Boys with posterior urethral valves have bladder dysfunction of varying severity. Early treatment of these children with anticholinergics is recommended by some teams, although there have never been any clear studies on the subject. To our knowledge, no comparative study of the evolution of valve bladders with or without treatment has been carried out to date.

Anticholinergic treatment, although it may be beneficial in patients with abnormal bladder function, such as the neurologic bladders ( in Spina Bifida) for example, may have side effects and may not be of benefit for this valve population. The evolution of the valves could be spontaneously favorable.

This study would be the first randomized clinical trial of early therapeutic drug intervention in the posterior urethral valve population.

Posterior urethral valves (VUPs) are the leading cause of subvesical obstruction in children with an incidence between 1 / 3,000 to 1 / 8,000 births. 25-45% of patients will have chronic renal failure and 10-20% will require a transplant. The association between long-term prognosis and bladder dysfunction is well known, leading many teams to suggest early initiation of treatment with anticholinergics.

However, this treatment has never been properly evaluated. In fact, a single study carried out in boys with valves taking oxybutynin from the age of 3 months to 2 years without a control group concluded that "the early use of anticholinergics in boys with VUP presenting high voiding pressures and low bladder capacity has a beneficial effect on bladder function. It is true that in children with neurologic bladders as in Spina Bifida, early treatment with anticholinergics seems to provide a benefit, but VUPs are not strictly speaking neurologic bladders. In addition, treatment with anticholinergics can have side effects and could even be harmful to the bladder, leading to myogenic bankruptcy. The only way to properly assess oxybutynin in this population is to conduct a prospective randomized study.

The proposed study includes a group treated with oxybutynin and a group without. Boys who have had valve resection for VUP within the first three months of life and who present an abnormal urodynamic assessment 3 months after valve resection will be included. Oxybutynin will be given at a dose of 0.1 mg / kg 2x / day, as syrup, in the treatment group. The control group will not have any treatment affecting bladder function. The pharmacokinetics of oxybutynin will be studied. Several urodynamic parameters including capacity or volume, voiding pressure and compliance will be studied. The objective is to perform a composite analysis that can reflect the complex functioning of the bladder. The children included will have urodynamics at the end of the study, after 9 months of treatment. The performance of urodynamic examinations will be standardized and there will be an external centralized analysis to validate the urodynamic results.

Inclusion Criteria:

• Boys
• Aged 3 to 6 months
• Diagnosed with posterior urethral valves, and having undergone valve resection within the first 3 months of life
• Children who have had their valve resection at least 3 months before inclusion
• Having undergone urodynamic studies between 10 weeks and 6 months of age andshowing abnormal urodynamics, notably: high voiding pressure (>60cm H2O)/ small capacity bladder (<70% expected bladder volume)and for those without pop-off mechanisms, poor compliance (<10ml/cmH2O)/
• Holders of parental authority affiliated to French national health insurance
• With informed consent signed by holders of parental authority

Exclusion Criteria:

• Boys with posterior urethral valves and normal urodynamics or no urodynamic assessment
• Boys in whom urodynamic assessment is not possible for medical or anatomical reasons
• Boys requiring dialysis before the age of 3 months
• Contra-indication to oxybutynin such as hypersensitivity to oxybutynin or any of the excipients, digestive obstruction, occlusive or sub-occlusive syndrome, megacolon, digestive stasis, intestinal atony, paralytic ileus, ulcerative colitis, Hemorrhagic rectocolitis, Crohn's disease, Inflammatory bowel disease, Inflammatory organic colopathy, myasthenia, congenital glaucoma

Boys, aged 3 to 6 months, diagnosed with posterior urethral valves. Urethral valves (PUV) are the most common form of congenital urethral obstruction with an incidence ranging from 1/3,000 and 1/8,000 male births.