Whole body [O-15]water pharmacokinetics measured in blood

Development of a nonlinear hierarchical model to describe the disposition of deuterium in mother-infant pairs to assess exclusive breastfeeding practice

The World Health Organization recommends exclusive breastfeeding (EBF) for the first 6 months after birth. The deuterium oxide dose-to-the-mother (DTM) technique is used to distinguish EBF based on a cut-off (< 25 g/day) of water intake from sources other than breastmilk. This value is based on a theoretical threshold and has not been verified in field studies. The aim of this study was to estimate the water intake cut-off value that can be used to define EBF practice. One hundred and twenty-one healthy infants, aged 2.5-5.5 months who were deemed to be EBF were recruited. After administration of deuterium to the mothers, saliva was sampled from mother and infant pairs over a 14-day period. Validation of infant feeding practices was conducted via home observation over six non-consecutive days with caregiver recall. A fully Bayesian framework using a gradient-based Markov chain Monte Carlo approach implemented in Stan was used to estimate the cut-off of non-milk water intake of EBF infants. From the original data set, 113 infants were determined to be EBF and provided 1500 paired mother-infant observations. The deuterium saliva concentrations were best described by two linked 1-compartment models (mother and infant), with body weight as a covariate on the mother's volume of distribution and infant's body weight on infant's water clearance rate. The cut-off value was based on the 90th percentile of the posterior distribution of non-milk water intake and was 86.6 g/day. This cut-off value can be used in future field studies in other geographic regions to determine exclusivity of breast feeding practices in order to determine their potential public health needs.

Pharmacokinetic analysis of absorption, distribution and disappearance of ingested water labeled with D₂O in humans

The kinetic parameters of absorption and distribution of ingested water (300 ml labeled with D(2)O; osmolality <20 mOsm kg(-1)) in the body water pool (BWP) and of its disappearance from this pool were estimated in 36 subjects from changes in plasma or urine deuterium to protium ratio (D/H) over 10 days using one- and two-compartment and a non-compartmental pharmacokinetic models (1-CM, 2-CM and N-CM which applied well to 58, 42 and 100% of the subjects, respectively). Compared with the volume and turnover of the BWP computed with the slope-intercept method (60.7 ± 4.1% body mass or 72.7 ± 3.2% lean body mass; turnover 4.58 ± 0.80 l day(-1): i.e., complete renewal in ~50 days; n = 36), the values were accurately estimated with the N-CM and 1-CM and were slightly overestimated and underestimated, respectively, with the 2-CM (~7-8% difference, significant for water clearance only). Ingested water appeared in plasma and blood cells within 5 min and the half-life of absorption (~11-13 min) indicates a complete absorption within ~75-120 min. The 2-CM showed that in 42% of the subjects, ingested water quickly distributed within a central compartment before diffusing with a very short half-life (12.5 ± 4.3 min) to a peripheral compartment (18.5 ± 4.3 and 31.6 ± 6.4 L, respectively), which were in complete equilibrium within ~90 min. Pharmacokinetic analyses of water labeled with D(2)O can help describe water absorption and distribution, for which there is no well defined reference method and value; depending on the characteristics of the subjects and the drinks, and of environmental conditions.

A positron-probe system for arterial input function quantification for positron emission tomography in humans

We developed an intra-arterial positron-probe (beta(+)-probe) system to measure the arterial time-activity concentration in humans for quantitative compartmental modeling of positron emission tomography studies. Performance was characterized in vitro, by using a uniform phantom to calculate dead time, linearity, and absolute detector sensitivity. In vitro evaluations in a uniform phantom showed a system dead time of 2.5 micros, linear regression between measured and true count rates with R(2)=0.999, and detector sensitivity of 6.9-7.0 counts/s kBq(-1) ml. These met or exceeded values of previously reported systems.