Penicillin doses for children need to be reviewed to take account of youngsters getting heavier, experts have said.
Dosing guidelines have remained unchanged for almost 50 years and are mostly based on children’s ages.
But experts argue the dose a child needs is determined by their weight - and the average weight of children has increased over the past 50 years by as much as 20 per cent.
Many children will not be receiving a large enough dose and low dosing could also potentially drive resistance to antibiotics, they warn.
Researchers from London, writing in the British Medical Journal, said: “Underdosing may result in the need for retreatment and increases the risk of severe complications.”
The authors also point out that many infections do not need treatment with antibiotics.
About five million children in England are estimated to receive oral penicillins each year.