Antibiotics are used to target serious infections
One in 500 children is carrying a gene variation which means they are more likely to be damaged by a commonly used hospital antibiotic, a study suggests.
Aminoglycosides, often used to target serious infections, can permanently harm hearing.
A team from the Institute of Child Health in London found the gene fault in 18 out of 9,371 children tested.
In the New England Journal of Medicine they say it should be possible to screen out at risk children.
While aminoglycosides are a cheap and effective way of getting to grips with certain types of bacterial infection, doctors have known for some time that they carry risks, and levels of the drug are normally carefully monitored.
However, in a small number of children, damage to hearing can happen even when given normal doses.
This side-effect has been more strongly linked to a genetic variation, which can lead to problems even at completely normal doses of the drug.
The ICH researchers wanted to know just how common the gene variation was, in order to work out whether it was realistic to test thousands of children about to be given the drugs.
With one in 500 children affected, Dr Maria Bitner-Glindzicz, one of the lead authors, said this should now be considered.
"These antibiotics are widely used on very sick children. We believe that it will be cost effective to genetically screen groups of patients who will almost certainly receive aminoglycoside antibiotics, to see if they carry the mutation, before administering the antibiotics.
"This will allow an alternative antibiotic to be given to anyone who has the mutation. In some groups of patients, such as those with leukaemia or cystic fibrosis, there is a window of opportunity to perform genetic testing before the need for antibiotics arises.
"The difficulty will be when the matter is clinically urgent, because of the time it currently takes to get the genetic results."
John Shanley, chief executive of research charity Sparks commented: "This is a major discovery with very important implications.
"Clearly, it is vital to avoid permanently deafening babies, children and adults who receive these particular antibiotics as part of their hospital treatment.
"The discovery explains one cause of deafness and we believe careful consideration should be given to screening all pregnant women to establish whether they are carrying the specific gene mutation."