Neonatal body water turnover: a putative index of perinatal morbidity

Impact of Deuterium Substitution on the Pharmacokinetics of Pharmaceuticals

Objective: Stable heavy isotopes of hydrogen, carbon, and other elements have been incorporated into drug molecules, largely as tracers for quantitation during the drug development process. Studies involving the human use of drugs labeled with deuterium suggest that these compounds may offer some advantages when compared with their nondeuterated counterparts. Deuteration has gained attention because of its potential to affect the pharmacokinetic and metabolic profiles of drugs. Deutetrabenazine (Austedo, Teva Pharmaceutical Industries, Ltd) is the first deuterated drug to receive Food and Drug Administration approval. This deuterated form of the drug tetrabenazine is indicated for the treatment of chorea associated with Huntington’s disease as well as tardive dyskinesia. Ongoing clinical trials suggest that a number of other deuterated compounds are being evaluated for the treatment of human diseases and not merely as research tools. Data Sources: A search of the MEDLINE (1946 to present) database was undertaken using the Ovid interface. The search was conducted using the heading deuterium and then limited to Administration & Dosage, Adverse Effects, Pharmacokinetics, Pharmacology, Poisoning, Therapeutic Use, and Toxicity. Study Selection and Data Extraction: All articles were reviewed and those with human information were included. Review articles were likewise interrogated for additional published human data. Conclusions: Deuterated compounds may, in some cases, offer advantages over nondeuterated forms, often through alterations in clearance. Deuteration may also redirect metabolic pathways in directions that reduce toxicities. The approval of additional deuterated compounds may soon follow. Clinicians will need to be familiar with the dosing, efficacy, potential side effects, and unique metabolic profiles of these new entities.

Neonatal aspects of intrauterine growth retardation

The growth-retarded fetus is susceptible to intrauterine death, perinatal asphyxia and subsequently neonatal morbidity. Recent technical advances have only moderately increased the obstetrician's ability to recognize the fetus with intrauterine growth retardation (IUGR) prior to delivery, compared with two decades ago when less than one-third of such infants were identified before labour and delivery.

Neonatal water metabolism: an objective postnatal index of intrauterine fetal growth

The water metabolism of 103 newborn babies was determined over the first 10 postnatal days, by measuring water turnover rates by means of an isotope dilution technique. This technique involves the oral administration of the non-radioactive isotope of water, 2H2O, and the measurement of its urinary excretion by infrared spectrophotometry. The slope of the excretion curve after equilibration with the infant's body water was mathematically expressed as the rate constant. Using multiple obstetric and paediatric criteria, the babies were clinically classified into one of three categories, fully grown ("normal'), borderline or clearly growth retarded. The median values of the rate constants X 10(4) (h-1) for the three groups were 73.3, 85.9 and 100.2 and were highly significantly different from each other (P less than 0.0005) with no overlap of the 97% non-parametric confidence limits of each group. Neonatal water turnover increased with the clinical degree of intrauterine fetal growth retardation and within the limits of this study, this finding was unaffected by gestational age, birth weight or the neonatal environment. The results suggest that neonatal water metabolism is an objective postnatal index of fetal growth retardation.

Hydration in the first 24 h of postnatal life in normal infants born vaginally or by caesarean section

A total of 65 infants, 48 born vaginally and 17 by segment caesarean section, were studied prior to labour for extracellular volume (ECV) (corrected bromide space) and total body water (TBW) (deuterium space) during the first 24 h of postnatal life. The infants were mature and growth retardation excluded. A 'heel stick' blood sample was taken for micro determination of Br and urine for 2H2O concentration. ECV varied from 343 +/- 27 ml/kg at 6 h to 358 +/- 21 ml/kg at 24 h and TBW was 75.5 +/- 3.4% of body weight. Contrary to current opinion, neither TBW nor cell hydration differed in infants born by caesarean section compared with those born vaginally. Such modern methodology to study infant body hydration and the critical assessment of growth and maturity demonstrates that hydration during the first 24 h of life is relatively stable and is not affected by the mode of delivery.