Quetiapine Excretion Into Human Breast Milk.

BACKGROUND: Risk assessment of the use of quetiapine during breastfeeding is challenging owing to a paucity of data. METHODS: A pharmacokinetic study was conducted in lactating women who were taking quetiapine. The primary endpoint was to determine quetiapine concentration profiles in milk and estimated infant exposure levels. Multiple milk and a single blood quetiapine concentrations were determined using a highly sensitive liquid chromatography with tandem mass spectroscopy method. RESULTS: Nine subjects receiving fast-release quetiapine (mean dose, 41 mg/d) were analyzed at steady state. The mean milk/plasma drug concentration ratio at 2-hour postdose was 0.47 (SD, 0.50; range, 0.13-1.67). The mean milk concentration of each patient was 5.7 ng/mL (SD, 4.5; range, 1.4-13.9 ng/mL). The mean infant quetiapine dose via milk per body weight relative to weight-adjusted maternal dose was 0.16 % (SD, 0.08; range, 0.04%-0.35%). CONCLUSIONS: Infant exposure levels to quetiapine via milk are predicted to be very small.

Pediatric reference intervals for lymphocyte vitamin C (ascorbic acid).

OBJECTIVE: To establish pediatric reference intervals for lymphocyte vitamin C. DESIGN AND METHODS: This was a prospective study of 194 well children aged 0-7 years old of mixed ethnicity who had blood drawn for the purpose of this study. Blood was collected during elective surgery under general anesthesia and lymphocytes isolated and stored as frozen ascorbic acid lymphocyte lysates for later HPLC analysis by previously described methodology. Reference intervals were established according to the Clinical and Laboratory Standards Institute (CLSI) and the International Federation of Clinical Chemistry (IFCC) guidelines (C28-A3). Horn-Pesce robust method was used to estimate the 95% confidence interval and 95% reference interval. RESULTS: Reference intervals were independent of age or gender and shown to be 12.9-52.8 µg/10(8) cells (lymphocytes). CONCLUSION: We have defined pediatric reference ranges for lymphocyte vitamin C in healthy, fasted children at a relevant age group (0-7 years). The new reference interval can now be used to more reliably explore possible implications of variation of vitamin C levels on bleeding and other clinical signs.

A pitfall of measuring lithium levels in neonates.

If lithium therapy is required during pregnancy or lactation, serum lithium monitoring may be indicated in the newborns. In the neonatal population, however, blood samples are often obtained with a sampling device containing lithium heparin. Given the infrequent nature of lithium measurement in the neonatal population, a risk of oversight on the use of these lithium-containing devices for lithium measurements exists. Two such neonatal cases are reported, which may have been mismanaged if the measured levels of lithium were not suspected to be spurious. Patient 1 was a 3-day-old infant with a congenital heart disease born at 31 weeks' gestation to a mother on lithium. After a surgical repair, because of a potential need to monitor lithium in the infant's serum during breastfeeding, a remaining sample of apparently serum from a previous blood testing on day 1 of life was measured for lithium as a baseline value. Despite the lack of toxic signs, the result showed a toxic lithium level of 4.19 mmol/L. Lithium levels in follow-up samples were 0.11 mmol/L (day 4) and undetectable (day 6). Patient 2 was a full-term infant exposed to maternal lithium throughout the fetal life and breastfeeding. Serum lithium at day three of life in a hospital was undetectable, but after discharge, the lithium concentrations increased to 1.1 mmol/L on day 18, with no sign of lithium toxicity or renal dysfunction. This raised a possibility of significant exposure through breastfeeding, but later they were found to be spurious due to the use of lithium-containing devices. Separate investigation of effects of sampling devices on lithium levels indicated that levels of >3 mmol/L were possible if a sampling volume of blood was substantially small compared with the capacity of a tube containing lithium heparin [corrected]

Pharmacokinetic disposition and clinical outcomes in infants and children receiving intravenous busulfan for allogeneic hematopoietic stem cell transplantation.

