patients had greater scores in the total and the sub-scales of medication knowledge, issues of reproduction, insurance, trade/work and adherence (p<0.05). When comparing the total score (by age), results from our Mexican youth were similar to those reported in youth from the USA. CONCLUSIONS In our Mexican cohort of youth with CKD, health care transition readiness is greater in older patients and in transplant recipients. Our cohorts overall score is low, indicating the need for a health care transition preparation program. The UNC TRxANSITION Scale™ results in Mexican youth with CKD are comparable to findings in youth from the USA.

Population pharmacokinetic analysis of tacrolimus in Mexican paediatric renal transplant patients: role of CYP3A5 genotype and formulation

AIMS The aims of this study were (i) to develop a population pharmacokinetic (PK) model of tacrolimus in a Mexican renal transplant paediatric population (n = 53) and (ii) to test the influence of different covariates on its PK properties to facilitate dose individualization. METHODS Population PK and variability parameters were estimated from whole blood drug concentration profiles obtained at steady-state using the non-linear mixed effect modelling software NONMEM® Version 7.2. RESULTS Tacrolimus PK profiles exhibited high inter-patient variability (IPV). A two compartment model with first order input and elimination described the tacrolimus PK profiles in the studied population. The relationship between CYP3A5 genotype and tacrolimus CL/F was included in the final model. CL/F in CYP3A5*1/*1 and *1/*3 carriers was approximately 2- and 1.5-fold higher than in CYP3A5*3/*3 carriers (non-expressers), respectively, and explained almost the entire IPV in CL/F. Other covariates retained in the final model were the tacrolimus dose and formulation type. Limustin® showed markedly lower concentrations than the rest of the formulations. CONCLUSIONS Population PK modelling of tacrolimus in paediatric renal transplant recipients identified the tacrolimus formulation type as a significant covariate affecting the blood concentrations and confirmed the previously reported significant effect of CYP3A5 genotype on CL/F. It allowed the design of a proposed dosage based on the final model that is expected to help to improve tacrolimus dosing.