Observational infant exploratory [(14)C]-paracetamol pharmacokinetic microdose/therapeutic dose study with accelerator mass spectrometry bioanalysis.

AIMS: The aims of the study were to compare [(14)C]-paracetamol ([(14)C]-PARA) paediatric pharmacokinetics (PK) after administration mixed in a therapeutic dose or an isolated microdose and to develop further and validate accelerator mass spectrometry (AMS) bioanalysis in the 0-2 year old age group. METHODS: [(14)C]-PARA concentrations in 10-15 µl plasma samples were measured after enteral or i.v. administration of a single [(14)C]-PARA microdose or mixed in with therapeutic dose in infants receiving PARA as part of their therapeutic regimen. RESULTS: Thirty-four infants were included in the PARA PK analysis for this study: oral microdose (n = 4), i.v. microdose (n = 6), oral therapeutic (n = 6) and i.v. therapeutic (n = 18). The respective mean clearance (CL) values (SDs in parentheses) for these dosed groups were 1.46 (1.00) l h(-1), 1.76 (1.07) l h(-1), 2.93 (2.08) l h(-1) and 2.72 (3.10) l h(-1), t(1/2) values 2.65 h, 2.55 h, 8.36 h and 7.16 h and dose normalized AUC(0-t) (mg l(-1) h) values were 0.90 (0.43), 0.84 (0.57), 0.7 (0.79) and 0.54 (0.26). CONCLUSIONS: All necessary ethical, scientific, clinical and regulatory procedures were put in place to conduct PK studies using enteral and systemic microdosing in two European centres. The pharmacokinetics of a therapeutic dose (mg kg(-1)) and a microdose (ng kg(-1)) in babies between 35 to 127 weeks post-menstrual age. [(14)C]-PARA pharmacokinetic parameters were within a two-fold range after a therapeutic dose or a microdose. Exploratory studies using doses significantly less than therapeutic doses may offer ethical and safety advantages with increased bionalytical sensitivity in selected exploratory paediatric pharmacokinetic studies.

Differences in resting energy expenditure between male and female children with cystic fibrosis.

OBJECTIVES: To evaluate which factors might contribute to raised resting energy expenditure (REE) in patients with cystic fibrosis (CF). STUDY DESIGN: REE and anthropometry were measured in 134 (males = 68) children with CF and 100 (males = 51) controls (range, 3-18.7 years) in an outpatient setting. Bacterial colonization, liver disease, inhaled steroid use, pancreatic and pulmonary function, sex, and genotype were determined and regression analysis was used to determine the predictors of REE in the group with CF. RESULTS: REE for children with CF was increased on average by 7.2% compared with controls. This increase was greater for females than for males. REE in males was positively associated with fat-free mass (FFM), pancreatic insufficiency (PI), and liver disease, and negatively associated with pulmonary function, whereas in females, REE was positively associated with FFM and PI. REE (adjusted for FFM) was higher in children with a severe mutation (5495 +/- 47 kJ) compared with a mild mutation (5,176 +/- 124 kJ, P <.02). CONCLUSIONS: PI, severe mutations, and female sex are the main contributing factors to elevated REE in patients with CF with near normal pulmonary function.