We conducted a retrospective pharmacokinetic analysis of i.v. busulfan in children undergoing hematopoietic stem cell transplantation (HSCT) and describe its relation to transplantation outcomes. Forty-five children (median age, 3 yr) underwent HSCT at The Hospital for Sick Children from April 2003 through January 2006 and received i.v. busulfan every 6 h as part of their conditioning regimen. Initial busulfan doses were based on actual patient weight: <9 kg, 0.95 mg/kg per dose; 9-16 kg, 1.2 mg/kg per dose; 16-23 kg, 1.1 mg/kg per dose; 24-34 kg, 0.95 mg/kg per dose; >34 kg, 0.8 mg/kg per dose. Plasma busulfan concentrations were obtained after the first dose. The fourth and subsequent busulfan doses were adjusted to achieve an area under the concentration versus time curve (AUC) of 900-1500 microM.min. Development of hepatic venous occlusive disease (HVOD; modified Baltimore criteria) and engraftment (absolute neutrophil count >or=0.5 x 10(9)/L) were evaluated. Busulfan pharmacokinetic parameters were calculated using 1-compartment methods. Mean busulfan pharmacokinetic parameters were maximum concentration (C(max); 4.7 +/- 0.75 microM), volume of distribution at steady state (0.68 +/- 0.17 L/kg), elimination rate constant (0.0051 +/- 0.0010 min(-1)), total body clearance (3.5 +/- 1.23 mL/[min.kg]), and AUC (1271 +/- 280 microM.min). Mean volume of distribution at steady state was larger in children <1 yr of age (0.77 +/- 0.24 vs 0.64 +/- 0.11 L/kg; P = .040) and children <4 yr of age (0.73 +/- 0.18 vs 0.60 +/- 0.11 L/kg; P = .001) than in older children. Compared with older children, mean weight-adjusted total body clearance was higher in children <4 yr of age (3.8 +/- 1.40 versus 3.0 +/- 0.76 mL/[min.kg]). HVOD was diagnosed in 8 children (18%), including 4 children <1 yr of age. Children who developed HVOD achieved a lower C(max) than did those without HVOD (4.2 +/- 0.68 versus 4.8 +/- 0.73 microM; P = .035). Other than C(max), no association was observed between busulfan disposition and development of HVOD in children for whom i.v. busulfan doses were adjusted to achieve a target AUC. The influence of factors other than busulfan disposition on transplantation outcomes, such as genetic polymorphisms, should be evaluated.

Ontogeny of renal P-glycoprotein expression in mice: correlation with digoxin renal clearance.

Digoxin is eliminated mainly by the kidney through glomerular filtration and P-glycoprotein (P-gp) mediated tubular secretion. Toddlers and young children require higher doses of digoxin per kilogram of bodyweight than adults, although the reasons for this have not been elucidated. We hypothesized there is an age-dependant increase in P-gp expression in young children. The objectives of this study were to elucidate age-dependant expression of renal P-gp and its correlation with changes in the clearance rate of digoxin. FVB mice were killed at different ages to prepare total RNA for P-gp expression studies. Semi-quantitative RT-PCR was conducted to analyze mdr1a and mdr1b ontogeny in the kidney at: birth, 7, 14, 21, 28 and 45-d old adults. The pharmacokinetics of digoxin (7 microg/kg) was studied in mice of the same age groups. Newborn and Day 7 levels of both mdr1a and mdr1b were marginal. Day 21 mdr1b levels were significantly higher than both Day 14 and Day 28 levels. Digoxin clearance rates were the highest at Day 21, with significant correlation between P-gp expression and clearance values. Increases in digoxin clearance rates after weaning may be attributed, at least in part, to similar increases in P-gp expression.

Measurement of intracellular vitamin C levels in human lymphocytes by reverse phase high performance liquid chromatography (HPLC).

OBJECTIVES: Vitamin C plays an active role in many important metabolic processes, such as collagen formation and the prevention of bleeding. Although overt scurvy is now rare, there is evidence that subclinical vitamin C deficiency is still quite common. Serum and plasma vitamin C measurements do not correlate well with tissue levels while lymphocyte vitamin C levels provide the most accurate assessment of the true status of vitamin C stores and are not affected acutely by circadian rhythm or dietary changes. We report a specific and reproducible reverse phase high performance liquid chromatographic method (HPLC) for the quantification of vitamin C in lymphocytes. METHODS: Reverse phase HPLC with a UV detection system was used. National Committee for Clinical Laboratory Standards (NCCLS) guidelines were followed for evaluation. Sample stability testing for lymphocyte vitamin C was performed for a period of 24 h at room temperature and 4 degrees C. Lymphocyte vitamin C levels were measured in 51 children. RESULTS: Lymphocyte vitamin C measurement with HPLC revealed very good analytical sensitivity with a 1.42 microg/10(8) lymphocyte lower limit of detection on repeated testing. An external standard curve was used for quantification, which showed a linear range of 1.25-100 microg/10(8) lymphocyte with a correlation coefficient of 0.989. Precision studies showed an inter-assay repeatability coefficient of variance (CV) between 0.25-9.98% and a within-assay coefficient of variance between 1.2-12.49%. The inter-assay CV for a period of 20 days was less than 10% for concentrations equal to or less than 1.42 microg/10(8) lymphocytes and less than 5.5% for concentrations between 5-100 microg/10(8) lymphocytes. Vitamin C was most stable at 4 degrees C, with a 0.31% decrease after 3 h and 2.35% after 4 h. At room temperature, vitamin C loss was more significant, with losses of 8.44% and 15.6% at 3 and 4 h, respectively, at a concentration of 29.9 microg/10(8) lymphocytes. CONCLUSIONS: The proposed HPLC method offers a reliable and reproducible technique for the quantification of intracellular vitamin C. Lymphocyte samples can be rapidly prepared and represent a more homogeneous tissue sample source for intracellular vitamin C measurement as compared to serum. To ensure stability, lymphocyte lysates should be prepared and stored at or below -20 degrees C within 2 h of blood collection.

