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GPs advised to up penicillin doses in children

Dosages of oral penicillin-like antibiotics should be raised for children, to take account of the increase in the average child's weight since guidelines were written, a study argues.

The authors of the study, published in the BMJ, warn that under-dosing children with penicillin V, amoxicillin and flucloxacillin is leading to therapeutic failure and driving antibiotic resistance.

Recommended dosages for penicillin V remain unchanged since the 1963-66 edition of the BNF; these suggest 125mg for children aged one to five years and 500mg for six to 12 year olds. But since then the average weight of a five-year-old has increased from 18Kg to 21kg and the mean weight of a ten-year-old from 30kg to 37kg.

The product characteristics summary for amoxicillin recommend a dosage of 40-90mg/kg/day, but following the BNF would result in a ten-year-old weighing 40kg receiving a dose of only 18mg/kg/day, the authors point out.

The authors call for a review of the dosing guidelines based on children's current average weights.

Co-author Dr Paul Long, senior lecturer in pharmacology at King's College London, said: ‘These days new medicines go through very rigorous testing processes, but we seem to forget about the old ones. For adults, penicillin dosages have been reviewed twice in the same period.'

Professor Paul Little, of the University of Southampton's school of medicine and a GP in the city, said there is no current evidence of any declining efficacy of penicillins in children.

He added that the study should not detract from the drive to reduce antibiotic prescribing: ‘The key issue I think are the number of antibiotic scripts issued, i.e. the main task is to reduce prescription rates.'

‘When thinking about giving an antibiotic the clear message is to save them for those who are more likely to benefit, but when prescribing probably best to give a reasonable dose that will do the job. So the authors may have a point.'

Dr Bill Beeby, chair of the GPC's clinical and prescribing committee, said: 'I'm not so convinced that the recommended doses should change, but we have to bear in mind the individual child we are prescribing for.'

'If a child comes in and you can see they are not in the usual weight range, we should be putting them on the scales to verify that we are actually treating them for their weight as well as for their age. We need to weigh children more often than we have done before and then do some quick sums. As long as you stay within the dosage range you should be OK.'

BMJ 2011; 343: d7803

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