Call for penicillin dose review as youngsters gain weight

Penicillin doses for children need to be reviewed to take account of the fact youngsters are 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 that the dose a child needs is determined by their weight - and the average weight of children has increased over the last 50 years.

The average weight today of a five-year-old is 21kg and 37kg for a 10-year-old - up to 20% higher than in 1963, they said.

Many children will actually not be receiving a large enough dose, they added.

Low dosing could also potentially drive resistance to antibiotics “with consequences for both the individual and the community”.

The researchers said: “Underdosing may result in the need for retreatment and increases the risk of severe complications.

“All the published risk-benefit analyses on the therapeutic balance of antibiotic prescribing for upper respiratory tract infections assume adequate antibiotic dosing.

“This is a real concern because clinically inadequate dosing would increase the number needed to treat to prevent any severe complications.”

The study, led by a team at King’s College London and St George’s, University of London, said they were “surprised at the lack of recent evidence” to support current dosing recommendations for penicillins.

Writing in the British Medical Journal (BMJ), they added: “The widely used doses of 62.5mg or 125mg are fractions of the adult dose recommended in the British National Formulary (BNF) and are still based on the original dosing principle of a big child = half an adult, small child = half a big child, baby = half a small child.”

The team analysed the actual dose that would be received today based on age bands recommended in the 2010/11 British National Formulary for Children and the current weights of children based on 2009 Health Survey for England data.

The results showed doses could be strikingly low.

“For example, a 10-year-old child weighing around 40 kg and receiving amoxicillin (a type of penicillin) 250 mg three times a day will receive only around 18 mg/kg/day, much lower than the 40-90 mg/kg/day recommended in the summary of product characteristics for Amoxil.”

The authors also pointed out that many infections do not need treatment with antibiotics.

Dr Paul Long, senior lecturer in pharmacognosy at King’s College London, said: “We were surprised at the lack of evidence to support the current oral penicillins dosing recommendations for children, as it is such a commonly used drug.

“Children’s average size and weight are slowly but significantly changing, so what may have been adequate doses of penicillin 50 years ago are potentially not enough today.

“It is important to point out that this study does not provide any clinical evidence that children are receiving sub-optimal penicillin doses that lead to harm, and we want to reassure parents of that.

“But what we are saying is that we should ensure that children with severe infections who need these antibiotics the most are still receiving an effective dose.”

Professor Mike Sharland from St George’s, University of London, said guidelines for older drugs needed to be checked carefully.

“We are not saying the current doses are wrong or unsafe and parents should always give the medicine at the doses prescribed by their GP.

“We are saying that we need to develop a clearer system to check the doses used for older medicines.”

Simon Keady, Royal Pharmaceutical Society spokesman on children’s medicines, said: “The use of penicillins over many years for a wide variety of conditions should not stop us from continuing to identify the most appropriate dose which gives us the most effective outcomes.

“The work clearly shows that the focus should not always be about new drugs but also looking at where we have historically centred dosing around age bands.”