ABSTRACT
Regardless of the age of a child receiving a drug, the dispositional characteristics of the drug will depend on the interaction between the physicochemical properties of the drug and the physiologic process in the patient. Physical properties of the drug include molecular size, charge, pKa or ionic disassociation constant, and lipid solubility. These factors will determine the drug's distribution, as well as the route of elimination. In general, water-soluble drugs have a small volume of distribution and can be eliminated unchanged in urine, whereas lipid-soluble drugs have a large volume of distribution and require metabolism to more water-soluble moieties prior to elimination.
