New Drugs: Prescribing for infants and children

The total volumes of body water and extracellular fluid related to body weight are the greatest during the neonatal period and infancy. These values decrease with age most appreciably during the first three months of life and thereafter more gradually. Water soluble drugs that are distributed mainly in extracellular water therefore have the largest volumes of distribution in the newborn and young infants.4 Furthermore, the blood-brain barrier may be functionally incomplete in the neonate, allowing increased penetration of some drugs. Though there are small differences in the extent of protein binding with age throughout childhood (lower values in newborns and young infants),2 these are generally not clinically important. The displacement of bilirubin from albumin by sulphonamides and some other drugs in the newborn is well recognised,5 and it should not be forgotten that the transfer of drugs in breast milk may be a source of inadvertent treatment to the neonate.