A new study has provided the strongest and most comprehensive evidence yet of the difference between how adults and infants and children process drugs.
The researchers say that when children are given smaller doses of drugs which have only been tested on adults they are at greater risk of harmful side effects.
Apparently most drugs given to newborn babies, and 50 per cent of those given to children of all ages, have not been tested to ensure that they are appropriate for them.
Previous studies show that under-18s suffer up to three times more side effects from drugs than adults.
This say the researchers is because the proportions of proteins in the body that control their effectiveness change as humans grow older.
The study by a team at the Children's Research Institute, Wisconsin, reveals quite surprising metabolic differences in how drugs are processed by the young and by adults, and the major changes occurring during human development in the types and levels of enzymes responsible for the disposition of drugs and environmental chemicals.
These enzymes they say are able to inactivate drugs, activate them, or do both, depending on the compound and the number of enzymes involved.
They also say some environmental toxicants are inactivated and some are activated, depending on the chemistry of the compound, and sometimes, the dose.
The study was led by Ronald N. Hines, Ph.D., professor of pediatrics and of pharmacology and toxicology, and associate director of the Children's Research Institute, Children's Hospital, which is a major teaching affiliate of the Medical College.
In the study the researchers used tissue samples from 240 children aged from eight weeks to 18 years old to study the levels of different enzymes compared with those in adults.