Antibiotic Prophylaxis (CAP) in VUR: Who Needs It, and for How Long?

Vesicoureteral reflux itself causes neither pain nor damage; the harm comes from pyelonephritis (kidney infection) — which occurs when bacteria in the bladder are carried up to the kidney during reflux — and the scarring it can leave behind. The purpose of antibiotic prophylaxis is to keep the urine free of bacteria during the years it takes for reflux to resolve on its own, breaking this chain of infection.

• For this reason, CAP does not treat the reflux itself and does not speed up the lengthening of the tunnel — it only buys time. Who receives it, and for how many years, is determined by weighing this benefit against the side effects of the antibiotic and the burden of resistance.

The RIVUR trial (NEJM 2014) followed 607 children with grade I–IV reflux who had had a prior UTI, for two years. Trimethoprim-sulfamethoxazole prophylaxis reduced recurrence of febrile or symptomatic UTI by roughly half (about 25% versus 13% — roughly one recurrence prevented in every 8 children). There was no significant difference between the two groups in new scarring on DMSA, and resistant E. coli increased significantly in the prophylaxis group. The greatest benefit was seen in children who presented with febrile infection and those with bladder-bowel dysfunction (BBD).

The shared approach in the EAU/ESPU 2024 and AUA guidelines is shaped by age, grade, infection history, and BBD. The decision is not a simple table but is based on the child's overall risk profile — still, the general trends are as follows.

• Under 1 year + febrile UTI, any grade: CAP
• Under 1 year, no UTI, grade III–V: CAP may be recommended (PREDICT)
• Over 1 year, low grade, no UTI/single episode: surveillance an option
• During BBD treatment: CAP accompanies it
• Scarring, recurrent UTI, high grade: CAP with close follow-up; corrective treatment discussed

The prophylactic dose is roughly one-quarter to one-third of the dose used to treat an active infection, and it is usually given as a single dose at bedtime. Night-time dosing is chosen because it keeps the drug present in the urine during the hours the bladder stays full the longest. The purpose of the low dose is to cleanse the urine alone while preserving the gut flora as much as possible.

CAP is not an indefinite treatment; it is generally reviewed in 6–12 month intervals. At each review, the child's age, any infections in the interim, ultrasound findings, and stage of toilet training are reassessed. CAP started in infancy is usually revisited around age one and again when toilet training is complete.