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Amoxicillin drives resistance in child UTIs

By Lilian Anekwe

GPs should avoid prescribing ampicillin to any child with a UTI who has been given amoxicillin at any time in the previous two months, say US researchers.

Researchers evaluated the impact of previous antimicrobial exposure on the development of antimicrobial resistance in 533 children aged six months to six years who presented at 27 outpatient paediatric centres with their first UTI.

The researchers examined the relationship between antimicrobial resistance in UTI isolates and exposure to either amoxicillin, amoxicillin-clavulanate, co-trimoxazole, azithromycin and cefdinir, a third-generation cephalosporin available in the US – in the previous 120 days.

Children who had been given amoxicillin in the previous 30 days were 3.6-times more likely to have an ampicillin-resistant infection compared to children who had not received an antibiotic. This fell slightly to a 2.8-fold increased risk of ampicillin-resistance in children who had been given amoxicillin in the previous 31 to 60 days.

Exposure to amoxicillin more than 30 days before a child presented was also associated with a 3.9-fold increase in resistance to amoxicillin-clavulanate. No association was found between exposure to other antimicrobial agents and resistance to any of the antibiotics.

The researchers conclude that in addition to avoiding the unnecessary prescription of antibiotics for childhood UTIs, GPs should not prescribe ampicillin to children who have had a course of antibiotic in the previous 60 days.

Dr Amanda Paschke, a paediatrician at the Children's Hospital of Philadelphia, concluded: ‘Recent antimicrobial exposure is associated with antimicrobial resistant UTIs among paediatric outpatients, and the magnitude of this association decreases with time since exposure.

‘Judicious antimicrobial prescribers should consider this association when selecting empiric antimicrobial agents for a new UTI and should use strategies to reduce unnecessary antimicrobial use to avoid development of resistant bacteria.'

Professor Chris Butler, professor of primary care medicine at the University of Cardiff and a GP in the city, said the study was useful as the work of US paediatricians providing primary care to children was analogous to UK GP practice.

‘The story of recent antibiotics being associated with resistant infections is important, especially in kids who are the largest recipients of unnecessary antibiotics,' he said.

Paediatrics 2010, published online 1 March

Key figures

• 8%, 14% and 21% of children were exposed to antibiotics within 30, 60 and 120 days before the UTI, respectively
• Amoxicillin exposure within 30 days increased resistance to ampicillin by 3.6 times and resistance to amoxicillin-clavulanate by 3.9 times

• Amoxicillin exposure within 31 to 60 days increased the odds to 2.8 times

Source: Pediatrics, published online March 1

Amoxicillin drives resistance in child UTIs


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