Analytical performance and workflow evaluation of the Roche E170 modular immunoassay analyzer in a pediatric setting.

OBJECTIVES: To evaluate the analytical performance of the Roche E170 modular analytics immunoassay analyzer and assess its impact on workflow efficiency and ability to consolidate workstations in a pediatric setting. DESIGN AND METHODS: Analytical performance of eleven common immunoassays was assessed. Total imprecision was determined using Roche PreciControl Universal controls, Bio-Rad Lyphochek Immuno Plus, Anemia controls, and a human serum pool. Method comparison was performed with approximately 100 patient specimens. High dose hook effect, sample carryover, and results comparison between the two measuring channels were evaluated. For the workflow study, the time required for sample and reagent handling, instrument preparation, and hands-on time were assessed. RESULTS: Correlation coefficients with existing methods ranged from 0.941 to 0.999. Biases of -19% to 70% were observed. Total imprecision ranged from 1.1 to 7.6%. No sample carryovers were encountered. Results from both measuring channels were comparable. CONCLUSION: E170 is suitable for use in a pediatric setting. The analytical performance is acceptable and gives equivalent results to our existing systems. The precision is comparable and acceptable. Some improvement in efficiency, workflow, cost saving, and consolidation of workstations is possible. Significant workflow improvements can only be realized when integrated with the chemistry modules.

Improved HPLC methodology for monitoring thiopurine metabolites in patients on thiopurine therapy.

OBJECTIVE: Standardization of thiopurine metabolite testing is currently lacking. This paper presents in-depth methodological analysis and optimization of two currently available HPLC procedures (Lennard-Singleton [J. Chromatogr. 583 (1992) 83] and Dervieux-Boulieu [Clin. Chem. 44 (1998) 551]) to improve precision, turn-around time, ruggedness, and cost effectiveness. DESIGN AND METHODS: Reversed-phase chromatography with UV detection was performed on a Waters HPLC system. The two protocols were improved with regards to internal standardization (IS), chromatographic conditions, as well as reagent preparation, storage, and use. 6-Thioguanine nucleotides (6-TGNs) were analyzed by our optimized techniques in samples from patients on thiopurine therapy (n = 24) and the results were compared. RESULTS: 6-Mercaptopurine (6-MP) was an ideal internal standard in either procedure. Isocratic elution with 5% acetonitrile (ACN) in 20 mmol/l phosphate buffer pH 2.5 allowed for minimal background interference in both protocols. 6-Thioguanine, 6-mercaptopurine, and 6-methylmercaptopurine (6-MMP) eluted at around 4, 5, and 6 min, respectively. Dithiothreitol (DTT) was critical only during the acid hydrolysis step. Less mercury-containing waste was generated in the Lennard-Singleton procedure. With our optimized protocols recovery of 6-TGNs was on average 1.38-fold higher in the Dervieux-Boulieu method over a range of 10-678 pmol/8 x 10(8) RBC and no interfering peaks hindered analysis. Specific extraction of thiopurines before their analysis as per Lennard-Singleton procedure may be redundant. CONCLUSIONS: We improved the quality and cost effectiveness of two known procedures for thiopurine metabolite assay. Through common chromatographic conditions and internal standardization, future comparison studies are now facilitated a great deal. The less tedious Dervieux-Boulieu procedure for routine thiopurine metabolite testing is warranted.