In this BMJ feature, the ‘Improving Children’s Antibiotic Prescribing UK Research Network’ suggests it’s time to abandon the historical rule of thumb for dosing of oral penicillins in children.

The authors note that despite their wide use over many decades, guidance on the correct dose of oral penicillins for children remains confusing: the SPC for Amoxil paediatric suspension in children weighing <40 kg is 40-90 mg/kg/day for all indications, whereas recommendations for amoxicillin, penicillin V, and flucloxacillin in the BNF-C are mostly based on age bands, although weight bands or weight based calculations (mg/kg) are given for some indications. The widely used doses of 62.5 mg or 125 mg are fractions of the adult dose recommended in the 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.

They conducted a historical review of the literature and earlier UK prescribing formularies to understand the origins of the age band dosing schedule, noting limited evidence for dosing regimens and that many children may be underdosed. They also note the lack of recent evidence to support the BNF’s current dosing recommendations for the oral penicillins and the same dosing recommendations seem to have been reused every year for the past 50 years. They highlight the following consequences:

• Low dosing will lead to subtherapeutic concentrations at the relevant target organ (especially the middle ear), potentially driving antimicrobial resistance, with consequences for both the individual and the community.

• 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.

It was highlighted that studies of paediatric antiretroviral dosing noted that complex schedules using weight bands often led to clinically important underdosing since changes in growth and obesity had not been accounted for. This led to substantial changes in the dosing recommendations for children on antiretrovirals and to standardised treatment guidelines across Europe. The authors call for a similar programme of work for oral penicillins and finish by saying “not only do we need to determine the effective doses for children of all ages and weights but we also need to establish more clearly which children really need antibiotics in the era of pneumococcal conjugate (PCV 13), Haemophilus influenzae B, and meningitis C vaccines. The rates of prescribing of oral penicillins for children are now rising again in England. Many of the 5 million children in England who receive oral penicillins each year may not need them, but those who do should receive them in an effective dose.”